No abstract

Monoclonal antibodies directed against sheep erythrocytes of the isotypes IgG1, IgG2b and IgG2a were used to analyze the specificity of antibody-induced suppression of the immune response. It was first shown that all monoclonals reacted against different antigenic determinants and they all suppressed the immune response to sheep erythrocytes when given shortly after the antigen to more than 50% as compared to 90-96% inhibition obtained with a polyclonal antiserum. Increasing the doses of monoclonals did not increase suppression. However, two different monoclonals administered together caused an additive, but not a synergistic inhibitory effect. No enhancement of the immune response was observed with any of the Ig classes tested. These findings show that four different antigenic determinants on sheep erythrocytes induced the synthesis of corresponding antibodies, with little or no signs of a dominant determinant. Passively administered monoclonal antibodies, even at supraoptimal doses, never suppressed the immune response to the same extent as a polyclonal antiserum, suggesting that each monoclonal only suppressed the synthesis of the corresponding antibody and did not affect antibody synthesis to other determinants.

Human and mouse immunoglobulins (Ig) or F(ab')2 fragments of rabbit Ig were conjugated to lipids and the conjugates inserted into the membrane of mouse spleen cells. It was found that nearly all B cells, but not T cells, became decorated with lipid immunoglobulin. Both endogenous Ig receptors and inserted Ig capped after the addition of cross-linking F(ab')2 antibodies and in both cases capping required energy. Capping of endogenous mouse Ig led to co-capping of inserted human Ig, but the reverse was not true.

RU 41.740, a glycoprotein extract from Klebsiella pneumoniae, is a polyclonal B cell activator in the thymus-independent category, and both RU 41.740 and its fraction F1 induce the production of interleukin 1 (IL 1). RU 41.740 alone appears to have no direct effect on T-enriched cells. However, we show here that when given in conjunction with concanavalin A (Con A), RU 41.740 enabled nylon wool-passed T cells, which had been accessory cell depleted and lost responsiveness to Con A, to proliferate in response to Con A. Analysis of this observation indicated that RU 41.740 probably acted via a residual accessory cell population and that contact of this cell with the T cell was necessary for Con A activation of the T cell. Because both lectin/antigen and a source of IL 1 are required to stimulate accessory cell-depleted T cells, the mechanism of action of RU 41.740 in this system may be by induction of IL 1 from residual accessory cells in the nylon wool-passed, T-enriched cell population. However, two other agents that stimulate IL 1 production, lipopolysaccharide (LPS) and F1, do not enable T-enriched cells to respond to Con A in this system.

When CBA X BALB/c mice are immunized with Th 1 hybrid prepared by fusing spleen cells from Dx-immunized mice with the AKR thymoma BW 5147, which secretes material that affects the anti-Dx response in CBA mice, antibodies are produced that in the ELISA are shown to bind to the material secreted by Th 1 but not to the material secreted by parent BW 5147. A fraction of the Th 1 secreted material that starts eluting on DEAE chromatography in 20 nM Tris with 0.13 M NaCl is shown to bind to Dx but not SRC or uncoated ELISA plates. This binding, like that of anti-Dx Ig, can be inhibited with 1-10 micrograms/ml concentrations of free Dx. However, the affinity of the product of Th 1 for Dx is apparently lower than that of anti-Dx Ig, since high concentrations of anti-Dx interfere with the binding of Th 1 products to Dx. On gel permeation chromatography, a similar Dx binding material elutes in two molecular weight areas, a high area of the molecular weight of IgG and less and a low area of the molecular weight of 43,000 and above, and both are found in samples of Th 1 ascites and hyperimmune CBA anti-Dx serum, but not (or less so) in normal CBA serum and not in the hyperimmune nude C57B1 anti-Dx serum. The Th 1-derived material that affected the anti-Dx response in previously shown experiments had similar elution characteristics. Since we also show that these fractions need not to contain Ig and that anti-Th 1 minimally cross-reacts with anti-Dx IgM or IgG, it is likely that that fraction of Th 1-secreted material represents a Dx-binding, non-Ig, anti-Dx response-regulating factor.