Mode of antigen presentation required for triggering of T cell response: analysis by use of azobenzenearsonate-tyrosine derivatives as antigens and L cells transfected with I-Ak genes as antigen presenting cells.

Our previous study demonstrated (1) that the presence of charged groups (amino and carboxyl groups) at the alpha-carbon of tyrosine is essential for activation of azobenzenearsonate-L-tryosine (ABA-L-Tyr specific T cells, and (2) that T cells recognizes ABA-L-Tyr in association with macromolecules on syngeneic spleen cells used as antigen presenting cells (APC). The present study was undertaken to confirm that the macromolecules on APC are Ia molecules, by using L cells transfected with A beta k and A alpha k genes as APC. I-Ak restricted ABA-L-Tyr specific cloned T cells, and T hybridoma cells were activated by ABA-L-Tyr in the presence of the L cell transfectants, of which expression of I-Ak molecules had been proven by specific binding of anti-I-Ak monoclonal antibody (MAb) 10.2.16 on the cell surface. The pattern of responses of I-Ak restricted ABA-L-Tyr specific T cells to various ABA-Tyr derivatives presented by the I-Ak expressing L cell transfectants was similar to the pattern obtained by using H-2k spleen cells as APC. Thus, ABA-L-Tyr and ABA-Tyr derivatives, which have both amino and carboxyl groups at the alpha-carbon of Tyr, presented by the L cell transfectants triggered good response of I-Ak restricted ABA-L-Tyr specific T cells. By contrast, ABA-Tyr derivatives, which lack the amino or carboxyl group, or both groups, at the alpha-carbon of Tyr, presented by the L cell transfectants could not activate the ABA-L-Tyr specific T cells at all. Furthermore, anti-I-Ak MAb, but not anti-I-Ek MAb, inhibited completely the response of I-Ak restricted ABA-L-Tyr specific T cells to ABA-L-Tyr presented by the L cell transfectants. These results indicate strongly that the macromolecules on APC which associate with ABA-L-Tyr are A beta k A alpha k gene products, i.e., I-Ak molecules.