CD4 and melanoma: First, we investigated CD74 expression in four melanoma cell lines (A375, SB2, SK-MEL-2, and MeWo) as well as five major immune-cell types (THP-1 MΦ cell line and primary culture CD4+ T cells, CD8+ T cells, B cells, NK cells, and MΦ) with or without IFN-γ stimulation, as IFN-γ is a strong inducer of CD74 expression [5].