CD45RB expression defines two interconvertible subsets of human CD4+ T cells with memory function

Reciprocal expression of CD45RA and CD45RO in human CD4⁺ T cells defines populations understood to be naive cells (CD45RA⁺CD45RO^?) and memory cells (CD45RA^?CD45RO⁺). We investigate two subsets of CD45RA^?CD45RO⁺ CD4⁺ human T cells which differ by fourfold in their expression of the CD45RB isoform; one is CD45RB^bright and the other is CD45RB^intermediate. In contrast, CD45RA⁺ naive cells are all CD45RB^bright. Both subsets of CD45RA^? cells proliferate in response to recall antigens so we designate them MEM 1 (CD45RO⁺RB^bright) and MEM 2 (CD45RO⁺RB^intermediate). CD45RA and CD45RB expression are regulated independently during in vitro activation of naive cells. When MEM 1 cells are activated they tend to down-regulate CD45RB expression, whereas activated MEM 2 cells tend to up-regulate CD45RB expression. Thus, in contrast to the stability of the CD45RA^?CD45RO⁺ phenotype, the MEM 1 and MEM 2 phenotypes are labile and may interconvert. MEM 1 and MEM 2 cells produced comparable amounts of interleukin(IL)?2, IL?4, and IL-5 though MEM 1 cells produced slightly more interferon(IFN)-γ (mean 1.7-fold more). MEM 1 cells consistently proliferated more (mean 2.3-fold more) than MEM 2 cells early during in vitro activation. Thus, differential expression of CD45RB within CD45RA^? cells defines two subsets that have similar properties except for somewhast greater IFN-γ production and proliferative responses by MEM 1 cells. Variability in CD45RB expression may represent a mechanism for fine-tuning the responsiveness of memory cells in vivo.     

CD3 expression distinguishes two γδT cell receptor subsets with different phenotype and effector function in tuberculous pleurisy

Tuberculous pleurisy is a naturally occurring site of Mycobacterium tuberculosis (Mtb) infection. Herein, we describe the expression of activation, natural killer (NK) and cell migration markers, as well as effector functions from γδT cells in peripheral blood (PB) and pleural effusion (PE) from tuberculosis patients (TB). We observed a decreased percentage of circulating γδT from TB patients and differential expression of NK as well as of chemokine receptors on PB and PE. Two subsets of γδT cells were differentiated by the CD3/γδT cell receptor (γδTCR) complex. The γδTCR^low subset had a higher CD3 to TCR ratio and was enriched in Vδ2⁺ cells, whereas most Vδ1⁺ cells belonged to the γδTCR^high subset. In PB from TB, most γδTCR^high were CD45RA⁺CCR7^‐ and γδTCR^low were CD45RA^+/?CCR7⁺CXCR3⁺. In the pleural space the proportion of CD45RA^‐CCR7⁺CXCR3⁺ cells was higher. Neither spontaneous nor Mtb‐induced interferon (IFN)‐γ production was observed in PB‐γδT cells from TB; however, PE‐γδT cells showed a strong response. Both PB‐ and PE‐γδ T cells expressed surface CD107a upon stimulation with Mtb. Notably, PE‐γδTCR^low cells were the most potent effector cells. Thus, γδT cells from PB would acquire a further activated phenotype within the site of Mtb infection and exert full effector functions. As γδT cells produce IFN‐γ within the pleural space, they would be expected to play a beneficial role in tuberculous pleurisy by helping to maintain a T helper type 1 profile.     

CD45RA expression on γδ and αβ T cells emigrating from the fetal and postnatal thymus

We have compared the expression of CD45RA on αβ and γδ T cells emigrating from the fetal and postnatal thymus. The fetal and postnatal thymus export both CD45RA⁺ and CD45RA^- T cells. The number of γδ⁺CD45RA⁺ T cells was remarkably constant regardless of stage of ontogeny or T cell maturity. Around 5--8% of γδ thymic emigrants, thymocytes and peripheral blood lymphocytes expressed CD45RA in both fetal and postnatal animals. In contrast to γδ T cells, up to one quarter of both fetal and postnatal αβ emigrants expressed CD45RA. Post-thymic maturation of CD45RA expression on αβ emigrants, which occurred both before and after birth, appeared to be antigen independent.     

Specific patterns of CD4-associated immunosenescence in vertically HIV-infected subjects

Vertical transmission of human immunodeficiency virus (HIV) represents an important world-wide health problem although the incidence in developed countries has been drastically reduced by the extensive use of highly active antiretroviral therapy. Vertically HIV-infected subjects have been exposed to the virus during the maturation of their immune systems and have suffered a persistent chronic activation throughout their lifetime; the consequences of this situation for their immune system are not fully understood. The objective of this study was to analyse immunosenescence-related parameters in different CD4 T-cell subsets. Fifty-seven vertically HIV-infected subjects and 32 age-matched healthy subjects were studied. Activation (HLA^– DR⁺), senescence (CD28^– CD57⁺) and proliferation (Ki67⁺) were analysed on different CD4 T-cell subsets: naive (CD45RA⁺ CD27⁺), memory (CD45RO⁺ CD27⁺), effector memory (CD45RO⁺ CD27^–) and effector memory RA (CD45RA⁺ CD27^–). Compared with healthy subjects, vertically HIV-infected subjects showed increased naive and memory CD4 T-cell frequencies (p 0.035 and p 0.010, respectively) but similar frequencies of both effector subsets. Whereas naive CD4 T cells were not further altered, memory CD4 T cells presented increased levels of senescence and proliferation markers (p <0.001), effector memory CD4 T cells presented increased levels of activation, senescence and proliferation markers (p <0.001) and effector memory RA CD4 T cells presented increased levels of activation and senescence (p <0.001) compared with healthy subjects. Despite long periods of infection, vertically HIV-infected subjects show specific patterns of immunosenescence, revealing a preserved CD4 T-cell homeostasis for subset differentiation and distribution. Nevertheless, excepting the naive subpopulation, all subsets experienced some immunosenescence, pointing to uncertain consequences of the future aging process in these subjects.     

CD8+ and CD45RA+ human peripheral blood lymphocytes are potent sources of macrophage inflammatory protein 1α, interleukin-8 and RANTES

The chemokines macrophage inflammatory protein 1α (MIP 1α), interleukin-8 (IL-8) and RANTES are potent regulators of leukocyte trafficking. Examination of chemokine secretion by human peripheral blood lymphocytes after stimulation with anti-CD3 or phorbol 12, 13 myristate acetate and ionomycin showed CD8⁺ cells were the dominant source of MIP 1α and RANTES. Although production of MIP 1α and IL-8 were similar in pharmacologically stimulated CD4⁺ CD45RA⁺, CD4⁺ CD45RO⁺, and CD8⁺ CD45RA⁺ cells, the largest amounts of MIP 1α and RANTES were secreted by CD8⁺ CD45RO⁺ lymphocytes. A parallel pattern of prolonged chemokine mRNA expression for at least 18 h after activation was observed in the T cell subsets. These results confirm that human T lymphocytes have a unique capacity for secretion of these three chemokines. In addition, CD8⁺ cells have an unrecognized role in recruiting cells to sites of inflammation, and adult human CD45RA⁺ cells have a physiologically significant secretory capacity.     

The effect of allogeneic in vitro stimulation and in vivo immunization on memory CD4+ T‐cell APOBEC3G expression and HIV‐1 infectivity

Allogeneic immunity is one of the most potent natural immune responses. APOBEC3G (A3G) is an intracellular anti‐viral factor that deaminates cytidine to uridine. Allogeneic stimulation of human CD4⁺ T cells in vitro upregulated A3G mRNA and a significant correlation was found between the mixed leukocyte reaction and A3G mRNA. The mechanism of upregulation of A3G mRNA involves interaction between HLA on DC and TCR of CD4⁺ T cells, which is ZAP70 and downstream ERK phosphokinase signalling dependent and induces CD40L and A3G mRNA expression in CD4⁺ T cells. Alloimmune‐induced A3G was found to be significantly increased in CD45RA^?, CCR5⁺ and CD45RA^?CCR7^? subsets of effector memory T cells. In vivo studies of women alloimmunized with their partners' PBMC also showed a significant increase in A3G protein in CD4⁺ T cells, CD45RO⁺ memory and CCR7^? effector memory T cells. The functional effect of allostimulation upregulating A3G mRNA was demonstrated by a significant decrease in in vitro infectivity, using GFP‐labelled pseudovirus and confirmed by a decrease in HIV‐1 (BaL) infection of primary CD4⁺ T cells. The results suggest that alloimmunization offers an alternative or complementary strategy in inducing an innate anti‐viral factor that inhibits HIV‐1 infection.     

Phenotypic characterization of regulatory T cells from antiretroviral‐naive HIV‐1‐infected people

Regulatory T (Treg) cells play a key role in dampening excessive immune activation. However, antiretroviral therapy (ART) ‐naive HIV‐1 infection maintains the immune system in a sustained state of activation that could alter both Treg cell surface markers and functions. As Treg cell surface markers are directly linked to their functions the overall objective of this study was to determine how ART‐naive HIV infection affects the phenotypic properties of Treg cells. Our data showed that in ART‐naive HIV‐1 infection, Treg cells are dominated by effector (CD45RA⁺ CD27⁻ CCR7⁻ CD62L⁻) and effector memory (CD45RA⁻ CD27⁻ CCR7⁻ CD62L⁻) cells. In contrast Treg cells from HIV‐negative individuals were mainly naive (CD45RA⁺ CD27⁺ CCR7⁺ CD62L⁺) and central memory (CD45RA⁻ CD27⁺ CCR7⁺ CD62L⁺) cells. Whereas effector and effector memory Treg cells showed enhanced expression of CD39 (P < 0·05), CD73 (P < 0·001), HLA‐DR and CD38 (P < 0·001); naive and central memory Treg cells showed a significant reduction in the expression of these markers. Overall Treg cell frequencies within total CD4⁺ T cells correlated positively with plasmatic HIV‐1 viral load. As increased viral load is associated with augmented CD4⁺ T‐cell destruction; this could suggest a resistance of peripheral Treg cells to HIV‐1 destruction. Hence the modulation of Treg cell phenotype and frequencies could be considered in designing immunotherapeutic strategies targeting immune system restoration during HIV‐1 infection.     

Selective disbalances of peripheral blood T lymphocyte subsets in human CD3γ deficiency

The selection of T lymphocytes in the thymus and their activation upon the encounter with foreign antigens in the periphery require the aggregation and signals of the Tcell receptor (TcR)/CD3 complex and several surface molecules termed coreceptors (notably CD4 or CD8 and CD45). The spatial arrangement and interactions of the different molecules in the resulting multimolecular recognition structure are mostly unknown. Here we report, from studies on a healthy human CD3γ deficiency, that the lack of the CD3γ component of the TcR/CD3 complex is associated with a long-term severe defect of peripheral blood CD4⁺CD45RA⁺ and CD8+ lymphocytes, whereas CD4⁺CD45RO⁺, B and natural killer lymphocytes are unaffected. These results suggest that the CD3y site of the TcR/CD3 complex is required for the peripheral representation of certain Tcell types.     

Role of γδ T lymphocytes in the development of Behçet's disease

Phenotypic and functional properties of γδ T cells, which play an important role in mucocutaneous immunity, were examined to elucidate whether immunological abnormality in Behc¸et's disease may be related to a specific T cell population. We found that CD45RA⁺Vγ9⁺Vδ2⁺γδ T cells, which constitute a minor population of γδ T cells in healthy individuals, were increased in number in Behc¸et's disease irrespective of disease activity. This CD45RA⁺ subset of γδ T cells in the active, but not inactive, phase of this disease expressed IL-2Rβ and HLA-DR, suggesting that they are activated in vivo in active Behc¸et's disease. In addition, the CD45RA⁺γδ T cells produced extreme amounts of tumour necrosis factor and contained perforin granules. These data indicate that a phenotypically distinct subset of γδ T cells, CD45RA⁺CD45RO⁻Vγ9⁺Vδ2⁺, may contribute to immunological abnormalities which may lead to complexity of pathophysiology in Behc¸et's disease.     

Flow Cytometric Identification of CD93 Expression on Naive T Lymphocytes (CD4<Superscript>+</Superscript>CD45RA<Superscript>+</Superscript> Cells) in Human Neonatal Umbilical Cord Blood

Human CD93 has a molecular weight of about 100 kDa and is selectively expressed by myeloid cell lineages in peripheral blood (PB) mononuclear cells. Although CD93 was initially identified as a receptor for complement component 1, subcomponent q phagocytosis (C1qRp) involved in the C1q-mediated enhancement of the phagocytosis of various antigens, several recent studies have reported that CD93 is not a receptor for the C1q-mediated enhancement of phagocytosis. The expression patterns of CD93 have been previously investigated in PB mononuclear cells (lymphocytes, monocytes, and granulocytes) from adult PB and neonatal umbilical cord blood (UCB), and the expression of CD93 was not found on lymphocytes from either normal adult PB or neonatal UCB. However, the detection of CD93 expression in neonatal UCB using CD93 monoclonal antibodies (mAbs) that recognize different antigenic epitopes remains poorly understood. In this study, we examined the expression of CD93 on lymphocytes, monocytes, and granulocytes from neonatal UCB using four different types of CD93 mAb detection probes, mNI-11, R139, R3, and X-2, using flow cytometric and western blot analyses. We found that CD93, as defined using all four mAbs, was expressed on monocytes and granulocytes in PB mononuclear cells from adult PB and neonatal UCB. On the other hand, we observed for the first time that the expression of CD93 on lymphocytes in neonatal UCB can only be detected using the mNI-11 mAb, established in our laboratory, and not with commercially available CD93 mAbs (R139, R3, and X-2). However, CD93 expression on lymphocytes from normal adults was not detected using any of the four CD93 mAbs. Two-color flow cytometric analyses showed that the CD93 recognized by mNI-11 mAb was expressed on CD3⁺ T lymphocytes (mainly CD4⁺ helper T lymphocytes), but not on CD19⁺ B lymphocytes or on CD8⁺ suppressor/cytotoxic T lymphocytes from neonatal UCB. In addition, CD93 was expressed on CD45RA⁺ (naive antigen) lymphocytes from neonatal UCB, but not on CD45RO⁺ (memory antigen) lymphocytes from neonatal UCB or on CD45RA⁺ and CD45RO⁺ lymphocytes from normal adult PB. Three-color flow cytometric analysis showed that CD93 was co-expressed on naive T lymphocytes (CD4⁺CD45RA⁺) from neonatal UCB. In a western blot analysis, the CD93 mAb (mNI-11) immunoprecipitated at a molecular weight of 98 kDa, identified as a CD93 molecule, in the CD4⁺CD45RA⁺ cells from neonatal UCB but not from adult PB, similar to the results in the human monocyte-like cell line U937 (human CD93-positive cells). Taken together, these results provide the first direct evidence of a novel/naive cell population (CD4⁺CD45RA⁺CD93⁺) in neonatal UCB that may have an important role in cell biology, transplantation, and immature/mature immune responses.     

The major population of PHA-stimulated PBMC infected by R5 or X4 HIV variants after a single cycle of infection is predominantly composed of CD45RO<Superscript>+</Superscript>CD4<Superscript>+</Superscript> T lymphocytes

Summary. PHA-stimulated peripheral blood mononuclear cells (PBMCs) are widely used for investigating replication and neutralization of HIV primary isolates in vitro. The objective of this study was to identify the T lymphocyte subset(s) that are found infected after one replication cycle by either R5- or X4-HIV-1 variants in PHA-stimulated PBMCs from healthy donors. Infected T lymphocytes were detected by intracellular p24 staining and characterized by cell surface immunophenotyping using flow cytometry. The predominant lymphocyte subset expressing p24 after 24 h of infection with either R5 or X4 HIV-1 strains was found to exhibit mainly the memory CD45RO phenotype, a greater percentage of CD62L⁺CD45RO⁺ central memory T lymphocytes was infected with X4 HIV strains. Although some CD45RA⁺ lymphocytes were also infected, these cells co-expressed CD45RO⁺. The proportion of lymphocytes expressing CD4 and CD4/CD45RO decreased by 20% after 24 h of infection. A 2-fold decrease of CD4⁺CD8⁺ T lymphocytes could also be recorded, even though this subset accounted for less than 5% of total lymphocytes in control cultures. Moreover, CD4⁺CD8⁺ T cells further decreased by 90% after 4 days of infection, a time at which they scored p24⁺. Therefore, our results indicate that the in vitro infection system of PHA-stimulated PBMC utilized in neutralization assays provides an appropriate model for the study of infected CD45RO⁺ lymphocytes but not CD45RA⁺ lymphocytes.     

mTOR signaling promotes a robust and continuous production of IFN‐γ by human memory CD8+ T cells and their proliferation

Human CD8⁺ T cells are functionally heterogeneous and can be divided into phenotypically and functionally distinct subsets according to CCR7 and CD45RA expression levels. Among these, CCR7^lowCD45RA^low effector memory CD8⁺ T cells (Tem) and CCR7^lowCD45RA^high CD8⁺ T cells, which are designated as Temra and considered to be terminally differentiated cells, are Ag‐experienced T cells but show different functionalities. Here, we show that, while Tem proliferate vigorously and produce IFN‐γ persistently and robustly, Temra proliferate poorly and lose the ability to produce IFN‐γ over time after TCR stimulation. Temra showed impaired cell growth upon TCR stimulation, which was associated with defective activation of the mammalian target of rapamycin (mTOR) signaling. Furthermore, rapamycin, an inhibitor of mTOR signaling, interfered with the robust and continuous proliferation of and IFN‐γ production by Tem at later time points after TCR stimulation. Thus, these data collectively indicate that activation of mTOR signaling is required for the robust functions of Tem cells in humans and suggest that defective mTOR signaling in Temra contributes to their functional impairment.     

Naive and memory T cell infiltrates in chronic hepatitis C: phenotypic changes with interferon treatment

The phenotypes of infiltrating lymphocytes in liver with chronic hepatitis C, including changes associated with interferon (IFN) treatment, were characterized. Specimens obtained from 22 patients treated with IFN were examined using avidin-biotin-peroxidase immunohistochemistry. In areas of lobular and periportal inflammation, most lymphocytes were CD8⁺ T cells of the CD45RO⁺ (memory) subset. The centres of lymphoid follicles were occupied by CD20⁺ B cells and a few CD4⁺ T cells which were CD45RA⁺ (naive subset). Follicular centres were surrounded mainly with CD4⁺ T cells. CD8⁺ T cells, mostly CD45RO⁺, were scattered through the mantle zones of follicles and extended around them. No significant changes in CD45RA⁺ lobular infiltrates accompanied IFN treatment. On the other hand, the number of CD45RO⁺ lobular infiltrates decreased after IFN treatment in complete responders (P <0.01). Moreover, there were significant correlations between CD45RO⁺ cell counts and serum alanine aminotransferase concentrations, CD45RO⁺ cell counts and the liver histologic grade and CD45RO⁺ cell counts and CD8⁺ cell counts. These results suggest that CD8⁺ memory T cells participate in hepatocyte injury in chronic hepatitis C, and that a decrease of CD8⁺ memory T cells correlates with the decreased liver inflammation with IFN treatment.     

Differential expression of lymphocyte homing receptors by human memory/effector T cells in pulmonary versus cutaneous immune effector sites

The heterogeneous expression of lymphocyte homing receptors (HR) by the (CD45RA^low/RO^high) memory/effector T cell population in the human is thought to define subsets with tissue-selective recirculatory potential. To investigate further the localization characteristics of these T cells, we used multiparameter flow cytometry to quantitate T cell subsets defined by expression of the skin-selective HR called the cutaneous lymphocyte-associated antigen (CLA), the peripheral lymph node (PLN) HR L-selectin, the mucosal-associated HR α4β7-integrin, and the mucosal-associated adhesion molecule αeβ7-integrin in either cutaneous or pulmonary immune effector sites and corresponding peripheral blood. Compared to peripheral blood, skin T cells were highly enriched for the CLA⁺/L-selectin⁺/αeβ7-integrin^? memory/effector subset, whereas lung memory/effector T cells were predominantly CLA^{?to low} L-selectin^?, and almost half were αeβ7-integrin⁺. α4β7-integrin expressing memory/effector T cells were diminished in both skin and lung, suggesting that this HR is not a major participant in determining localization specificity in either of these sites. The characteristic pulmonary T cell HR phenotype did not significantly differ between the normal subjects and those with pulmonary inflammatory disease, and did not correlate with markers of T cell activation. Induction of a rapid up-regulation of pulmonary inflammation via intrabronchial allergen challenge in asthmatic patients tended to decrease localization specificity, resulting in a more general importation of memory/effector subsets. Taken together, these results suggest that tissue microenvironments play a major role in determining the character of local T cell infiltrates via their ability to import and retain memory/effector subsets selectively or, more generally, depending on the intensity of local inflammatory stimuli.     

Selective infection of CD4 effector memory T lymphocytes leads to preferential depletion of memory T lymphocytes in R5 HIV-1-infected humanized NOD/SCID/IL-2Rγ mice

To investigate the events leading to the depletion of CD4⁺ T lymphocytes during long-term infection of human immunodeficiency virus type 1 (HIV-1), we infected human CD34⁺ cells-transplanted NOD/SCID/IL-2Rγ^null mice with CXCR4-tropic and CCR5-tropic HIV-1. CXCR4-tropic HIV-1-infected mice were quickly depleted of CD4⁺ thymocytes and both CD45RA⁺ naïve and CD45RA⁻ memory CD4⁺ T lymphocytes, while CCR5-tropic HIV-1-infected mice were preferentially depleted of CD45RA⁻ memory CD4⁺ T lymphocytes. Staining of HIV-1 p24 antigen revealed that CCR5-tropic HIV-1 preferentially infected effector memory T lymphocytes (T_EM) rather than central memory T lymphocytes. In addition, the majority of p24⁺ cells in CCR5-tropic HIV-1-infected mice were activated and in cycling phase. Taken together, our findings indicate that productive infection mainly takes place in the activated T_EM in cycling phase and further suggest that the predominant infection in T_EM would lead to the depletion of memory CD4⁺ T lymphocytes in CCR5-tropic HIV-1-infected mice.     

CD3 antigen-mediated calcium signals and protein kinase C activation are higher in CD45R0+ than in CD45RA+ human T lymphocyte subsets

T lymphocytes may be separated into subsets according to their expression of CD45 isoforms. The CD45R0⁺ T cell subset has been reported to proliferate in response to recall antigen and to mitogenic mAb to a much greater extent than the CD45RA⁺ subset. This difference could be due to more efficient coupling of the T cell antigen receptor complex to mitogenic signaling pathways. To investigate this possibility, CD3 antigen-induced calcium signals, diacylglycerol (DAG) production and protein kinase C (PKC) activation levels were compared in CD45RA⁺ and CD45R0⁺ human T lymphocyte subsets derived from peripheral blood. The mean CD3-induced rise in intracellular calcium was 80% greater in CD45R0⁺ than in CD45RA⁺ cells. Basal DAG levels in CD45R0⁺ cells were found to be, on average, 60% higher than in CD45RA⁺ cells (p = 0.002), but the CD3-induced production of DAG over background was not different in the two subsets (p = 0.4). Basal PKC activity, and CD3-induced PKC activation levels over background, were found to be 50% and 140% higher, respectively, in CD45R0⁺ cells than in CD45RA⁺ cells (p = 0.015 and 0.023). The CD45R0⁺ subset contained a higher proportion of cells expressing activation markers, such as CD25, CD71 and major histocompatibility complex class II, when compared to the CD45RA⁺ subset. Our results suggest that the elevated basal DAG levels observed in the CD45R0⁺ subset may reflect the recent activation of these cells. Both the higher basal DAG and CD3-induced elevation in intracellular calcium observed in the CD45R0⁺ cells may contribute to the greater PKC activation signals triggered by CD3 mAb in this subset. These findings elucidate the greater response of CD45R0⁺ T cells to mitogenic stimuli compared to CD45RA⁺ cells.     

Distinct structural and functional epitopes of the αEβ7 integrin

Intestinal intraepithelial lymphocytes (iIEL) are predominantly CD3⁺, CD8⁺ T lymphocytes located above or adjacent to the mucosal basement membrane. Although they are positioned to interact with intercellular luminal antigen or with enterocytes, the function of iIEL remains unknown. Most (> 85%) of the iIEL express the α^Eβ₇ integrin which appears to be involved in the adhesion of lymphocytes to epithelial cells. We report the characterization of three monoclonal antibodies (mAb) termed αE7-1, αE7-2, and αE7-3, that react with the α^Eβ₇ integrin recognized by the previously described mAb HML-1 as demonstrated by identical sodium dodecyl sulfate – polyacrylamide gel electrophoresis mobility and charge. Flow cytometric analysis of antibody cross-blocking indicated that these mAb recognize distinct epitopes of α^Eβ₇. While all of the mAb were capable of blocking the adhesion of cultured iIEL to a breast epithelial cell line, only HML-1 and αE7-1 (which recognize an identical or closely related epitope) were co-stimulatory with suboptimal concentrations of anti-CD3 mAb in inducing proliferation of cultured iIEL. Thus, these mAb appear to recognize functionally distinct epitopes of α^Eβ₇ and will be useful to study relationships between the structure and function of this integrin.     

Differential expression of type I insulin-like growth factor receptors in different stages of human T cells

Insulin-like growth factor I (IGF-I) has been implicated to play a regulatory role in T cell development and in T cell function. We investigated the expression of type I IGF receptors on human peripheral T cells related to the maturation and activation stage using the type I IGF receptor-specific monoclonal antibody αIR3. It appeared that 87% of the CD4⁺CD45RA⁺ cells and 66% of the CD8⁺CD45RA⁺ cells were αIR3⁺, whereas only 37% of the CD4⁺CD45RO⁺ cells and 38% of the CD8⁺CD45RO⁺ cells bound αIR3. We also found that the fraction of αIR3⁺ cells within in vivo or in vitro activated (HLA-DR⁺) T cells is markedly lower than in nonactivated (HLA-DR^?) cells. In vitro phytohemagglutinin-activated T cells and CD4⁺CD45RO⁺ cells activated with recall antigens also contained less αIR3⁺ cells (1–6%) than nonactivated cells (30–54%).     

CD57+ T lymphocytes are derived from CD57− precursors by differentiation occurring in late immune responses

CD3⁺ T cells expressing the 110-kDa CD57 antigen are found in survivors of renal, cardiac and bone marrow transplants, in patients with acquired immune deficiency syndrome and in patients with rheumatoid arthritis. They are also present in normal individuals and expand upon ageing. They do not grow in culture and their role in the immune response is poorly understood. The expression of the various isoforms of the leukocyte common antigen (CD45) identifies a spectrum of differentiation in CD4⁺ and CD8⁺ T cells ranging from naive (CD45RA⁺CD45RB^brightCD45RO^?) through early primed cells (CD45RA^?RB^brightRO^dull) to highly differentiated memory cells which are CD45RA^?RB^dullRO^bright. CD45 isoforms expressed by CD57⁺ T cells showed distinct differences between CD4⁺ and CD8⁺ populations, but in each case indicated an advanced state of differentiation. The expression of T cell receptor Vβ families was highly variable between individuals, but both CD57⁺ and CD57^? cells show a full range of the specificities tested. Vβ expression was more closely related within either the CD4⁺ or the CD8⁺ subsets, irrespective of CD57 expression, than between these subsets, suggesting a relationship between CD57⁺ and CD57^? cells within the same T cell pool. This possibility was supported by experiments showing that CD3⁺CD57⁺ lymphocytes were similar to CD3⁺CD57^? T cells in terms of the production of basic T cell cytokines [interleukin (IL)-2, IL-4, and interferon-γ]. Furthermore, in vitro stimulation of CD3⁺CD57^? T cells in secondary mixed leukocyte reaction or by co-culture with IL-2 and IL-4 induced the appearance of CD3⁺CD57⁺ cells with phenotypic and functional similarities to in vivo CD3⁺CD57⁺ cells. These data strongly suggest that the expression of CD57 is a differentiation event which occurs on CD57^? T cells late in the immune response.