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 RTLBI-restricted ovalbumln (OVA)-speclflc rat T cell done. Short-term preculture of the EC resulted in diminished OVA presenting capacity of the LC. Row cytometry (FCM) analysis of class II and γ chain expression revealed an up-regulatlon of class II on the LC's cell surface, consistent with earlier findings in mouse and human. However, while the presence of γ chains in mouse LC was reported to decline to negligible levels during culture we observed substantial γ surface expression on 3 day cultured rat LC, accompanied by increasing quantities of γ Inside the cells as revealed by FCM analysis on permeablllzed cells. Biosynthetlc labeling of pannlng-enrlched LC from fresh and cultured EC confirmed and extended the Immunocytologlcal analysis. In contrast to the synthesis of class II proteins, that declined during culture to background levels, γ 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 dlmers exhibiting the compact (C)-type folding form. On the basis of our findings a novel function of the invariant γ chain Is suggested to be effective in LC.