Determinants of immunogenicity: flogging the old ovalbumin, again (APP5P.116)

Abstract

Abstract During antigen presentation, the products of intracellular proteolysis capable of binding MHC I are presented to T cells on the cell surface in context of MHC I. We queried the sequence of ovalbumin (OVA) with the NetMHC 3.0 algorithm and based on a suitable NetMHC Matrix score or predicted IC50 values, identified 19 putative epitopes with potential to bind H-2Kb or H-2Db. Generally, IC50 of 500 nM is used as a threshold to distinguish between candidate and non-candidate epitopes; sequences with an IC50 <=500 nM are considered to be good binders and candidate epitopes (Assarsson et al. J Immunol. 2007). We observe that 10 of the 19 putative epitopes of OVA have measured IC50 <= 500 (range: 1.5 nM - 248 nM). The remaining nine putative epitopes are weak binders (IC50 > 500; range: 928 nM- 13219 nM). Interestingly, three of the nine weak binders elicit antigen specific responses in C57BL/6 mice. Six of the ten strong binders also elicit such responses, while four do not. Altogether, we have identified nine novel MHC class I restricted epitopes of ovalbumin, one of the most exhaustively used model antigens. Finally, we observe that synthetic peptides corresponding to two epitopes of OVA (one weak binder and one strong binder) do not elicit specific responses upon immunization; at the same time, responses against these epitopes can be observed upon immunization with OVA. We are exploring the molecular mechanisms of these observations.