Phorbol ester treatment enhances binding of mononuclear leukocytes to autologous and allogeneic gamma-interferon-treated keratinocytes, which are blocked by anti-LFA-1 monoclonal antibody.

To extend our previous observation in which the binding of resting allogeneic peripheral blood mononuclear leukocytes (PBML) to recombinant gamma-interferon (IFN-gamma)-treated keratinocytes was characterized, we examined the influence of phorbol ester activation of the PBML to both autologous and allogeneic IFN-gamma-treated keratinocytes. The activation of PBML by phorbol esters (5 to 100 ng/ml) for brief periods of time (5 min to 1 h) at 37 degrees C led to an increase in the relative percentage of adherence to IFN-gamma-treated keratinocytes from 15% for non-activated PBML to 30% for phorbol ester-treated PBML. A biologically inert phorbol ester derivative did not enhance the binding reaction. No significant binding of phorbol ester-activated PBML was observed to non-IFN-gamma-treated keratinocytes. Both reduction in temperature to 4 degrees C and preincubation of the phorbol ester-treated PBML with anti-LFA-1 monoclonal antibody, led to complete inhibition of this adherence reaction indicating a role for the LFA-1 molecule in phorbol ester-activated PBML/IFN-gamma-treated keratinocyte reactions. Immunophenotypic analysis of the adherent cell population of the phorbol ester-activated PBML to the IFN-gamma-treated keratinocytes revealed that the predominant adherent cell type was the CD8+ T-cell subset (44%) versus the CD4+ T-cell subset (33%) with 23% monocytes and no binding of B lymphocytes. These results suggest that phorbol ester-activated PBML binds twice greater than resting PBML to IFN-gamma-treated keratinocytes, and this increased adherence may further contribute to homing of activated lymphocytes to the epidermis and mononuclear cell trafficking in the skin of inflammatory dermatoses.