EPIDERMAL EXPRESSION OF INTERCELLULAR-ADHESION MOLECULE-1 IS NOT A PRIMARY INDUCER OF CUTANEOUS INFLAMMATION IN TRANSGENIC MICE

Keratinocytes at sites of cutaneous inflammation have increased expression of intercellular adhesion molecule 1 (ICAM-1), a cytokine-inducible adhesion molecule which binds the leukocyte integrins LFA-1 and Mac-1. Transgenic mice were prepared in which the expression of mouse ICAM-1 was targeted to basal keratinocytes by using the human K14 keratin promoter. The level of constitutive expression attained in the transgenic mice exceeded the peak level of ICAM-1 expression induced on nontransgenic mouse keratinocytes in vitro by optimal combinations of interferon gamma and tumor necrosis factor alpha or in vivo by proinflammatory stimuli such as phorbol 12-myristate 13-acetate. In vitro adhesion assays demonstrated that cultured transgenic keratinocytes were superior to normal keratinocytes as a substrate for the LFA-1-dependent binding of mouse T cells, confirming that the transgene-encoded ICAM-1 was expressed in a functional form. However, the high level of constitutive ICAM-1 expression achieved on keratinocytes in vivo in these transgenic mice did not result in additional recruitment of CD45(+) leukocytes into transgenic epidermis, nor did it elicit dermal inflammation. Keratinocyte ICAM-1 expression also did not potentiate contact-hypersensitivity reactions to epicutaneous application of haptens. The absence of a spontaneous phenotype in these transgenic mice was not the result of increased levels of soluble ICAM-1, since serum levels of soluble ICAM-1 were equal in transgenic mice and controls. We conclude that elevated ICAM-1 expression on keratinocytes cannot act independently to influence leukocyte trafficking and elicit cutaneous inflammation.