The membrane receptor complex regulating induction and clonal expansion of normal murine B lymphocytes

A model system for the analysis of B-cell activation and effector T-cell functions. T cell-dependent B-cell responses facilitated by anti-I-A antibodies

We have attempted to develop an in vitro system where polyclonal B lymphocyte responses could be induced in 'antigen-like' conditions, that is, where surface immunoglobulin-dependent binding mediates interaction with a mitogen. Monoclonal anti-mu and anti-delta antibodies were covalently bound to lipopolysaccharide (LPS) and these complexes were shown to display mitogenic activity. Polyclonal plaque-forming cell (PFC) responses, however, were diminished in cultures stimulated by anti-mu-LPS (but not by anti-delta-LPS) indicating that 'anti-mu inhibition' of terminal B-cell differentiation also applies to 'specific' antibody responses. Moreover, the analysis of the functional activity of monoclonal antibodies to major histocompatibility complex (MHC) class II molecules revealed a surprising synergy between low, non-stimulatory concentrations of anti-mu-LPS (but not anti-delta-LPS) with anti-I-A antibodies. These responses are T-cell dependent and synergy with anti-mu-LPS conjugates can also be obtained with 'naturally' activated CD4+ cells isolated from normal donors. A model of molecular and cellular interactions was derived, which accounts for the present findings and is applicable in antigen-dependent lymphocyte collaboration.

Immunoresponses to Neisseria meningitidis epitopes: immunomodulation by meningococcus B acts on more than one meningococcal surface epitope

Neisseria meningitidis group B strain M986 (serotypes 2a, 7) (NMB) elicits a specific primary antiphosphorylcholine immune response in mice but not a secondary response. The ability of other serotype and serogroup meningococci to induce similar primary responses in mice was studied, as was the immunogenicity of trinitrophenyl coupled NMB (TNP-NMB) in primary and secondary antitrinitrophenyl responses. Except for NMB, all other strains tested (three serogroup B and one serogroup A meningococcal strains) were found to be very poor phosphorylcholine immunogens. TNP-NMB, however, though proving to be a very good TNP antigen, was only a weak phosphorylcholine antigen. Priming NBF1 female mice with TNP-NMB one month or more before challenging them with the same antigen induced a strong depression of anti-TNP response in the subsequent challenge. However, this effect was not observed with Xid NBF1 male mice. Furthermore, priming mice with NMB weakly affected the anti-TNP response, but greatly depressed the antiphosphorylcholine response, after TNP-NMB challenge. In addition, whereas apparently only one TNP-specific B cell subpopulation was responding in unprimed mice challenged simultaneously with TNP-NMB and TNP-Ficoll (non-additive response), priming mice with NMB appeared to facilitate the independent activation of two different TNP-specific B cell subpopulations (additive response).

The role of I-A/E molecules in B-lymphocyte activation. II. Mechanism of inhibition of the responses to lipopolysaccharide by anti-I-A/E antibodies

We have previously demonstrated that monoclonal anti-I-A/E antibodies inhibit B-cell responses to lipopolysaccharide (LPS). In the present report, the inhibitory effects were shown to be carried out directly on B cells, and to be totally independent of the LPS concentration used, thereby showing that antibodies do not mediate their effect through blocking of accessory cells or steric hindrance of LPS-receptors. Of the three different phases in B-cell activation/induction, proliferation, and maturation, induction was shown to be the most sensitive to inhibition by anti-I-A/E antibodies. Thus, kinetic studies showed that anti-I-A/E antibodies are only inhibitory for the first 16 h of LPS activation, after which B cells can no longer be inhibited by these antibodies. Class II MHC molecules appear, therefore, to be part of a membrane molecular complex which regulates delivery of activation signals to resting B cells. Since it was also shown that this time period corresponds approximately to the time required for B cells to express functional reactivity to growth factors, we suggest that anti-I-A/E antibodies act on resting B lymphocytes to inhibit mitogen-dependent induction of growth receptor expression.