Accessory molecules and T cell activation I. Antigen receptor avidity differentially influences T cell sensitivity to inhibition by monoclonal antibodies to LFA‐1 and L3T4

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Abstract
A series of BALB/c‐derived T hybridoma cells, capable of producing interleukin 2 (IL2) in response to poly(Glu60, Ala30, Tyr10) (GAT) presented by syngeneic B lymphoma cells in the context of Ad restriction determinants, was used as a model system to evaluate the roles of LFA‐1 and L3T4 accessory molecules in antigen‐specific T cell activation. Examination of the antigen requirement for optimal IL2 responses revealed marked differences in the apparent avidity of these cells for GAT/Ad complexes. A relationship was observed between this parameter and the susceptibility of T hybridoma cells to inhibition by monoclonal antibodies directed at 5 distinct epitopes of LFA‐1, and at Aβd allodeterminants. In contrast, L3T4a‐specific monoclonal antibodies were found to block in a similar fashion the antigen‐specific IL2 responses of T hybridoma cells, regardless of the apparent avidity of their antigen receptors. It was also shown that both L3T4+ and L3T4− T hybridoma cells were capable of recognizing GAT plus Ad with high avidity. Thus, the quality of T cell antigen recognition appears to critically influence the involvement of LFA‐1, and only to a marginal extent that of L3T4, in antigen‐specific T cell activation. The implications of these findings are discussed in the context of recent data indicating that L3T4 may not only be an la‐binding protein.

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