CD4 and melanoma: CD4+ T cell recognition of glycosylated peptides has been reported in rheumatoid arthritis (O-linked) (Michaëlsson et al., 1996) and cancer (N-linked) (Housseau et al., 2001), and CD4+ peptides in the melanoma antigen tyrosinase require the presence of N-linked glycosylation to elicit a T cell response (Housseau et al., 2001).