Dendritic cells in cutaneous, lymph node and pulmonary lesions of sarcoidosis.

To determine whether dendritic cells (DC) are a consistent feature of lesions of sarcoidosis, we have used monoclonal antibodies to identify the HLA-DR-expressing populations of cells in cryostat sections of 15 lymph node, pulmonary and cutaneous lesions. The commonest HLA-DR positive cells in granulomas were epithelioid and giant cells, although lymphocytes within granulomas and tissue macrophages around them were also positive. Dendritic cells with Langerhans cells (NA1/34+ = OKT6+) and interdigitating cell (RFD1+) phenotype were consistently associated with granulomas only in skin lesions. In lymph nodes, interdigitating cells (NA1/34-/RFD1+/HLA-DR++) were confined to paracortical zones as in normal nodes, although a small area of NA1/34+/RFD1+ cells was found in one of three nodes. In lung lesions NA1/34+/RFD1+ dendritic cells were uncommon or absent, except in one chronic case. We conclude that while sometimes present in extracutaneous sites, DC are not an essential feature of sarcoid lesions, and that cells of the classical macrophage group are the most significant HLA-DR-expressing population. We suggest that the presence of DC in lesions of sarcoidosis may indicate an immunological response distinct from that causing granulomas to form. The variability of their involvement may have immunoregulatory significance.