Efficiency of antigen presentation to T cell clones by (B cell X B cell lymphoma) hybridomas correlates quantitatively with cell surface ia antigen expression.

A series of B cell hybridomas was used as a model system to assess quantitatively the role of Ia molecules in antigen presentation to allo- or soluble antigen-reactive T cell clones. These hybrid cell lines were established by fusion between the HGPRT-BALB/c B cell lymphoma M12.4.1 and LPS-stimulated spleen blasts from B10.BR (H-2k) mice. Quantitative cellular absorption of appropriate anti-Ia monoclonal antibodies and flow cytofluorometric analyses revealed that the B cell hybridomas examined herein expressed constitutively a number of surface I-Ak or I-Ek molecules that varied in an order of magnitude of 1 to 5. Such quantitative differences could be correlated precisely with (a) the capacity of B cell hybridomas to activate T cell clones to proliferate and/or to produce interleukin 2 in response to E beta k allodeterminant or to poly(Glu60Ala30Tyr10) presented in the context of I-Ak restriction element, and (b) the amount of monoclonal anti-I-Ak antibody required to inhibit antigen presentation to T cell clones. The possible implications of these data are discussed in the context of current models of regulation of Ia antigen expression by antigen-presenting cells.