A novel human T cell antigen preferentially expressed on mature T cells and shared by both well and poorly differentiated B cell leukemias and lymphomas

A new lymphocyte differentiation antigen shared by all normal T cells and some malignant B cells was defined by a monoclonal antibody designated 12.1. This antibody reacted with all peripheral blood T cells but not with normal B cells and B cell lines. Analysis with a fluorescence activated cell sorter showed that the expression of 12.1 antigen changes during T cell maturation. Most thymocytes, blasts of acute T cell leukemia, and cells from established leukemic T cell lines bear a small amount of 12.1 antigen. In contrast the majority of peripheral blood T cells, activated T cells, and leukemic T cells of the Sezary syndrome bear a large amount of 12.1 antigen. Unexpectedly, antibody 12.1 reacted with leukemic cells from most patients with B-type chronic lymphocytic leukemia (CLL) and some patients with lymphosarcoma cell leukemia (LSCL). Among these leukemias, expression of the 12.1 antigen was not correlated with the stage of B cell maturation, with the amount of surface immunoglobulin on the cells, or with the presence or absence of monoclonal gammapathy. In a comparative serologic analysis the antigen defined by antibody 12.1 was distinct from the p67 T cell antigen (defined by monoclonal antibody 10.2) that is also known to be expressed by B-type CLL cells.     

Monoclonal antibodies reactive with swine lymphocytes. II. Detection of an antigen on resting T cells down-regulated after activation

The expression of an antigen on porcine T lymphocytes detected by murine monoclonal antibody (mAb) 8/1 was investigated by functional studies and dual-parameter immunofluorescence. mAb 8/1 reacts with greater than 95% of thymocytes and in peripheral blood with all T lymphocytes and with cells of the monocyte/macrophage lineage, but not with B cells, erythrocytes, and platelets. Pretreatment of peripheral blood lymphocytes with mAb 8/1 plus complement abrogated the proliferative response in vitro to mitogen, soluble antigen, and MHC determinants. Dual-parameter immunofluorescence revealed that resting porcine T8+ as well as T4+ lymphocytes express the 8/1 antigen, whereas after in vitro activation, cell surface expression of the antigen was low or absent in both T cell subsets. Thus, the 8/1 antigen represents a marker that discriminates between resting and activated T lymphocytes. Distribution and functional criteria indicate that 8/1 represents a novel marker not described before for any other mammalian species.     

Characterization of a monoclonal antibody to guinea pig T cells that inhibits rosette formation of the cells with rabbit erythrocytes: similarity of the antigen to E-receptor on human T cells

A monoclonal antibody, GPT-1, was prepared by fusion of the splenic cells of mice immunized with guinea pig thymocytes with a mouse myeloma cell line. GPT-1 completely inhibited spontaneous rosette formation of T cells with papain-treated rabbit erythrocytes. GPT-1 reacted with 90% of thymocytes, 70% of peripheral blood lymphocytes, and 45% of splenic lymphocytes, but not with B cells. These results indicate that GPT-1 has pan-T reactivity. The antibody specifically bound to a single polypeptide chain with a molecular size of 50-65 kD. The surface density of the antigen was higher on thymocytes than on peripheral T cells, suggesting that the antigen is a certain differentiation antigen on T cells. Phytohemagglutinin-activated T cells expressed more antigen molecules than resting T cells. In addition, GPT-1 suppressed the proliferation of T cells induced by the mitogen, indicating that GPT-1 recognizes a T cell-specific surface antigen which is associated with T cell activation. Based on these results, it was concluded that GPT-1 reacts with a guinea pig T cell surface antigen which is similar to the E-receptor protein on human T cells (CD2 molecule).     

Development and distribution of a human B cell subpopulation identified by the HB-4 monoclonal antibody

Monoclonal antibodies have been successfully used to identify B cell differentiation antigens, few of which mark discrete B cell subpopulations. We have produced a monoclonal antibody, HB-4, against a cell surface antigen on the human B cell line, BJAB, which has an unusual distribution on normal lymphoid cells. HB-4, an IgM antibody, was found to react with an antigen that is expressed by a subpopulation of B cells, approximately 50% of natural killer cells, and not by other types of cells in bone marrow, blood, and lymphoid tissues. In two-color immunofluorescence assays, the HB-4-reactive antigen was found on less than 5% of immature IgM+ B cells in fetal liver and bone marrow and on 25% of B cells in fetal spleen. The HB-4 antibody reacted with 40% of IgM+ cells in newborn blood and 60% of B cells in adult blood. In contrast, only 2 to 26% of IgM+ B cells in the peripheral lymphoid tissues of adults were HB-4+. HB-4+ B cells could be induced to proliferate by cross-linkage of their surface immunoglobulins but not by T cell-derived growth factors. The subpopulation of activated B cells that is responsive to T cell-derived differentiation factors was HB-4-, as were plasma cells. The HB-4 antibody was reactive with some but not all B cell malignancies and cell lines, and not with malignancies or cell lines of other lineages. The HB-4 antigen may therefore serve as a useful nonimmunoglobulin marker for the identification of a subpopulation of mature resting B cells that are present in the highest frequency in the circulation.     

Tp44 molecules involved in antigen-independent T cell activation are expressed on human plasma cells

We have analyzed cells of the B lineage for expression of the Tp44 antigen, a 44,000 homodimer detected by monoclonal antibody 9.3 on approximately 80% of mature human T lymphocytes. Previous evidence has suggested that Tp44 may function as a receptor for accessory signals in T cell activation. High level Tp44 expression was observed on plasmacytomas grown in cell culture and on plasma cells from bone marrow biopsies of multiple myeloma patients. This antigen is not present on resting B cells from either peripheral blood or lymphoid organs, or on any other B cell tumor. The growth kinetics and Ig production in plasmacytomas are not affected by the binding of antibody 9.3. Moreover, the Tp44 molecule is co-expressed with PCA-1, an antigen characteristic of plasma cells, on peripheral blood B cells stimulated in vitro to differentiate toward plasma cells. Tp44 may represent a later stage of B cell differentiation than PCA-1 because unlike the PCA-1 antigen, this molecule could not be detected on any EBV-transformed cell line or Burkitt's lymphoma lines. The m.w. of the Tp44 molecule expressed on plasma cells and on T cells is identical, as determined by immunoprecipitation of radioiodinated cell surface proteins with monoclonal antibody 9.3. This antigen might be useful in studying the mechanism of growth and differentiation of human B cells, the heterogeneity within plasma cell populations, and B cell interactions with other components of the immune system.     

A unique antigen on mature B cells defined by a monoclonal antibody

A novel 42,000 dalton antigen (MB-1) expressed by mature human B cells in blood and tonsil was identified and characterized by utilizing a hybridoma monoclonal antibody. A comparison of MB-1 with other known B cell antigens suggests that the MB-1 antigen has not been previously identified. From one-and two-color immunofluorescence studies, it appears that the MB-1 antigen is found on all normal immunoglobulin (Ig)-expressing cells, but not on T cells, thymocytes, granulocytes, or platelets. Studies of malignant B cell tumors reveal that the antigen is expressed by virtually all Ig-expressing B cell tumors but only 10% of SIg- B-lineage leukemias. Data from these studies suggest that the MB-1 antigen is expressed late in B cell ontogeny before the expression of SIg.     

A Monoclonal Antibody Defining Human B Cell Differentiation Antigen (HLB-1 Antigen)

A new monoclonal antibody specific for human B cell differentiation antigen (HLB-1) is produced by a hybridoma established by fusion of splenocytes of mice immunized with the Epstein-Barr virus (EBV)-transformed peripheral B cell line, RPMI-8057. This monoclonal, antibody designated anti-HLB-1 monoclonal antibody (anti-HLB-1), reacted with surface immunoglobulin (sIg)-positive B cells of normal peripheral blood and lymphoid tissues and sIg-positive leukemic cells. The cells of T cell leukemia, non-T non-B acute lymphoblastic leukemia (ALL) and nonlymphoid leukemia were HLB-1 negative. These data were further confirmed by studying a panel of cultured human hematopoietic cell lines. Anti-HLB-1 reacted with B cell lines derived from pre-B, Burkitt's lymphoma, B cell type ALL and EBV-transformed peripheral B cells. Anti-HLB-1 was reactive with only one of three human myeloma cell lines, and with none of the T cell, myeloid and non-T non-B ALL cell lines. This newly defined HLB-1 antigen is different from other conventional human B cell markers such as sIg, Ia antigens, and receptors for the Fc portion of Ig and complement C3.     

B4, a human B lymphocyte-associated antigen expressed on normal, mitogen-activated, and malignant B lymphocytes

The characterization of a new B cell-specific antigen (B4) is described in this report. With the use of a monoclonal antibody to B4, it was shown that B4 is present on B cells isolated from peripheral blood and lymphoid organs, on cell lines derived from normal and malignant B cells, and on tumor cells isolated from patients with B cell-derived neoplasms. B4, in contrast, was not detected on normal, activated, or malignant cells of T or myeloid origin. The B4 antigen is distinct from known B cell antigens, including sIg, Ia, B1, B2, Fc, and C3. Examination of mitogen-stimulated B lymphocytes suggests that the B4 antigen initially increases with B cell activation and then is lost at the terminal stage of B cell differentiation. Moreover, the observation that B4 is expressed on almost all early B cell tumors suggests that it may precede B1, CALLA, cytoplasmic mu, and B2 in early B cell ontogeny.     

Detection of HLA-DRw (Ia-like) antigens on human T lymphocytes grown in tissue culture.

Human T lymphocytes that proliferate in the presence of conditioned medium from PHA-stimulated allogeneic peripheral blood cells were shown to express IPA antigens after the 8th culture day. Ia antigens as detected by xenogeneic antisera were present on 80 to 90% of the cultured cells which were also strongly reactive with xenogeneic antisera defining a human T cell antigen and formed E rosettes. Control cultures with PHA or no conditioned medium expressed T cell but not Ia antigens. These cultured T cells also express the same HLA-DRw determinants as the B cells of the donor they were derived from. Absorption of xenogeneic Ia, and HLA-DRw alloantisera with cultured T cells completely removed the reactivity of these sera for enriched peripheral blood B lymphocytes from normal donors.     

Dual fluorochrome analysis of human B lymphocytes: phenotypic examination of resting, anti-immunoglobulin stimulated, and in vivo activated B cells

B cell-enriched preparations were prepared from human peripheral blood and lymphoid tissues by the depletion of T cells and monocytes. Only B cells by virtue of their staining with anti-B1 conjugated to fluorescein were additionally examined. Dual fluorescence staining and flow cytometric analysis demonstrated that the majority of "resting" human peripheral blood and splenic B cells co-express the B cell-restricted B1 and B2 antigens and lack B5, a B cell-restricted activation antigen, and interleukin 2 receptor (IL 2R). In contrast, nearly 2/3 and 1/3 of B1+ cells isolated from lymph node expressed IL 2R and B5 antigens, respectively. When B1+ B cells from peripheral blood and spleen were "activated" by anti-Ig, they lost the B2 antigen and acquired the B5 and/or IL 2R antigens. 2/3 of B1+ cells strongly expressed IL 2R, and up to 1/2 of B1+ cells co-expressed B5. Delineation of increased numbers of B1+ cells that co-express B5 and/or IL 2R within lymphoid tissues obtained from patients with diseases characterized by "activated" B cells provides in vivo confirmation that these phenotypic changes correlate with B cell activation. We believe that the identification and isolation of these and similar subsets of cells defined by differing cell surface phenotypes should further our understanding both of normal B cell activation and the pathophysiology of B cell disease states.     

Production and characterization of a bovine T cell-specific monoclonal antibody identifying a mature differentiation antigen

A monoclonal antibody (MAb), BLT-1, with specificity for bovine mature T cells was prepared by somatic cell hybridization of myeloma NS-1 and spleen cells from BALB/c mice hyperimmunized with bovine T lymphocytes. The MAb reacted with over 92% of nylon wool-nonadherent lymphocytes (T cells) but not with nylon wool-adherent EAC-positive lymphocytes (B cells) in the indirect immunofluorescence assay. It is an IgM, with kappa-light chains, which fixed complement well and killed over 95% of mature T cells in complement-mediated cytotoxicity assays. It reacted with the same proportions of peripheral lymphoid cells (peripheral blood, lymph nodes, and spleen) as the polyclonal goat anti-bovine thymocyte serum (GABTS), but only with 25% of GABTS-positive thymocytes. Immunoperoxidase staining of frozen tissue sections showed that the BLT-1-positive cells were located in the medulla of the thymus and in the T lymphocyte areas of lymph nodes. Western immunoblotting assays showed that the BLT-1-reactive membrane antigen is a 22,000 m.w. protein which was inducible in bovine thymocytes with bovine thymic hormones, thymosin fraction 5, thymosin alpha 1, and thymopentin ORF-18150, indicating that it is a mature T lymphocyte differentiation antigen. The thymosin alpha 1 and thymopentin were found to show additive effects on mature T cell antigen expression by bovine thymocytes.     

Characterization of an antigen expressed by human natural killer cells

A monoclonal antibody, anti-N901, was produced by fusing NS-1 myeloma cells with spleen cells of a mouse immunized with human CML cells. This antibody was reactive with a subpopulation of peripheral blood LGL, including the natural killer cells. Monocytes, granulocytes, B cells, T cells (T3+ cells), erythrocytes, and platelets were nonreactive. The N901-positive cells in the peripheral blood were heterogeneous with respect to expression of other cell surface antigens. The majority of N901+ cells co-expressed T11, Mo1, and HNK-1, whereas a smaller percentage expressed T8. Ia, T3, T4, Mo2, or B1 antigens were very uncommon on N901+ cells. The heterogeneity of the N901+ LGL was further investigated by examining the expression of N901 antigen on a series of cloned normal human NK cell lines. N901 antigen was expressed by each of the NK cell lines tested, and by a minority of cloned T cell lines without NK activity. Anti-N901 does not block NK activity and can be used to rapidly purify functional NK cells for further study.     

B5, a new B cell-restricted activation antigen

The characterization of a new human B cell-restricted activation antigen (B5) is described in this report. With the use of a monoclonal antibody to B5, we show that B5 can be detected on peripheral blood or splenic B cells after 1 day of stimulation with either anti-immunoglobulin, protein A, Epstein Barr virus, or pokeweed mitogen. In contrast, B5 was not expressed on resting B, T, or myeloid cells. More important, B5 could not be detected on activated T cells or monocytes. The B5 antigen was expressed on some lymphoblastoid B cell lines and B cell neoplasms but was not expressed on leukemias or lymphomas of T or myeloid origin. The B5 antigen is distinct from previously reported B cell activation antigens by its m.w. and pattern of cellular expression. These studies suggest that B5 is a novel B cell-restricted activation antigen, which may be useful to study the events of early human B cell activation.     

Monoclonal antibodies to the human C3b/C4b receptor (CR1) enhance specific B cell differentiation

The addition of monoclonal antibodies against the human C3b/C4b receptor (CR1) to cultures of peripheral blood lymphocytes in the presence of suboptimal amounts of TNP bound to polyacrylamide beads enhanced by 150 to 400% the specific anti-TNP response, as measured by a plaque-forming cell assay on day 7. Anti-CR1 antibodies similarly enhanced the anti-fluorescein antibody response. Enhancement only occurred in cultures performed in the presence of the relevant antigen. No enhancing effect on the anti-TNP response was observed on addition to cultures of monoclonal antibodies directed against other surface antigens of B cells or an anti-T cell antibody of the same subclass as that of anti-CR1 antibodies. Anti-CR1 antibodies alone did not induce nonspecific B cell proliferation and did not provide B cells with a first signal for proliferation in the presence of a source of B cell growth factors. Anti-CR1 antibodies did not enhance the nonspecific proliferative response of B cells to growth factors derived from PHA-stimulated T cells, semi-purified BCGF 20 KD, BCGF 50 KD, or recombinant IL 2 in the presence of anti-mu. In this respect, the effect of anti-CR1 antibodies differs from that of anti-CR2 antibodies which interact with early stages of B cell activation. In contrast, anti-CR1 antibodies enhanced specific differentiation of antigen-activated B cells in the absence of T cells when soluble T cell factors were provided. Similar results were obtained by using either of two sources of differentiation factors, the MLA-144 supernatant or a 30 to 15 KD fraction from PHA-stimulated T cells. These results indicate that triggering of CR1 on B cells positively regulates the specific antibody response to low doses of antigen by enhancing B cell differentiation whether T cell help is provided by intact T cells or by T cell-derived differentiation factors.     

Characterization of a human B cell-specific antigen (B2) distinct from B1

A human B lymphocyte-specific antigen (B2) was identified and characterized by the use of a monoclonal antibody. By indirect immunofluorescence and quantitative absorption, B2 was shown to be expressed exclusively on Ig+ B cells isolated from peripheral blood and lymphoid tissues. In contrast, B2 was not found on monocytes, resting and activated T cells, Null cells, or granulocytes, nor was it found on cell lines or tumor cells of T cell or myeloid origin. Functional studies demonstrated that only B2 antigen-positive splenocytes could be induced to differentiate into plasma cells under the stimulus of pokeweed mitogen, further confirming the B cell specificity of B2. It was then demonstrated that the B2 antigen was distinct from the previously described B cell-surface determinants including surface immunoglobulin, Ia-like antigens, and Fc and C3 receptors. More importantly, the B2 antigen has been clearly shown to be distinct from the previously described B cell-specific antigen, B1, by its m.w. and expression on normal and malignant B lymphocytes. The distinct distribution of B2 on normal and malignant lymphocytes supports the notion of B cell heterogeneity and provides further evidence for existence of subpopulations of human B lymphocytes.     

Three distinct antigen systems on human B cell subpopulations as defined by monoclonal antibodies

Three novel antigen systems (L22, L23, and L24) expressed on human B cell subpopulations were identified by using TB1-2C3, TB1-2B3, and TB1-3C1 monoclonal antibodies, respectively. L22 was expressed on a minor subpopulation of B cells in human lymphoid tissues and in the peripheral blood. These B cells associated with L22 were resting small B cells mainly located in the mantle zone of lymphoid follicles, most of which also expressed IgM and IgD on their cell membrane. This antigen was absent from all cultured hemopoietic cell lines including B cell-derived cell lines as well as from all human B cell malignancies, except for B cell-type chronic lymphocytic leukemia and hairy cell leukemia. L23 and L24, on the other hand, existed on approximately two-third of B cells in blood and lymphoid tissues. These L23 and L24 antigens were expressed largely on small lymphocytes located in the mantle zone of lymphoid follicles and to a lesser extent on large blastic cells within lymphoid germinal centers. L23 and L24, like L22, seem to disappear from B cells during their differentiation into antibody-secreting cells, because they were not expressed on normal and neo-plastic plasma cells. This is additionally confirmed by the observation that L23 and L24 were expressed little or not at all on pokeweed mitogen-activated and Epstein-Barr virus-transformed B cells, and were absent from some of B cell malignancies that have been thought to correspond to the later stages of B cell development. Although L23, but not L22 and L24, was faintly expressed on mature granulocytes and monocytes, none of L22, L23, or L24 existed on human thymus and T cells. Immunoprecipitation studies showed that L23 and L24 were different molecular species consisting of a single glycoprotein with m.w. of 205,000 and 145,000, respectively. L22 antigen is presently under study.     

A novel cell surface antigen (T305) found in increased frequency on acute leukemia cells and in autoimmune disease states

Monoclonal antibody T305, prepared by immunizing mice with the T-ALL derived cell line RPMI-8402, immunoprecipitates a single chain glycoprotein with m.w. 160,000 daltons (under reducing conditions) or 180,000 daltons (under nonreducing conditions). In immunofluorescence assays, antibody T305 reacted with a subpopulation of T cells in normal blood (22 +/- 6%), thymus (28 +/- 11%), and lymph node (24 +/- 6%). Increased frequency of T cells reactive with antibody T305 was found in peripheral blood of patients with infectious mononucleosis (greater than 80%), graft-vs-host disease after bone marrow transplantation (65 +/- 11%), acquired immunodeficiency syndrome (53 +/- 12%). The T cells in synovial fluid of patients with rheumatoid arthritis had increased frequency of antibody T305 reactive cells (59 +/- 8%) as compared to their peripheral blood (18 +/- 7%). Two color immunofluorescent studies demonstrated that the T305+ T cells predominantly co-stained with antibody Leu 2a (suppressor/cytotoxic subset) in both normals and disease state blood. After cell sorting to obtain T305+ and T305- subpopulations, we demonstrated that a) natural killer and antibody-dependent cellular cytotoxicity activity in normal blood was in the T305+ but not T305- T cells; b) cytotoxic T cells induced by mixed lymphocyte reaction were predominantly T305+; c) T305- T cells could be induced in vitro to express T305 antigen by mitogens or allogeneic B cells; d) the DNA content of T305+ and T305- T cells in normal blood was similar (greater 95% of cells with G0/G1 level); e) after mitogen stimulation, T305 antigen induction on previously T305- cells occurs before S-phase; and f) significantly more [3H]-thymidine after mitogen stimulation was incorporated by originally T305- cells than by originally T305+ cells (p less than 0.001). The T305 antigen was not restricted to T cells because it was also found on myeloid precursors in bone marrow but was not present on polymorphonuclear leukocytes, red blood cells, platelets, muscle, liver, skin, kidney, lung, or brain. Antibody T305 was found on 24/25 cases of acute leukemia (6 T-ALL, 10/11 cALL, 7 AML, and 1 AMOL) but not on 18 cases of chronic leukemia (B-CLL, T-CLL, null CLL, CML). The importance of the T305 antigen is that it is present on a high number of T cells in certain autoimmune diseases and on virtually all acute leukemia cells. Its distribution on immature and in vitro activated cells suggests that it may represent a receptor for signals related to cellular replication or differentiation.     

Lymphocyte function-associated antigen (LFA-1) is involved in B cell activation

Human LFA-1 is a widely expressed leukocyte antigen present on cells of myeloid and lymphoid lineage. Monoclonal antibodies to LFA-1 have been shown to inhibit in vitro T cell immune functions. However, a role for LFA-1 in B cell activation has not been documented. To investigate this possibility, we examined the distribution of LFA-1 on normal, neoplastic, and EBV-transformed B cells as well as the ability of a monoclonal anti-LFA-1 antibody (NB-107) to inhibit B cell mitogenesis. NB-107 immunoprecipitates a noncovalently linked heterodimer of approximately 170,000 and 95,000 daltons. Sequential immunoprecipitation and cross-blocking studies showed that NB-107 identified a distinct epitope on the LFA-1 molecule. NB-107-defined LFA-1 was present on peripheral blood mononuclear cells (PBMC) from all normal individuals (N = 27) and on EBV-transformed cell lines (N = 9), but was absent from four of seven neoplastic B lymphoma lines. NB-107 was observed to profoundly inhibit the response of PBMC to the B cell mitogens anti-IgM (mean 71% inhibition) and lipopolysaccharide (mean 80% inhibition). In order to investigate the mechanism of inhibition, B cells were sequentially purified from PBMC by using a combination of E rosette depletion of T cells, monocyte removal by glass adherence, and finally cell sorting. These extensively enriched populations of B cells, although still responding to anti-mu, showed no evidence of inhibition by NB-107. Growth of EBV-transformed cell lines, cultured in the presence of NB-107, also was not inhibited by this antibody. When tested in assays for T cell function, NB-107 was shown to inhibit the mixed lymphocyte response, but had no effect on phytohemagglutinin stimulation of PBMC nor on the clonal growth and differentiation of granulopoietic, erythropoietic, and pluripotent progenitor cells. We conclude that anti-LFA-1 monoclonal antibody inhibits B cell mitogens via indirect effects on monocytes and/or T cells, rather than by a direct antiproliferative effect on B cells.     

A feline thymocyte antigen defined by a monoclonal antibody (FT2) identifies a subpopulation of non-helper cells capable of specific cytotoxicity

A monoclonal antibody, FT2 (IgG1 kappa) prepared against cat thymocytes, was found to be reactive with an antigenic determinant expressed by approximately 76% of thymocytes, 15% of blood mononuclear cells, 14% of splenocytes, and 1% of bone marrow cells. The FT2-reactive determinant was not expressed on B cells, macrophages, granulocytes, or erythrocytes. Both FT2+ and FT2- populations of peripheral blood mononuclear cells were capable of proliferative responses to the T cell mitogens Con A and PHA. When splenocytes were sensitized to the lymphoblastoid cell line, 79p90, cytotoxic T cells were found in the FT2+ population and were absent from the FT2- population. Conversely, the FT2- population contained the helper T cell activity required for pokeweed mitogen-induced B cell differentiation. Under nonreducing conditions, the FT2 antigen had an apparent m.w. of 71,000. When reduced, subunits of 31,000 and 38,000 apparent m.w. were observed. The data suggest that the FT2 antibody identifies the feline analog of the human T8/Leu-2, murine Ly-2 molecules expressed by cytotoxic/suppressor T cells.     

M241 (CD1) expression on B lymphocytes

The human thymus leukemia-like antigens (CD1a-c) consist of three similar glycoproteins found on subpopulations of normal thymocytes, T cell acute leukemias, and cutaneous dendritic cells. The CD1c antigen recognized by the M241 monoclonal antibody was detected on the circulating mononuclear cells of three children with severe combined immunodeficiency disease (SCID). Two-color immunofluorescence analysis demonstrated that M241 expression (43 to 95%) was limited to cells expressing the B cell-restricted antigens B4 (CD19), B1 (CD20), and surface immunoglobulin. To confirm M241 expression on normal cells of the B lineage rather than aberrant expression limited to SCID B cells, its expression was demonstrated serologically and biochemically on purified B cells from spleen, tonsil, and peripheral blood. Parallel analyses with monoclonal antibodies NA1/34 and 4A76 demonstrated that the CD1a and CD1b molecules were negative on all B cells that were studied. It has been hypothesized that the CD1 molecules represent the human counterpart of the murine thymus leukemia antigens due to their similar size, limited tissue distribution, and association with beta 2-microglobulin. This study suggests that a subset of CD1 antigens detected by M241 (CD1c) may represent a human analog of a murine Qa antigen due to its extended distribution on normal peripheral B cells.