Allele-dependent association of chicken MHC class I molecules with the invariant chain

Invariant chain (Ii) associates with MHC class I molecules in cross-presentation pathway in mouse, but the association of Ii with MHC class I molecules in chicken was not clear. In this study we selected five typical alleles from about 100 B-FA and some B-FB sequences and tested. Confocal microscopy revealed that only two alleles of α chain (CD type) rather than β chain showed incomplete co-localization with Ii own, or as a combined cytosolic and transmembrane domains in the co-transfected 293T cells, while other allele types, CK and CL, had no this ability. Co-immunoprecipitation (IP) indicated that one of both alleles bound only full-length Ii. Interestingly, further analysis of five sequences showed that the types CK had a tail and the most variable sites (39/44) localize within MHC I α1 and α2 regions, this suggests that the tail and multi-sites are crucial to the association with Ii. Additionally, qRT-PCR revealed that Ii transcription levels in different organs were positively correlated with those of B-FA or B-FB gene. These results suggest that the allele-dependent association of chicken MHC class I molecules with its Ii with bases on a multi-site determinative spatial structure and that Ii as carrier potentially perform similar roles in MHC II as well as in MHC I antigen peptide presentation.