RECONSTITUTION OF INVARIANT CHAIN FUNCTION IN TRANSGENIC MICE IN-VIVOBY INDIVIDUAL P-31 AND P41 ISOFORMS

MHC class II molecules associate with invariant chain (Ii) during bios ynthesis. li facilitates folding of class II molecules, interferes wit h their association with peptides, and is involved in their transport. The murine ii gene encodes two chains, p31 and p41. The role of these isoforms has been studied in vitro only in inappropriate antigen-pres enting cells. To circumvent this problem, we have generated invariant chain-deficient mice (Delta li), which express exclusively the p31 and p41 isoforms. Low level expression of p31 or p41 is not sufficient fo r rescuing high levels of cell surface class II expression. However, l ow levels of the typical compact dimer conformation indicative of tigh t peptide binding are observed. Thus, both isoforms participate in cla ss II folding and assembly. Furthermore, p31 and p41 retrieve the CD4( +) T cell population, which is reduced in the (Delta li) mice. Moreove r, the immune response to protein antigen is restored by both isoforms .