Calcium dependency of antigen-specific (T3-Ti) and alternative (T11) pathways of human T-cell activation.

Human T lymphocytes are activated by two lineage-specific surface components: the antigen/major histocompatibility complex receptor (T3-Ti) and the unrelated T11 molecule. Interaction of either of these with their respective ligands leads to T-cell proliferation via an interleukin 2(IL-2) dependent autocrine mechanism. To begin to characterize the molecular details of the activation process, the role of Ca2+ was examined using human T-cell clones and monoclonal antibodies directed against their surface components. Here, we show that within minutes of triggering either the T3-Ti or T11 molecule, there is a large increase in intracellular Ca2+ concentration, as measured by quin-2 fluorescence. This is essential for induction of T-cell proliferation in inducer, suppressor, and cytotoxic clones and therefore presumably is required at an early step in the autocrine growth pathway. Thus, chelating exogenous Ca2+ with EGTA specifically inhibits proliferation triggered by anti-T3-Ti or anti-T11 monoclonal antibodies, but it does not affect triggering by exogenous IL-2. In addition, the Ca2+ ionophore A23187 can, by itself, initiate clonal proliferation.     

Clonal analysis of human cytotoxic T lymphocytes: T4+ and T8+ effector T cells recognize products of different major histocompatibility complex regions.

Alloreactive human T lymphocytes were cloned in soft agar or by limiting dilution and subsequently propagated with interleukin 2 and alloantigen for 8 months or more. By indirect immunofluorescence every clone was reactive with anti-Ia antibodies as well as the T cell-specific antibodies anti-T3 and anti-T11 and expressed either T4 or T8 antigens. All 15T8+ clones were highly cytotoxic for the sensitizing alloantigen. In contrast, only two of seven T4+ clones mediated cytotoxic effector function. The specificity of T4+ and T8+ clones and subclones was analyzed on a panel of typing cells and by antibody blocking studies of major histocompatibility complex (MHC) determinants on the stimulating alloantigen. It was found that T8+ clones killed targets that shared class I MHC antigens (HLA-A,B) with the original stimulator cells whereas cytotoxic T4+ clones were directed at class II MHC antigens (Ia-related). Preincubation of the allogeneic target cell with a monoclonal antibody to a nonpolymorphic HLA alpha-chain determinant inhibited killing by the T8+ clones but did not affect T4+ cytotoxic function. In a reciprocal fashion, anti-IA antibodies to common framework structures on the same target cell blocked killing by T4+ but not by T8+ clones. These results indicate that T4+ and T8+ T lymphocytes have receptors for different classes of MHC antigens and suggest tha cytotoxic T4+ subpopulations might be important in human transplantation and autoimmune disorders.     

Antigen-specific helper T-cell clone supernatant is sufficient to induce both polyclonal proliferation and differentiation of small resting B lymphocytes.

Gradient-purified resting B lymphocytes can be polyclonally stimulated by antigen-specific major histocompatibility complex (MHC)-restricted helper T lymphocytes as well as by antigen-activated helper T-cell supernatant. In contrast to what has been described so far, we show that helper T-cell supernatant (in the absence of any other added stimulus, such as that provided by anti-mu antibodies) is sufficient to induce both proliferation of resting B cells and their differentiation into IgM-secreting cells. The stimulation induced by the helper T-cell supernatant takes place in serum-free medium and is not MHC-restricted. Our findings strongly support the existence of a B-cell activating factor acting on the resting B cell and causing it to enter the G1 phase of the cell cycle in a MHC-unrestricted manner.     

In situ immunologic characterization of cellular constituents in lymph nodes and spleens involved by Hodgkin's disease

The cellular constituents in lymph nodes and spleens of patients with Hodgkin's disease were studied with a series of monoclonal antibodies directed against human thymocyte, peripheral T-cell, and la antigens. Utilizing both an immunoperoxidase technique on frozen tissue sections and indirect immunofluorescence on cell suspensions, wer found that a majority of lymphocytes were T cells, since they stained with anti-T1 and anti-T3 antibodies, which react with all peripheral T cells. In addition, most of these cells were reactive with anti-T4 antibody, which defines the helper/inducer T-cell population, whereas only a minority of cells stained with anti-T5 and anti-T8 antibodies, which are reactive with suppressor/cytotoxic T cells. Moreover, a large proportion of T cells expressed T10 antigen, which is found on activated T cells. A minority of the T cells also expressed la antigen(s), again suggesting that some of the T cells are activated. In contrast, the Reed-sternberg cells did not react with any of these anti- T-cell antibodies or with anti-IgM antiserum, but displayed strong membrane and cytoplasmic staining with anti-la antibody. Taken together, these findings suggest that Reed-Sternberg cells are not of T- cell lineage but may be derived from antigen-presenting reticulum cells in the thymus-dependent areas of lymphoid tissues; these cells are normally associated with T4+ cells.     

Autoreactive CD4(+) T-cell clones to beta2-glycoprotein I in patients with antiphospholipid syndrome: preferential recognition of the major phospholipid-binding site

Autoreactive CD4(+) T cells to beta2-glycoprotein I (beta2GPI) that promote antiphospholipid antibody production were recently identified in patients with antiphospholipid syndrome (APS). To further examine antigen recognition profiles and T-cell helper activity in beta2GPI-reactive T cells, 14 CD4(+) T-cell clones specific to beta2GPI were generated from 3 patients with APS by repeated stimulation of peripheral blood T cells with recombinant beta2GPI. At least 4 distinct T-cell epitopes were identified, but the majority of the beta2GPI-specific T-cell clones responded to a peptide encompassing amino acid residues 276 to 290 of beta2GPI (KVSFFCKNKEKKCSY; single-letter amino acid codes) that contains the major phospholipid-binding site in the context of the DRB4*0103 allele. Ten of 12 beta2GPI-specific T-cell clones were able to stimulate autologous peripheral blood B cells to promote anti-beta2GPI antibody production in the presence of recombinant beta2GPI. T-cell helper activity was exclusively found in T-cell clones capable of producing interleukin 6 (IL-6). In vitro anti-beta2GPI antibody production induced by T-cell clones was inhibited by anti-IL-6 or anti-CD40 ligand monoclonal antibody. In addition, exogenous IL-6 augmented anti-beta2GPI antibody production in cultures of the T-cell clone lacking IL-6 expression. These results indicate that beta2GPI-specific CD4(+) T cells in patients with APS preferentially recognize the antigenic peptide containing the major phospholipid-binding site and have the capacity to stimulate B cells to produce anti-beta2GPI antibodies through IL-6 expression and CD40-CD40 ligand engagement. These findings are potentially useful for clarifying the pathogenesis of APS and for developing therapeutic strategies that suppress pathogenic antiphospholipid antibody production in these patients.     

Regulation of T-cell function by antibodies: enhancement of the response of human T-cell clones to hepatitis B surface antigen by antigen-specific monoclonal antibodies.

Eight mouse monoclonal antibodies specific for hepatitis B surface antigen (HBsAg) were examined for their effects on the antigen-induced proliferative response and lymphokine production of human HBsAg-specific T-cell clones in vitro. While all specifically enhanced the T-cell proliferative response, antibodies of the IgG class were generally more effective than those of the IgM class. Both the divalent F(ab')2 and the monovalent Fab fragments of an IgG monoclonal antibody had no effects, indicating that the Fc portion of the antibody molecules was required. Since antigen-presenting cells bear surface receptors for the Fc of IgGs and fewer or none for that of IgMs, the above results also suggest that antibodies enhance the capture of antigens by antigen-presenting cells as a result of the binding of antigen-antibody complexes to the Fc receptors on these cells. In addition to potentiating the proliferation of the T-cell clones, antibodies also increased the antigen-induced production of interferon-gamma by these cells. The present in vitro studies suggest that antibodies may regulate immune responses and do so by enhancing antigen presentation and thus augmenting antigen-induced activation and clonal expansion of T cells.     

B-cell stimulatory factor 1 activates resting B cells.

B-cell stimulatory factor 1 (BSF-1) is a T-cell-derived lymphokine that acts together with low concentrations of anti-IgM antibodies to stimulate resting B cells to enter the G1 phase of the cell cycle and to synthesize DNA. We show here that supernatants from EL-4 cells, rich in BSF-1 activity, and BSF-1 purified by high-pressure liquid chromatography (HPLC-BSF-1) act on resting B cells, in the absence of anti-IgM antibodies, to prepare them to respond to anti-IgM and BSF-1. A 24-hour preculture with BSF-1 speeds the entry into S phase of B cells subsequently cultured with anti-IgM and BSF-1 by approximately equal to 12 hours and causes substantial increase in cell volume of all resting B cells. Both of these effects, stimulated either by EL-4 supernatants or by HPLC-BSF-1, are inhibited by a monoclonal anti-BSF-1 antibody. These results lead us to propose that BSF-1 should be regarded as a B-cell activation factor.     

Inhibition of normal B-cell function by human immunodeficiency virus envelope glycoprotein, gp120.

Despite the occurrence of hypergammaglobulinemia in human immunodeficiency virus (HIV) infection, specific antibody production and in vitro B-cell differentiation responses are frequently impaired. In this study, we have examined the effects of HIV envelope glycoprotein gp120 on T-helper cell function for B cells. In the culture system used, B-cell functional responses were dependent on T-B-cell contact, since separation of T and B cells in double chambers by Transwell membranes rendered the B cells unresponsive in assays of antigen-induced B-cell proliferation and differentiation. Cytokines secreted by T cells were also essential, since anti-CD3 monoclonal antibody (mAb)-activated, paraformaldehyde-fixed T-cell clones failed to induce B-cell proliferation and differentiation. Pretreatment of the CD4+ antigen-specific T cells with gp120 was found to impair their ability to help autologous B cells, as determined by B-cell proliferation, polyclonal IgG secretion, and antigen-specific IgG secretion. The gp120-induced inhibition was specific in that it was blocked by soluble CD4. Furthermore, only fractionated small B cells (which are T-cell-dependent in their function) manifested impaired responses when cultured with gp120-treated T cells. Antigen-induced interleukin (IL)-2 and IL-4, but not IL-6, secretion were markedly reduced in gp120-treated T-cell clones. Addition of exogenous cytokines failed to compensate for defective helper function of gp120-treated T cells. The findings in this study indicate that gp120 impairs helper functions of CD4+ T cells by interfering with T-B-cell contact-dependent interaction; the inhibitory effects of soluble envelope proteins of HIV may contribute to the immunopathogenesis of the HIV-associated disease manifestations.     

Polarized expression of cytokines in cell conjugates of helper T cells and splenic B cells.

We describe the intracellular localization, by double immunofluorescence microscopy, of four cytokines that were produced during the prolonged interaction of cloned helper T cells with resting splenic B cells. When two rabbit immunoglobulin-specific helper-T-cell clones were mixed, either separately or together, with splenic B cells in the presence of the antigen rabbit anti-mouse immunoglobulin antibodies, stable T-cell-B-cell conjugates were seen up to 29 hr later. Microscopic observations of these cells revealed that interferon gamma and interleukin 2, inside one of the T-cell clones, and interleukins 4 and 5, inside the other T-cell clone, were concentrated very close to the T-cell-B-cell contact area. The cytokines were not seen in the T cells prior to their interaction with the B cells and their production was strictly antigen-specific. These studies show, at the single-cell level, that helper-T-cell clones can remain bound to splenic B cells long enough for the T cells to produce cytokines, which are synthesized near the bound B cells. We propose that the polarized synthesis of the cytokines may result in their directed secretion toward the bound B cells. By locally secreting the cytokines, which are not antigen-specific, at the contacting T-cell-B-cell membranes, where T- and B-cell surface receptors are engaged and clustered, the helper T cells can induce selective and specific B-cell responses.     

T cell-dependent activation of resting B cells: requirement for both nonspecific unrestricted and antigen-specific Ia-restricted soluble factors.

Cloned murine helper T cells, restricted to the Iab antigens of the major histocompatibility locus and specific for horse erythrocytes as a foreign antigen, produce, in cooperation with antigen and histocompatible adherent cells, soluble factors that replace the helper T cells in their action on B cells. Three types of factors can be distinguished on the basis of molecular weight: proteins having apparent Mr 30,000 (p30) that act antigen- and Ia-nonspecifically as replication- and maturation-inducing factors and proteins having apparent Mr 55,000 (p55) and 125,000 (p125) that act on resting B cells in an Ia-specific, restricted fashion. Neither horse erythrocytes (a T-cell specific antigen) nor p55 and p125, alone or together, stimulate resting B cells to proliferation and maturation. Double occupancy by antigen and p55 or p125, however, renders Ia-compatible, but not Ia-incompatible, resting B cells susceptible to stimulation. The subsequent addition of p30 to these "excited" B cells then results in the proliferation and maturation of clones of horse erythrocyte-specific resting B cells, which then replicate under the stimulatory action of p30. p30 do not bind antigen, nor do they bind anti-Ia or anti-immunoglobulin antibodies. p55 are bound by anti-heavy chain variable region antibodies. p55 are bound by anti-heavy chain variable region antibodies, but not by anti-heavy or anti-light chain constant region antibodies or anti-Ia antibodies. p125 molecules bind horse but not sheep erythrocytes and are bound by anti-heavy chain variable region, but not by anti-heavy or light chain constant region or anti-Ia antibodies. p55 and p125 are likely to be soluble analogues of the antigen-specific, Ia-restricted T-cell receptors of the cloned helper T cells.     

Polyspecific natural antibodies and autoantibodies secreted by human lymphocytes immortalized with Epstein-Barr virus

Recent studies have shown that autoreactive B cells and autoantibodies are present in pathological as well as in normal situations. In the present study, we immortalized human B cell lines from normal individuals and from patients with malignant or benign dysglobulinemia with Epstein-Barr virus and examined, after cloning, the autoantibody reactivities of the immunoglobulins secreted by these cells. Forty-two supernatants were analyzed by enzyme-immunoassay on a panel of 13 self and non-self antigens: trinitrobenzenesulfonic acid (TNP), DNA, L- glutamine, L-alanine, L-tyrosine (GAT), actin, myosin, tubulin, albumin, renin, spectrin, transferrin, thyroglobulin, myoglobin, peroxidase, and by immunofluorescence in tissue sections. Fourteen (33%) of the immunoglobulin-secreting cell lines were found to have an autoantibody function; seven secreted IgM, six IgA, and one IgG. The light chains were of the kappa type in 11 cases. The vast majority of these clones reacted with more than five antigens of the panel and all of them reacted with TNP. No correlation was found between a given isotype and an antibody specificity. More than half of these antibodies also reacted with cellular antigens present in tissue sections. None of the four cell lines secreting monoclonal antiviral antibodies reacted with any of the antigens of the panel. The results indicate that immunoglobulins secreted by human monoclonal lymphoid cell lines can have polyspecific autoantibody functions, similar to those found in normal human polyclonal antibodies, in human monoclonal paraproteins and in natural monoclonal antibodies synthesized by murine or rat clones obtained from physiologically normal animals.     

Establishment and characterization of human T hybrid cells secreting immunoregulatory molecules.

Hybridization of human T cells with an azaguanine-resistant human T cell line gave rise to T hybrid cell lines secreting several immunoregulatory molecules. Analyses of karyotypes, HLA phenotypes, and other surface phenotypes, such as T-cell-specific antigens or receptors for sheep erythrocytes and the patterns of mitogen responsiveness confirmed that the hypoxanthine/aminopterin/thymidine-resistant cell lines were human T-T hybridomas. One of the established hybrid clones (24-A) secreted human interleukin-2 (IL-2). The culture supernatants induced the proliferation of concanavalin A-stimulated murine T cells and supported the proliferation of an IL 2-dependent human cytotoxic T-cell line. In a clone (38-B) that did not show any IL-2 activity in culture supernatants, the addition of macrophages induced IL-2 production in the presence of phytohemagglutinin, suggesting that interleukin-1 induced IL-2 production in T hybrid cells. Hybrid cells secreting killer helper factor were also established. The culture supernatants from this clone, 55-A, helped the induction of cytotoxic T cells against UV-treated human B-blastoid cells but did not show any IL-2 activity.     

Isolation and characterization of lymphokine cDNA clones encoding mouse and human IgA-enhancing factor and eosinophil colony-stimulating factor activities: relationship to interleukin 5.

Conditioned medium from the Con A-treated mouse helper T-cell clone Ly1+2-/9 contains activities that enhance the production of IgA by mouse B cells and induce human cord blood cells to form eosinophil colonies. We have isolated a cDNA sequence that expresses IgA-enhancing factor and eosinophil colony-stimulating factor activities from a cDNA library prepared from activated Ly1+2-/9 cells. Based on homology with the mouse cDNA sequence, a human cDNA sequence coding for an interleukin with IgA-enhancing factor and eosinophil colony-stimulating factor activities was isolated from a cDNA library prepared from a human T-cell clone stimulated with anti-T3 antibody and phorbol 12-myristate 13-acetate. DNA sequence analyses revealed that mouse and human cDNA clones encode proteins of 133 and 134 amino acids, respectively, that are identical to cDNA clones encoding the T-cell replacing factor I and B-cell growth factor II activities. These results establish that a single cDNA clone encodes a protein that acts as a growth and differentiation factor for both B cells and eosinophils.     

Functional helper activity of monoclonal T cell populations: antigen-specific and H-2 restricted cloned T cells provide help for in vitro antibody responses to trinitrophenyl-poly(LTyr,Glu)-poly(DLAla)--poly(LLys).

The ability of long-term cultured and monoclonal T cell populations to provide antigen-specific help was assessed in a system of Ir gene-controlled in vitro antibody responses to soluble antigens. T-cell colonies and monoclonal T-cell lines were generated which proliferated specifically in response to poly(LTyr,Glu)-poly(DLAla)--poly(LLys) [(T,G)-A--L] and were I-A restricted in these proliferative responses. These (T,G)-A--L-specific T-cell populations were evaluated for their ability to help unprimed and T-cell depleted spleen cell populations in the generation of antibody responses to trinitrophenyl (TNP)-(T,G)-A--L in vitro. It was found that long-term T-cell lines, including monoclonal T-cell populations derived by limiting dilution, were highly efficient helper cells for IgM responses to TNP-(T,G)-A--L. These helper T cells were both antigen-specific and I-A restricted in their ability to be activated and to cooperate with T-cell depleted spleen cell populations. Once specifically activated, however, these clones provided help that was antigen nonspecific. These studies have thus demonstrated the ability of antigen-specific and H-2-restricted monoclonal T-cell populations to provide help for responses to soluble antigens in vitro.     

Monoclonal antibodies specific for a murine cytotoxic T-lymphocyte clone.

Two antibody-secreting murine hybridomas, F1G3.1 and F2A11.5, have been established from B10.D2 mice immunized with cells from the murine cytotoxic T-lymphocyte clone G4. The two clones used, G4 and B10, were derived from BALB.B (H-2b) mice and the target antigen specificity of both maps to the Dd region of the murine H-2 complex. However, B10 has a lower affinity for the target cells, as shown by its lower specific killing of blasts and its higher susceptibility to blocking by anti-Lyt-2 monoclonal antibody 53-6.75. The monoclonal antibodies, F1G3.1 and F2A11.5, react only with cells from clone G4. Similarly, they block only the specific cytolysis mediated by G4; no effect on cytotoxicity mediated by B10 or by heterogeneous populations of cytotoxic T lymphocytes was found. F1G3.1, especially, is very active in stimulating G4 to secrete immune interferon; B10 in contrast did not show any induction on treatment with these monoclonal antibodies. The structure of the surface antigen on G4 cells recognized by these monoclonal antibodies was revealed by immunoprecipitation studies of radioiodinated cell surface proteins. A protein dimer could be identified with an apparent molecular size of 80,000 daltons consisting of monomers migrating as 42,000-dalton proteins on reduction. So far, electrophoresis in the presence of NaDodSO4 does not indicate any heterogeneity in the size of the monomers. This molecule can be distinguished from the Lyt-2 complex.     

Selection and characterization of T-cell variants lacking molecules involved in T-cell activation (T3 T-cell receptor, T44, and T11): analysis of the functional relationship among different pathways of activation

A clone of the interleukin 2-producing Jurkat leukemia cell line termed JA3 (surface phenotype, T3+, Ti+, T44+, T11+, T40+) has been used to induce and select cell variants lacking surface molecules involved in T-cell activation. Following 200 rad of gamma-radiation (1 rad = 0.01 Gy), cells were treated with monoclonal antibodies (mAbs) directed to T3, Ti, T44, or T11 antigen and complement. After growth of the residual cells in culture, "negative" cells were cloned under limiting conditions. Depending on the specificity of the mAb used for the immunoselection, three groups of variants were obtained. (i) The use of mAbs directed to T3 or Ti resulted in cell variants that expressed the T3 Ti- T44+ Leu1+ T11+ T40+ 4F2+ HLA class I+ surface phenotype. (ii) Immunoselection with anti-T44 mAb resulted in 2 variants that shared the T3- Ti- T44- Leu1- T11+ T40+ 4F2+ HLA class I+ phenotype. (iii) Cell treatment with anti-T11 mAb resulted in 15 variants characterized by the lack of T11 antigen expression and of all the other T-cell-specific surface antigens. Therefore, it appears that the different sets of JA3 cell variants, like T cells at discrete stages of intrathymic differentiation, may follow a coordinated expression of surface differentiation antigens. Analysis of the functional responsiveness of the three distinct groups of JA3 cell variants to different stimuli showed that all produced interleukin 2 in response to A23187 calcium ionophore plus phorbol 12-myristate 13-acetate. The first group of variants (T3- Ti-) did not respond to stimulation with anti-T3, anti-Ti, or anti-T44 mAbs. Eight of 9 did not respond to phytohemagglutinin either; however, all responded to appropriate stimulatory combinations of anti-T11 mAbs (and to calcium ionophore). The second group of variants (T3-, Ti-, T44-, T11+), similar to the first group, did not respond to anti-T3, anti-Ti, anti-T44 mAbs, and phytohemagglutinin, but they were fully responsive to anti-T11 mAb. The last group of variants (lacking all the T-cell-specific surface antigens) only responded to calcium ionophore A23187.     

A neutralizing monoclonal antibody (mAb A24) directed against the transferrin receptor induces apoptosis of tumor T lymphocytes from ATL patients

Adult T-cell leukemia/lymphoma (ATL) is an aggressive lymphoid proliferative disease that exists under diverse clinical forms ranging from chronic to acute. Although leukemic cells from patients with ATL exhibit an intrinsic resistance to chemotherapy, monoclonal antibodies directed against CD25 (interleukin 2 receptor alpha [IL-2Ralpha] antibody) have been used as specific therapeutic agents. However, significant clinical results with these antibodies have been demonstrated only in chronic forms of ATL. In contrast to resting T cells, human T-cell lymphotropic virus type 1 (HTLV-1)-infected cells constitutively express high levels of surface transferrin receptor (TfR). Herein, we report the characterization of a new monoclonal antibody (mAb A24) directed against the human TfR and the evaluation of its capacity to block the proliferation of ATL cells ex vivo. We determined that A24 binds TfR with an equilibrium constant (K'd) of 2.7 nM and competes with transferrin for binding to TfR. A24 also inhibited [55Fe]-transferrin uptake in activated T cells and blocked T-cell proliferation. Moreover, A24 reduced and impaired TfR expression and recycling, respectively. Most important, we showed that A24 blocked the ex vivo proliferation of malignant T cells from both acute and chronic forms of ATL, through induction of programmed cell death. Therefore efficient therapeutic tools to treat acute forms of ATL might be derived from A24.     

Decreased suppressor T-lymphocytes in autoimmune thyroid diseases detected by monoclonal antibodies

Monoclonal antibodies reacting with cell surface antigens of helper (T4), suppressor (T8) T cells and common T-cell antigen (T3) were used by an immunofluorescence technique to enumerate peripheral T-lymphocytes in 42 patients with Graves' disease and 16 patients with Hashimoto's thyroiditis. The percentages of total T cells (cells which react with anti-T3) and helper/inducer cells (cells which react with anti-T4) among peripheral mononuclear cells in Graves' and Hashimoto's patients were not significantly different from those found in normal controls, except for a decrease in cells which react with anti-T3 in toxic Graves' disease without medication. The most important finding was a decrease in the percentage of cytotoxic/suppressor T cells (cells which react with anti-T8) in toxic Graves' disease and Hashimoto's thyroiditis. In patients with Graves' disease who were hyperthyroid or euthyroid on propylthiouracil treatment and euthyroid after radioactive iodide treatment, the percentage of cells which react with anti-T8 was also decreased, but this did not reach statistical significance. These findings support the hypothesis of defects in suppressor T-lymphocytes in autoimmune thyroid diseases.     

Dissection of distinct human immunoregulatory T-cell subsets by a monoclonal antibody recognizing a cell surface antigen with wide tissue distribution.

A monoclonal antibody, PVR-11, was obtained after hybridization of X63Ag8.653 murine myeloma cells with spleen cells from a mouse immunized with human lymphocytes. It recognizes a 175,000- to 185,000-dalton surface antigen present on approximately 80% of normal human peripheral T lymphocytes, 50% of non-T non-B cells, and less than 10% of B cells as determined by complement-dependent microcytotoxicity. It is also present on various leukemia T cells, on some but not all T lymphoblastoid cell lines, and on a small fraction of some B lymphoblastoid cell lines. Some B-cell chronic lymphocytic leukemia cells also express the PVR-11 antigen. Functional analysis of normal human T lymphocytes demonstrated that the PVR-11-depleted T-cell subset contains the precursors of both cytotoxic and suppressor cells but lacks helper cells. On the other hand, cytotoxic effector T cells express the PVR-11 antigen. These results demonstrate that antigenic determinants with relatively wide tissue distribution can dissect functionally distinct human immunoregulatory T-cell subsets.