Recombinant gamma interferon increases the binding of peripheral blood mononuclear leukocytes and a Leu-3⁺T lymphocyte clone to cultured keratinocytes and to a malignant cutaneous squamous carcinoma cell line that is blocked by antibody against the LFA-1 Molecule

Because keratinocytes (KCs) express HLA-DR in a wide variety of skin diseases in which mononuclear leukocytes are observed in close apposition to KCs (i.e., graft-versus-host disease), and since gamma interferon (IFN-γ) induces HLA-DR expression on KCs, we asked whether IFN-γ treatment of KCs would influence the adherence of mononuclear leukocytes. When allogeneic peripheral blood mononuclear leukocytes (PBML) and a Leu-3⁺ T cell clone were coincubated with IFN-γ-treated KCs (300 U/ml, 3 days), there was a marked increase in binding compared with nontreated KCs. Similar binding results were obtained using a cutaneous squamous carcinoma cell line (SCL-1) after IFN-γ treatment. The IFN effect was relatively specific for IFN-γ, as neither IFN-α nor-β had any effect. Tumor necrosis factor exposure (500 U/ml, 3 days) increased the binding of the Leu-3⁺ T cell clone to both KCs and SCL-1 cells. Neutrophils displayed a less marked (but statistically significant) increase in binding to IFN-γ-treated KCs. Using the Leu-3⁺ cell clone and SCL-1 cells, detailed kinetic analysis of the effect of IFN-γ on binding was performed. The increased adherence between the cells began to appear after only 7 hours of treatment with r-IFN-γ (300 U/ml) and reached a plateau at 48 hours, with significantly enhanced binding continuing for at least 48 hours after removal of IFN-γ. The mechanism of binding was explored by preincubation of the PBML/Leu-3⁺ T cells with anti-LFA-1 (lymphocyte function-associated antigen) antibody (0.6-6.0 μg/ml), which totally inhibited the binding with no effect by anti-LFA-2 or-3 or class I or II antibodies despite documented binding of these antibodies to the cells. These results suggest that, after exposure to IFN-γ, the ability of KCs to bind mononuclear leukocytes is strongly enhanced, and this adherence may be important in leukocyte trafficking in the skin as well as contributing to altered KC-leukocyte interaction, which may be of fundamental importance in a variety of skin disease.