The invariant chain (li) has been shown to play a critical role in the
assembly, intracellular transport and function of MHC class II molecu
les. Recent studies suggest that these distinct activities can in many
cases be attributed to distinct isoforms of li or to specific regions
within it. Thus, regulation of li synthesis, post-transcriptional eve
nts, and post-translational modification has the potential to dramatic
ally modulate immune responses.