Viral antigens are presented to cytotoxic T cells (CTL) in the form of endogenously processed peptides bound to major histocompatibility complex (MHC) class I molecules. A variety of different methods for measuring the ability of peptides to bind to MHC class I have been described. Several of these methods use the murine lymphoma mutant cell line RMA-S, which has a peptide loading defect resulting in a low expression of surface class I molecules that can be upregulated if a synthetic binding peptide with class I binding ability is added to the culture medium. In order to be able to screen for peptides with MHC class I binding ability, we developed an enzyme immunoassay for quantitation of MHC class I expression on RMA-S cells. 107 synthetic peptides derived from the E6 and E7 regions of human papillomavirus type 16 were screened for ability to upregulate class I expression of Kb or Db alleles. At a concentration of about 300 microM, 9/107 peptides were found to restore expression of Db to equal or greater levels than found in the RMA-S parental cell line RMA, while 35/107 peptides were able to partially restore Db expression. For Kb, 16/107 peptides were able to restore expression and 40/107 peptides induced partial upregulation. Titration experiments showed that upregulation of class I expression by these peptides was dependent on a high peptide concentration, since consistent upregulation could in no case be detected at concentrations below 10 microM. The class I binding peptides identified in the present study may be useful in the study of the CTL response to HPV in mouse model systems. The enzyme immunoassay used could facilitate the rapid search for class I binding peptides.
Journal of immunological methods