The function of autoreactive T cells in B-cell activation.
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Animals↗
Biomedical subjects
B W Needleman
Publications and source records attributed to B W Needleman.
An analysis of functional T cell recognition sites on I-E molecules.
The recognition of I-E molecules by antigen-specific T cells was studied to determine if one or multiple topographic sites on the I-E molecules can function as restricting elements for T cells. A panel of 14 I-Ek-specific monoclonal antibodies (mAb) was used to inhibit T cell proliferation induced by antigens, the recognition of which was restricted by I-E-encoded determinants. These antibodies gave patterns of inhibition that were similar for three long-term antigen-specific T cell lines. Multiple distinct patterns of inhibition, however, were observed when a series of antigen-specific I-E-restricted T cell clones was studied. Differences were identified even among clones expressing apparently similar antigen specificities and MHC restriction. The observed inhibition by these antibodies appeared to be caused by specific steric or allosteric interference with T cell recognition of antigen and Ia. Based on the differences in patterns of inhibition, it was possible to infer the existence of distinct sites or conformations on the I-E molecule that are functionally involved in antigen-specific T cell recognition.
Animals↗
Complement inhibits immune responses: C3 preparations inhibit the generation of human cytotoxic T lymphocytes.
C3 fragments have been shown to inhibit mitogen- and antigen-induced human lymphocyte blastogenesis. In this study, C3 preparations and a small fragment of C3 (contained in a preparation called Fraction 2) were examined for their capacity to regulate cytotoxic T lymphocytes (CTL) and proliferative mixed lymphocyte responses (MLR). We found that both preparations inhibited the generation of allogeneic human CTL as well as MLR in a dose-related manner. In contrast, Fraction 1, which contained native C3 and C3b, did not inhibit the generation of CTL nor did it inhibit the MLR. The kinetics of inhibition of proliferation were divergent from the kinetics of inhibition of CTL generation; the active preparations inhibited proliferation significantly when added as late as day 5 of a 6-day culture, whereas no inhibition of CTL generation was seen when these preparations were added after day 3 of culture. Cultures in which C3 preparations caused complete inhibition of CTL generation had normal levels of the nonspecific, anomalous killer cell activity, as assayed on K 562 target cells. Furthermore, C3 preparations and Fraction 2 had no effect on the lytic function of differentiated CTL, on "spontaneous" natural killer cell activity or on interferon-induced augmentation of natural killer cell activity. These findings indicate that C3 fragments may play a negative role in the regulation of CTL responses.
Adult↗
Inhibition of secondary in vitro antibody responses by the third component of complement.
Purified human C3 was found to inhibit rat in vitro secondary antibody responses. Fifty percent inhibition of antibody-forming cell development occurred with C3 concentrations of 26 micrograms/ml. This decrease was not the result of a general toxicity or a shift in the antibody response kinetics. Using cell mixing experiments, we could not detect a C3-induced suppressor lymphocyte or macrophage. C3 was active when added to culture early (day 0 or 1 or during a 24-hr antigen prepulse) or late (day 3, 5, or 7)--the early addition being more suppressive. Regardless of the addition time, there was a characteristic 48- to 72-hr lag before the inhibitory effect was manifested. C3 could inhibit antibody-forming cell development after stimulation with the thymus-independent antigens, trinitrophenyl-Brucella abortus and dinitrophenyl-Ficoll, as well as the thymus-dependent antigens, dinitrophenyl-bovine gamma-globulin and chicken gamma-globulin suggesting that C3 was not selective for B memory cell subpopulations. Further characterization of our C3 preparation indicated that the majority of the suppressive activity resided in a small m.w. protein resembling the C3a fragment of C3. Human C3a preparations generated either by trypsin cleavage or zymosan activation of C3 were also tested in our antibody response system and were able to inhibit antibody-forming cell development. These data implicate C3 cleavage products as negative regulators of antibody formation.
Anaphylatoxins↗
Inhibition of human lymphocyte blastogenesis by C3: the role of serum in the tissue culture medium.
Preparations of the third component of human complement (C3) inhibit human lymphocyte blastogenic response to mitogens and antigens when cultured in serum-free medium or in medium supplemented with 5% autologous serum (AS). In contrast, when the culture medium was supplemented with 5% foetal calf serum (FCS), C3 failed to inhibit responses to mitogen (concanavalin A) or to antigen (streptolysin O); some FCS lots allowed stimulation rather than inhibition of the lymphocyte responses. Moreover, when lymphocytes were cultured in serum containing equal amounts of FCS and AS, no inhibition was seen. Our findings may explain previous studies which suggest that C3 enhances or has no effect on lymphocyte responses.
Antigens↗
Human lymphocyte transformation induced by mitogens and antigens in a serum-free tissue culture system.
The use of serum to supplement lymphocyte tissue culture media introduces uncontrolled variables; different serum sources, lots and concentrations can produce variability in experimental results, serum can stimulate or inhibit lymphocytes, and components of serum can react with substances whose effects on lymphocytes are being studied. To avoid these problems, we studied the ability of human peripheral mononuclear cells to survive and to respond to stimulation in an entirely synthetic medium, RPMI-1640 supplemented with L-glutamine, gentamicin, HEPES buffer and magnesium. Optimal cell concentration in this serum-free RPMI-1640 was 2.5 x 10(6) cells/ml, whereas optimal cell concentration in serum containing RPMI-1640 was 1 x 10(6) cells/ml. In this serum-free RPMI-1640, 50% of the cellular input was recovered as viable cells after 7 days of culture, which was similar to results in serum containing RPMI-1640. Mononuclear cell transformation transformation was induced by phytohemagglutinin, concanavalin A, pokeweed mitogen, streptolysin O and candida. Optimal doses of stimulants and the kinetics of the responses were similar in serum-free and serum containing RPMI-1640. This system can be used to avoid the problems inherent in systems which supplement tissue culture media with serum.
Antigens↗
The third component of complement inhibits human lymphocyte blastogenesis.
Purified human C3 was studied for its ability to regulate human peripheral blood lymphocyte activation in a serum-free tissue culture system. C3 and its fragments formed by trypsin digestion were not mitogenic. However, C3 inhibited both mitogen- and antigen-induced lymphocyte proliferation in a dose-related manner. The observed inhibition by C3 increased with an increase in the dose of mitogen, with 50% inhibition seen at a C3 dose of 2.5 to 25 microgram/ml. Inhibition was induced even when C3 was added at 69 hr in a 99-hr culture, suggesting an effect on late events in activation. The inhibition was not mediated through generalized cytotoxicity, was not an artifact of kinetic alteration and still occurred in macrophage-depleted cultures. A small m.w. fragment of C3 which contained the inhibitory capacity in our C3 preparation was similar to C3a in size, anaphylatoxin activity, heat and acid stability and inhibition by serum. Our results indicate that cleavage products by C3 may play a negative role in lymphocyte activation.
Blood↗
Lack of an association between diffuse systemic sclerosis and HLA-DR1 or HLA-DR5.
The HLA-DR locus of the major histocompatibility complex encodes class II molecules which participate in immune responses through regulation of T cell interaction with antigen presenting cells. Previous association studies between HLA-DR antigens and the autoimmune disease, systemic sclerosis (or scleroderma), have yielded conflicting results. Some investigators have reported an association between this disease and HLA-DR1, while others have demonstrated an association with HLA-DR5. In this study, we used restriction fragment length polymorphisms in the HLA-DR locus to compare allelic frequencies of HLA-DR1 and HLA-DR5 in scleroderma patients with diffuse disease and healthy control subjects. No significant difference in the allelic frequency of either antigen was observed between the groups. These results suggest that HLA-DR1 and HLA-DR5 antigens are unlikely to contribute significantly to disease susceptibility in scleroderma.
Alleles↗