Antigen presentation of myoglobin: profiles of T cell proliferative responses following priming with synthetic overlapping peptides encompassing the entire molecule.

Recently, the regions of myoglobin, which are recognized by T cells (T sites), were localized by a comprehensive synthetic strategy in which uniform synthetic overlapping peptides encompassing the entire protein chain were examined for stimulation of T cell proliferative activity. In this study, we report about the proliferative response to these peptides, as well as to the native protein, of lymph node cells from mice primed with the overlapping peptides either individually or in a mixture. Some, but not all, of the T site-containing peptides were effective in priming for an anti-myoglobin T cell response. Further, several peptides, which were highly immunogenic as free synthetic peptides, were not associated with any of the known T sites in this protein. Thus, the pattern of T cell recognition following priming with the overlapping peptides differs from the pattern observed when the native protein is the priming antigen. If antigen processing proceeds via fragmentation, then only those regions containing T sites would be expected to be effective in priming for a T cell response to the intact protein and, conversely, highly immunogenic peptides would correspond to T sites of the protein. Therefore, these findings indicate that the current concept of antigen fragmentation as a prerequisite for its presentation must be reappraised. We suggest that, in the presentation of a protein antigen, the protein is recognized predominantly intact and that the crucial aspects of presentation are determined by interaction with the cell membrane which trigger cellular activating events.