Abstract

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.