Antibodies raised against peptide fragments of bovine αs1-casein cross-react with the intact protein only when the peptides contain both B and T cell determinants

Abstract In order to compare the immune response to peptides with that to the native protein, we used bovine αs1-casein (αs1-CN), a major milk protein whose conformation seems to be in a highly disordered state in solution, as the model antigen. Firstly, the T and B cell determinants on this protein were localized by a T cell proliferation assay and an enzyme-linked immunosorbent assay (ELISA), using 13 synthetic overlapping peptides encompassing the entire sequence of αs1-CN. T cells from αs1-CN-primed C3H/He mice, a high responder to αs1-CN, strongly proliferated in the presence of peptides 91–110, 61–80 and 46–65. In addition, peptides 151–170, 136–155 and 106–125 were also found to contain T cell determinants. On the other hand, peptides 181–199, 46–65, 76–95 and 106–125 were generally found to be immunodominant B cell determinants, while peptides 121–140, 136–155, 91–110 and 151–170 also had antibodybinding activity. The peptides were then tested for their ability to elicit a specific antibody. This revealed that only peptides 91–110, 106–125, 136–155 and 46–65 were able to produce specific antibodies that bound to the native protein as well as the peptides themselves. These peptides contained both B and T cell determinants on the intact protein. Thus, we confirmed that a peptide corresponding to both T and B cell determinants on αs1-CN was capable of eliciting a specific antibody that reacted with the protein as well as the peptide itself.