gamma(c) cytokines provide multiple homeostatic signals to naive CD4(+) T cells

Cytokines signaling through receptors sharing the common gamma chain (gamma(c)), including IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are critical for the generation and peripheral homeostasis of B, T and NK cells. To identify unique or redundant roles for gamma(c) cytokines in naive CD4(+) T cells, we compared monoclonal populations of CD4(+) T cells from TCR-Tg mice that were gamma(c) (+), gamma(c) (-), CD127(-/-) or CD122(-/-). We found that gamma(c) (-) naive CD4(+) T cells failed to accumulate in the peripheral lymphoid organs and the few remaining cells were characterized by small size, decreased expression of MHC class I and enhanced apoptosis. By over-expressing human Bcl-2, peripheral naive CD4(+) T cells that lack gamma(c) could be rescued. Bcl-2(+) gamma(c) (-) CD4(+) T cells demonstrated enhanced survival characteristics in vivo and in vitro, and could proliferate normally in vitro in response to antigen. Nevertheless, Bcl-2(+) gamma(c) (-) CD4(+) T cells remained small in size, and this phenotype was not corrected by enforced expression of an activated protein kinase B. We conclude that gamma(c) cytokines (primarily but not exclusively IL-7) provide Bcl-2-dependent as well as Bcl-2-independent signals to maintain the phenotype and homeostasis of the peripheral naive CD4(+) T cell pool.     

Contribution of CD8(+) T cells to gamma interferon production in human tuberculosis

The proportions of peripheral blood mononuclear cells (PBMC), CD4(+) T cells, and CD8(+) T cells that produce gamma interferon (IFN-gamma) in response to Mycobacterium tuberculosis were markedly reduced in tuberculosis patients, particularly in those with severe disease. Depletion of CD4(+) but not CD8(+) cells prior to stimulation of PBMC with M. tuberculosis abolished IFN-gamma production. These results show that (i) IFN-gamma production by CD8(+) and CD4(+) cells correlates with the clinical manifestations of M. tuberculosis infection and (ii) IFN-gamma production by CD8(+) cells depends on CD4(+) cells.     

CD4(+)CD25(+) regulatory T cells contribute to the therapeutic effects of glatiramer acetate in experimental autoimmune encephalomyelitis

CD4(+)CD25(+) regulatory T cells (Tregs) are potent immunosuppressors that are pivotal in the maintenance of self-tolerance. The involvement of Tregs in therapies for immune-mediated diseases has been proposed, but direct supporting evidence is still lacking. While investigating mechanisms underlying the clinical benefits of glatiramer acetate (GA) in an animal model of multiple sclerosis (MS), i.e., experimental autoimmune encephalomyelitis (EAE), we recently demonstrated that GA can protect mice deficient in the Th(2) cytokines IL-4, IL-10 and IL-4/IL-10 from acquiring EAE, suggesting that mechanisms other than Th(2) cells may be responsible for the therapeutic effects of GA. Here we demonstrate that GA treatment boosts the expression of Foxp3 on Tregs during EAE. Furthermore, adoptive transfer of purified Tregs from GA-treated EAE mice is more effective in preventing EAE development than Tregs from untreated EAE controls. Thus, our current data provide evidence that Tregs may be the major contributor to GA's therapeutic action in EAE and, possibly, MS. Further mechanistic studies to reveal the molecular events linking GA with Tregs may optimize GA treatment and lead to the development of new, even more effective therapies that utilize this mechanism of action.     

Change of mouse CD5(+) B1 cells to a macrophage-like morphology induced by gamma interferon and inhibited by interleukin-4

The in vitro effects of gamma interferon (IFN-gamma) on the mouse CD5(+) B1-cell line, TH2.52, a hybridoma between mouse B lymphoma and mouse splenic B cells that expresses a series of B1 markers, were investigated. A significant number of macrophage-like cells appeared in the cultures of TH2.52 cells exposed to IFN-gamma, these adhering to plastic dishes and exhibiting phagocytic activity. Positive for esterase staining, the macrophage-like cells returned to the original TH2.52 morphology upon removal of IFN-gamma. The change was prevented by treatment with SB202190, an inhibitor of p38 mitogen-activated protein (MAP) kinase and by transfection of a p38 MAP kinase dominant-negative mutant. Further, interleukin-4 (IL-4) inhibited IFN-gamma-induced phosphorylation of p38 MAP kinase and the appearance of macrophage-like cells. IFN-gamma and IL-4 exhibited contradictory actions on morphological change of CD5(+) B1 cells into macrophage-like cells. Differential regulation of CD5(+) B1 cells by IFN-gamma, a Th1 cytokine, and IL-4, a Th2 cytokine, may have clear immunological significance.     

Heterogeneity of CD4(+) and CD8(+) T cells

There is extensive plasticity in the T-cell response to antigen. Helper CD4(+) T cells, cytotoxic CD8(+) T cells, the progression from na?ve to effector and memory T cells, and differentiation into Th1, Tc1, Th2 and Tc2 subsets have long been recognized. More recently it has become apparent that T-cell populations display additional diversity in terms of phenotype, anatomical distribution and effector function.     

Age-related changes in the occurrence and characteristics of thymic CD4(+) CD25(+) T cells in mice

Natural regulatory CD4(+) CD25(+) T cells play an important role in preventing autoimmunity by maintaining self-tolerance. They express CD25 constitutively and are produced in the thymus as a functionally mature T-cell population. Changes in the potential of these cells to regulate the activity of conventional effector lymphocytes may contribute to an increased susceptibility to infection, cancer and age-associated autoimmune diseases. In this study we demonstrated that the thymi of aged mice are populated by a higher percentage of CD4(+) CD25(+) thymocytes than in young animals. The expression of several surface markers (CD69, CD5, CD28, CTLA-4, CD122, FOXP3), usually used to characterize the phenotype of CD4(+) CD25(+) T regulatory cells, was compared between young and aged mice. We also examined the ability of sorted thymus-deriving regulatory T cells of young and aged BALB/c mice to inhibit the proliferation of lymph node lymphocytes activated in vitro. Natural regulatory T cells isolated from the thymi of young mice suppress the proliferation of responder lymph node cells. We demonstrated that thymus-deriving CD4(+) CD25(+) T cells of old mice maintain their potential to suppress the proliferation of activated responder lymphocytes of young mice. However, their potential to inhibit the proliferation of old responder T cells is abrogated. Differences in the occurrence and activity of CD4(+) CD25(+) thymocytes between young and old animals are discussed in relation to the expression of these surface markers.     

Increased host resistance against Pneumocystis carinii pneumonia in gammadelta T-cell-deficient mice: protective role of gamma interferon and CD8(+) T cells

Although a clear relationship between alphabeta T-cell receptor-positive (alphabeta-TCR(+)) CD4(+) T cells and susceptibility to Pneumocystis carinii infection exists, the role of other T-cell subsets is less clearly defined. Previous studies have shown that gammadelta-TCR(+) T cells infiltrate into the lung during P. carinii pneumonia. Therefore, the present study examined the role of gammadelta-TCR(+) T cells in host defense against P. carinii pneumonia. C57BL/6 (control) and B6.129P2-Tcrd(tm1Mom) (gammadelta-TCR(+) T-cell-deficient) mice were inoculated intratracheally with P. carinii. At specific time points, mice were sacrificed and analyzed for P. carinii burden, T-cell subsets, and cytokine levels in lung tissue. Analysis of P. carinii burden showed a more rapid and complete resolution of infection in gammadelta-TCR(+) T-cell-deficient mice than in C57BL/6 controls. This augmented resolution was associated with elevated gamma interferon (IFN-gamma) levels in bronchoalveolar lavage fluid predominantly produced by CD8(+) T cells, as well as an increased recruitment of CD8(+) T cells in general. In separate experiments, neutralization of IFN-gamma or depletion of CD8(+) T cells early during infection abolished the augmented resolution previously observed in gammadelta-TCR(+) T-cell-deficient mice. These results show that the presence of gammadelta-TCR(+) T cells modulates host susceptibility to P. carinii pneumonia through interactions with pulmonary CD8(+) T cells and tissue production of IFN-gamma.     

Selective expansion of memory CD4(+) T cells by mitogenic human CD28 generates inflammatory cytokines and regulatory T cells

Costimulatory signals are important for development of effector and regulatory T cells. In this case, CD28 signaling is usually considered inert in the absence of signaling through the TCR. By contrast, mitogenic rat CD28 mAb reportedly expand regulatory T cells without TCR stimulation. We found that a commercially available human CD28 mAb (ANC28) stimulated PBMC without TCR co-ligation or cross-linking; ANC28 selectively expanded CD4(+)CD25(+)FOXP3(-) (Teff) and CD4(+)CD25(+)FOXP3(+) (Treg) cells. ANC28 stimulated the CD45RO(+) CD4(+) (memory) population, whereas CD45RA(+)CD4(+) (naive) cells did not respond. ANC28 also induced inflammatory cytokines. Treg induced by ANC28 retain the Treg phenotype longer than costimulated Treg. Treg induced by ANC28 suppressed CD25(-) T cells through a contact-dependent mechanism. Purity influenced the response of CD4(+)CD25(+ )cells because bead-purified CD4(+)CD25(+ )cells (85-90% pure) responded strongly to ANC28, whereas 98% pure FACS-sorted CD4(+)CD25(bright) (Treg) did not respond. Purified CD4(+)CD25(int) cells responded similarly to the bead-purified CD4(+)CD25(+) cells. Thus, pre-activated CD4(+) T cells (CD25(int)) respond to ANC28 rather than Treg (CD25(bright)). The ability of ANC28 to expand both effectors producing inflammatory cytokines as well as suppressive regulatory T cells might be useful for ex vivo expansion of therapeutic T cells.     

Resting CD4(+) T cells with CD38(+)CD62L(+) produce interleukin-4 which contributes to enhanced replication of T-tropic human immunodeficiency virus type 1

A significant increase in the CD38(+) population among T lymphocytes has been observed in human immunodeficiency virus type 1 (HIV-1)-infected carriers. We previously reported a higher replication rate of T-tropic HIV-1 in the CD4(+)CD38(+)CD62L(+) than CD38(-) subset under conditions of mitogen stimulation after infection. Here, we revealed a similarly high susceptibility in the CD38(+) subset on culture with conditioned medium containing Th2 cytokine, interleukin (IL)-4 that was produced endogenously from this subset on stimulation with mitogen or anti-CD3 antibody for 3 days. The contribution of IL-4 to the upregulated production of virus in the CD38(+) subset was confirmed by culture of this subset with recombinant human IL-4. In contrast, the rate of replication in the CD38(-) subset was not augmented in the conditioned medium from either subset or with IL-4. However, there were no differences in the surface expression of IL-4 receptor or HIV-1 receptors CD4 and CXCR4 between the two subsets. Thus, the CD4(+)CD38(+)CD62L(+) subset comprises a specific cell population secreting endogenous Th2 cytokine that contributes to the efficient production of T-tropic HIV-1 through upregulation at a certain stage of the viral life cycle, probably after the adsorption step.     

Functions of tetramer-stained HIV-specific CD4(+) and CD8(+) T cells

Significant insight has been gained into constraints on the sensitivity and specificity of staining with class I tetramers. The function of the populations that are defined varies with the clinical situation. Insight has also been gained into the determinants of the CD8(+) T cell response during primary and chronic HIV infection. Human class II tetramers have been synthesised but their role in defining CD4(+) T cell function in HIV infection remains to be determined.     

Enhanced gamma interferon production through activation of Valpha14(+) natural killer T cells by alpha-galactosylceramide in interleukin-18-deficient mice with systemic cryptococcosis

We showed recently that activation of Valpha14(+) natural killer T cells (NKT cells) by alpha-galactosylceramide (alpha-GalCer) resulted in increased gamma interferon (IFN-gamma) production and host resistance to intravenous infection with Cryptococcus neoformans. In other studies, interleukin-18 (IL-18) activated NKT cells in collaboration with IL-12, suggesting the possible contribution of this cytokine to alpha-GalCer-induced IFN-gamma synthesis. Here we examined the role of IL-18 in alpha-GalCer-induced Th1 response by using IL-18KO mice with this infection. In these mice, levels of IFN-gamma in serum and its synthesis in vitro by spleen cells stimulated with live organisms were not reduced, but rather enhanced, compared to those in wild-type (WT) mice, while such production was completely absent in IL-12KO mice. The enhanced production of IFN-gamma correlated with increased IL-12 synthesis but not with reduced production of IL-4, which was rather increased. IFN-gamma synthesis in IL-18KO mice was abolished by neutralizing anti-IL-12 antibody and significantly inhibited by neutralization of endogenous IL-4 with a specific monoclonal antibody. In addition, administration of recombinant IL-4 significantly enhanced the production of IFN-gamma in WT mice. Finally, the enhanced production of IFN-gamma in IL-18KO mice correlated with increased host defense against cryptococcal infection, as indicated by enhancement in alpha-GalCer-related clearance of microorganisms. Our results indicated that in IL-18KO mice, IFN-gamma synthesis was enhanced through overproduction of IL-12 and IL-4 after intravenous infection with C. neoformans and a ligand-specific activation of Valpha14(+) NKT cells.     

Requirements for CD4+ cells and gamma interferon in resolution of established Cryptosporidium parvum infection in mice.

The importance of CD4+ cells and gamma interferon (IFN-gamma) in the resolution of established Cryptosporidium parvum infection was investigated with a murine model of cryptosporidiosis in severe combined immunodeficient (SCID) mice. C. parvum-infected SCID mice were reconstituted with spleen cells from immunocompetent donors. The recipients were able to resolve their C. parvum infection by 17 days postreconstitution. Treatment of reconstituted SCID mice with either anti-CD4 monoclonal antibodies to deplete them of CD4+ cells or with anti-IFN-gamma to neutralize IFN-gamma activity reduced or eliminated their ability to resolve C. parvum infection whereas treatment with either anti-CD8 monoclonal antibodies or anti-asialo-GM1 antibodies had no effect. We also found C. parvum-specific antibodies in serum samples from two of four reconstituted SCID mice killed on postreconstitution day 17 but not in unreconstituted SCID mice. Moreover, anti-CD4-treated mice had no detectable specific antibodies to C. parvum, whereas all mice treated with either anti-CD8 or anti-asialo-GM1 had substantial levels of specific antibodies in their serum. Although the role of the specific antibody is not known, these findings clearly indicate that resolution of an established C. parvum infection in immunologically reconstituted SCID mice is dependent on both CD4+ cells and IFN-gamma.     

Total glucosides of paeony induces regulatory CD4(+)CD25(+) T cells by increasing Foxp3 demethylation in lupus CD4(+) T cells

Total glucosides of paeony (TGP), an active compound extracted from Paeony root, has been used in therapy for autoimmune diseases. However the molecular mechanism of TGP in the prevention of autoimmune response remains unclear. In this study, we found that TGP treatment significantly increased the percentage and number of Treg cells in lupus CD4(+) T cells. Further investigation revealed that treatment with TGP increased the expression of Foxp3 in lupus CD4(+) T cells by down-regulating Foxp3 promoter methylation levels. However, we couldn't observe similar results in healthy control CD4(+) T cells treated by TGP. Moreover, our results also showed that IFN-γ and IL-2 expression was enhanced in TGP-treated lupus CD4(+) T cells. These findings indicate that TGP inhibits autoimmunity in SLE patients possibly by inducing Treg cell differentiation, which may in turn be due to its ability to regulate the methylation status of the Foxp3 promoter and activate IFN-γ and IL-2 signaling.     

Cytolytic CD4(+) T cells in viral immunity

It is generally believed that the role of CD4(+) T cells is to coordinate the different arms of the adaptive immune system to shape an effective response against a pathogen and regulate nonessential or deleterious activities. However, a growing body of evidence suggests that effector CD4(+) T cells can directly display potent antiviral activity themselves. The presence of cytolytic CD4(+) T cells has been demonstrated in the immune response to numerous viral infections in both humans and in animal models and it is likely that they play a critical role in the control of viral replication in vivo. This article describes the current research on virus-specific cytolytic CD4(+) T cells, with a focus on HIV-1 infection and the implications that this immune response has for vaccine design.     

Cognate CD4(+) T cell licensing of dendritic cells in CD8(+) T cell immunity

Several studies have indicated that CD8(+) T cells require CD4(+) T cell help for memory formation. Evidence suggests that such help can be antigen independent, challenging whether the 'licensing' of dendritic cells (DCs) by CD4(+) T cells is ever required for cytotoxic T lymphocyte (CTL) responses. We show here that help is essential for the generation of CTL immunity to herpes simplex virus 1 and that CD4(+) T cells mediate help in a cognate, antigen-specific way. We provide direct in vivo evidence for DC licensing by helper T cells and show that licensing is rapid and essential for the formation of effector and memory CTLs. In situations in which DCs are poorly licensed by pathogen-derived signals, our findings suggest that CTL immunity may be heavily dependent on cognate DC licensing.     

LACK-specific CD4(+) T cells that induce gamma interferon production in patients with localized cutaneous leishmaniasis during an early stage of infection

The profile of cytokines induced by soluble leishmania antigen (SLA) and the Leishmania homologue of the mammalian receptor for activated C kinase (LACK), a candidate vaccine against leishmaniasis, and the cellular source of the cytokines produced in response to these antigens were analyzed in patients infected with Leishmania guyanensis. Gamma interferon (IFN-gamma) and interleukin-10 (IL-10) were produced in response to LACK. Although LACK-specific CD4(+) cells producing IFN-gamma were isolated only during the early phase of infection (less than 30 days following the onset of infection), cells producing IL-10 in response to LACK were detected in all patients. CD4(+) T cells producing IFN-gamma and IL-13 were produced in response to SLA in all patients. SLA- and LACK-specific T cells are effector memory cells, as they are CD45RA(-) CCR7(-) CD4(+) T cells. CD4(+) T cells producing IFN-gamma are CD62L(-), and CD4(+) T cells producing IL-10 are CD62L(+), indicating that these cells have different tissue-homing capacities. These findings show that SLA and LACK induce both type 1 (IFN-gamma) and type 2 (IL-10 or IL-13) cell responses.     

Immunity to murine Chlamydia trachomatis genital tract reinfection involves B cells and CD4(+) T cells but not CD8(+) T cells

CD4(+) T-helper type 1 (Th1) responses are essential for the resolution of a primary Chlamydia trachomatis genital tract infection; however, elements of the immune response that function in resistance to reinfection are poorly understood. Defining the mechanisms of immune resistance to reinfection is important because the elements of protective adaptive immunity are distinguished by immunological memory and high-affinity antigen recognition, both of which are crucial to the development of efficacious vaccines. Using in vivo antibody depletion of CD4(+) and CD8(+) T cells prior to secondary intravaginal challenge, we identified lymphocyte populations that functioned in resistance to secondary chlamydial infection of the genital tract. Depletion of either CD4(+) or CD8(+) T cells in immune wild-type C57BL/6 mice had a limited effect on resistance to reinfection. However, depletion of CD4(+) T cells, but not CD8(+) T cells, in immune B-cell-deficient mice profoundly altered the course of secondary infection. CD4-depleted B-cell-deficient mice were unable to resolve a secondary infection, shed high levels of infectious chlamydiae, and did not resolve the infection until 3 to 4 weeks following the discontinuation of anti-CD4 treatment. These findings substantiated a predominant role for CD4(+) T cells in host resistance to chlamydial reinfection of the female genital tract and demonstrated that CD8(+) T cells are unnecessary for adaptive immune resistance. More importantly, however, this study establishes a previously unrecognized but very significant role for B cells in resistance to chlamydial reinfection and suggests that B cells and CD4(+) T cells may function synergistically in providing immunity in this model of chlamydial infection. Whether CD4(+) T cells and B cells function independently or dependently is unknown, but definition of those mechanisms is fundamental to understanding optimum protective immunity and to the development of highly efficacious immunotherapies against chlamydial urogenital infections.     

Bovine gamma globulin-specific CD4+ T cells are retained by bovine gamma-globulin-tolerant mice.

Immunological tolerance is an acquired state of antigen-specific nonresponsiveness which is generally attributed to either the deletion or suppression of tolerogen-specific T helper cell clones. Unresponsiveness to xenogeneic immunoglobulins can be readily induced and has been extensively studied in order to ascertain the means by which tolerance is established and maintained. As an absence of reactivity to foreign immunoglobulin has been noted in situations where suppressor cell activity was minimized, this tolerant state has often been ascribed to clonal deletion. The present study demonstrates that bovine gamma-globulin (BGG)-tolerant mice are unable to generate humoral responses to BGG in vivo and yet harbor BGG-specific CD4+CD8- T cells which can divide and secrete interleukin 2 when stimulated in vitro. Indeed, the in vitro reactivity to BGG of these cells exceeded that of a similar population of non-immune cells. This is in direct opposition to the loss of response that would be expected if clonal deletion were operative. The presence of BGG-specific CD4+ T cells, which appear to be at least partly primed, in mice unresponsive to BGG, indicates that tolerance to BGG is likely to be dependent on unidentified immunoregulatory processes rather than clonal deletion.     

Control of T cell hyperactivation in IL-2-deficient mice by CD4(+)CD25(-) and CD4(+)CD25(+) T cells: evidence for two distinct regulatory mechanisms

In IL-2-deficient mice, antigen-activated CD4 T cells accumulate and cause lethal immune pathology. Wild-type cells of hematopoietic origin present in the same animal are able to prevent this hyperactivation of T cells, but the mechanisms and cells controlling the IL-2-deficient cells are unknown. Here we show that IL-2(-) CD4 cells with an ovalbumin-specific transgenic TCR (IL-2(-) OVAtg) undergo both clonal expansion and clonal contraction when transferred to euthymic recipients and challenged with antigen, but continuously expand in athymic hosts. Cotransfer of wild-type CD4 T cells prevents the accumulation of IL-2-deficient cells. On the residual IL-2(-) TCRtg cells CD69 and CD25 are up-regulated, suggesting that activation per se is not suppressed and that the cells had received an IL-2 signal. Since IL-2 is able to restore the defective antigen-induced cell death (AICD) of IL-2-deficient T cells in vitro, paracrine IL-2 provided by the wild-type CD4 cells may thus be able to allow clonal contraction of IL-2-deficient cells also in vivo. Interestingly however, regulatory CD4(+)CD25(+) cells also efficiently contain the clone size of antigen-stimulated IL-2-deficient T cells. Since CD4(+)CD25(+) cells do not produce IL-2, this suggests a mechanism of suppression distinct from paracrine IL-2 delivery. In keeping with this, the residual IL-2(-) TCRtg cells recovered after cotransfer of regulatory CD4(+)CD25(+) cells do not show increased CD25 or CD69 expression, suggesting that they had not received paracrine IL-2 and that clonal containment occurred at the level of initial activation rather than clonal contraction by AICD. IL-2 deficiency therefore may upset T cell homeostasis by two distinct mechanisms: the failure to program expanding T cells for apoptosis, and the failure to generate functional CD4(+)CD25(+) regulatory cells.     

Role of new population of peripheral CD11c(+)CD8(+) T cells and CD4(+)CD25(+) regulatory T cells during acute and remission stages in rheumatoid arthritis patients.

BACKGROUND AND PURPOSE: Rheumatoid arthritis (RA) is a CD4(+)-dependent chronic systemic inflammatory disease with autoimmune features. Autoreactive CD4(+) T-cell activation can result in autoimmune diseases. One of the key regulators is the CD4(+)CD25(high) regulatory T (Treg) cell. In an animal arthritis model, CD11c(+)CD8(+) T cells were found to be elevated, and could suppress pathogenic CD4(+) T cells after cross-linking with CD137. The purpose of this study was to compare the expression of CD137, CD4(+)CD25(high) Treg cells, and CD11c(+)CD8(+) in the peripheral blood T lymphocytes of RA patients during active and remissive states, and evaluate the correlation with disease activity. METHODS: Thirty nine RA patients treated at the rheumatology outpatient clinic at the Changhua Christian Hospital were assessed clinically for disease activity and classified as either highly active or remissive by the Disease Activity Score 28. Peripheral blood mononuclear cells were isolated from these patients and compared against normal controls. RESULTS: The presence of CD11c(+)CD8(+) T cells or the expression of CD137 molecules in peripheral blood cells was not related to disease activity. In contrast, CD4(+)CD25(high) Treg cell levels were increased significantly in patients with active RA compared with patients with remissive RA or controls (p<0.05). These lymphocytes were intact, without evidence of apoptosis. CONCLUSIONS: Our results indicate that CD4(+)CD25(high) Treg cells play an important role in modulating RA disease activity and can serve as a parameter of disease activity.