Combined immunological and histochemical analysis of skin and lymph node lesions in histiocytosis X.

The immunological phenotype of the cells involved in skin and lymph node lesions from two cases of histiocytosis X (H-X) were analysed by immunofluorescence techniques using combinations of heterologous and monoclonal antisera to Ia-like antigen and human cortical thymocyte (HTA-1) determinant. These cells were also characterised by a new technique using simultaneous immunofluorescence and enzyme histochemistry for acid phosphatase (ACPase). The major cell type in the lesions was found to express the same Ia+, HTA-1+ phenotype as normal epidermal Langerhans' cells (LC) and was unreactive for ACPase. Additional cell types included Ia-, HTA-1- multinucleate giant cells and residual lymphoid populations. These findings endorse previous concepts that H-X is a proliferation of abnormal LC and emphasise the heterogeneous nature of the cells involved in the disease.