Normal human keratinocytes contain an interferon-like protein that may modulate their growth and differentiation

Epidermal growth and differentiation is a complex process which depends upon a balance between positive and negative growth signals, and in normal skin the majority of the cells in the germinative basal layer do not proliferate unless stimulated. Using the indirect immunofluorescent method, it can be demonstrated that purified polyclonal epidermis in cross sections of normal skin and to the basal layer of cultured keratinocyte colonies. Furthermore, extracts of keratinocyte cultures contain interferon bioactivity. With Western blot analysis, antibodies to interferon recognize a band of approximately 40 kD both in keratinocyte lanes and in recombinant interferon lanes that give in addition a band of approximately 20 kD. Addition of interferon to rapidly growing keratinocytes inhibits their growth by as much as 90% and promotes their terminal differentiation. The growth inhibitory effect of interferon is completely reversible. These data demonstrate that interferon or a closely related protein is present in human epidermis and suggest that this protein may act as a physiologic modulator of keratinocyte growth and differentiation.