Low affinity of kappa chain bearing (4-hydroxy-3-nitrophenyl)acetyl (NP)-specific antibodies in the primary antibody repertoire of C57BL/6 mice may explain lambda chain dominance in primary anti-NP responses.

The primary anti-(4-hydroxy-3-nitrophenyl)acetyl (anti-NP) antibody response of C57BL/6 mice was analyzed by several methods. Serum analyses by solid-phase radioimmunoassay (RIA) showed that stimulation with the thymus-independent (TI) type 1 antigen NP-LPS results in an anti-NP antibody response dominated by kappa (kappa) light chain bearing antibodies, whilst responses to NP-Ficoll (a TI-2 antigen) and NP-KLH (a thymus dependent antigen) are dominated by lambda (lambda) 1 light chain bearing antibodies. However, in all these responses NP-specific plaque-forming cells (PFCs) were predominantly heteroclitic, and inhibitable by anti-lambda antiserum. In addition, kappa-bearing IgM-producing hybridomas obtained by fusion of spleen cells from NP-LPS-immunized mice, although producing NP-specific antibodies detectable by RIA, were unable to produce NP-specific plaques. Direct determination of the affinity of 5 of those hybridomas by fluorometric titrations showed that their affinity is indeed lower than 10(-5) M. These results suggest that most NP-specific antibodies stimulated by NP-LPS are of too low affinity to be detected in a direct PFC assay, with the exception of a population of lambda-bearing antibodies. Therefore, the differential expression of kappa- or lambda-bearing antibodies in primary responses to the hapten NP presented on different carriers may be due to different affinity requirements for B-cell triggering via different activation pathways.