Definition of human cytomegalovirus-specific target antigens recognized by cytotoxic T cells generated in vitro by using an autologous lymphocyte system

We developed an in vitro system for the generation of human cytomegalovirus (CMV)-specific cytotoxic T cells (CTL) that avoids the necessity of constituting a panel of HLA-typed fibroblasts. Autologous donor leucocytes were coated with CMV antigens and were used as both stimulator and target cells. With the use of this system, CMV-specific effector cells were efficiently generated from seropositive but not seronegative donors. These CMV-specific effectors were HLA-restricted and had characteristics of T cells. Maximum lymphoproliferation preceded the appearance of maximum CTL activity by 3 to 4 days, and a close correlation was seen between both activities. Mouse anti-CMV monoclonal antibodies were used in blocking experiments in an attempt to define target antigens recognized by CMV-specific cytotoxic lymphocytes. Monoclonal antibodies directed against an early CMV membrane antigen, against neutralization epitopes, or against nuclear inclusion body protein all specifically inhibited CMV-sensitized effector cell activity but did not affect influenza virus-specific lysis. Monoclonal antibodies directed against a normal cell determinant or against poliovirus did not affect CMV-specific CTL activity. CMV-immune cytotoxic T cells could be consistently and specifically inhibited in their lytic activity by pretreating antigen-coated target cells with monoclonal antibodies directed against CMV-related proteins.     

Characterization of T8 epitopes by enzymatic digestion, crossblocking, and involvement in cell-mediated lympholysis

Eleven monoclonal antibodies, directed versus the T8 glycoprotein, were compared using enzyme digestion, phylogenetic comparisons, cross-blocking of antibody binding, and blocking of specific cell-mediated lympholysis (CML). It was found that none of the 11 anti-T8 antibodies tested define the same epitope on the T8 glycoprotein. Some of these antibodies react, however, with closely related structures, as shown by cross-blocking of antibody binding and similar enzyme sensitivity of the epitopes. Moreover, these structural related epitopes show a similar involvement in the effector phase of CML reactions, since the antibodies to these neighboring epitopes inhibit the same CML reactions. Thus, it is possible to apply structural and functional criteria to define "regions" on the T8 glycoprotein, some of which are consistently involved in CML reactions, some never, and some of these regions appear to be involved in specific effector-target cell combinations only.     

Effector functions of CD8-positive guinea pig T lymphocytes

The response of guinea pig T lymphocytes to different stimuli was analysed with focus on the functions of CD8-positive T cells, which so far had been poorly defined in this animal model. For identification and purification of guinea pig cytotoxic T lymphocytes, three monoclonal antibodies, directed against the CD8 differentiation antigen were characterized and compared with respect to expression pattern and biochemical characteristics of the corresponding cell surface antigen. The antibodies were used for the identification of the cytotoxic T lymphocyte subpopulation within alloreactive T cell lines, and for the depletion of CD8-positive cells in in vitro assays. Purified CD4- and CD8-positive cells were tested for their ability to proliferate in response to antigen, mitogen or anti-guinea pig Thy-1 monoclonal antibodies. Both, CD4- and CD8-positive cells showed IL-2 release and subsequent proliferation after polyclonal stimulation. Cytotoxic activity in CD8-positive alloreactive T cells was expressed in vitro only after repeated stimulation.     

Specificity of T lymphocyte cytotoxicity to autologous hepatocytes in chronic hepatitis B virus infection: evidence that T cells are directed against HBV core antigen expressed on hepatocytes

Peripheral blood T lymphocytes from 21 patients with chronic HBV infection were incubated with autologous hepatocytes in a microcytotoxicity assay. Cytotoxicity was significantly increased in 13 cases, and in 12 of these the cytotoxic effect of the T lymphocytes was inhibited by preincubating the liver cells with IgG containing antibodies to the hepatitis B core antigen (HBcAg). Normal human IgG and IgG containing antibodies to the hepatitis B surface antigen (HBsAG) were without effect. Control experiments using autologous fibroblasts as target cells showed low levels of T cell cytotoxicity and no blocking effect of anti-core antibody. All patients in whom it was possible to demonstrate HBcAg in liver tissue had significantly increased T cell cytotoxicity to autologous hepatocytes. These studies suggest that T cell cytotoxicity in patients with chronic HBV infection is directed against determinants resembling the hepatitis B core antigen on the plasma membrane of hepatocytes.     

Cellular and biochemical responses of human T lymphocytes stimulated with streptococcal M proteins

Purified group A streptococcal M proteins, pep M5 and pep M6, bearing heart cross-reactive epitopes were compared with pep M24, which lacks such epitopes, in their ability to induce functional differentiation of human T lymphocytes. Lymphocytes activated by pep M5 and pep M6 demonstrated cytotoxic activity against cultured heart cells, whereas pep M24-activated cells differentiated into suppressor T cells, which specifically blocked cytotoxic T lymphocytes against cultured human myocardial cells and not NK cell activity against K562 cells. Pep M5 and not pep M24 induced an increase in the number of CD4, 4B4, helper/inducer T cells. In addition, these M proteins appear to induce different biochemical changes in T lymphocytes. Both pep M5 and pep M24 induced the phosphorylation of a 35-kDa cytoplasmic protein; however, only pep M5 induced the phosphorylation of a 28-kDa membrane protein, primarily in CD4 T cells. These data indicate that the virulent M protein Ag of group A streptococci may exert their effect on the human immune system via different mechanisms. Determining these mechanisms and the biochemical pathways involved in T cell differentiation triggered by these Ag may be important in understanding the pathogenesis of post-streptococcal diseases.     

Carbohydrate differentiation antigens of murine T cells: expression on intestinal lymphocytes and intestinal epithelium

Carbohydrate differentiation antigens (CT antigens) which previously had been shown to be associated with cytotoxic T cells were found at high levels on intestinal intraepithelial lymphocytes (IEL) and on the intestinal epithelium. Histological examination of intestinal sections demonstrated that the CT1 MAb defined epitopes on IEL and on epithelial cells located in the base of the villi crypts. The CT2 MAb reacted with IEL but also bound to the majority of cells in the intestinal epithelium. When isolated intestinal cell populations were analyzed by flow cytometry, two major size classes of cells were evident. The smaller cells, corresponding to lymphocytes, were primarily Lyt-2+, with a high proportion expressing CT antigens. Another differentiation antigen defined by the MAb J11d was absent from IEL, indicating that those IEL of T cell origin are likely to be mature because thymocytes, but not peripheral T cells, express the J11d antigen. Two-color fluorescence analysis indicated that the CT determinants were present on the Thy-1+, Lyt-2+, and the Thy-1-, Lyt-2+ subsets of IEL. However, the small percentage of L3T4+ IEL were CT-, further supporting our previous demonstration of a correlation between CT expression and Lyt-2 expression. Interesting phenotypic characteristics of IEL other than CT antigen expression were also detected. IEL did not express the MEL-14 lymphocyte homing receptor, and the cell surface level of LFA-1 was significantly lower than that of other peripheral lymphocytes. It was also shown that a small percentage of IEL express a T cell receptor allotypic marker, indicating that at least some of the cells are mature in terms of T cell receptor gene rearrangements. The large intestinal cells, although CT+, were not hematopoietic in origin because they were T200- and were shown by using chimeric mice not to be bone marrow-derived. In contrast to previously reported results, the cytotoxic activity of IEL was negligible with detectable lysis against NK-sensitive cells and other tumor cells, being observed in only one of seven experiments. Thus, the expression of the CT determinants was not indicative of cytotoxic ability, as previously suggested. The presence of specific carbohydrate residues on the cell surface of a subset of lymphocytes in an anatomically distinct immune compartment suggests that a unique differentiation pathway is followed by these cells.     

Definition of the T-lymphocyte inducer of suppression in primates using a monoclonal antibody

Since some of the conserved antigens between man and phylogenetically lower primate species may be more immunodominant on lymphocytes of the lower primate species, we reasoned that immunization of mice with lymphocytes from lower primates might prove a useful strategy for developing monoclonal antibodies which recognize functionally important structures on both human and nonhuman primate lymphocytes. In employing this approach for the development of monoclonal antibodies, we have developed the antibody anti-2H4 which recognizes a structure on both T on non-T mononuclear cells of a wide array of primate species. 2H4+ rhesus monkey T lymphocytes exhibited a greater proliferative response to lectin and alloantigenic stimulation than 2H4- cells, suggesting that anti-2H4 might separate primate T lymphocytes into functionally distinct cell populations. In fact, helper activity for antibody production by rhesus monkey B lymphocytes in response to pokeweed mitogen (PWM) resided in the 2H4- T-cell population. Furthermore, the 2H4+ T-lymphocyte population activated the suppressor function of T8+ rhesus monkey cells. The fact that the surface antigen which defines this T-cell subset is widely conserved in nonhuman primates suggests that anti-2H4 recognizes a functionally important structure.     

Modulation of surface antigens of a human monocyte cell line, U937, during incubation with T lymphocyte-conditioned medium: detection of T4 antigen and its presence on normal blood monocytes

The human monocyte line, U937, derived from an individual with histiocytic lymphoma, undergoes morphological and functional changes when incubated with medium conditioned by lectin-stimulated cloned human T lymphocytes. Using monoclonal antibodies and flow cytometry, we therefore analyzed alterations in surface components that might accompany these morphological changes, in comparison with components present on normal blood monocytes. The U937 cells possess three surface antigens in common with blood monocytes, detected with OKM1, 4F2, and anti-monocyte.2 (the last monocyte specific). DR antigen was not detectable on U937 cells with three anti-DR framework antibodies but was detected on blood monocytes. Unexpectedly, OKT4, a monoclonal antibody to T4 antigen previously believed to be restricted to helper T lymphocytes, also reacted with U937 cells. Six monoclonal antibodies to other epitopes on T4 also reacted with U937 cells. None of these could be inhibited by blocking of Fc receptors. T4 with its various epitopes were also expressed on normal human blood monocytes. Other lymphocyte surface markers (T3, T8, T6) and fibronectin were not detectable on U937 cells or monocytes. An individual, whose lymphocytes lacked the epitope detected with OKT4 but had epitopes detected with OKT4 A, B, C, and D, had monocytes with identical reactivity, evidence that the T4 on monocytes and lymphocytes are products of the same structural gene. Stimulation of U937 cells for 24 hours with supernatants from Con A-stimulated T lymphocyte clones caused an increase in expression of OKM1 and Fc receptor activity and a decrease in expression of T4, consistent with a more mature phenotype of blood monocytes. Although the function of the T4 molecule is unknown, it is notable that it is displayed by two cells of distinct lineage which interact in the response to soluble antigens.     

Lymphokine-activated cell-associated antigen involved in broad-reactive killer cell-mediated cytotoxicity

Spleen cells from rats which had been hyperimmunized with mouse lymphokine-activated killer (LAK) cells, were fused with the mouse myeloma cell line, P3 X 63 Ag8.653. Antibodies secreted by 1500 cultures were selected by their blocking effect on LAK cell-mediated cytotoxicity in the absence of complement. Two monoclonal antibodies (KBA4 and KBA6) greatly inhibited the cytotoxic activity of LAK cells, which were induced from mouse spleen cells by culture with recombinant human interleukin 2 (r-IL-2). These antibodies also blocked the cytotoxic activity of natural killer (NK) cells, but activated macrophages (A-M phi) were only slightly sensitive to them. However, no effect of the antibodies on the cytotoxic activity of cytotoxic T lymphocytes (CTL) was detected. These data suggest that the specific antigen, lymphokine-activated cell-associated (LAA) antigen, defined by these monoclonal antibodies may be associated with the recognition mechanisms of broad-reactive killer (BRK) cell-mediated cytotoxicity. The observation that low levels of LAA antigen are distributed in all lymphoid cells and that it was significantly enhanced by treatment of the cells with r-IL-2 suggests that the antigen may be involved in lymphocyte-activation mechanisms. We also found that the LAA antigen consists of two distinct polypeptides with Mr of 180,000 and 95,000 Da, which are similar to that of LFA 1 antigen. However, the biological characteristics of LAA antigen did not coincide with those of LFA 1. Therefore, KBA MAb may recognize a carbohydrate epitope distinct from that of LFA 1.     

Mucin-1-related T cell infiltration in colorectal carcinoma

 Mucins (MUC) are highly glycosylated molecules widely expressed on epithelia of different origins, including colonic mucosa. Altered glycosylation processes in tumour cells result in the exposure of normally cryptic peptide epitopes, which may then be recognized as tumour-specific antigens. Recently, MUC1-specific antibodies were detected in the serum of a broad range of cancer patients, and from different tumours tumour-specific cytotoxic T lymphocytes (CTL) were isolated that recognized MUC1. Absence of HLA restriction in the recognition has been ascribed to the highly repetitive sequence of the polypeptide core, allowing simultaneous recognition of multiple identical epitopes and cross-linking and aggregation of T cell receptor on mucin-specific T cells. We investigated the expression of MUC1 epitopes in 56 cell suspensions from Dukes’ B to D colorectal carcinomas using antibodies that recognize distinct peptide sequences on the glycosylated or deglycosylated MUC1 protein backbone. No relation was observed between MUC1 expression, or the extent of its glycosylation, and Dukes’ stage, tumour location and tumour differentiation, but a positive correlation was detected between the percentages of tumour cells expressing mucin-1 and the numbers of CD3⁺ infiltrating cells. These tumour-infiltrating lymphocytes contained, however, only a few MUC1-specific T lymphocytes, as CTL showing preferential killing of MUC1-expressing target cells were only obtained from one tumour. Since, in addition, the majority of colorectal carcinomas were found to express the fully glycosylated MUC1 glycoprotein, its potential role as a target antigen for T-lymphocyte-mediated immunotherapy in this tumour type is probably limited. Received: 2 April 1996 / Accepted: 28 May 1996     

Generation of monoclonal antibodies blocking cytotoxic reactions by human NK clones: further characterization of a 40/80-kDa target cell receptor

To study NK target antigen(s), mice were immunized with pooled cells from five human hematopoietic cell lines (K562, MOLT4, JM, CEM, U937) known to be susceptible to Natural Killer activity. Cells fusions were performed and 4 out of approximately 2000 hybridoma supernatants were selected because of their ability to block cytotoxic reactions between a human NK clone (termed JT9) and MOLT4 cells. Functional characterization of the four monoclonal antibodies (Mabs) indicated that individual treatment of each immunizing target cells resulted in a decreased cytotoxicity. This inhibition was very specific because it was exclusively observed when three clones, JT9, JT10, and JT11, which express the same clonotypic structure (NKTa), were used as effector cells. Parallel and sequential immunoprecipitations showed that the four reagents termed anti-TNKtar 1, 2, 3, and 4 were directed at the same 40/80-kDa heterodimeric structure previously identified by anti-TNKtar Mab. However, cross-blocking experiments indicated that TNKtar and TNKtar 1-4 represent two distinct epitopic clusters. Finally, it was shown that anti-TNKtar 1-4 recognition sites are either identical or closely related to that of an additional antibody termed 4F2. Together, the present data strengthen the hypothesis that the activation antigen recognized by these series of Mab serves as a target cell receptor for at least a minor population of NK active lymphocytes.     

T lymphocyte-mediated cytotoxicity against autologous EBV-genome-bearing B cells

We have stimulated human peripheral blood lymphocytes in vitro with autologous EBV-infected or noninfected B cells. A cytotoxic response was obtained only when virally infected cells were used. The activity of the effector cells was restricted by the major histocompatibility complex and was directed against EBV-genome-bearing targets. The highest cytolytic response was obtained when lymphocytes of individuals previously exposed to the virus (EBV-VCA positive) were used. Lymphocytes of noninfected donors (EBV-VCA negative) gave a low response; the relative frequency of their effector cells was at least 4-fold lower. Lymphocytes of newborns did not respond. The cytotoxic activity was mediated by T lymphocytes of the cytotoxic/suppressor subset, as determined by cytofluorographic analysis and antibody plus complement-mediated lysis, using monoclonal antibodies to human lymphocyte surface antigen.     

The Fc receptor for IgG on human natural killer cells: phenotypic, functional, and comparative studies with monoclonal antibodies

We compare five monoclonal antibodies ( B73 .1, 3G8 , Leu- 11a , Leu- 11b , and VEP13 ) that react with natural killer (NK) cells and polymorphonuclear cells (PMN). We show that all of these antibodies are directed against and inhibit the functional properties of the receptor for the Fc portion of IgG (FcR). Modulation of the FcR on NK cells after reaction with immune complexes induces the disappearance of the antigen(s) recognized by each of the five antibodies. Conversely, the antibodies block binding of IgG-sensitized erythrocytes to the NK cells and PMN and inhibit their ability to mediate cytotoxicity against antibody-sensitized tumor target cells. By using two-color immunofluorescence techniques, we characterize directly the lymphocyte population recognized by these antibodies and show that it is a homogeneous subset that does not bear markers of either B or T cells, with the exception of the 33,000 dalton antigen characteristic of suppressor/cytotoxic T cells present in 20 to 50% of the cells, and the 45,000 dalton receptor for sheep erythrocytes present on 80 to 90% of the cells. The phenotype of the cells reacting with the monoclonal antibodies corresponds to that of NK cells. Cross-competition experiments indicate that these antibodies detect at least two distinct epitopes on FcR, one ( B73 .1) preferentially expressed on NK cells and one or more ( 3G8 /Leu- 11a /Leu- 11b / VEP13 ) preferentially expressed on PMN. The lack of reactivity of these antibodies with B cells suggests that human B cells bear a different FcR from that on NK cells and PMN.     

Distinct epitopes on the T cell antigen receptor of HPB-ALL tumor cells identified by monoclonal antibodies

The T cell antigen receptor is a approximately 90,000 dalton disulfide linked heterodimer that is non-covalently associated with the CD3 complex. Prior studies have demonstrated that anti-CD3 or -Ti antibodies can mimic antigen and induce cellular proliferation and the secretion of lymphokines. An early event in activation via CD3/Ti is a rapid increase in concentration of intracellular Ca2+ levels. In the present studies, we have produced a panel of monoclonal antibodies (MAb) against the Ti expressed on HPB-ALL tumor cells. All MAb immunoprecipitate a approximately 90,000 dalton disulfide linked heterodimer and induced co-modulation of Ti and CD3. On the basis of competitive binding studies, four distinct epitopes on the Ti of HPB-ALL were identified with MAb L38, L39, L41, and L42. These epitopes were additionally discriminated on the basis of reactivity with normal polyclonal T cell populations and functional effects on HPB-ALL. L39 reacted with a monomorphic epitope present on approximately 2 to 5% of peripheral blood T lymphocytes from all donors examined and was specifically mitogenic for peripheral blood T cells expressing this epitope. L39+ T cells in blood included both CD4+ and CD8+ lymphocytes. In contrast, L38, L41, and L42 failed to react with peripheral blood T cells and were not mitogenic for peripheral blood lymphocytes. Anti-Leu-4, L38, L39, and L41 MAb all induced a rapid increase in (Ca2+)i in HPB-ALL tumor cells, similar to previous findings with anti-CD3 and anti-Ti MAb against various tumor cells and peripheral blood T cells. In contrast, L42 MAb did not induce a substantial increase in (Ca2+)i. Failure of L42 to induce a substantial increased (Ca2+)i could not be attributed to the apparent titer, avidity, or isotype of the antibody. These findings suggest that induction of increased (Ca2+)i upon binding of Ti is epitope dependent. Furthermore, these data demonstrate that several distinct public and private epitopes can be identified on the T cell antigen receptor.     

Expression of a sheep red blood cell receptor by a murine lymphoma.

Murine 6C3HED lymphoma cells were found to rosette with sheep red blood cells (SRBC). Normal C3H lymphocytes did not exhibit this property. This rosetting capacity of 6C3HED cells was found to be an accurate and reproducible means for discriminating between normal and tumor cells. The SRBC receptor on these lymphoma cells appeared to be serologically distinct from that expressed by normal human T lymphocytes since reciprocal blocking experiments demonstrated that inhibitory antisera were not cross-reactive. The expression of the SRBC receptor by the 6C3HED cells appeared to correlate with the expression of a tumor-associated antigen and was spatially related to an antigen expressed by 6C3HED and normal neonatal but not adult mouse cells.     

Monoclonal antibodies against simian virus 40 nuclear large T tumour antigen: epitope mapping, papova virus cross-reaction and cell surface staining.

Thirty six cloned hybridomas have been isolated which produce monoclonal antibodies directed against simian virus 40 (SV40) large T tumour antigen. They have been shown to recognize at least six different epitopes along the T antigen polypeptide according to their reaction with the various truncated forms of T antigen expressed by adenovirus-SV 40 hybrid viruses. Sixteen antibodies cross-react with cells infected by the closely related human BK virus. Only two antibodies, PAb1604 and PAb1614, directed against different epitopes of the SV40 T antigen, cross-react with polyoma large T tumour antigen which has a more limited amino acid sequence homology. This cross-reaction is rarely seen with polyclonal antibodies. Monoclonal antibody PAb1620 gave nuclear immunofluorescence only with murine cells transformed by SV40 and was found to react with a complex of T-antigen and 53 000-dalton host-coded protein. All the monoclonal antibodies react with nuclear T antigen and all but four antibodies stained the surface of SV40-transformed cells. These were four of the five antibodies directed against the central third of the T antigen. Thus the monoclonal antibodies show that cell surface T antigen differs from nuclear T antigen, either in accessibility or structure.     

Evolution of epitopes on human and nonhuman primate lymphocyte cell surface antigens

The T- and B-cell surface polypeptides detected by an international workshop panel of 100 mouse monoclonal antibodies (M.Ab) were biochemically defined by radioimmunoprecipitation. Eight T-cell-associated molecules and eight B-cell-associated molecules were identified by multiple antibodies in the panel. Clusters of antibodies specific for the same polypeptide were then compared for their reactivity against peripheral blood mononuclear cells (PBMC) from 11 nonhuman primate species. All the major T- and B-cell antigens present in humans were also expressed in some nonhuman primates. M.Ab to the same antigen were found to react with distinct epitope groups that differed in their phylogenetic distribution. Some epitopes were highly conserved, while other epitopes on the same molecule were only expressed in hominoids and were not detected in old world and new world monkeys. Our detailed analysis of the phylogeny of 37 T-cell antigen epitopes on ten different molecules revealed there was no clear correspondence between the number of epitopes shared and evolutionary distance. Rather the data suggest that parallelism with back mutation may be a common mechanism in the evolution of T-cell antigens. The data also show that the tissue distribution of T-cell antigens can differ between primate species; for example, M.Ab to human Tp45 Tla-Qa-like antigens that did not react with human PBMC did react with PBMC from new world monkeys.     

Utilization of leucine methyl ester for the generation of hybridomas producing monoclonal antibodies specific to tumor-associated antigens

In an attempt to obtain monoclonal antibodies specific to tumor-associated antigens. C3H/He mice were immunized with syngeneic MM2 tumor cells, and the primed spleen cells were fused with P3-X63-Ag8.653 myeloma cells. The outgrowth of hybridomas, however, was extremely low and monoclonal antibodies were not obtained. The reason for the low hybridoma growth was studied. It was found that MM2 cells used as the immunogen, the fusion partner myeloma cells and the resulting hybridomas shared at least one tumor-associated antigen, namely Q5 antigen. Because of this common antigen, cytotoxic cells, presumably cytotoxic T lymphocytes, which were lytic to the hybridomas, were induced during the culture for generation of the hybridomas. Removal of lysosome-rich cells, including cytotoxic T lymphocytes, from the primed spleen cells before the fusion by treatment with leucine methyl ester, a lysosomotropic agent, drastically improved the outgrowth of hybridomas. By this method, seven stable hybridoma clones producing monoclonal antibodies specific to tumor-associated antigens were obtained. Two of the seven clones were found to secrete monoclonal IgM species, which reacted with the extra-cellular region of the Q5 antigen. This procedure will be an option when production of monoclonal antibodies specific to cell-surface antigens is intended and outgrowth of hybridomas is unexpectedly low.     

An alternative pathway of T-cell activation: A functional role for the 50 kd T11 sheep erythrocyte receptor protein

A series of seven monoclonal antibodies was produced against the T-lineage-specific 50 kd T11 sheep erythrocyte rosette (SRBC) receptor protein in order to define the function of the molecule. Three distinct epitopes were detected: T11₁, the SRBC binding site expressed on all T lymphocytes and thymocytes; T11₂, an epitope unrelated to the SRBC binding site but with a similar distribution; and T11₃, a neo-epitope expressed only upon T-cell activation. Simultaneous triggering of T11₂ and T11₃ epitopes by monoclonal antibodies induces T lymphocytes to proliferate and mediate their functional programs in the absence of antigen and/or antigen-presenting cells. This antigen-independent mode of triggering is distinct from that involving the T3-Ti antigen receptor complex and represents an alternate pathway of T-cell activation. Given that T11 is the earliest T-lineage surface glycoprotein to appear in thymic ontogeny and is thus expressed before T3-Ti, the former may be involved in clonal expansion and/or differentiation during early development.     

Characterization of warm-reactive IgG anti-lymphocyte antibodies in systemic lupus erythematosus. Relative specificity for mitogen-activated T cells and their soluble products

In addition to previously described cold-reactive IgM anti-lymphocyte antibodies maximally cytotoxic for resting cells at 15 degrees C, sera from patients with systemic lupus erythematosus (SLE) were found to contain a new type of antibody preferentially reactive at physiologic temperatures with mitogen-activated lymphocytes. This antibody lacked specificity for unstimulated lymphocytes, and was shown to be of the IgG class both by indirect immunofluorescence and in immunochemical experiments. Certain SLE sera also contained IgG antibodies with the capacity to develop plaques with mitogen-activated T lymphocyte preparations used in a reverse hemolytic plaque assay, indicating reactivity with products released by activated cells. The elimination of the ability of SLE sera to develop plaques after absorption with viable mitogen-stimulated lymphocytes, but not with resting cells, suggested that these antibodies were directed toward activation "neoantigen(s)" shed from the cell surface membrane. Surface membrane phenotype analyses performed by using a variety of monoclonal antibody reagents indicated that the plaque-forming cells (PFC) detected with SLE sera were activated T lymphocytes not restricted to single OKT4+, OKT8+, or Ia antigen+ subpopulations. Essentially all PFC expressed transferrin receptors. The present data raise the possibility that certain of the interesting effects of anti-lymphocyte antibodies on immunologic function in SLE may be mediated by interactions of these new type(s) of antibodies with activated lymphocytes or their products, rather than through blocking or depletion effects on resting precursor cells.