A comparison of the stimulatory effects of cytokines on normal and psoriatic keratinocytes in vitro

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Abstract
Keratinocytes from normal and psoriatic skin were tested for their in vitro proliferative response to a range of concentrations of rIL-6, rTGFα, rIL-8 and rGM-CSF using a serum-free culture system. With one exception, all normal cultures (11/12) were stimulated by 1000 ng/ml IL-6 (PP=0.05). As a group, the response by psoriatic keratinocytes to IL-6 was significantly less than that of normal keratinocytes (P=0.02). TGFα at 1 ng/ml induced proliferation in approximately 60% of both normal (8/12,PP<0.1) keratinocyte cultures; there was no significant difference between the responses of the two groups to this cytokine. In addition, small numbers of both normal and psoriatic cultures responded to TGFα over a concentration range of 0.1 to 100 ng/ml. Approximately half of the normal and psoriatic cultures were stimulated by 10–1000 ng/ml IL-8. However, the effect was not significant for the group at any of the concentrations tested. GM-CSF had minimal to no effect on most of the normal and psoriatic cultures tested. This study showed that psoriatic keratinocytes are equally responsive to the stimulatory effects of TGFα and IL-8, but are less susceptible to IL-6 compared to keratinocytes from normal skin. These findings are consistent with a role for these cytokines in the maintenance of a hyperproliferative epidermis in psoriasis.