Epidermal cells (EC) prepared from Lewis rat skin contained 2-3% class II+, LCA+ Langerhans cells (LC). LC enriched from freshly isolated EC suspensions proved highly effective accessory cells when presenting the nominal antigen OVA to an RT1.Bl-restricted ovalbumin (OVA)-specific rat T cell clone. Short-term preculture of the EC resulted in diminished OVA presenting capacity of the LC. Flow cytometry (FCM) analysis of class II and gamma chain expression revealed an up-regulation of class II on the LC's cell surface, consistent with earlier findings in mouse and human. However, while the presence of gamma chains in mouse LC was reported to decline to negligible levels during culture we observed substantial gamma surface expression on 3 day cultured rat LC, accompanied by increasing quantities of gamma inside the cells as revealed by FCM analysis on permeabilized cells. Biosynthetic labeling of panning-enriched LC from fresh and cultured EC confirmed and extended the immunocytological analysis. In contrast to the synthesis of class II proteins, that declined during culture to background levels, gamma chain synthesis was strongly augmented after 1 day in culture and remained at prominent levels throughout the culture period. In LC pulse labeled for 4 h and subjected to a 3 day chase period prominent quantities of labeled class II complexes were detectable with the majority of the dimers exhibiting the compact (C)-type folding form. On the basis of our findings a novel function of the invariant gamma chain is suggested to be effective in LC.