Murine CD4+ T-cell subsets

Characterization of a murine thymic CD4(+) T cell subset-TCRalphabeta (+) 3G11 (-) 6C10 (-) CD4 (+) CD8 (-) thymocytes

The presence of a relatively mature CD4(+) CD8(-) (SP) T cell subset in mouse thymus has been demonstrated. Composing of 10% of total CD4SP thymocytes, this subset is defined by the absence of 3G11 and 6C10 expression with a phenotype of CD69(+/-), HSA(med/lo) and heterogeneous for Qa-2 expression. The proliferation capability of TCRalphabeta(+) 3Gl l(-) 6C10(-) CD4(+) CD8(-) thymocytes was high while using Con A stimulus. And Con A stimulation could result in secretion of IL4, IL-10, IL-6 and a little amount of IFNgamma. IL-2 was barely detectable. This is distinct from typical Th0 type cytokines. The cells of this subset were NK1.1 negative, but strongly expressed GATA-3 mRNA. The results suggest that the CD4(+) subset of 3G11(-) 6C10(-) NK1.1(-) phenotype possesses immunocompetent cells with functions characteristic of Th2-like cytokines, which may indicate the cells at transitional status from Th0 to Th2, with a propensity to Th2.

Sialylation regulates peripheral tolerance in CD4+ T cells

Decreased binding by the 6C10 auto-antibody serves as a unique marker for CD4+ T cell unresponsiveness after the induction of T cell tolerance in Vbeta8.1 TCR transgenic mice. We further define the nature of the epitope recognized by the 6C10 antibody to be a subset of Thy-1 bearing incompletely sialylated N-linked glycans, and furthermore, we demonstrate that tolerant CD4+ T cells have an increased degree of cell-surface sialylation. To test the significance of the altered glycosylation state identified by the 6C10 auto-antibody in the tolerant CD4+ T cell population, surface sialic acid was cleaved enzymatically. Treatment of purified peripheral CD4+ T cells with Vibrio cholerae sialidase (VCS) leads to increased 6C10 binding, significantly enhances proliferation in the tolerant CD4+ population and corrects defects in phosphotyrosine signaling observed in the tolerant CD4+ T cell. Furthermore, in vivo administration of VCS enhances proliferation in both tolerant and naive CD4+ T cell subsets. These studies suggest that sialylation of glycoproteins on the surface of the CD4+ T cell contributes to the regulation of T cell responsiveness in the tolerant state.

Responses against complex antigens in various models of CD4 T-cell deficiency: surprises from an anti-CD4 antibody transgenic mouse

The most common models of CD4 T-cell deficiency are mice exogenously injected with anti-CD4 antibody (Ab), CD4 knockout (CD4-/-) and major histocompatibility complex (MHC) class II knockout (class II-/-) mice. We recently described the anti-CD4 Ab transgenic mouse (GK) as an improved CD4 cell-deficient model. This review compares this new GK mouse model with the widely available class II-/- and CD4-/- mice, when exposed to complex antigens (foreign grafts and during bacterial or viral infection). We highlight here the cytometric and functional differences (including Ab isotype, viral or bacterial clearance, and graft survival) among these CD4 cell-deficient models. For example, whereas grafts are generally rejected in class II-/- and CD4-/- mice as quickly as in wild-type mice, they survive longer in GK mice. Also, CD4-/- mice produce IgG against both simple model and complex antigens, but class II-/- and GK mice produce small amounts of IgG2a against complex antigens but not simple model antigens. These differences harbinger the caveats in the use of these various mice.

Heterogeneity within medullary-type TCRalphabeta(+)CD3(+)CD4(-)CD8(+) thymocytes in normal mouse thymus

The functional maturation process of medullary-type CD4(-)CD8(+) [CD8 single-positive (SP)] thymocytes remains largely uncharacterized. We describe a phenotypic analysis of CD8 SP medullary-type thymocytes and find a remarkable heterogeneity within this thymic cell population. While mature CD8(+) T cells in the periphery are relatively homogeneous (TCRalphabeta(+)CD3(+)Qa-2(+) HSA(-)3G11(-)6C10(-)CD69(-)), CD8 SP medullary-type thymocytes contain discrete subpopulations that can be identified by differential expression of several cell-surface markers. We have identified at least six discrete subpopulations in the subset of TCRalphabeta(+)CD3(+) CD8 SP cells in the thymus. According to the expressed phenotypes, a linear developmental pathway is predicted among these CD8 SP subpopulations as follows: 6C10(+)CD69(+)HSA(hi)3G11(+)Qa-2(-) --> 6C10(-)CD69(+)HSA(hi/int)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(int)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(lo)3G11(+)Qa-2(-) --> 6C10(-)CD69(-)HSA(-/lo)3G11(-)Qa-2(-) --> 6C10(-)CD69(-)HSA(-/lo)3G11(-)Qa-2(+). This study provides a framework for understanding CD8 SP T cell maturation in the thymic medulla.

Suppressor T cells regulate the nonanergic cell population that remains after peripheral tolerance is induced to the Mls-1 antigen in T cell receptor Vbeta 8.1 transgenic mice

We have found suppressor T cells that inhibit the proliferative response of naive CD4(+) T cells in T cell receptor (TCR) Vbeta8.1 transgenic mice rendered tolerant in vivo by inoculation of Mls-1(a)-positive cells. This suppression was mediated by CD4(+) T cells but not by CD8(+) T cells or double-negative (DN) cells, and splenic CD4(+) T cells from tolerant mice displayed a greater suppression than lymph node CD4(+) T cells. Cell contact was required for efficient suppression, and known inhibitory cytokines such as IL-4, IL-10, and transforming growth factor beta were not involved. Suppressor T cells inhibited IL-2 production by naive CD4(+) T cells, and the addition of exogenous IL-2 diminished the suppressed activity while having little activity on tolerant T cells. Suppression was abolished by the elimination of CD25(+) T cells in the tolerant CD4(+) T cell subset. CD25(+)CD4(+) T cells suppressed the proliferative response of the residual fraction of the nonanergic population, namely, 6C10(+)CD4(+) T cells still present in the tolerant mice. However, 6C10(-)CD4(+) T cells still had reduced reactivity to Mls-1(a) even after CD25(+)CD4(+) T cells were removed and exogenous IL-2 was added. Suppressor cells appear to affect only residual nonanergic cells in situ, thereby facilitating the maintenance of the unresponsive state in vivo. These data provide a framework for understanding suppressor T cells and explain the difficulties and variables in defining their activity in other systems, because suppressor T cells apparently control only a small population of nonanergic cells in the periphery and may be viewed as a homeostatic mechanism.

Effect of murine thymic epithelial cell line (MTEC1) on the functional expression of CD4(+)CD8(-) thymocyte subgroups

To determine the effect of thymic stromal cells on the functional maturation of CD4 single-positive (SP) thymocytes, the functional status of isolated CD4 SP thymocyte subgroups was investigated by means of cell proliferation and cytokine production in response to concanavalin A (Con A) prior and after co-culturing with a murine thymic epithelial cell line (MTEC1). Mouse medullary CD4 SP thymocytes were phenotypically divided into seven discrete subgroups predicted to reflect the maturation pathway from newly emerging CD4 SP thymocytes to terminally differentiated cells. For functional analysis, six major subgroups (6C10(+)CD69(+), 6C10(-)CD69(+), 6C10(-)CD69(-)3G11(+)Qa-2(-), 6C10(-)CD69(-)3G11(+)Qa-2(+), 6C10(-)CD69(-)3G11(-)Qa-2(-) and 6C10(-)CD69(-)3G11(-)Qa-2(+)) cells were isolated and their functional status in response to Con A stimulation assessed. A functional hierarchy is revealed among these subgroups, consistent with their phenotypic maturation status, which may imply that these cells undergo a functional maturation process within thymic medulla. The function of cytokine production by CD4 SP thymocytes is acquired in a stepwise manner from a low to high level and characterized by T(h)0-type cytokines in the main stream of differentiation pathway. However, a minor subgroup that appeared at the late stage as 3G11(-)6C10(-) cells was biased to produce T(h)2-type cytokines. Nevertheless, the functional capacity of the final two Qa-2(+) subgroups of CD4 SP thymocytes was still significantly lower than that of spleen CD4(+) T cells. After co-cultivation with MTEC1 cells, four subgroups of TCRalphabeta(+)CD4(+)CD8(-) thymocytes exhibited significantly higher levels of proliferation capability and modulation in cytokine production capability. However, co-culturing with MTEC1 cells did not change the pattern of T(h)0- or T(h)2-like cytokine production by respectively medullary CD4 SP thymocyte subgroups nor could MTEC1 induce CD4 SP thymocytes to secrete T(h)1-type cytokines. The results suggest that MTEC1 can regulate the functional status of these thymocyte subgroups.

Peripheral CD4+ T Cell Maturation Recognized by Increased Expression of Thy-1/CD90 Bearing the 6C10 Carbohydrate Epitope

The SM6C10 IgM autoantibody recognizes a surface determinant, 6C10, that is highly expressed on all immature thymocytes. In contrast, its expression on peripheral T cells appears developmentally regulated, i.e., absent from most naive T cells in spleen of neonatal mice, but expressed on 40–80% of naive CD4+ T cells in adult. In this paper, we demonstrate that SM6C10 recognizes a carbohydrate epitope on the Thy-1 glycoprotein using immunoprecipitation analysis, by binding to affinity-purified Thy-1 in an ELISA, and by sensitivity to N-glycosidase-F treatment. Retroviral Thy-1 gene transduction experiments into Thy-1− variant T cell lines and a pro-B cell line provide evidence that 6C10 glycosylated Thy-1 expression is not restricted to T cells but depends on the recipient cell. Therefore, differences in 6C10 levels among Thy-1+ T cells in mice likely reflect developmental regulation of posttranslational modification of the Thy-1 glycoprotein. The ability of naive CD4+ T cells to respond to anti-Thy-1 stimulation increases from neonate to adult, and 6C10− naive cells from adult mice respond poorly compared with 6C10+ cells, similar to the cells in neonatal mice. These results suggest that there is functional maturation by peripheral CD4+ T cells that coincides with 6C10 glycosylated Thy-1 up-regulation, and natural autoantibody recognizes this 6C10 carbohydrate epitope.

Phenotypic identification of the subgroups of murine T-cell receptor alphabeta+ CD4+ CD8- thymocytes and its implication in the late stage of thymocyte development

Phenotypic analysis of the medullary-type CD4+ CD8- [CD4 single-positive (SP)] thymocytes has revealed phenotypic heterogeneity within this cell population. The characteristic phenotype of mature peripheral T cells can be uniquely marked as Qa-2+ HSA- CD69-, whereas in the medullary-type CD4 SP thymocytes, the expression patterns of many markers were quite different. This suggests that there are many subgroups in the population, which reflects that medullary-type CD4 SP thymocytes may undergo phenotypic maturation. According to the results of two-colour flow cytometry, seven discrete phenotypes were identified by the expression capacity of Qa-2, HSA, CD69, 3G11 and 6C10 molecules. Consequently, the phenotypic precursor-progeny relationship can be envisaged as: 3G11- 6C10+ CD69+ HSAhi -->3G11+ 6C10+ CD69+ HSAhi --> 3G11+ 6C10- CD69+ HSAint -->3G11+ 6C10- CD69- HSAint Qa-2- -->3G11+ HSA-/lo Qa-2lo. At the stage of 3G11+ 6C10- CD69- HSAint Qa-2-, a branch pathway could be initiated, which gave rise to 3G11- HSAl degrees Qa-2- cells, which then, in turn, developed into 3G11- HSA-/loQa-2hi cells, a minor subgroup of the most mature CD4 SP cells. Consistent with this predicted pathway, experiments indicated that the first two subgroups were still cortisone sensitive, whereas the others were cortisone resistant. The cells in the last two Qa-2-positive subgroups are probably ready for emigration into the periphery.

The avidity spectrum of T cell receptor interactions accounts for T cell anergy in a double transgenic model

The mechanism of self-tolerance in the CD4(+) T cell compartment was examined in a double transgenic (Tg) model in which T cell receptor (TCR)-alpha/beta Tg mice with specificity for the COOH-terminal peptide of moth cytochrome c in association with I-Ek were crossed with antigen Tg mice. Partial deletion of cytochrome-reactive T cells in the thymus allowed some self-specific CD4(+) T cells to be selected into the peripheral T cell pool. Upon restimulation with peptide in vitro, these cells upregulated interleukin (IL)-2 receptor but showed substantially lower cytokine production and proliferation than cells from TCR Tg controls. Proliferation and cytokine production were restored to control levels by addition of saturating concentrations of IL-2, consistent with the original in vitro definition of T cell anergy. However, the response of double Tg cells to superantigen stimulation in the absence of exogenous IL-2 was indistinguishable from that of TCR Tg controls, indicating that these self-reactive cells were not intrinsically hyporesponsive. Measurement of surface expression of Tg-encoded TCR alpha and beta chains revealed that cells from double Tg mice expressed the same amount of TCR-beta as cells from TCR Tg controls, but only 50% of TCR-alpha, implying expression of more than one alpha chain. Naive CD4(+) T cells expressing both Tg-encoded and endogenous alpha chains also manifested an anergic phenotype upon primary stimulation with cytochrome c in vitro, suggesting that low avidity for antigen can produce an anergic phenotype in naive cells. The carboxyfluorescein diacetate succinimidyl ester cell division profiles in response to titered peptide +/- IL-2 indicated that expression of IL-2 receptor correlated with peptide concentration but not TCR level, whereas IL-2 production was profoundly affected by the twofold decrease in specific TCR expression. Addition of exogenous IL-2 recruited double Tg cells into division, resulting in a pattern of cell division indistinguishable from that of controls. Thus, in this experimental model, cells expressing more than one alpha chain escaped negative selection to a soluble self-protein in the thymus and had an anergic phenotype indistinguishable from that of low avidity naive cells. The data are consistent with the notion that avidity-mediated selection for self-reactivity in the thymus may lead to the appearance of anergy within the peripheral, self-reactive T cell repertoire, without invoking the induction of hyporesponsiveness to TCR-mediated signals.

Maturation of CD4+ Lymphocytes in the Aged Microenvironment Results in a Memory-Enriched Population

With advancing age the CD4+ T lymphocyte compartment becomes enriched for memory cells in both humans and experimental animals. Although it has been assumed that the shift from a naive to a memory-dominant population is due to a lifetime of antigenic exposure and selection as well as a loss of naive cell input due to reduced thymopoiesis, the present data suggest that the aged microenvironment influences the maturation of newly produced CD4+ T cells. In two models, aged and young mice were compared for the ability to reconstitute their peripheral CD4+ T cell pools following depletion, and both age groups were found to be competent to renew this population. However, the phenotype and lymphokine profile of populations arising in aged animals were distinctly different from those in the young mice. In contrast to the expectation that depletion and reconstitution might give rise to a naive-dominant T cell pool, aged mice reconstituted a population nearly indistinguishable from that found in control age-matched individuals. The majority of the CD4+ pool were CD44high CD45RBlow Mel-14low and upon activation with anti-CD3 these CD4+ T cells produced mRNA for IL-2, IL-4, IL-5, and IFN-γ. In aged bone marrow-transplanted mice, the same phenotypic profile and cytokine mRNA pattern were found in CD4+ T cells of host and donor origin. In contrast, the majority of CD4+ T cells in young reconstituted mice were CD44low CD45RBhigh Mel-14high. These lymphocytes, when activated, produced high levels of mRNA for IL-2, with little or no IL-4, IL-5, or IFN-γ mRNA.

HIV peptide conjugated to heat-killed bacteria promotes antiviral responses in immunodeficient mice

Enhancement of immunity in the setting of HIV infection is difficult owing to loss of functional CD4+ T cells. The MHC class II-deficient mouse (II-/-) environment simulates that of the immunocompromised HIV-infected individual, since these mice have low CD4+ T cell numbers, defective CD4-dependent responses, and are susceptible to opportunistic infection. This strain was used to test whether heat-killed Brucella abortus (BA), covalently conjugated to the V3 peptide of HIV-1 (MN), could elicit anti-HIV responses. V3-BA, but not the T-dependent antigen V3-KLH, induced high levels of IL-12, IFN-gamma, and IL-10 mRNA in both wild-type (WT) and II-/- mice within 24 hr of injection. V3-BA-treated, but not V3-KLH-treated, II-/- mice developed serum IgG and IgA anti-V3 antibodies, with IgG2b and IgG3 as the predominant isotype. Viral neutralization studies, using a syncytium inhibition assay, demonstrated that the antibodies generated by V3-BA in II-/- mice were capable of neutralizing HIV. These experiments demonstrate that a heat-inactivated bacterium such as BA, when used as a carrier, can generate a cytokine environment that results in the production of neutralizing antiviral antibodies in an immunodeficient host. Such strategies could be important in the development of immunotherapies and vaccines for HIV-1 patients.

Unique molecular surface features of in vivo tolerized T cells

Differential expression of surface markers can frequently be used to distinguish functional subsets of T cells, yet a surface phenotype unique to T cells induced into an anergic state has not been described. Here, we report that CD4 T cells rendered anergic in vivo by superantigen can be identified by loss of the 6C10 T cell marker. Inoculation of Vbeta8.1 T cell antigen receptor (TCR) transgenic mice with a Vbeta8.1-reactive minor lymphocyte-stimulating superantigen (Mls-1(a)) induces tolerance to Mls-1(a) by clonal anergy. CD4 lymph node T cells from Mls-1(a) inoculated transgenic mice enriched for the 6C10(-) phenotype neither proliferate nor produce interleukin-2 upon TCR engagement, whereas 6C10(+) CD4 T cells retain responsiveness. Analysis of T cell memory markers demonstrate that 6C10(-) T cells remain 3G11(hi) but express heterogeneous levels of CD45RB, CD62L, CD44, and the CD69 early activation marker, suggesting that T cells at various degrees of activation can be functionally anergic. These studies demonstrate that anergic T cells can be purified based on 6C10 expression permitting examination of issues concerning biochemical and biological features specific to T cell anergy.

Biochemical features of anergic T cells

T cell anergy is a functionally defined state of hyporesponsiveness in which T cells neither proliferate nor produce IL2 following subsequent TCR ligation. Recent biochemical data from in vitro studies suggest that anergic cells do not utilize all of the signaling pathways normally initiated by TCR triggering. These findings appear to hold true for T cells rendered anergic in vivo, as well; however, biochemical studies on clonal anergy in vivo have been limited by the inability to recover a homogeneous population of anergic T cells. Here we review progress on TCR mediated signaling pathways as well as the description of surface marker phenotypes specific to T cell anergy.

Continuous ambulatory peritoneal dialysis impairs T lymphocyte selection in the peritoneum

Peritoneal lymphocytes (PCL) of 45 healthy individuals, four uremic patients with end-stage renal disease (ESRD) and 25 long-term continuous ambulatory peritoneal dialysis (CAPD) patients were characterized by flow cytometry to investigate whether CAPD alters the phenotype of PCL. B lineage cells constitute a minority of PCL (2.5% of cells). Although the majority of peritoneal T cells expressed alpha beta T cell receptor (TcR), 7% expressed gamma delta TcR, a proportion which was significantly higher than that in peripheral blood (PBMC) (approximately 4%). The majority of PCL T cells exhibited markers of the thymus-dependent lineage (CD2, CD3, TcR alpha beta, CD8 alpha beta or CD4) and surface antigens associated with memory and activation (CD45RO, CD11a, CD18, CD49d, HLA-DR). An average of 75% of both CD4+ and CD8+ PCL T cells of healthy subjects and CAPD patients were CDw60+, thus characterizing the T cell subset containing the helper activity for the mitogen-driven B cell differentiation. CD44s was abundantly expressed on PCL T cells. In contrast to PCL T cells of healthy subjects peritoneal T lymphocytes of CAPD patients exhibited CD44 splice variants containing products of exon-v9 and the proportion of CD44v9+ cells correlated with the frequency of peritonitis episodes the patients had gone through. The majority of PCL T cells of both healthy subjects and CAPD patients were CD8+. A large proportion of CD8+ PCL T cells from healthy subjects expressed the homodimeric CD8 alpha alpha isoform; however, such cells were not found in CAPD patients. In healthy subjects mRNA for the recombination activating gene 1 (RAG-1) was detectable in a PCL population containing CD7-CD34+ and CD7+CD34+ cells. In contrast, neither mRNA transcripts of the RAG-1 gene nor CD34+ cells were detectable in PCL of CAPD patients.

Cytokine production pathway in the elderly

It is well known that aging is associated with various alterations in lymphoid cell functions, particularly with a progressive decline in immune responsiveness to exogenous antigens and increasing incidence of autoimmune phenomena. Many studies have been focused on the mechanisms of the immunologic features of aging. this review describes our results of studies performed to determine the influence of age on the capacity to produce interleukin-2 (IL-2), interferon-gamma (IFN-gamma), interleukin-4 (IL-4), interleukin-t (IL-5), interleukin-6 (IL-6) and tumor necrosis factor (TNF). Mitogen-stimulated cultures of mononuclear cells (MNC) from human beings were assessed for cytokine-producing capacity. A significant decrease in IFN-gamma and IL-2 production by MNC cultures from elderly individuals was observed. No significant difference was instead observed between cultures from elderly individuals and those from young ones as regards TNF-alpha, IL-4 and IL-6 production. Mitogen or antigen-stimulated cultures of MNC from aged mice also displayed a significant decrease in IFN-gamma and IL-2 production as well as TNF-beta. Instead IL-4 and IL-5 production significantly increased in these cultures. We suggest that this imbalanced cytokine production may well account for the pattern of immune response which may be observed in the elderly, i.e. a normal or increased humoral response (including autoimmune responses) in face of a low T cell immune responsiveness.

T lymphocytes from normal human peritoneum are phenotypically different from their counterparts in peripheral blood and CD3- lymphocyte subsets contain mRNA for the recombination activating gene RAG-1

The surface antigens of peritoneal lymphocytes of healthy human individuals were studied. B lineage cells comprised 2.3% of the total peritoneal lymphocyte population. Although the majority of peritoneal cavity lymphocyte (PCL) T cells expressed alpha beta T cell receptor (TcR), up to 17% expressed gamma delta TcR. The majority of PCL exhibited markers of the thymus-dependent lineage (CD2+ CD3+ TcR alpha beta + CD4+ or CD8 alpha + beta +) and surface antigens associated with memory and activation (CD45RO+ CD11a+ CD18+ CD49d+ HLA-DR). Up to 92% of both CD4+ and CD8+ T cells bore CDw60, thus characterizing the T cell subset containing helper activity for mitogen-driven B cell differentiation. The majority of PCL T cells were CD8+ and, in addition, up to 60% of this population expressed the homodimeric CD8 alpha + beta -. Messenger RNA for the recombination activating gene RAG-1 was examined in CD3- PCL depleted of CD19+ lineage cells. The PCL population which comprised cells containing RAG-1 mRNA transcripts was CD19-, surface IgM-, cytoplasmic IgM- and CD2- CD3- CD4- CD8- CD56-. However, this population was CD7+ (approx. 75%), and contained both CD7- CD34+ (up to 3%) and CD7- CD34+ (up to 3%) cells. These findings are compatible with the hypothesis that the adult human peritoneum provides a microenvironment capable of supporting a thymus-indenpendent differentiation of T lymphocytes.

Heterogeneity in P-glycoprotein (multidrug resistance) activity among murine peripheral T cells: correlation with surface phenotype and effector function

P-glycoprotein (P-gly) is the transmembrane efflux pump responsible for multidrug resistance in tumor cells. Functional P-gly activity can be conveniently assessed microfluorometrically using the fluorescent dye rhodamine 123 (Rh123), which is an artificial substrate for the P-gly transporter. Here we assess P-gly activity in subsets of mouse peripheral T lymphocytes using the Rh123 efflux assay. Our data indicate that virtually all CD8+ cells extrude Rh123 efficiently, whereas only a subset of CD4+ cells exhibit P-gly activity. Correlation of P-gly activity in CD4+ cells with the expression of a panel of surface markers revealed that cells bearing an "activated/memory" phenotype (CD45RB-, CD44hi, CD62L-, CD25+, CD69+) were exclusively found in the fraction that can extrude Rh123. In contrast "naive" phenotype CD4+ cells (CD45RB+, CD44lo, CD62L+, CD25-, CD69-) could be further subdivided into two major subsets based on P-gly activity. In functional studies of sorted cell populations the Rh123-extruding subset of "naive" CD4+ cells proliferated more strongly and secreted higher levels of interleukin (IL)-2 than its Rh123-retaining counterpart when activated by a variety of polyclonal stimuli. Furthermore, this subset produced detectable levels of interferon (IFN)-gamma upon stimulation but no IL-4 or IL-10. As expected, the Rh123-retaining "naive" subset produced only IL-2 after stimulation, whereas the "memory" subset produced IFN-gamma, IL-4 and IL-10 in addition to low levels of IL-2. Collectively, our data indicate that P-gly activity is a novel parameter that can be used to distinguish a subset of "preactivated" CD4+ cells that would be considered as naive on the basis of their surface phenotype.

Turnover of naive- and memory-phenotype T cells

On the basis of their surface markers, T lymphocytes are divided into subsets of "naive" and "memory cells". We have defined the interrelationship and relative life spans of naive and memory T cells by examining the surface markers on murine T cells incorporating bromodeoxyuridine, a DNA precursor, given in the drinking water. Three findings are reported. First, using a new method we show that the release of newly formed naive T cells from the unmanipulated thymus is very low (confirming the findings of others with surgical approaches). Second, in thymectomized mice, T cells with a naive phenotype remain in interphase for prolonged periods; however, some of these cells divide and retain (or regain) their "naive" markers. Third, most T cells with a memory phenotype divide rapidly, but others remain in interphase for many weeks. Collectively, the data indicate that long-lived T cells have multiple phenotypes and contain a mixture of memory cells, naive (virgin) cells, and memory cells masquerading as naive cells.

Two distinct non-T helper type 2 interleukin-4+ cell subsets in mice as revealed by single-cell cytokine analysis

We have previously defined four murine CD4+ peripheral T cell subsets, fractions (Fr.) I-IV, based on expression of the 6C10 and 3G11 determinants (Hayakawa, K. and Hardy, R. R., J. Exp. Med. 1988. 168: 1825). These subsets also show distinctive levels of other cell surface markers: the two minor subsets, Fr. III and Fr. IV, are both CD45RBlow/-, L-selectin (Mel-14)- and CD44hi, characteristic of secondary T cells. The patterns and levels of cytokine production by individual cells in each subset were determined by bioassay for interleukin (IL)-2/IL-4 or IL-4/interferon (IFN)-gamma production after anti-CD3 stimulation. Our data revealed that these four phenotypically defined subsets largely coincide with clusters of cells showing uniform distinctive cytokine profiles, i.e. IL-2+/IFN-gamma-/IL-4- (Fr. I and Fr. II, L-selectin+), IL2+/IFN-gamma +/IL-4+ (Fr. III, L-selectin-), and IL-2-/IFN-gamma low/-/IL-4+ (Fr. IV, L-selectin-). Besides these subsets, an L-selectin-negative cell subfraction within Fr. II appears to represent a transitional population between the IL-2+/IFN-gamma-/IL-4- stage and the IL-2+/IFN-gamma +/IL-4+ stage. Taken together, these results demonstrate the presence of two IL-4+ secondary T cell subsets with distinct cytokine production patterns, and show that the majority of IL-4+ cells found in healthy adult laboratory mice co-produce IFN-gamma, and thus are not typical T helper type 2 cells.

Severe immunodeficiency associated with a human immunodeficiency virus 1 NEF/3'-long terminal repeat transgene

We have generated several transgenic mouse strains carrying a human immunodeficiency virus 1 (HIV-1) NEF/3' long terminal repeat (LTR) transgene under control of a T cell-specific promoter-enhancer element, showing a depletion of CD4+ T cells in the thymus and periphery. The immunological functions of the line with the most dramatic changes in lymphocyte populations, B6/338L, were analyzed in greater detail. The presence of the transgene in the heterozygous animal is associated with a dominant severe immunodeficiency. Older animals develop lymph-adenopathy and splenomegaly. CD4+CD8+ and CD4+CD8- single positive thymocytes already are depleted in these mice at the earliest stages in ontogeny, and peripheral T cells are reduced in frequency and present cell surface marker expression, which is characteristic for memory and activated T cells. The immunological response of B6/338L mice to several viral infections is also greatly impaired. Thus, the HIV-1 NEF/3' LTR as transgene in T cells can cause immunodeficiency and disease with striking similarities to a known retrovirus-induced immunodeficiency called murine AIDS (H. C. Morse III, S. K. Chattopadhyay, M. Makino, T. N. Frederickson, A. W. Hügin, and J. W. Hartley. 1992. AIDS. 6:607).

Aging and lymphokine production by T cell subsets

From sexual maturity to old age, the mammalian immune system undergoes progressive changes, some of which may predispose individuals to infectious, neoplastic and degenerative diseases. These age-associated changes are prominent in the T lymphocyte compartment and encompass both the CD4+ and CD8+ T cell subpopulations. In this review, we focus on the mouse model system and summarize current information on the existence of functionally distinct subsets within each of the CD4+ and CD8+ cell subpopulations. We describe how the representation of these subsets is altered during the aging process, with consequent changes in the lymphokine production repertoires and other functional attributes of the T cell pool. Lastly, we present evidence showing that similar changes occur in aging humans and discuss the potential impact of these changes on immune responsiveness in late life.

Environmental modulation of the autonomy of cytotoxic T lymphocytes

The extent to which one compartment of the immune system depends on another for efficient function is important to establish to fully comprehend disease phenotypes arising from selective immunodeficiency. Just how much the major histocompatibility complex class I-restricted cytotoxic T cell responses depend on class II-restricted T cell help has been controversial. Using the influenza A virus system, we show that mice unable to make class II-restricted T cell responses due to an engineered defect in class II molecule expression are able to mount virtually normal cytotoxic responses when bred under specific-pathogen-free conditions. However, when exposed to the more diverse environmental challenges of a conventional breeding facility, a situation that more closely parallels immunodeficient states in man, they show impaired cytotoxic responses.

Selective differentiation of CD4+ T helper cell subsets

During the past year significant advances have been made in our understanding of the factors contributing to the differentiation of CD4 T helper cell subsets. These have been driven, in part, by the realization that signals (cytokines) from the innate immune response are critical in T cell subset differentiation. In addition, several studies have also elucidated how the antigen-presenting cell, the antigenic epitope and the antigen concentration may contribute to the selective development of a particular T helper cell subset.

Selective enrichment of major histocompatibility complex class II-specific autoreactive T cells in the thymic Thy0 subset

We show here a unique enrichment of autoreactive T cells in the CD4+ mouse thymic subset, Thy0. A single- and 10-cell AMLR (autologous mixed leukocyte reaction) assay demonstrates that more than 30% (one cell per well) and almost all (10 cells per well) Thy0 cultures from normal mice exhibit reactivity specific to autologous cells, resulting in induction of interleukin 3 secretion. In contrast, no other mature thymic or splenic CD4+ T cell subsets showed such a high frequency. The majority of this AMLR reactivity in the Thy0 subset is accounted for by reactivity with self-major histocompatibility complex class II. Furthermore, antigenic selection in generating Thy0 subset is suggested by studies with T cell hybrids from a T cell receptor (TCR) V beta transgenic mouse line, 2B4 beta EH. TCR V-gene analysis of T cell hybrids revealed that those from Thy0, half of which responded to self-class II, consisted predominantly of cells that expressed endogenous TCR V beta s alone (without the transgene), unlike hybrids generated from peripheral naive T cells. Thus, we suggest that the presence of Thy0 results from selective stimulation of cells expressing TCR with sufficient affinity for autoantigens in the thymic CD4+ T cell repertoire.

Another view of the selective model of thymocyte selection

Thymocyte commitment to the CD4 helper versus CD8 cytotoxic lineage has not been satisfactorily established. Two models have been elaborated: one based on instruction, the other on selection. Most previous results support the instructive model, but our comparison of thymocyte differentiation in MHC class II-, class I- and double-deficient mice provides data challenging it. There exists a significant population of CD4 single positive cells in class II-deficient animals that is intermediate in maturity between CD4+CD8+ and end-stage CD4+CD8- thymocytes and is selected on class I molecules; an equivalent CD8+CD4- population occurs in class I-deficient animals. We propose a selective model entailing two TCR-MHC molecule engagements: the first provokes random down-modulation of either CD4 or CD8 and a degree of differentiation; the second, requiring participation of the appropriate coreceptor, permits end-stage differentiation.

Compartmentalization of the peripheral immune system

The periphery of the immune system--as opposed to the central lymphoid organs--contains inhomogeneously distributed B and T cells whose phenotype, repertoire, developmental origin, and function are highly divergent. Nonconventional lymphocytes bearing a phenotype that is rare in the blood, spleen, or lymph nodes of undiseased individuals are encountered at high frequency in different localizations, e.g., alpha/beta TCR+CD4-CD8- cells in the bone marrow and gut epithelium, particular invariant gamma/delta TCR+CD4-CD8 alpha+CD8 beta- and gamma/delta TCR+CD4-CD8 alpha-CD8 beta- T cells in various epithelia, or CD5+ B cells in the peritoneum. The antigen receptor repertoire is different in each localization. Thus, different gamma/delta TCR gene products dominant in each site, and the proportion of cells expressing transgenic and endogenous alpha/beta TCR and immunoglobulin gene products follows a gradient, with a maximum of endogenous gene expression in the peritoneum, intermediate values in other peripheral lymphoid organs (spleen, lymph nodes), and minimum values in thymus and bone marrow. Forbidden T cells that bear self-superantigen-reactive V beta gene products are physiologically detected among alpha/beta TCR+CD4-CD8- lymphocytes of the bone marrow, as well as in the gut. Violating previous ideas on self-tolerance preservation, self-peptide-specific gamma/delta T cells are present among intestinal intraepithelial lymphocytes, and CD5+ B cells produce low-affinity crossreactive autoantibodies in a physiological fashion. It appears that, in contrast to the bulk of T and B lymphocytes, certain gamma/delta and alpha/beta T cells found in the periphery, as well as most CD5+ B cells, do not depend on the thymus or bone marrow for their development, respectively, but arise from different, nonconventional lineages. In addition to divergent lineages that are targeted to different organs guided by a spatiotemporal sequence of tissue-specific homing receptors, local induction or selection processes may be important in the diversification of peripheral lymphocyte compartments. Selection may be exerted by local antigens, antigen-presenting cells whose function varies in each anatomical localization, cytokines, and cell-matrix interactions, thus leading to the expansion and maintenance of some clones, whereas others are diluted out or deleted. The spatial compartmentalization of lymphocytes in different microenvironments has major functional consequences and leads to a partial fragmentation of immunoregulatory circuits at the local level. Lymphocytes residing in certain antigen-exposed compartments are likely to combat tissue-specific pathogens or self-proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Murine thymic CD4+ T cell subsets: a subset (Thy0) that secretes diverse cytokines and overexpresses the V beta 8 T cell receptor gene family

We demonstrate here the presence of a distinct mature CD4+8- T cell subset in mouse thymus. This subset, termed "Thy0," is delineated by the absence of 3G11 expression from about half of the 6C10-/HSAlow/- fraction of CD4+8- thymic cells. Thy0 is detectable from the neonatal period and largely contributes the Th0-type diverse cytokine production previously reported for the HSAlow/-CD4+ thymic population. Further, cells expressing the T cell receptor V beta 8 gene family are found at increasing frequency in Thy0 with age, comprising 40-60% of Thy0 in adult BALB/c mice. This alteration of V beta 8+ cell frequency is unique to Thy0, since no other CD4+ subset in thymus or spleen shows such V beta 8 overusage. All functional CD4+ T cell subsets, including Thy0, show appropriate V beta clonal deletion associated with endogenous superantigens. Thus, it appears that Thy0 is an intrathymically generated secondary cell subset produced after CD4+ T cell selection.