Low Relative Frequencies of CD26+ CD4+ Cells in Long-Term Nonprogressing Human Immunodeficiency Virus Type 1-Infected Subjects

A broad antibody panel was used for immunophenotyping of human immunodeficiency virus type 1 (HIV-1)-infected patients who were long-term nonprogressors (LTNP). The LTNP were compared with patients in the early phase of infection and patients who had progressed to advanced immunodeficiency. Changes in CD8⁺ subset distribution were observed mainly at acquisition of HIV-1 infection, whereas CD4⁺ subset changes appeared during progression of HIV-1 infection. The decreasing levels of CD4⁺ cells were characterized by an increasing frequency of cells expressing the activation markers HLA-Dr and CD45RO but not the CD28 surface antigen. The LTNP exhibited significant changes compared to HIV-negative patients in almost all markers. Compared to patients in the early phase of infection, the only difference was a relatively lower frequency of CD4⁺ cells expressing CD26 among the LTNP. The results show that HIV-1-infected persons who have no signs of immunodeficiency despite many years of infection have an immunophenotypic pattern that is substantially different from that of noninfected persons. Despite the long duration of infection, the LTNP exhibit a pattern similar to that of newly infected persons, with the exception of lower expression of CD26 on CD4⁺ cells.     

CD4+ CD25+ T-Cell Production in Healthy Humans and in Patients with Thymic Hypoplasia

Regulatory T cells are found primarily in the CD4⁺ CD25⁺ fraction of T cells and play an important role in the prevention of autoimmunity. We examined CD4⁺ CD25⁺ T cells in 33 healthy children and adults and compared them to a population with an inherited form of thymic hypoplasia and a predisposition to autoimmune disease. Absolute numbers of CD4⁺ CD25⁺ T cells were markedly higher in healthy infants than in infants with chromosome 22q11.2 deletion syndrome.     

Low CD4+ T-Lymphocyte Values in Human Immunodeficiency Virus-Negative Adults in Botswana

CD4⁺-lymphocyte counts (LCs) play a crucial role in the management and monitoring of HIV infection. Variability in CD4⁺ LCs has been reported to occur as a result of measurement techniques and/or biological variations. We report on the CD4⁺ LCs of healthy human immunodeficiency virus (HIV)-seronegative adults in Botswana. Samples were obtained from HIV-seronegative blood donors. The median CD4⁺ LC was 726 cells/mm³ (for females, 782 cells/mm³; for males, 698 cells/mm³). The median CD8⁺ LC was 488 cells/mm³ (for females, 494 cells/mm³; for males, 485 cells/mm³). The median CD4⁺-to-CD8⁺ ratio was 1.57 (for females, 1.66; for males, 1.51). Our findings of low CD4⁺ LCs among HIV-negative adults in Botswana are significant and have important implications for the management of HIV disease in the population of this sub-Saharan African country.     

Expansion of a Novel Pulmonary CD3− CD4+ CD8+ Cell Population in Mice during Chlamydia pneumoniae Infection

A new pulmonary T-cell-like lymphocyte population with the phenotype CD3⁻ CD4⁺ CD8⁺ was discovered in mice. CD4⁺ CD8⁺ but CD3⁺ cells among murine intestinal intraepithelial lymphocytes have previously been described. We describe herein a dramatic expansion of the CD3⁻ CD4⁺ CD8⁺ cell population in response to experimental respiratory infection. After intranasal Chlamydia pneumoniae infection, CD4⁺ CD8⁺ cells became transiently the dominant lymphocyte type (maximum of 87% of all lymphocytes) in the lungs of NIH/S mice but remained virtually undetectable in spleen and blood. The enrichment of these cells was not a C. pneumoniae-specific event, since infection of NIH/S mice with influenza A virus also resulted in an increase in the number of CD4⁺ CD8⁺ cells (maximum of 42% of all lymphocytes). In addition to outbred NIH/S mice, two other mouse strains were studied: BALB/c (H-2^d) and C57BL/6 (H-2^b). C. pneumoniae-infected BALB/c mice responded with an intermediate increase in the number of CD4⁺ CD8⁺ cells in lungs, whereas C57BL/6 mice did not respond. The double-positive CD4⁺ CD8⁺ cells lacked a major part of the T-cell receptor complex, being both CD3⁻ and TCR αβ⁻. However, when they were stimulated in vitro with a T-cell mitogen, they responded by proliferation but did not secrete gamma interferon. The dramatic expansion of this cell population at the infection site suggests an active role for them in respiratory infection, but the specification of this requires further study.     

Frequency of Measles Virus-Specific CD4+ and CD8+ T Cells in Subjects Seronegative or Highly Seropositive for Measles Vaccine

The protective effect of measles immunization is due to humoral and cell-mediated immune responses. Little is known about cell-mediated immunity (CMI) to measles vaccine virus, the relative contribution of CD4⁺ and CD8⁺ T cells to variability in such immune responses, and the immunologic longevity of the CMI after measles vaccination in humans. Our study characterizes cellular immune response in subjects seronegative or highly seropositive for measles vaccine immunoglobulin G-specific antibody, aged 15 to 25 years, previously immunized with two doses of measles-mumps-rubella II vaccine. We evaluated the ability of subjects to respond to measles vaccine virus by measuring measles virus-specific T-cell proliferation. We examined the frequencies of measles virus-specific memory Th1 and Th2 cells by an ELISPOT assay. Our results demonstrated that proliferation of T cells in seronegative subjects was significantly lower than that for highly seropositive subjects (P = 0.003). Gamma interferon (IFN-γ) secretion predominated over interleukin 4 (IL-4) secretion in response to measles virus in both groups. The median frequency of measles virus-reactive CD8⁺ T cells secreting IFN-γ was 0.09% in seronegative subjects and 0.43% in highly seropositive subjects (P = 0.04). The median frequency of CD4⁺ T cells secreting IL-4 in response to measles virus was 0.03% in seronegative subjects and 0.09% in highly seropositive subjects (P = 0.005). These data confirm the presence of measles virus-specific cellular immune responses post-measles vaccine immunization in humans. The detection of measles virus-induced IFN-γ and IL-4 production by ELISPOT can be used to identify measles virus-specific low-frequency memory T cells in subjects immunized with measles vaccine. These differences agree in directionality with the observed antibody response phenotype.     

Comparative Analysis of Human Cytomegalovirus-Specific CD4+ T-Cell Frequency and Lymphoproliferative Response in Human Immunodeficiency Virus-Positive Patients

Evaluation of human cytomegalovirus (HCMV)-specific T-helper immunity could contribute in optimizing anti-HCMV therapy in human immunodeficiency virus (HIV)-infected patients. Testin the lymphoproliferative response (LPR) is the standard technique used to evaluate T-helper response, but its use in the routine diagnostic laboratory setting can be problematic. The most promising new alternative technique is the determination of HCMV-specific CD4⁺ T-cell frequency by flow cytometry detection of intracellular cytokine production after short-term antigen-specific activation of peripheral blood mononuclear cells. HCMV-specific LPR and CD4⁺ T-cell frequency were compared in a group of 78 blood samples from 65 HIV-infected patients. The results showed concordance in 80.7% of samples. In addition, comparative analysis of sequential blood samples from 13 HIV-infected patients showed that while in about half of patients the T-helper HCMV-specific immune response remained stable during highly active antiretroviral therapy (HAART), in the other half declining levels of the HCMV-specific CD4⁺-mediated immune response were determined by either one or both assays. In conclusion, our data suggest that the determination of HCMV-specific CD4⁺ T-cell frequency can be considered a valuable alternative to the LPR test for the detection of HCMV-specific T-helper response in HIV-infected patients. It could facilitate wider screening of anti-HCMV T-helper activity in HIV-infected patients, with potential benefits for clinicians in deciding strategies of discontinuation or maintenance of anti-HCMV therapy.     

CD8+-T-Cell Immunity against Toxoplasma gondii Can Be Induced but Not Maintained in Mice Lacking Conventional CD4+ T Cells

T-cell immunity is critical for survival of hosts infected with Toxoplasma gondii. Among the cells in the T-cell population, CD8(+) T cells are considered the major effector cells against this parasite. It is believed that CD4(+) T cells may be crucial for induction of the CD8(+)-T-cell response against T. gondii. In the present study, CD4(-/-) mice were used to evaluate the role of conventional CD4(+) T cells in the immune response against T. gondii infection. CD4(-/-) mice infected with T. gondii exhibited lower gamma interferon (IFN-gamma) messages in the majority of their tissues. As a result, mortality due to a hyperinflammatory response was prevented in these animals. Interestingly, T. gondii infection induced a normal antigen-specific CD8(+)-T-cell immune response in CD4(-/-) mice. No difference in generation of precursor cytotoxic T lymphocytes (pCTL) or in IFN-gamma production by the CD8(+)-T-cell populations from the knockout and wild-type animals was observed. However, the mutant mice were not able to sustain CD8(+)-T-cell immunity. At 180 days after infection, the CD8(+)-T-cell response in the knockout mice was depressed, as determined by pCTL and IFN-gamma assays. Loss of CD8(+)-T-cell immunity at this time was confirmed by adoptive transfer experiments. Purified CD8(+) T cells from CD4(-/-) donors that had been immunized 180 days earlier failed to protect the recipient mice against a lethal infection. Our study demonstrated that although CD8(+)-T-cell immunity can be induced in the absence of conventional CD4(+) T cells, it cannot be maintained without such cells.     

Expanded CD14+ CD16+ Monocyte Subpopulation in Patients with Acute and Chronic Infections Undergoing Hemodialysis

Infections are frequent complications in end-stage renal failure patients undergoing hemodialysis (HD), and peripheral blood monocytes are important cells in host defense against infections. The majority of circulating monocytes express high levels of lipopolysaccharide receptor antigen CD14 and are negative for the immunoglobulin Fcγ receptor type III (CD16). We studied the occurrence of a minor subpopulation coexpressing low levels of CD14 together with CD16 in HD patients. In healthy controls CD14⁺ CD16⁺ monocytes account for 8% ± 4% of CD14⁺ monocytes, with an absolute number of 29 ± 14 cells/μl. In stable HD patients the CD14⁺ CD16⁺ subpopulation was significantly elevated (14% ± 3%, or 66 ± 28 cells/μl), while the number of CD14⁺⁺ monocytes (monocytes strongly positive for CD14) remained constant. In HD patients suffering from chronic infections a further rise in CD14⁺ CD16⁺ monocytes was observed (128 ± 71 cells/μl; P < 0.01) such that this subpopulation constituted 24% of all blood monocytes. In contrast, numbers of CD14⁺⁺ cells did not change compared to those for stable HD patients, indicating that the CD14⁺ CD16⁺ monocyte subpopulation was selectively expanded. During acute infections the CD14⁺ CD16⁺ cell subpopulation always expanded. A whole-blood assay revealed that CD14⁺ CD16⁺ monocytes exhibited a higher phagocytosis rate for Escherichia coli bacteria than CD14⁺⁺ monocytes, underlining their role during host defense. In addition, CD14⁺ CD16⁺ monocytes expressed higher levels of major histocompatibility complex (MHC) class II antigens (HLA-DR, -DP, and -DQ) and equal amounts of MHC class I antigens (HLA-ABC). Thus, CD14⁺ CD16⁺ cells constitute a potent phagocytosing and antigen-presenting monocyte subpopulation, which is expanded during acute and chronic infections commonly observed in chronic HD patients.

Peripheral blood monocytes are members of the mononuclear phagocytic system, which plays a central role in immunoregulation and host defense against immunopathogenic organisms (7). Monocytes are activated through molecular signals provided by structures of the infective organisms (8, 27, 28, 34, 35) or inflammatory mediators and chemotactic factors released by other cells during the infective challenge (22, 44, 47). However, blood monocytes represent a heterogeneous cell population and can be distinguished by variations in morphology (38, 58), membrane antigen expression (39), and release of inflammatory mediators (12, 25, 41).While the lipopolysaccharide (LPS) receptor antigen CD14 is expressed by nearly all circulating peripheral blood monocytes, monocytes differ markedly in cell surface CD14 density as well as in the expression of immunoglobulin Fcγ receptors (53, 67). The majority of monocytes strongly positive for CD14 (CD14⁺⁺) express Fcγ receptor I (CD64) and Fcγ receptor II (CD32) and are negative for Fcγ receptor III (CD16) (18). Only a small population was identified by the absence of Fcγ receptors (63). Nevertheless, a subset of monocytes characterized by low-level expression of CD14 and expression of the CD16 antigen has also been described (40). In healthy subjects these CD14⁺ CD16⁺ cells account for about 10% of all monocytes and are thought to be more mature cells than the regular CD14⁺⁺ monocytes, as they exhibit features of tissue macrophages (66). In various infectious or inflammatory diseases such as AIDS and asthma the CD14⁺ CD16⁺ monocyte subpopulation is markedly expanded (36, 43, 50). A more than 10-fold increase of these cells during septicemia was demonstrated, and CD14⁺ CD16⁺ cells become the predominant type of monocytes in some septic patients (14).Patients with end-stage renal failure undergoing chronic hemodialysis (HD) show an impaired immune response (10) with a high prevalence of infectious complications (17). Most of these infections are of bacterial origin, representing a major cause of morbidity and mortality in chronic HD patients (24). Furthermore, acute or chronic inflammatory processes, among them pneumonia and vascular access site infections, are common hazards in uremic patients undergoing chronic regular HD. Despite some data on the functional abnormalities of polymorphonuclear leukocytes in uremia (19), little information exists on the level of monocytes and their subsets in maintenance dialysis patients.In an effort to further understand the importance of the distinct monocyte population expressing Fcγ receptor type III, we determined the levels of these cells in patients with end-stage renal failure undergoing chronic HD. This allowed the level of CD14⁺ CD16⁺ cells to be compared to that of CD14⁺⁺ cells and the total monocyte count in whole blood. To investigate the proinflammatory role of CD14⁺ CD16⁺ monocytes, stable patients as well as patients with acute or chronic signs of infections or inflammatory processes were studied. Furthermore, we analyzed cell surface HLA expression of CD14⁺ CD16⁺ monocytes by immunophenotyping and compared their phagocytic competence with that of regular CD14⁺⁺ blood monocytes.     

In Vitro Expansion of T-Cell-Receptor Vα2.3+ CD4+ T Lymphocytes in HLA-DR17(3), DQ2+ Individuals upon Stimulation with Mycobacterium tuberculosis

The T-cell receptor (TCR) Valpha/beta gene product expression upon in vitro stimulation with mycobacteria was investigated to assess whether T-cell proliferation was associated with any specific TCR V gene usage. T-cell-enriched populations from peripheral blood of Mycobacterium bovis BCG-vaccinated healthy blood donors were stimulated in vitro with live or killed M. tuberculosis or with a soluble extract thereof. TCR Valpha/beta repertoire analysis of reactive CD4(+) and CD8(+) T cells revealed a selective HLA-DR17(3), DQ2-restricted expansion of Valpha2.3(+) CD4(+) T cells upon stimulation with live M. tuberculosis or its soluble extract. Third-complementarity-determining-region (CDR3) length analysis of the expanded Valpha2.3(+) T cells indicated an oligoclonal pattern with short CDR3 lengths in six of seven HLA-DR17(3), DQ2(+) individuals tested. In addition, Valpha/Vbeta repertoire analysis of T lymphocytes from a DR17(3), DQ2(+) donor before and after BCG vaccination revealed that positivity of skin test reactivity was associated with expansion of Valpha2.3(+) CD4(+) T lymphocytes with preferential use of a short CDR3 peak length after in vitro stimulation. Separation of M. tuberculosis soluble extract by fast protein liquid chromatography (FPLC) purification indicated that fractions corresponding to molecular masses of 60 to 70 and 15 to 25 kDa were particularly effective in eliciting Valpha2.3(+) CD4(+) T-cell expansion.     

Processing of Mycobacterium tuberculosis Bacilli by Human Monocytes for CD4+ αβ and γδ T Cells: Role of Particulate Antigen

Mycobacterium tuberculosis readily activates both CD4⁺ and Vδ2⁺ γδ T cells. Despite similarity in function, these T-cell subsets differ in the antigens they recognize and the manners in which these antigens are presented by M. tuberculosis-infected monocytes. We investigated mechanisms of antigen processing of M. tuberculosis antigens to human CD4 and γδ T cells by monocytes. Initial uptake of M. tuberculosis bacilli and subsequent processing were required for efficient presentation not only to CD4 T cells but also to Vδ2⁺ γδ T cells. For γδ T cells, recognition of M. tuberculosis-infected monocytes was dependent on Vδ2⁺ T-cell-receptor expression. Recognition of M. tuberculosis antigens by CD4⁺ T cells was restricted by the class II major histocompatibility complex molecule HLA-DR. Processing of M. tuberculosis bacilli for Vδ2⁺ γδ T cells was inhibitable by Brefeldin A, whereas processing of soluble mycobacterial antigens for γδ T cells was not sensitive to Brefeldin A. Processing of M. tuberculosis bacilli for CD4⁺ T cells was unaffected by Brefeldin A. Lysosomotropic agents such as chloroquine and ammonium chloride did not affect the processing of M. tuberculosis bacilli for CD4⁺ and γδ T cells. In contrast, both inhibitors blocked processing of soluble mycobacterial antigens for CD4⁺ T cells. Chloroquine and ammonium chloride insensitivity of processing of M. tuberculosis bacilli was not dependent on the viability of the bacteria, since processing of both formaldehyde-fixed dead bacteria and mycobacterial antigens covalently coupled to latex beads was chloroquine insensitive. Thus, the manner in which mycobacterial antigens were taken up by monocytes (particulate versus soluble) influenced the antigen processing pathway for CD4⁺ and γδ T cells.

Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, is spread readily from person to person by inhalation of aerosolized mycobacteria (8). A hallmark of M. tuberculosis infection is the ability of most healthy individuals to control the infection by mounting an acquired immune response, in which antigen-specific T cells and mononuclear phagocytes arrest the growth of M. tuberculosis bacilli and maintain control over dormant bacilli within granulomas (reviewed in reference 25). This protective cellular immune response results in conversion of the tuberculin skin test from negative to positive and probably in increased resistance to reinfection with tubercle bacilli.CD4⁺ αβ-T-cell-receptor (αβ TCR)-bearing T cells (CD4⁺ T cells) are readily activated by mycobacterial antigens and have a dominant role in the protective immune response to M. tuberculosis in humans (2, 34). These CD4⁺ T cells not only secrete cytokines but also serve directly as cytotoxic effector cells against M. tuberculosis-infected macrophages (6). In addition to CD4⁺ T cells, M. tuberculosis antigens activate other human T-cell subsets such as γδ TCR⁺ T cells (γδ T cells) (15, 16, 18). Vδ2⁺ and Vγ9⁺ γδ T cells are particularly responsive to live M. tuberculosis (15). A role for both γδ and CD4⁺ T cells in protective immunity to acute M. tuberculosis infection has been demonstrated in murine models (20, 21, 26, 27). A recent study of humans suggests that Vγ9⁺ and Vδ2⁺ γδ T-cell numbers and function are reduced in tuberculosis patients (23).Functional comparisons of human CD4⁺ and γδ T-cell responses of healthy tuberculin-positive persons demonstrate that both T-cell subsets have similar cytotoxic effector functions for M. tuberculosis-infected monocytes and produce large amounts of gamma interferon (IFN-γ), with γδ T cells being slightly more efficient producers of IFN-γ than CD4⁺ T cells (37). Despite similarities in function, these two T-cell subsets differ in the mycobacterial antigens recognized by their TCRs and the manners in which antigens are presented to them by M. tuberculosis-infected mononuclear phagocytes. CD4⁺ T cells recognize a wide diversity of mycobacterial peptides in the context of class II major histocompatibility complex (MHC) molecules, which include secreted as well as somatic antigens (6, 13, 33, 37). In contrast, Vγ9⁺ and Vδ2⁺ γδ T cells, the dominant γδ TCR subsets activated by M. tuberculosis, recognize mycobacterial antigens in a non-MHC-restricted manner and the repertoire of antigens includes small phosphate-containing antigens such as TUBag’s (5, 9, 19, 22, 29, 36).Both blood monocytes and alveolar macrophages infected with M. tuberculosis are efficient antigen-presenting cells for mycobacterial antigen-specific CD4⁺ and γδ T cells (1, 5). However, little is known about how M. tuberculosis-infected mononuclear phagocytes process antigens for these two T-cell subsets. M. tuberculosis bacilli are taken up by mononuclear phagocytes through a variety of surface receptors, including complement receptor 4, mannose receptor, and complement receptor 3 (17, 31, 32). Within mononuclear phagocytes, the mycobacteria reside within phagosomes and modulate the phagosome by preventing fusion with acidic lysosomal compartments (7). Although the vacuolar membranes surrounding the phagosome acquire endosomal markers, the vesicular proton ATPase is actively excluded, resulting in an elevated pH of 6.3 to 6.5 compared to the normal lysosomal pH of 4.5 (7, 35). The elevated pH in the phagosome does not appear to inhibit the ability of mycobacterial antigens to be processed and presented to CD4⁺ and Vδ2⁺ γδ T cells. This study was undertaken to gain insight into the mechanisms used by monocytes infected with live M. tuberculosis bacilli to process mycobacterial antigens for presentation to both CD4⁺ and γδ T cells.     

Most CD56+ Intestinal Lymphomas Are CD8+CD5− T-Cell Lymphomas of Monomorphic Small to Medium Size Histology

The expression of the natural killer (NK) cell marker CD56 has been reported to occur in NK cell lymphomas/leukemias and a small group of peripheral T-cell lymphomas but has not been studied extensively in primary intestinal non-B-cell lymphomas. Normal human jejunal intraepithelial lymphocytes (IELs) are mainly T-cell receptor (TCR)-αβ⁺CD3⁺CD8⁺CD5^low and include an ~15% fraction of CD56⁺ cells that could be the cells of origin for CD56⁺ intestinal T-cell lymphoma (ITL). To test this hypothesis, 70 cases diagnosed as ITL were immunophenotyped, and 15 CD56⁺ cases (21%) were identified. The majority of the CD56⁺ lymphomas was of monomorphic small to medium-sized histology, shared the common phenotype βF1^±CD3ε/cyt⁺CD8⁺CD4⁻CD5⁻CD57⁻TIA-1⁺ and had clonally rearranged TCR γ-chain genes. In contrast, the CD56⁻ lymphomas were mainly composed of pleomorphic medium and large cells or had a morphology most consistent with anaplastic large-cell lymphoma and were mostly CD8⁻. These findings suggest that the majority of CD56⁺ intestinal lymphomas are morphologically and phenotypically distinct T-cell lymphomas most likely derived from activated cytotoxic CD56⁺CD8⁺ IELs. Some overlapping histological and clinical features between CD56⁺ and CD56⁻ ITLs indicate that the former belong to the clinicopathological entity of ITL. The consistent expression of cytotoxic-granule-associated proteins introduces ITL (both CD56⁺ and CD56⁻) into the growing family of usually aggressive extranodal lymphomas of cytotoxic T-cell and NK-cell derivation. In contrast to putative NK-cell lymphoma of the sinonasal region, intestinal NK-cell lymphoma seems to be very rare.     

Role of Leishmania donovani and Its Lipophosphoglycan in CD4+ T-cell Activation-Induced Human Immunodeficiency Virus Replication

Chronic immune activation by coinfecting pathogens has been suggested as a cofactor in human immunodeficiency virus (HIV) disease progression, particularly in the setting of developing countries. Here, we used in vivo-infected mononuclear cells to examine the role of the protozoan parasite Leishmania donovani and its major membrane constituent, lipophosphoglycan (LPG), in mediating CD4+ T-lymphocyte activation-induced HIV replication and CD4+ T-cell death. We found that Leishmania antigens upregulated HIV replication in CD8-depleted peripheral blood mononuclear cells from asymptomatic HIV-infected donors compared to unstimulated cells. L. donovani-induced viral replication was associated with cellular proliferation, increased expression of the cellular immune activation markers CD25 and HLA-DR within the CD4+ subpopulation, and enhanced secretion of tumor necrosis factor alpha (TNF-alpha), interleukin 2 (IL-2), and IL-6. LPG induced TNF-alpha secretion in the absence of increased expression of cellular activation markers. Moreover, in a few cases we observed that L. donovani induced HIV replication without significant cellular activation but with cytokine secretion. The rate of apoptosis was accelerated in these latently infected CD4+ T cells primed with Leishmania antigens compared to controls, and TNF-alpha production appeared to be the central event necessary for this effect. Furthermore, we demonstrate that thalidomide inhibited Leishmania-induced virus replication coupled with abrogated Leishmania-induced TNF-alpha secretion but not IL-2 or IL-6 production. Furthermore, thalidomide did not affect Leishmania-induced apoptosis. The results suggest that Leishmania and its product, LPG, up-regulate HIV replication in latently infected cells through distinct antigen-specific and non-antigen-specific cellular immune activation mechanisms and that TNF-alpha secretion is pivotal in this process. The immunomodulatory role of thalidomide raises interest as a potential adjuvant to reduce HIV disease progression in Leishmania-HIV coinfected individuals.     

Increased Foxp3+ CD4+ Regulatory T Cells with Intact Suppressive Activity but Altered Cellular Localization in Murine Lupus

Foxp3⁺ CD4⁺ regulatory T (T_reg) cells play a pivotal role in the maintenance of dominant self tolerance. Understanding how the failures of immune control by T_reg cells are involved in autoimmune diseases is important for the development of effective immunotherapies. In the present study, we analyzed the characteristics of endogenous T_reg cells in (NZB × NZW) F1 (BWF1) mice, a murine model of systemic lupus erythematosus. Unexpectedly, T_reg number and frequency in aged BWF1 mice with developing lupus nephritis were increased, not decreased, and in vitro suppressive activity in lymphoid organs was intact. In addition, T_reg cells trafficked to target organs because cells were present in the kidney and lung. T_reg cells of aged BWF1 mice exhibited altered localization within lymph organs, however, and an altered phenotype, with higher expression levels of chemokine receptors and activation markers, suggesting a highly activated cellular state. Notably, the expression levels of co-stimulatory molecules were also markedly enhanced in the T_reg cells of aged BWF1 mice. Furthermore, T_reg cells of BWF1 mice did not show any suppressive effects on antibody production in vitro. Taken together, we conclude that T_reg cells in BWF1 mice are not predisposed to functional incompetence but rather are present in a highly activated state.     

Control of Leishmania infantum Infection Is Associated with CD8+ and Gamma Interferon- and Interleukin-5-Producing CD4+ Antigen-Specific T Cells

Visceral leishmaniasis is a severe and lethal disease caused by the protozoan parasites of the genus Leishmania. In areas where leishmaniasis is endemic, most infected individuals control the infection and remain asymptomatic; chemotherapy of visceral leishmaniasis restores some immunity which protects against relapses. In the present study, Leishmania-specific T-cell clones were established from six asymptomatic and five cured patients. Cytokines production by these clones was analyzed. A large fraction of the parasite-specific T-cell clones from asymptomatic patients were CD8(+) and produced high amounts of gamma interferon (IFN-gamma). Most CD4(+) T-cell clones from two asymptomatic subjects exhibited an unusual phenotype: production of high levels of IFN-gamma low levels of interleukin-4, (IL-4), but high levels of IL-5. In contrast, only few parasite-specific CD8(+) T-cell clones were obtained from cured patients after chemotherapy; moreover, CD4(+) T-cell clones from these patients exhibited an heterogeneous profile of cytokines from Th1-like to Th2-like phenotypes. These results point to CD8(+) T cells and to IL-5- and IFN-gamma-producing CD4(+) T cells as possible contributors to human resistance to Leishmania infection. They should stimulate new immunological approaches in the control of this disease.     

Increase in Gamma Interferon-Secreting CD8+, as Well as CD4+, T Cells in Lungs following Aerosol Infection with Mycobacterium tuberculosis

Although it is well established that CD4(+) T cells are required for the protective immune response against tuberculosis (TB), there is some evidence that CD8(+) T cells are also involved in the host response to Mycobacterium tuberculosis. There is, however, a paucity of information on the pulmonary CD8(+) T-cell response during infection. We therefore have compared the changes in both CD8(+) and CD4(+) T cells following aerosol infection with M. tuberculosis. There was an observed delay between the peak of infection and the activated T-cell response in the lung. The kinetics of CD8(+) and CD4(+) T-cell responses in the lung were identical, both peaking at week 8, 4 weeks later than the peak of cellular response in draining lymph nodes. Similar changes in activation/memory phenotypes occurred on the pulmonary CD8(+) and CD4(+) T cells. Following in vitro restimulation, both subsets synthesized gamma interferon, a cytokine essential for controlling M. tuberculosis infection. Since lung CD8(+) T cells are actively expanded during aerosol M. tuberculosis infection, it is important that both CD8(+) and CD4(+) T cells be targeted in the design of future TB vaccines.     

Primary Role for CD4+ T Lymphocytes in Recovery from Oropharyngeal Candidiasis

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity and is commonly seen in human immunodeficiency virus positive individuals and AIDS patients. A model for oral candidiasis in T-cell-deficient BALB/c and CBA/CaH nu/nu mice was established. After inoculation with 10(8) Candida albicans yeasts, these mice displayed increased levels of oral colonization compared to euthymic control mice and developed a chronic oropharyngeal infection. Histopathological examination of nu/nu oral tissues revealed extensive hyphae penetrating the epithelium, with polymorphonuclear leukocyte microabscess formation. Adoptive transfer of either naive or immune lymphocytes into immunodeficient mice resulted in the recovery of these animals from the oral infection. Reconstitution of immunodeficient mice with naive CD4(+) but not CD8(+) T cells significantly decreased oral colonization compared to controls. Interleukin-12 and gamma interferon were detected in the draining lymph nodes of immunodeficient mice following reconstitution with naive lymphocytes. This study demonstrates the direct requirement for T lymphocytes in recovery from oral candidiasis and suggests that this is associated with the production of cytokines by CD4(+) T helper cells.     

Association of CD4+ CD25+ T Cells with Prevention of Severe Destructive Arthritis in Borrelia burgdorferi-Vaccinated and Challenged Gamma Interferon-Deficient Mice Treated with Anti-Interleukin-17 Antibody

CD4⁺ CD25⁺ T cells are a population of regulatory T cells responsible for active suppression of autoimmunity. Specifically, CD4⁺ CD25⁺ T cells have been shown to prevent insulin-dependent diabetes mellitus, inflammatory bowel disease, and pancreatitis. Here, we present evidence that CD4⁺ CD25⁺ T cells also play a major role in controlling the severity of arthritis detected in Borrelia burgdorferi-vaccinated gamma interferon-deficient (IFN-γ°) C57BL/6 mice challenged with the Lyme spirochete. When B. burgdorferi-vaccinated and challenged IFN-γ° mice were treated with anti-interleukin-17 (IL-17) antibody, the number of CD4⁺ CD25⁺ T cells increased in the local lymph nodes. Furthermore, histopathologic examination showed the mice to be free of destructive arthritis. When these anti-IL-17-treated B. burgdorferi-vaccinated and challenged mice were also administered anti-CD25 antibody, the number of CD4⁺ CD25⁺ T cells in the local lymph nodes decreased. More importantly, severe destructive arthropathy was induced. In addition, delayed administration of anti-CD25 antibody decreased the severity of the arthritis. These results suggest that CD4⁺ CD25⁺ T cells are involved in regulation of a severe destructive arthritis induced with an experimental model of vaccination and challenge with B. burgdorferi.     

Affordable CD4+-T-Cell Counting by Flow Cytometry: CD45 Gating for Volumetric Analysis

The flow cytometers that are currently supported by industry provide accurate CD4⁺-T-cell counts for monitoring human immunodeficiency virus disease but remain unaffordable for routine service work under resource-poor conditions. We therefore combined volumetric flow cytometry (measuring absolute lymphocyte counts in unit volumes of blood) and simpler protocols with generic monoclonal antibodies (MAbs) to increase cost efficiency. Volumetric absolute counts were generated using CD45/CD4 and CD45/CD8 MAb combinations in two parallel tubes. The percentage values for the various subsets were also determined within the leukocyte and lymphocyte populations utilizing a fully automated protocol. The levels of agreement between the newly developed method and the present industry standards, including both volumetric and bead-based systems using a full MAb panel for subset analysis, were tested by Bland-Altman analyses. The limits of agreement for CD4 counts generated by the volumetric methods using either CD45/CD4 (in a single tube) or the full Trio MAb panel (in three tubes) on the CytoronAbsolute flow cytometer were between −29 and +46 cells/mm³ with very little bias for CD4 counts (in favor of the Trio method: +8 CD4⁺ lymphocytes/mm³; 0.38% of lymphocytes). The limits of agreement for absolute CD4 counts yielded by the volumetric CD45/CD4 method and the bead-based method were between −118 and +98 cells/mm³, again with a negligible bias (−10 CD4⁺ lymphocytes/mm³). In the volumetric method using CD45/CD8, the strongly CD8⁺ cells were gated and the levels of agreement with the full Trio showed a minor bias (in favor of the Trio; +40 CD8⁺ cells/mm³; 5.2% of lymphocytes) without a significant influence on CD4/CD8 ratios. One trained flow cytometrist was able to process 300 to 400 stained tubes per day. This workload extrapolates to a throughput of >30,000 samples per year if both CD45/CD4 and CD45/CD8 stainings are performed for each patient or a throughput of >60,000 samples if only CD45/CD4 counts are tested in a single tube. Thus, on the basis of the high efficiency and excellent agreement with the present industry standards, volumetric flow cytometers with automated gating protocols and autobiosamplers, complemented by generic CD45, CD4, and CD8 MAbs used in two-color immunofluorescence, represent the most suitable arrangements for large regional laboratories in resource-poor settings.     

Gamma Interferon Expression in CD8+ T Cells Is a Marker for Circulating Cytotoxic T Lymphocytes That Recognize an HLA A2-Restricted Epitope of Human Cytomegalovirus Phosphoprotein pp65

Antigen-specific CD8⁺ T cells with cytotoxic activity are often critical in immune responses to infectious pathogens. To determine whether gamma interferon (IFN-γ) expression is a surrogate marker for cytotoxic T lymphocytes (CTL), human cytomegalovirus-specific CTL responses were correlated with CD8⁺ T-cell IFN-γ expression determined by cytokine flow cytometry. A strong positive correlation was observed between specific lysis of peptide-pulsed targets in a ⁵¹Cr release assay and frequencies of peptide-activated CD8⁺ T cells expressing IFN-γ at 6 h (r² = 0.72) or 7 days (r² = 0.91). Enumeration of responding cells expressing perforin, another marker associated with CTL, did not improve this correlation. These results demonstrate that IFN-γ expression can be a functional surrogate for identification of CTL precursor cells.