Immune response against two epitopes on the same thymus-independent polysaccharide carrier. 1. Role of epitope density in carrier-dependent immunity and tolerance.

Immunogenicity and tolerogenicity of two epitopes (alpha 1-6 and FITC) on the same dextran B 512 carrier were investigated. The following conclusions were made: (1) Both epitopes were thymus-independent and immunogenic and tolerogenic as well. (2) The marked dose differences between the two epitopes with regard to tolerance induction were found to be a consequence of the affinity and the heterogeneity of the responding B cells as well as the epitope density employed for detecting the PFC in a predictable way. (3) The alpha 1-6 response, in contrast to the anti-FITC response, was homogeneous and of low affinity and the number of precursor B cells was low. (4) Different mouse strains were found to be high-, low- or non-responders to alpha 1-6, but all the strains tested responded to the FITC epitope coupled to dextran. (5) Dextran and FITC-dextran were polyclonal B cell activators in the strains tested, irrespective of their ability to respond to the alpha 1-6 epitope. The findings indicate that epitope density and mol. wt of the immunogen as well as Ig receptor affinity for the epitope on the B cells are variables which markedly influence the binding of the immunogen to the specific B cells and therefore affect the delivery of the non-specific triggering signal.