Melanocyte-conditioned medium stimulates while melanocyte/keratinocyte contact inhibits keratinocyte proliferation.

The interaction between melanocytes and keratinocytes in epidermal tissue suggest a bidirectional interchange between these two cell types. Although keratinocytes appear to affect melanocyte function, there are no reported effects of melanocytes on keratinocytes. Using cell strains, we examined the effect of melanocytes on keratinocyte proliferation. Two conditioned medium techniques were used: one was a co-culture system, where both cell types, grown on separate surfaces shared a common volume of medium. The second was simply feeding keratinocytes melanocyte-conditioned medium. Mixed cultures (both cell types together in a monolayer) where also studied. Our results showed that melanocyte-conditioned medium and melanocytes in co-culture significantly stimulated keratinocyte proliferation as measured by bromodeoxyuridine incorporation assay. However, growth of both cell types together in culture did not affect the growth rate of either cell type. Our results showed that cultured human melanocytes produce one or more soluble factors that stimulate the growth of cultured keratinocytes.