Direct demonstration of the human suppressor inducer subset by anti-T cell antibodies

Prior studies indicated that sera of patients with active juvenile rheumatoid arthritis (JRA) contain anti-T cell antibodies reactive with the T4+ inducer population. More important, depletion of this T cell subset with JRA anti-T cell antibodies (JRA+ T cells) and C abrogated T5/T8+ suppressor T cell function. In the present study, we utilized Ig-coated plate techniques and JRA anti-T cell antibodies to fractionate the T4+ population into T4+JRA+ and T4+JRA- subsets and characterize the individual T4+ inducer subset. It was shown that whereas only the T4+JRA- population responded maximally to the soluble antigens, TT and mumps, both T4+JRA+ and T4+JRA- subsets proliferated equally well to mitogens and alloantigens. Furthermore, B cell immunoglobulin production induced by T4+JRA- T cells was approximately twice that induced by the reciprocal T4+JRA+ subset. In contrast, the T4+JRA+ subset alone activated T8+ T cells to become suppressor effector cells. These results suggest that the T4+JRA+ subset is the inducer of suppressor subpopulation whereas the T4+JRA- subset functions maximally as the inducer of B cells. It is believed that the suppressor inducer population may have a central role in the immunoregulatory network in man.     

Two functionally distinct subpopulations of human T cells that collaborate in the generation of cytotoxic cells responsible for cell-mediated lympholysis.

A human thymus-dependent differentiation antigen, TH2 was defined by a rabbit anti-human T cell serum absorbed with autologous B lymphoblasts and leukemic cells bearing T cell markers from a patient with chronic lymphocytic leukemia. Anti-TH2 reacted specifically with thymus-derived lymphoid cells and exhibited two distinct profiles of reactivity with normal peripheral T cells as detected by indirect immunofluorescence on a FACS I. Isolation of strongly reactive, TH2+, from weakly reactive, TH2- T cells by fluorescence-activated cell sorting revealed that the TH2+ subset contained most of the killer activity in cell-mediated lympholysis (CML), but had a diminished response in MLC and a suboptimal or negligible proliferative response to soluble antigens (mumps, PPD, tetanus toxoid). In contrast, the TH2- subset contained markedly less killer activity but amplified cytotoxicity by TH2+ cells and exhibited a proliferative response to both alloantigen and soluble antigens that was often significantly greater than the response by unseparated T cells. The relevance of these findings to previously described human T cell subsets and to functional subpopulations of murine T cells is discussed.     

Markers of human T cell subsets identified by alloantisera.

Analysis by the indirect fluorescence test followed by fluorescence-activated cell sorter (FACS) analysis has shown that antisera recognizing subsets of human T lymphocytes can be produced by planned immunizations involving HLA-A and HLA-B compatible donors. The reactivity of these antisera against some individuals of a population but not others shows that they recognize a polymorphic cell surface component. The reactive subpopulation largely overlaps with the JRA+ subset, which was previously shown to possess regulatory properties in functional assays. The specificity of the antisera for a T cell subset and the unrelatedness of the anti-B cell activity of the same antisera has been confirmed by two-color fluorescence tests.     

Con A-inducible suppression of MLC: evidence for mediation by the TH2 + T cell subset in man.

Human peripheral lymphoid cells pretreated with Concanavalin A for 48 hr can markedly suppress the proliferative response of untreated autologous lymphoid cells in MLC. Isolation studies with Sephadex G-200 anti-F(ab')2 affinity chromatography, nylon adherence, and E rosetting indicate that the Con A-induced suppressor cell is a T cell. Further fractionation into TH2+ and TH2- cell subsets with an equine-anti TH2 serum show that both subsets can be activated by Con A to an equivalent degree. After activation only the TH2+ subset can suppress autologous responder cells in MLC. The TH2- subset, which comprises 80% of peripheral human T cells, although induced by Con A to proliferate, cannot itself suppress the MLC response. Nevertheless, the TH2- subset can be shown to modulate the generation of suppressor TH2+ cells at 24 hr but not at 48 hr. These studies support the notion that the Con A-induced suppressor cell is confined to a distinct T cell subset in man and that T-T interactions are important in the overall expression of the immune response.     

A monoclonal antibody reactive with the human cytotoxic/suppressor T cell subset previously defined by a heteroantiserum termed TH2

A hybridoma-secreting monoclonal antibody was produced from the spleen cells of a mouse immunized with human thymocytes. This hybridoma antibody, termed OKT5, was reactive by indirect immunofluorescence with 80% of human thymocytes but only 20% of peripheral blood T cells. Moreover, OKT5 was unreactive with normal B cells, null cells, and macrophages at any dilution tested. A similar pattern of reactivity was seen with an equine antiserum to human thymocytes termed anti-TH2. Fluorescence-activated cell sorting demonstrated that the OKT5 antibody reactivity on peripheral T cells was restricted to the majority of the previously defined TH2+ subpopulation. In functional studies, the OKT5+ subset, like the TH2+ subset, proliferated well to the mitogen Con A and to alloantigens, and contained cytotoxic effector cells after sensitization in MLC, and suppressor effector cells after activation with Con A. In addition, like the TH2+ T cell, the OKT+ T cell was virtually unresponsive to soluble antigen. Thus, the OKT5 monoclonal antibody is reactive with the cytotoxic/suppressor T cell subset. OKT5 should provide an important probe to assess the status of suppressor cells in human disease.     

The isolation and characterization of the human suppressor inducer T cell subset

Immunization of mice with lower primate lymphoid cells has provided a useful strategy for raising monoclonal antibodies against functionally important surface determinants on human T lymphocytes. We have developed a monoclonal antibody, anti-2H4, which defines functionally unique human T cell subsets. This anti-2H4 antibody was reactive with approximately 42% of unfractionated T cells, 41% of T4+ inducer cells, and was reactive with approximately 54% of T8+ cytotoxic/suppressor population. Anti-2H4 was not reactive with human thymocytes, but reacted with subsets of peripheral blood B cells and null cells. This antibody subdivided peripheral blood T4+ cells into two functionally distinct populations. The T4+2H4+ subset proliferate well to concanavalin A (Con A) stimulation, but poorly to soluble antigen stimulation, and provides poor help to B cells for PWM-induced Ig synthesis. The T4+2H4- subset, in contrast, proliferates poorly upon stimulation with Con A, but well on exposure to soluble antigen, and provides a good helper signal for PWM-induced Ig synthesis. What is, perhaps, most important, the T4+2H4+ subset functions as the inducer of the T8+ suppressor cells. Previous attempts to define the latter subset of cells has relied heavily on the use of specific autoantibodies present in the sera of patients with juvenile rheumatoid arthritis (JRA) and systemic lupus erythematosus (SLE). The present results suggest that anti-2H4 antibody defines the human suppressor induced subset of lymphocyte previously described as T4+JRA+. Last, the results reemphasize the previously documented remarkable structural conservation of certain T cell-specific determinants on lymphocytes of phylogenetically distant primates.     

Functional studies of T4+ lymphocyte subsets distinguished by the monoclonal antibody 5/9: suppressor-effector T4+ lymphocytes derive from the 5/9+ subset

Human T lymphocytes bearing the cell surface antigen T4 are functionally heterogeneous, exerting helper/inducer, suppressor-inducer, suppressor-effector, and cytotoxic activities. Other cell surface antigens with a more restricted expression may help separate T4+ lymphocytes into functionally distinct subsets. This report describes the regulatory functions of T4+ lymphocytes fractionated by the monoclonal antibody 5/9, which detects a cell surface antigen present on 50-60% of T4+ lymphocytes. The results indicate that both 5/9+ and 5/9- T4 subsets contain helper/inducer and suppressor-inducer cells. Suppressor-effector activity, however, is found predominantly within the 5/9+ T4 subset. The 5/9 antibody thus identifies the suppressor-effector subset of T4+ lymphocytes, although it does not distinguish between T4+ cells with or without helper/inducer and suppressor-inducer functions.     

The T4 molecule differentially regulating the activation of subpopulations of T4+ cells

It has been demonstrated that the T4+2H4+ subset functioned as a suppressor inducer cell, whereas the reciprocal T4+2H4- subset provided help for B cell Ig production. In the present studies, a series of monoclonal antibodies to cell surface structures expressed on these subsets of cells were examined for their effects on the proliferative and immunoregulatory functions generated in AMLR. We demonstrated that anti-T4 antibody preferentially inhibited the proliferative response of the T4+2H4+ but not T4+2H4- cells against self-MHC antigens. In contrast, anti-T3 and anti-Ia antibodies inhibited the response of both subsets of cells. This subset preference of anti-T4 antibody was not attributable to either the isolation procedures used or a shift in the kinetics of proliferation to autologous self-MHC antigens. Moreover, both IL 2 production and the immunoregulatory function of the T4+2H4+ subset was profoundly inhibited by anti-T4 antibody, whereas the T4+2H4- subset was minimally influenced. In the absence of Ia molecules, T4+2H4+ but not T4+2H4- cell proliferation was inhibited with anti-T4 antibody. Together, these results suggest that the T4 molecule plays a distinct functional role in the differential triggering of subsets of T4+ cells.     

Functional subsets of human monocytes defined by monoclonal antibodies: a distinct subset of monocytes contains the cells capable of inducing the autologous mixed lymphocyte culture

The induction of most immune responses requires the close cooperation between T cells and antigen-presenting cells (APC), presumably of monocyte/macrophage (M phi) lineage. To characterize human APC further, we used two monoclonal antibodies, OKM1 and OKM5, to isolate and identify M phi subsets. OKM1 has been described and recognizes cell surface antigens on most M phi and granulocytes. OKM5 recognizes cell surface determinants present on the majority of human M phi but does not recognize other hematopoietic cell types. A small subset of peripheral blood M phi is OKM1-OKM5+. Human peripheral blood E- cells were separated into OKM1+ and OKM1- subsets by a rosetting technique utilizing anti-Ig-coated red cells. The capacity to present self antigens in the autologous mixed lymphocyte culture (AMLC) resided predominantly within the E-OKM1- subset, even if surface membrane Ig-positive cells were eliminated. Similar experiments showed that the ability to stimulate in AMLC was contained in the E-OKM5+ population and in fact resided primarily within the E-OKM1-OKM5+ subset. All of these subsets were able to trigger allogeneic T cells to proliferate. The capacity of these APC subsets to present soluble antigens (mumps, tetanus toxoid) was also examined. The data demonstrated that although the majority of these APC are E-OKM1+, E-OKM1-OKM5+ cells can also present foreign antigen. Taken together, these data suggest OKM1 and OKM5 can be used to isolate two functionally distinct human M phi subsets. One subset (E-OKM1+) is capable of presenting soluble antigens but shows minimal ability to trigger AMLC. The other subset (E-OKM1-OKM5+) can also present soluble antigens but is the predominant subset that can trigger AMLC.     

Heterogeneity of human T4+ inducer T cells defined by a monoclonal antibody that delineates two functional subpopulations

A monoclonal antibody termed anti-T4 that detected approximately 60% of peripheral blood T lymphocytes was shown to define the human inducer population. In the present study, we characterized three additional monoclonal antibodies, anti-T4A, anti-T4B, and anti-TQ1, that were reactive with a similar percentage of T lymphocytes. Anti-T4A, anti-T4B, and anti-T4 delineated identical cell populations, while those defined by anti-TQ1 differed in several respects: 1) Anti-TQ1 stained a minority (less than 7%) of thymocytes, whereas the other antibodies stained a majority (80%); 2) Anti-TQ1 reacted with 70 to 85% of T4+ lymphocytes, but also stained 50% of T cells within the T4- (T8+) cytotoxic/suppressor subset; 3) The antigen defined by anti-TQ1 was not restricted in its expression to T cells; it defined a fraction of normal B and null lymphocytes as well as non-T cell lines. In vitro studies indicated that the subpopulations of T4+ T lymphocytes delineated by anti-TQ1 were functionally distinct. Although T4+TQ1+ and T4+TQ1- T cells proliferated in an equal fashion to soluble antigen and alloantigen, only the T4+TQ1+ subset was responsible for maximal proliferation in autologous MLR. This T4+TQ1+ subset contained a population of lymphocytes reactive with the previously defined JRA autoantibody. In contrast, the T4+TQ1-, but not the T4+TQ1+, subset provided the majority of T cell help for B cell immunoglobulin production in a pokeweed-driven system. We conclude that the subpopulation of T4+ inducer cells responsible for maximal helper activity in T-B interactions is restricted to a minor subpopulation of T4+ lymphocytes.     

Effector mechanisms in cyclosporine A-induced syngeneic graft-versus-host disease. Role of CD4+ and CD8+ T lymphocyte subsets

Syngeneic graft-versus-host disease (SGVHD) is a T cell-mediated autoimmune disease occurring postsyngeneic bone marrow transplantation and the administration of the potent immunosuppressive agent, cyclosporine A. Paradoxically, cyclosporine A disrupts the immunologic homeostasis governing self-tolerance. Our studies using an adoptive transfer model attempted to identify effector mechanisms associated with the autoimmune disease. Both CD4+ and CD8+ splenic T cells isolated from autoimmune donors were required for the adoptive transfer of active disease into lethally irradiated secondary recipients reconstituted with normal bone marrow. Doses of more than 5 x 10(6) of nylon wool depleted splenocytes from autoimmune donors effectively transferred disease into lethally irradiated secondary recipients. Splenocytes that are T cell depleted or CD4(+)-enriched cells did not elicit disease upon adoptive transfer. Nylon wool fractionated CD8+ splenocytes also failed to adoptively transfer disease unless high doses (greater than or equal to 30 x 10(6)) were used. The disease transferred with the CD8+ subset presented as acute type SGVHD and was self-limiting. The recombination of the individually isolated T cell subsets not only restored but also enhanced immune reactivity upon adoptive transfer. Moreover, use of the recombined subsets resulted in progressive disease with the development of chronic type SGVHD. The titration of each subset to the other suggested that a minimal number of CD4+ T cells was required to potentiate the CD8+ autoreactive cells in vivo. Further analysis of the helper cell involved demonstrated that it had a CD4+ CD45r- phenotype, characteristic of an amplifying helper cell population. Administration of IL-2 did not substitute for CD4+ Th cells but yet amplified the activity of unfractionated cells or recombined subsets implicating the role of other factors in the pathogenesis of SGVHD. Delineation of the effector mechanisms involved in SGVHD is critical in determining the underlying events that trigger either the production of autoreactive cells or the perturbation of the regulation of these autoreactive cells, culminating in autoimmunity.     

Characterization of a phenotypically distinct subpopulation of Leu-2+ cells that suppresses T cell proliferative responses

Two new monoclonal antibodies (termed 2D2 and D12) have been used to identify and to analyze phenotypically distinct subpopulations of human T cells. The 2D2 antibody recognized an antigenic determinant closely related, if not identical, to that reactive with the anti-Leu-2 monoclonal antibody. The D12 antibody reacted with a variety of cell types, which included a subpopulation of Leu-2+ (2D2+) T cells. These antibodies were used to isolate four phenotypically distinct T cell populations by sequential cell sorter techniques. Functional analyses demonstrated that the 2D2+D12+ subset was unique in its ability to suppress the antigen-induced proliferation of T cells. These cells also suppressed the proliferative responses of other T cell subsets stimulated with mitogens. Pretreatment of 2D2+D12+ T cells with mitomycin C before culture abrogated the suppressor cell activity of these cells. We propose that the cells within the Leu-2+ cytotoxic/suppressor T cell subpopulation that suppress T cell proliferation are phenotypically distinct and express the 2D2+D12+ membrane antigenic phenotype.     

The isolation and characterization of the human helper inducer T cell subset

Monoclonal antibody anti-4B4 was produced by fusing NS1 myeloma with spleen cells of a mouse immunized with Saguinus oedipus lymphocyte. This anti-4B4 antibody defines a 135-KD cell surface protein that is widely distributed throughout the hematopoietic system. More importantly, anti-4B4 is reactive with functionally unique human T cell subsets. Anti-4B4 antibody was reactive with approximately 41% of unfractionated T cells, 41% of T4+ inducer cells, and approximately 43% of T8+ cytotoxic/suppressor population. This antibody subdivided peripheral blood T4+ cells into two functionally distinct populations. The T4+4B4+ subset proliferates relatively poorly upon stimulation with Con A and autologous cell antigens (AMLR) but well on exposure to soluble antigens, and it provides a good helper signal for PWM-induced Ig synthesis. The T4+4B4- subset, in contrast, proliferates well to Con A stimulation and autologous cell antigen (AMLR) but relatively poorly to soluble antigen stimulation, and provides little help to B cells for PWM-induced Ig synthesis. The T4+4B4- subset is largely 2H4+ and functions as the inducer of the T8+ suppressor cells. Thus, the present results suggest that one can divide the human T4 population into two major subsets that are phenotypically and functionally distinct, the human helper inducer subset (T4+4B4+/H.I.) and its reciprocal population defined by anti-2H4, the suppressor inducer subset (T4+2H4+/S.I.).     

Induction of immunoglobulin-secreting cells in the allogeneic mixed leukocyte reaction: regulation by helper and suppressor lymphocyte subsets in man

The existence of functionally distinct T lymphocyte subsets in man, initially demonstrated with heteroantisera, has been confirmed with monoclonal reagents. Two major subsets have been defined: Leu-2 cells, which effect cell mediated lymphocytotoxicity (CML), and Leu-3 cells, which amplify CML and other T cell functions. This study is an effort to determine the effects of these subsets on the immunoglobulin secretion induced in the human mixed leukocyte reaction (MLR). T cells were separated from non-T cells by rosetting with sheep erythrocytes and were fractionated into Leu-2 and Leu-3 subsets by solid phase immunoabsorption with monoclonal antibodies. T cell subsets were cultured with autologous non-T cells and irradiated allogeneic stimulator non-T cells. Secretion of IgM and IgG was measured by a reverse hemolytic plaque assay. MLR-induced antibody secretion was specifically dependent on the Leu-3 T lymphocyte subset. The Leu-2 subset was incapable of generating large numbers of IgM- or IgG-secreting cells, and, in fact, suppressed the Leu-3-induced response. Exposure of Leu-3 cells to a dose of irradiation sufficient to prevent their proliferation in MLR did not reduce induced immunoglobulin secretion. Leu-2-mediated suppression, however, was sensitive to low dose irradiation. Thus Ig secretion in human MLR is regulated by a balance of helper activity from the Leu-3 subset and suppressor activity from the Leu-2 subset.     

Subpopulations of the T4+ inducer T cell subset in man: evidence for an amplifier population preferentially expressing Ia antigen upon activation

Prior studies demonstrated that Ia molecules were expressed on a fraction of human peripheral T4+ inducer cells upon stimulation by soluble antigen. In the present study, we utilized a fluorescence-activated cell sorter to separate antigen-activated T4+,Ia+ and T4+,Ia- populations and characterized their function. It was found that the T4+,Ia+ population contained the majority of proliferating T cells as assessed by tritiated thymidine incorporation. This proliferation largely appeared to be nonspecific. Despite macrophage repletion, elimination of the Ia+ subset of T cells with monoclonal anti-Ia antibody and complement treatment equally diminished subsequent proliferation to both the triggering antigen and an unrelated antigen. Moreover, the antigen-induced Ia+ subset of T cells alone produced a nonspecific helper factor, LMF. In contrast, the the T4+,Ia- population showed minimal proliferation to soluble antigen and did not generate LMF. Nevertheless, both T4+,Ia+ and T4+,Ia- inducer T cells were required to generate maximal immunoglobulin production by B cells in an antigen-driven system. We conclude that the human T4+ inducer T cell subset is comprised of at least 2 functionally distinct subpopulations, which are capable of acting in a synergistic fashion to provide help to B cells.     

Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins

A panel of antigen-specific mouse helper T cell clones was characterized according to patterns of lymphokine activity production, and two types of T cell were distinguished. Type 1 T helper cells (TH1) produced IL 2, interferon-gamma, GM-CSF, and IL 3 in response to antigen + presenting cells or to Con A, whereas type 2 helper T cells (TH2) produced IL 3, BSF1, and two other activities unique to the TH2 subset, a mast cell growth factor distinct from IL 3 and a T cell growth factor distinct from IL 2. Clones representing each type of T cell were characterized, and the pattern of lymphokine activities was consistent within each set. The secreted proteins induced by Con A were analyzed by biosynthetic labeling and SDS gel electrophoresis, and significant differences were seen between the two groups of T cell line. Both types of T cell grew in response to alternating cycles of antigen stimulation, followed by growth in IL 2-containing medium. Examples of both types of T cell were also specific for or restricted by the I region of the MHC, and the surface marker phenotype of the majority of both types was Ly-1+, Lyt-2-, L3T4+, Both types of helper T cell could provide help for B cells, but the nature of the help differed. TH1 cells were found among examples of T cell clones specific for chicken RBC and mouse alloantigens. TH2 cells were found among clones specific for mouse alloantigens, fowl gamma-globulin, and KLH. The relationship between these two types of T cells and previously described subsets of T helper cells is discussed.     

Identification of suppressor T cells in virgin non-responder spleen cells responsible for primary unresponsiveness to L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT)

T cell subsets that regulate antibody responses to L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT) in mice that are Ir gene non-responders have been further characterized. We previously defined several T cell subsets in GAT-primed non-responder mice. The Lyt-2+ suppressor-effector T cells suppress responses to GAT and GAT complexed to methylated BSA (GAT-MBSA). The Lyt-1+ cell population is complex and can be separated into I-J- Th cells, which support responses to GAT and GAT-MBSA. After priming, the Lyt-1+, I-J+ cell population contains suppressor-inducer cells that activate precursors of suppressor-effector cells to suppress responses to GAT and GAT-MBSA as well as Ts cells that directly inhibit responses to GAT but not GAT-MBSA. By contrast, the Lyt-1+ cells from virgin mice contain only cells that directly suppress responses to GAT but not GAT-MBSA. The major question addressed in the present studies was whether the Lyt-1+, I-J+ Ts cells in virgin and primed mice and the suppressor-inducer cells in GAT-primed mice were functionally and serologically distinct subsets. The studies used mAb and panning procedures to separate cell populations and inhibition of PFC cell responses to functionally define the activity of the cell populations. We used the following two mAb that were raised by immunizing rats with GAT-specific suppressor factors: 1248A4.10 (known to react with suppressor-inducer cells) and 1248A4.3, another reagent from the same fusion. Lyt-1+ cells from virgin spleens contained Ts cells that were A4.10-, A4.3+ and no suppressor-inducer T cells, whereas Lyt-1+ cells from GAT-primed spleens contained Ts cells that were A4.10-, A4.3+ as well as A4.10+, A4.3- suppressor-inducer cells. Thus, the Lyt1+, I-J+ cell subset can be divided into two functionally and serologically distinct subsets, direct Ts cells (1248A4.3+), which suppress responses to GAT but not GAT-MBSA, and GAT-primed suppressor-inducer T cells (1248A4.10+).     

Development and homeostasis of T cell memory in rhesus macaque.

The rhesus macaque (RM) is a critical animal model for studies of viral pathogenesis and immunity, yet fundamental aspects of their cellular immune response remain poorly defined. One such deficiency is the lack of validated phenotypic signatures for their naive and memory T cell subsets, and the resultant unavailability of accurate information on their memory T cell development, homeostasis, and function. In this study, we report a phenotypic paradigm allowing definitive characterization of these subsets and their comprehensive functional analysis. Naive T cells are optimally delineated by their homogeneous CD95(low)CD28(high)beta(7) integrin(int) (CD4+) or CD95(low)CD28(int)CD11a(low) (CD8+) phenotypes. This subset 1) was present in blood and secondary lymph tissues, but not effector sites; 2) vastly predominated in the fetal/neonatal immune system, but rapidly diminished with postnatal age; 3) lacked IFN-gamma production capability, and specific responses to RM CMV; and 4) demonstrated low in vivo proliferative activity. CD4+ and CD8+ memory subsets were CD95(high), but otherwise phenotypically heterogeneous and included all IFN-gamma production, RM CMV-specific responses, effector site T cells, and demonstrated high in vivo proliferative activity ( approximately 10 times the naive subset). These analyses also revealed the RM "effector memory" subset within the overall memory population. This population, best defined by lack of CD28 expression, contained the majority of RM CMV-specific cells, was highly enriched in extralymphoid effector sites, and comprised an increasing proportion of total memory cells with age. The effector memory subset demonstrated similar in vivo proliferative activity and survival as CD28+ "central memory" T cells, consistent with independent homeostatic regulation.     

Functional and ontogenetic analysis of murine CD45Rhi and CD45Rlo CD4+ T cells

CD4+ murine T cell clones, TH1 and TH2, can be distinguished by both functional responses and by their patterns of lymphokine secretion. Recently, a mAb, 23G2, which reacts with a subset of CD45 molecules (CD45R), has been reported to bind differentially to clones of TH1 and TH2 cells. In the present study, normal splenic T cells were analyzed for differences in 23G2-reactivity and were separated into two populations based on their density of CD45R (CD45Rhi and CD45Rlo). The CD45Rhi cells secrete more IL-2 than IL-4 after stimulation in vitro; the reverse is true for the CD45Rlo cells. Because neither population secretes only IL-2 or IL-4, we were unable to classify cells as TH1 or TH2. In vivo and in vitro analyses of the CD45Rhi and CD45Rlo cells suggest a lineage relationship between the two subsets that correlates with the degree of Ag exposure and the state of maturation of the mice. In newborn mice and mice raised under sterile conditions, splenic CD4+ T cells are predominantly CD45Rhi. Under conditions of increased antigenic exposure and maturation of the mice, CD45Rlo cells develop; after long term priming in vivo, the majority of specific Ag-reactive cells are CD45Rlo. Adoptive transfer studies using BALB/c nu/nu recipients demonstrate that CD45Rhi cells become CD45Rlo cells and that the recall response (IgG) to specific Ag is mediated by CD45Rlo cells. Taken together, these data indicate that the level of expression of CD45R on CD4+ T cells distinguishes virgin (CD45Rhi) from primed/memory (CD45Rlo) T cells in normal mice.     

Expression of CD161 (NKR-P1A) defines subsets of human CD4 and CD8 T cells with different functional activities

A subset of T cells in human peripheral blood expresses CD161 (NKR-P1A) receptors that are primarily associated with NK cells. In the current study we isolated blood T cell subsets according to the expression of CD161 and examined their contents of naive, central memory, and effector memory cells and their capacities for proliferation, cytokine secretion, and natural cytolysis. We found that CD4+CD161- and CD8+CD161- subsets contained predominantly naive T cells that secreted high levels of IL-2 after in vitro stimulation, and CD4+CD161int and CD8+CD161int subsets contained predominantly effector and central memory T cells that secreted high levels of IFN-gamma and TNF-alpha. All of these subsets showed vigorous proliferation after stimulation in vitro, but none had NK lytic activity. Unexpectedly, the CD8+CD161+ cells contained an anergic CD8alpha+CD8betalow/-CD161high T cell subset that failed to proliferate, secrete cytokines, or mediate NK lytic activity.