Langerhans' cells and lymphocytic infiltrate in AIDS-associated Kaposi's sarcoma. An immunohistochemical study

The epidermal Langerhans' cells are dendritic cells of the skin capable of triggering cutaneous immune responses. They possess the membrane antigens required to this effect: class II histocompatibility antigen, CD1a and CD4; the latter acts as receptor for the human immunodeficiency virus. The skin is the organ primarily affected by Kaposi's sarcoma (KS). In epidemic KS, the local immunologic conditions of the skin are little known. We therefore studied 12 patients with AIDS-associated KS, evaluating the density and phenotypic expression in KS-affected and unaffected skin of the following antigens: CD1a, HLA-DR, CD4 in dendritic epidermal cells and dermis, and CD3, CD4 and CD8 in cells of the inflammatory infiltrate, using monoclonal antibodies applied to frozen sections with the avidin-biotin-peroxidase technique. Langerhans' cells in the AIDS-KS skin lesions were found to be decreased in number. This decrease was even more pronounced in the case of cells expressing HLA-DR antigen. A number of them were also revealed with CD4. The tumour lymphocytic infiltrate was almost exclusively composed of CD3+ CD8+ phenotype lymphocytes. The dermis also revealed CD4+ dendritic cells. The basal keratinocytes focally expressed HLA-DR. These phenotypical alterations of the Langerhans' cells and the local immunological imbalance observed may contribute to the growth and continuity of the KS lesions.