To gauge the proximity between cooperating T and B cells required for effective triggering of antibody production, guinea pigs were immunized with bifunctional antigens in which the haptenic and carrier determinants were separated by rigid spacers of varied dimension. These took the form 2,4-dinitrophenol-(proline)n-L-tyrosine-p-azobenzenearsonate, where n varied from 1 to 40 proline residues. Animals immunized with n = 10 and n = 22 compounds made strong anti-DNP antibody responses, whereas animals immunized with bifunctional compounds containing longer spacers did not make antibody detectable by precipitation. It can be calculated on the basis of very strong physicochemical evidence for the rigidity and axial translation of poly-L-proline chains in solution that the cut-off point for effective interaction between T and B cells lies between 69 and 97 A U.
Shared idiotypy between B- and T-cell receptors specific for the antigen L-tyrosine-p-azophenyltrimethylammonium [tyr(TMA)] was studied in an antigen-binding assay using idiotypic antisera. These idiotypic reagents were prepared by inoculation of rabbits with purified anti-tyr(TMA) antibody raised in strain 13 guinea pigs. The antisera blocked 78-83% of the antigen-binding T cells (T-ABC) and 50-55% of the antigen-binding B cells (B-ABC) from tyr(TMA)-immune strain 13 and outbred lymph node cells (LNC). An excess of normal guinea pig Ig in the ABC assay did not affect the ability of the idiotypic antisera to block T- and B-ABC. Nylon wool-passed tyr(TMA)-immune LNC were trypsin treated resulting in a 75% loss of T-ABC. The trypsin-treated population was then cultured for 16 h which resulted in a return of T-ABC to 92% of pretrypsin values. 77% of these regenerated T-ABC could be blocked with idiotypic antisera. Specificity of the idiotypic antisera was tested in L-tyrosine-p-azobenzenearsonate-immune guinea pig LNC. Neither T- nor B-ABC were blocked in this heterologous system. Further blocking experiments were performed to characterize the nature of the T-ABC receptor. A variety of anti-Ig reagents, some of which block B-ABC, do not inhibit T-ABC suggesting that variable regions on T cells are not linked to Ig Constant regions.
Strain A/J mice made secondary indirect plaque-forming cell (PFC) responses to azobenzenearsonate (ABA) conjugates of giant keyhole limpet hemocyanin (KLH), a thymic-dependent antigen, but not to conjugates of Ficoll, a T-independent antigen. ABA-Ficoll was also unable to elicit a response in animals primed with ABA-KLH, which have an expanded anti-ABA memory cell pool. On the other hand, ABA-Ficoll rendered mice unresponsive to ABA-KLH when administered before priming or boosting with the T-dependent immunogen. Hence, the T-independent antigen was able to tolerize but unable to trigger B-memory cells responsive to the T-dependent antigen. A/J mice immunized with dinitrophenyl conjugates of Ficoll or bovine IgG (BGG) made vigorous IgM and IgG PFC responses. PFC responses to ABA-KLH and 2,4-dinitrophenyl (DNP)-BGG were abrogated by depleting mice of C3 with cobra venom factor, whereas the IgM and IgG PFC responses to DNP-Ficoll were unaffected. B lymphocytes were fractionated on the basis of receptors for C3 and the subpopulations were assayed for in vitro PFC responses to DNP-Ficoll. Very little response was obtained from complement receptor lymphocyte [CRL(+)] B cells, whereas CRL(-) cells were more responsive than unfractionated B cells. Both populations responded to a polyclonal B-cell mitogen (lipopolysaccharide). On the other hand, the in vitro PFC response to a T-dependent antigen (sheep erythrocytes) correlated with the presence of CRL(+) B cells in the cultures. However, a minor component of this response, sensitive to anti-Thy-1 serum, was made by CRL(-) B cells, indicating the existence of subpopulations of T-dependent B cells with different signalling requirements. The results suggest that most B cells responsive to T-dependent antigens possess receptors for C3 and that C3 plays an obligatory role in the response of these cells. A distinct subpopulation of B cells which lack C3 receptors respond to T-independent antigens. The precursors of PFC for the ABA epitope reside largely or exclusively in the CRL(+) compartment in A/J mice, whereas precursors for the DNP determinant are found in both compartments.