Tumor and histocompatibility antigen interaction: direct visualization by a double-label bridging technique for immuno-electron microscopy

The nature of the interaction between the I_b tumor-associated surface antigen (I_b-TASA) and the D^k and K^k (D^k/K^k) regions of the major histocompatibility complex on the surface of line I_b lymphocytes was evaluated by immuno-electron microscopy using a double-label bridging technique. Quantitation of antigenic sites by direct counts showed 44% of the I_b-TASA sites coincident with D^k/K^k antigens. This is greater than the predicted random interaction of two independent cell surface determinants suggesting an associative interaction, i.e. 'altered-self' antigen. The remaining 56% of the I_b-TASA sites were in a non-associative mode. On the basis of data presented here, we postulate that the interaction between 'self'- and 'non-self' antigens is not an 'all or none' phenomenon.