Fc gamma-receptor as a functional marker on epidermal Langerhans' cells in situ.

Fc gamma-receptors (FcR) in cryostat sections of normal human skin were detected with soluble immune complexes of horseradish peroxidase (HRP) and rabbit IgG anti-HRP (HRP-anti-HRP). The binding of HRP-anti-HRP to Langerhans' cells (LC) was demonstrated using a double immunofluorescence staining in which LC were identified with a CD1a specific monoclonal antibody (Leu 6). The immune complexes gave granular staining of CD1a+ epidermal cells in sections of all specimens from normal skin. The mean percentage of CD1a+ cells that were FcR+ was 49 +/- 11 (n = 8). The FcR+/CD1a+ cells had a clearly defined dendritic pattern. The staining intensity of LC with HRP-anti-HRP was weaker than the intense staining of CD1a-macrophages in the dermis. Results of inhibition experiments indicate that human epidermal LC express low affinity FcR, but the presence of high affinity FcR as well cannot be excluded. The demonstration of FcR expression on normal LC clarifies previous uncertainty on LC membrane receptors, though the functional significance of these receptors is still not well understood.