anti-Ia Antibodies Research Articles

Polyclonal B cell activation by a B cell differentiation factor, B151-TRF2. III. B151-TRF2 as a B cell differentiation factor closely associated with autoimmune disease.

We demonstrated previously that B151K12 T cell hybridoma produces two distinct B cell differentiation factors, B151-TRF1 and B151-TRF2, capable of inducing differentiation of antigen-activated and unstimulated B cells into antibody-forming cells, respectively. In the present study we investigated the pathophysiologic relation of these factors with factors obtained from MRL/MP-lpr/lpr(MRL/lpr) mice and (C57BL/6 X DBA/2)F1 (BDF1) mice undergoing chronic graft-vs-host reaction (GVHR), representing a murine model of systemic lupus erythematosus with polyclonal B cell activation associated with the T cell hyperfunction. The functional and biochemical analyses revealed that B151-TRF2-like, but not B151-TRF1-like, activity was found in culture fluid supernatant (CFS) of lymphoid cells from MRL/lpr mice with lymphoproliferative syndrome. On the other hand, both B151-TRF1- and B151-TRF2-like activities were detected in CFS prepared from spleen cells of BDF1 mice undergoing chronic GVHR by the inoculation of parental DBA/2 spleen cells. Interestingly, spleen cells of BDF1 mice transferred with DBA/2 thymocytes preferentially elaborated B151-TRF1-like factor. Because BDF1 mice transferred with DBA/2 spleen cells but not with DBA/2 thymocytes developed a SLE-like syndrome exemplified by the appearance of Coombs' antibody and proteinuria, it seemed likely that production of B151-TRF2-like factor was closely associated with the onset of autoimmune disease. In fact, B151-CFS containing B151-TRF2 but not B151-TRF1 activity could induce a striking autoantibody production both in vivo and in vitro as detected by PFC responses of normal mice to bromelain-treated mouse red blood cells (BrMRBC). Moreover, it was demonstrated that in vitro anti-BrMRBC PFC responses induced by semipurified B151-TRF2 was markedly inhibited by addition of relevant anti-Ia antibody to the culture. Thus, the present study demonstrates that B151-TRF2 represents one of the B cell differentiation factors responsible for polyclonal B cell activation leading to autoantibody production.

Activation of specific T cell lines by the antigens avidin and myelin basic protein in the absence of antigen‐presenting cells

We have investigated the specific activation by soluble antigen of rat or mouse long-term T helper cell lines using antigen-presenting cell (APC)-free culture conditions. Some T cell lines specific for avidin or myelin basic protein responded to native antigen in the absence of added APC. Responses in the absence of APC were substantial and specific although, as would be expected, lower than in the presence of APC. Proliferation could not be inhibited by culture with anti-Ia antibodies and the ability of lines to respond to antigen in the absence of APC did not correlate with the endogeneous surface Ia expression of the lines. Furthermore, irradiated T cells were unable to act as presenting cells for lines cells of the same or a different specificity. This suggests that the T cells did not present antigen to each other, and demonstrates, along with other data shown, that activation cannot be attributed to undetected APC remaining in the cultures. Anti-avidin T cell lines differed markedly in their ability to respond to avidin in the absence of added APC.S2, an anti-avidin line of H-2s genotype consistently responded well to avidin seen in the absence of added APC; K2, an H-2k anti-avidin line, responded moderately and B3, and H-2b anti-avidin line, although the most prolific responder in the presence of APC, never responded to antigen in their absence. Z1a, a Lewis rat-derived T cell line specific for myelin basic protein, proliferated well in response to the antigen in the absence of added APC. The present findings demonstrate that some T cells can recognize and respond to native antigens without the mediation of specialized APC.

Soluble antigen induces T lymphocytes to secrete an endoglycosidase that degrades the heparan sulfate moiety of subendothelial extracellular matrix

The antigen-mediated induction of heparanase, an endoglycosidase capable of degrading heparan sulfate from the subendothelial extracellular matrix (ECM), was investigated in a rat T lymphocyte cell line reactive against the basic protein (BP) of myelin. We found that nonactivated T lymphocytes could be induced to express heparanase activity following exposure to soluble but not to ECM-bound BP. The induction of heparanase was immunologically specific and independent of the presence of syngeneic or allogeneic antigen presenting cells (APC). However, anti-IA antibodies inhibited heparanase expression. Soluble BP induced secretion of heparanase into the culture medium within minutes, despite inhibition of protein synthesis. Cell lysates of T lymphocytes contained heparanase activity. Thus, T lymphocytes secrete a preformed heparanase following exposure to specific antigen.

Evidence for an Activated Subpopulation of T8-Bearing Cells in Male Homosexuals with Lymphadenopathy

Data are presented that male homosexuals with chronic lymphadenopathy and reduced numbers of T4-antigen-bearing cells have an increased incidence of activated T8-antigen-bearing cells. Evidence suggesting an increase in activated T cells in these subjects includes an increase in incidence of T10-antigen-bearing cells, an increase in Ia-bearing T cells and an increase in the intensity of staining of a fraction of the T8-antigen-bearing cells with fluorescein-labeled OKT8 monoclonal antibody. It was shown by double staining that most of the Ia-bearing T cells also bore the T8 marker. The heterogeneity of the Ia, assayed by reactivity with several monoclonal anti-Ia antibodies which detect different epitopes on the Ia molecule, was comparable in lymphadenopathy subjects and controls.

Two roles for Ia in antigen-specific T lymphocyte activation.

In this study we examined the mechanism by which a PPD-specific murine T cell hybridoma, 8B2, recognized PPD associated with antigen-presenting cells (APC) in a manner genetically restricted by I-Ad. It was found that PPD-pulsed APC that were glutaraldehyde-fixed and treated with anti-Ia monoclonal antibody (abbreviated as PGM) were unable to stimulate the 8B2 T cells, as expected, due to inhibition caused by antibody binding to the Ia. However, addition of non-antigen-treated, glutaraldehyde-fixed APC (abbreviated as G) to cultures containing 8B2 T cells and PGM restored T cell activation, as determined by IL 2 production. This second non-antigen-specific function provided by the additional APC, G, was attributed to Ia and could be substituted by APC plasma membranes and by soluble membrane extracts. Genetic restriction analysis in which a variety of Ia-positive and Ia-negative cell lines and B cell blasts from different mouse strains were used as PGM or as G showed that each APC provided different Ia determinants that were specifically recognized by the T cells. PGM cells had to express I-Ad in order to present the PPD determinant, whereas the non-antigen-specific function was specific for I-Ad or I-Ab. These results suggest that the anti-Ia antibody does not interfere with the PPD/I-Ad-specific determinant bound by the antigen-specific T cell receptor, but prevents a second non-antigen-specific interaction with another region of the Ia molecule, which is provided by G. These two roles for Ia (antigen-specific and non-antigen-specific) were also found for activation of normal polyclonal PPD-specific T cell responses; thus they are not unique to the 8B2 T cell, but are generally applicable. In addition, T cell interactions with PGM and with G each provide different intracellular activation signals. This was determined by substituting the PGM or the G with either the tumor promoter phorbol 12-myristate 13-acetate (PMA) or the Ca++ ionophore, ionomycin. It was found that 8B2 T cells cultured with PGM and ionomycin, but not with PGM and PMA, were activated for IL 2 production. Neither PMA nor ionomycin in conjunction with G resulted in T cell activation. Taken together, these results indicate that 8B2 T cell activation involves APC Ia antigens in two different ways: one is to contribute to the presentation of the foreign PPD antigen, and a second is a non-antigen-specific Ia-T cell interaction necessary to provide additional intracellular activation signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Polyclonal B cell activation by B cell differentiation factor B151-TRF2. I. Involvement of self-Ia recognition process mediated by B cells.

The present study examined the functional role of Ia antigens on B cells in polyclonal B cell activation induced by a B cell differentiation factor, B151-TRF2. The polyclonal IgM PFC responses by B151-TRF2 were inhibited by monoclonal antibodies specific for class II MHC antigens (Ia antigens) but not class I MHC antigens. Such inhibition by anti-Ia antibodies was haplotype-specific and was observed in the absence of both T cells and accessory cells. Moreover, the anti-Ia antibody-induced inhibition of the B151-TRF2 responses was not due to the blocking of binding of B151-TRF2 to the corresponding B cell receptor. A series of kinetic studies revealed that some Ia-mediated cellular activation process occurs before the resting B cells become responsive to B151-TRF2. Thus, the B151-TRF2-mediated B cell responses consist of at least two distinct phases. The early phase is an Ia-dependent but B151-TRF2-independent process, whereas the late phase is an Ia-independent but B151-TRF2-dependent process. To further characterize the functional role of Ia antigens on B cells, an additional experiment was carried out by using F1 B cells which co-dominantly express both parental Ia antigens on the surface. Interestingly, it was observed that the degree of inhibition of the B151-TRF2-mediated responses of F1 B cells by anti-parental Ia antibody was, at best, one-half that of the parental B cells, suggesting that F1 B cells may be separated into two subpopulations with the restriction specificity for the respective parental Ia antigens. To examine this possibility, (B10 X B10.BR)F1 B cells were separated into adherent and nonadherent cell populations by their ability to bind to either one of the parental B cell monolayers, and the specificity of inhibition of their responses to B151-TRF2 by anti-Ia antibodies was assessed. It was found that the responses of (B10 X B10.BR)F1 B cells adherent to the B10 B cell monolayer or the B10.BR B cell monolayer were almost completely inhibited by anti-I-Ab and anti-I-Ak antibodies, whereas those of nonadherent cells were now selectively inhibited by anti-I-Ak and anti-I-Ab antibodies, respectively. These findings are interpreted as indicating that the B151-TRF2-responsive F1 B cells consist of at least two subpopulations with the restriction specificity for either one of the parental Ia antigens.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in anti-lymphocyte and anti-Ia antibodies during pregnancy in systemic lupus erythematosus

Anti-lymphocyte antibodies reactive with monocyte-depleted lymphocytes, T cells, or B cells were studied in 43 nonpregnant and 23 pregnant systemic lupus erythematosus (SLE) patients. Anti-Ia specificity was assayed in an enzyme-linked immunosorbent assay system. No difference in mean lymphocytotoxicity was noted between pregnant and nonpregnant SLE patients; however, anti-Ia lymphocyte antibody associated with disease activity was lower ( P < 0.01) in pregnant than in nonpregnant SLE patients. Lymphocytotoxic or anti-Ia antibody activity did not reliably predict the outcome of individual pregnancies.

Photoaffinity labeling demonstrates binding between Ia molecules and nominal antigen on antigen-presenting cells.

We have used radioiodinated photoreactive bovine insulin as antigen to examine the molecular nature of immunogenic complexes that form on antigen-presenting cells. The probe was allowed to bind to either insulin-presenting B-hybridoma cells, lipopolysaccharide-stimulated blasts, or bovine insulin-specific helper-T-hybridoma cells in the dark. Samples were then exposed to light to induce crosslinkage, solubilized, and analyzed by gel electrophoresis. Two protein bands at about 36 kDa and 27 kDa were specifically labeled on antigen-presenting cells but not on helper T cells. Treatment of these bands with dithiothreitol or endo-beta-N-acetylglucosaminidase F showed that each is composed of a single glycoprotein. These proteins are immunoprecipitable with haplotype-specific but not control anti-Ia antibodies. This identifies the labeled bands as the alpha and beta subunits of class II major histocompatibility antigens. We conclude that a molecular complex may form between Ia and antigen on antigen-presenting cells and that formation of this complex does not require the presence of a helper-T-cell antigen receptor.

Study of the biological activities of toxic shock syndrome toxin-1. I. Proliferative response and interleukin 2 production by T cells stimulated with the toxin.

The mitogenic and interleukin 2 (IL 2) production-inducing effects of toxic shock syndrome toxin-1 (TSST-1) on murine lymphocytes were investigated. TSST-1, an exotoxin produced by Staphylococcus aureus recovered from patients with toxic shock syndrome (TSS), is thought to be a causative agent of the syndrome. TSST-1 was mitogenic for splenic T cells and peanut agglutinin (PNA)-negative thymocytes, but not for T cell-depleted spleen cells, PNA-positive thymocytes or IL 2-dependent CTLL 2-cells. A factor mitogenic for CTCC-2 cells with a molecular weight of 30-35 kdaltons was obtained by stimulating spleen cells with TSST-1 and it was absorbed by CTLL-2 cells, indicating that the factor is IL 2. For substantial amounts of IL 2 to be produced, 10 ng or more of TSST-1 per ml and 48 hr or more of incubation were required. Removal of T cells abrogated the IL 2 production by spleen cells. T cells obtained by the nylon wool column method alone produced IL 2 on TSST-1 stimulation in the presence of either macrophages or a macrophage lysate containing interleukin 1. However, T cells obtained by a combination of the nylon wool column method and anti-Ia antibody treatment produced IL 2 in the presence of macrophages but not of the macrophage lysate, indicating that IL 2 production by TSST-1-stimulated T cells is absolutely dependent on the presence of accessory cells.

Characterization of a two-signal-dependent, Ia+ mononuclear phagocyte progenitor subpopulation that is sensitive to inhibition by ferritin.

Evidence is presented that the ferritin-inhibitable, Ia+ monocyte progenitor in murine marrow requires two signals for stimulation of clonal proliferation. Escherichia coli K235 lipopolysaccharide (LPS) at 0.1 ng/ml enhanced macrophage colony formation by 25 to 70% in murine marrow cultures stimulated with colony-stimulating factor (CSF-1). The progenitors which responded to LPS and CSF-1 represented a distinct subpopulation. Pretreatment of marrow cells with complement plus anti-Ia, anti-H2, anti-asialo GM1, and anti-Mac-1 antibodies specifically depleted the two-signal-requiring progenitors. In addition, the same progenitors were depleted by preincubation with hydroxyurea, indicating that these cells were in cell cycle when removed from the marrow. When compared with the quiescent progenitors, the Ia+, cycling cells were more sensitive to the antiproliferative effects of interferon alpha/beta but were more resistant to inhibition by E prostaglandins. Pretreatment with T cell-specific antibodies and complement specifically enhanced cloning of quiescent progenitors without affecting cloning of the Ia+, cycling subpopulation. Moreover, rat liver ferritin at 10(-8) to 10(-10) M specifically inhibited clonal proliferation of the Ia+ progenitors. Finally, the requirement for LPS as the additional stimulant could be replaced by the addition of haplotype-specific anti-Ia antibody to CSF-stimulated cultures. In contrast to LPS, anti-IA was competitive with inhibitory ferritin in clonal proliferation of the Ia+ progenitors. The significance of these observations in regulation of monocytopoiesis is discussed.

Production of T cell differentiation factor in syngeneic lymphocyte macrophage culture for cytotoxic T lymphocyte generation.

This study demonstrated that T cell differentiation factor (TCDF) was produced in syngeneic lymphocyte-macrophage cultures. Conditioned medium containing TCDF and interleukin 2 (IL 2) induced the differentiation of leukoagglutinin (LA)-activated cytotoxic T lymphocyte precursors (CTLp) into cytotoxic T lymphocyte (CTL) effectors. The production of TCDF and IL 2 peaked at day 4 to 5 in cultures containing normal spleen cells, syngeneic peritoneal macrophages, and indomethacin. Macrophages and T cells with Thy-1+, L3T4+, and Lyt-2- phenotype were needed for TCDF production. There was no requirement for xenogeneic serum in the culture medium; thus, TCDF could be produced in a syngeneic system. Recognition of self Ia molecules appeared to be essential for TCDF production, which was completely abolished by the addition of monoclonal anti-Ia antibody. In our experiments, removal of IL 2 from conditioned medium containing TCDF abolished its ability to generate LA-activated CTL. However, the cytotoxic response could be restored by the addition of a small amount (5 U/ml) of purified human recombinant IL 2 (HRIL 2), which alone was unable to generate LA-activated CTL at this dose. The generation of LA-activated CTL by high dose HRIL 2 (greater than 50 U/ml) was likely due to the endogenous production of TCDF. The bulk of TCDF could be separated from IL 2 by gel filtration in a Sephadex G-100 column. The peak of TCDF activity was concentrated at a m.w. of 16K dalton, and there was very little IL 2 activity in these fractions. When added alone to the LA-activated lymphocyte cultures, these active fractions were unable to induce CTL; supplementation of exogenous IL 2 was needed to restore the cytotoxic responses. Our findings indicate that both IL 2 and TCDF, which are needed in CTL generation. are produced in syngeneic cultures in the absence of antigenic or mitogenic stimulation.

Ia-positive nonlymphoid cells and T cell development in murine fetal thymus organ cultures: monoclonal anti-Ia antibodies inhibit the development of T cells.

A fetal thymus organ culture system has been developed to study the differentiation of murine thymus-derived immunocompetent cells (T cells) such that cell yields can be easily monitored. This system has been used to study the effects of monoclonal anti-I-A antibodies on the growth of T cells. The addition of anti-I-A antibodies, but not anti-H2K monoclonal antibodies, to fetal thymus organ cultures resulted in a decreased yield of lymphoid cells. Anti-I-A-treated cultures did not produce cells that gave an immune response in MLC assays. Anti-I-A antibodies stained a small subpopulation of nonlymphoid cells in untreated cultures by indirect immunofluorescence that were no longer detectable in cultures that had been pretreated with anti-I-A antibody. Culture of fetal thymus lobes at low temperature (20 degrees C) for 1 wk resulted in a decrease in lymphocyte production, as well as a concomitant increase in the frequency of Ia-positive nonlymphoid cells. Co-culture of fetal liver or anti-thy-1 plus complement-treated adult bone marrow with such Ia-positive cell-enriched fetal thymus lobes at 37 degrees C resulted in the production of T cells. Anti-Thy-1.1 or -1.2 staining by indirect immunofluorescence of cells obtained from co-cultures that differed at the Thy-1 locus showed that the T cells produced were derived from the bone marrow or fetal liver. T cell production occurred in both syngeneic and allogeneic cocultures. However, if co-cultures were made by using 14-day gestation fetal thymus instead of fetal liver or bone marrow as donors of T cell precursors, T cell growth was observed only in syngeneic combinations. These results suggest that Ia-positive nonlymphoid cells play a role in the development of T cells in the fetal thymus, and that "thymus processed" T cell progenitors (but not the more immature progenitors in the fetal liver or bone marrow) are self-Ia restricted in their differentiation.

Alteration of the T cell self-specificity repertoire by treatment with anti-Ia antibody during embryonic life.

The effect of anti-Ia antibody on the development of murine neonatal self-Ia-reactive T lymphocytes in the thymus was studied. A C57BL/6 (B6) mouse pregnant with (B6 X C3H/He)F1 (B6C3F1) embryos was injected with monoclonal anti-I-Ek (m alpha I-Ek) antibody every other day starting from the 12th day of gestation. The mixed leukocyte culture reaction (MLR) responses of thymocytes from m alpha I-Ek-treated neonatal mice were assayed against adult B6 (H-2b), C3H/H3 (H-2k) or BALB/c (H-2d) splenic stimulator cells. The syngeneic MLR response of m alpha I-Ek-treated B6C3F1 neonatal thymocytes against C3H stimulator cells was augmented compared to that of untreated neonatal thymocytes. Experiments utilizing recombinant inbred strains of mice as well as monoclonal anti-Ia antibody blocking experiments suggested that the antigen(s) responsible for this augmentation of syngeneic MLR resided in the I-Ek molecule. The MLR response against B6 or BALB/c stimulator cells was not influenced by m alpha I-Ek treatment. We speculate that m alpha I-Ek antibody blocked the expression of I-Ek molecules in B6C3F1 embryos and this resulted in the alteration of T cell self-specificity repertoire in the thymus. Our results support the concept that Ia molecules play important roles for the elimination of self-reactive T lymphocyte clones in the thymus.

Activated lymphocytes in patients with newly diagnosed type 1 (insulin-dependent) diabetes mellitus.

The expression of activation antigens (transferrin receptor, IL-2 receptor and Ia antigen) on circulating T lymphocytes from Japanese children with Type 1 diabetes was studied using five monoclonal antibodies (Ab), OKT9, anti-Tac Ab, OKIa1, anti-human HLA-DR Ab and OKT3. For detecting Ia positive T cells, the dual staining technique using OKT3 and anti-Ia antibody was employed. Four out of six patients (67%) with newly diagnosed Type 1 diabetes showed a raised level of either OKT9 or Tac positive cells when examined at diagnosis. These patients, however, rapidly lost these activation antigens after the insulin therapy was started. In contrast, in 32 long-standing patients, only 2 (6%) had a high percentage of OKT9 positive cells and none of them demonstrated Tac positive cells. One out of six newly diagnosed patients or three out of 21 long-standing patients had a significantly high percentage of Ia-positive T cells compared with normal subjects. In poorly controlled long-standing patients whose HbA1 value was higher than 14%, none of them had an increased number of activated lymphocytes. Therefore, it is unlikely that insulin deficiency and hyperglycemia were responsible for the changes observed in these studies. Activated lymphocytes might be related to activation of the immune system involved in pathogenesis of Type 1 diabetes.

Effect of anti-Ia treatment on the production of anti-DNA antibody by NZB mice.

A cell transfer system was used to study the effect of anti-Ia antibodies on anti-DNA-producing B cells. B cells from autoimmune New Zealand Black (NZB) mice were necessary and sufficient to transfer anti-DNA antibody production to congenic NZB. xid recipients. Anti-Ia treatment of either donors or recipients led to a significant reduction in the number of B cells secreting anti-DNA antibody. This effect was detectable after as little as 3 days of treatment and persisted for at least 1 month after the cessation of therapy. In this system, we could find no evidence of suppressor cell induction. These data suggest that anti-Ia antibodies directly suppress autoantibody-producing B lymphocytes.

The effect of cyclosporin-A, low-temperature culture, and anti-Ia antibodies on prevention of rejection of rat islet allografts

The effect of cyclosporin-A, low-temperature culture, and anti-Ia antibodies on prevention of rejection of rat islet allografts

The distribution of Ia antigen in the lesions of rat acute experimental allergic encephalomyelitis.

Ia antigen, encoded within the major histocompatibility complex, plays an important role in the activation of T lymphocytes. Since experimental allergic encephalitis is an essentially T cell-mediated disease, Ia antigen in the central nervous system (CNS) may be pathogenetically relevant. The occurrence of Ia antigen in the CNS of normal rats and of rats with experimental allergic encephalitis was studied by light and electron microscope immunocytochemistry using the monoclonal anti-Ia antibodies Ox 4 and Ox 6. In normal, unsensitized animals a district population of stellate cells in the meninges and some perivascular mononuclear cells in the nervous tissue carried Ia antigen. In rats with experimental allergic encephalitis a dramatic increase of Ia-positive cells was found. In addition to the positive cells found in normal animals, monocytes, macrophages and many lymphocytes in the meningeal perivascular and parenchymal inflammatory infiltrates as well as "activated microglia" stained for Ia antigen. We did not find evidence for Ia expression on endothelial cells, astrocytes or other components of the CNS in either normal or diseased rats.

Requirement of Ia-positive accessory cells in the MLR response against class II antigen on human B cell tumor line.

In this report we have made a comparative study of the capacity of normal human stimulator cells and Epstein-Barr virus-transformed human B cell line Wa (EBV-Wa) cells to stimulate alloreactive T cells. Class II antigen (presumably HLA-DR4 determinant) on EBV-Wa cells was shown to act as a stimulating molecule in the mixed lymphocyte reaction (MLR) through a blocking study by using anti-Ia antibodies. Furthermore, it was found that HLA-DR-positive accessory cells in the responder population were required to elicit MLR responses against HLA-DR antigen on EBV-Wa cells. In contrast, HLA-DR-positive accessory cells in the responding cell population were not essential for elicitation of MLR responses against HLA-DR antigen on normal allogeneic peripheral blood mononuclear cells, as reported. The cell-cell interaction between responder HLA-DR-positive accessory cells and responding T cells in a major histocompatibility complex (MHC)-restricted manner was required for eliciting MLR responses against class II antigen on EBV-Wa cells such as antigen-presenting cell-T cell interaction in soluble antigen-specific T cell proliferative responses. The function of HLA-DR-positive accessory cells in the responder population could not be substituted for by the presence of interleukin 1. Furthermore, there was no obvious correlation between the degree of surface HLA-DR antigen expression on EBV-Wa cells and its stimulating ability. Thus, two distinct types of allo-class II, antigen-specific T cell activation between normal human stimulator cells and EBV-Wa cells were shown to exist.

Heterogeneity of Ia antigen expression by proliferating nonlymphocytic leukemia blast cells.

In vitro systems were used to detect Ia-like antigens on proliferating normal myeloid and acute nonlymphocytic leukemia (ANLL) blast cells. Incubation of normal bone marrow cells with a monoclonal anti-Ia antibody and complement resulted in toxicity for both granulocyte/macrophage progenitors (CFU-GM) (toxicity 79%-100%) and cells proliferating in liquid culture in response to placenta-conditioned medium colony-stimulating factor (CSF) or medium conditioned by normal, phytohemagglutinin (PHA)-stimulated mononuclear cells. In contrast, effects of anti-Ia antibody and complement on blast colony-forming cells and 3H-TdR incorporation in liquid culture from eight patients with ANLL were variable. Colony growth with CSF after treatment was 0% to 91% of control growth and did not correlate with display of Ia-like antigens. Survival of ANLL cells growing in liquid cultures was even more variable after anti-Ia+ complement treatment (28%-227% of control). The presence of Ia-like antigens did not distinguish ANLL cells responding to PHA-conditioned medium from those responding to CSF in either colony or liquid culture. Dose-response curves for ANLL cells in liquid culture were similar before and after treatment with anti-Ia+ complement. In contrast to normal myeloid precursor cells, which show uniform display of Ia-like antigens, display of Ia antigen by proliferating leukemia cells is highly variable from patient to patient. Anti-Ia reagents such as this one would not be effective in treating ANLL marrow for autologous transplantation.

Activated human T cells can present alloantigens but cannot present soluble antigens

Human T cells, when activated by antigen or mitogen, express Ia antigens. We have examined the capacity of activated T cells to stimulate autologous and allogeneic T cells and their ability to present soluble antigen. Interleukin 2-dependent T-cell lines (TCL), free of accessory cells, were used for antigen-presenting cells. These activated T cells were potent stimulators in an autologous mixed lymphocyte reaction (AMLR), more so than autologous irradiated non-T mononuclear cells. Activated T cells were also able to stimulate proliferation of allogeneic T cells in the absence of any other accessory cells, and this stimulation was blocked by anti-Ia antibodies. Resting unstimulated T cells were unable to stimulate autologous or allogeneic responses. Thus, activated T cells were able to present self antigens and alloantigens. However, activated T cells could not present soluble antigens to autologous T cells or to antigen-specific TCL even if exogenous interleukin 1 was added to cultures. The ability of activated T cells to stimulate an AMLR in vitro may reflect an important immunologic amplification mechanism in vivo. The ability of activated T cells to present alloantigens but not soluble antigens suggests an inability to process antigen, and this may provide further insights into the complexities of antigen presentation.