Immuno-histochemical characterisation of cells involved in dermatopathic lymphadenopathy.

Normal and pathological lymph nodes exhibiting the features of dermatopathic lymphadenopathy were analysed by immunochemical methods. Various antisera to human Ia-like antigens, to immunoglobulin, to T cells and myelo-monocytic cells were used. The paracortical enlargement typical of the condition was due to interdigitating cells containing Ia-like antigens on their membrane, and to adjacent T lymphocytes. The intensity of staining with anti-Ia-like serum on the interdigitating cells was comparable to the very strong staining of the fewer reticular cells present in the T dependent areas of normal nodes and normal spleen, and to the staining of Langerhans cells in the skin and appear to be higher than that seen on B lymphoid cells. These cells do not exhibit immunoglobulin and do not react with antisera made against circulating granulocytic and monocytic cells. Since sinus histiocytes of normal nodes and histiocytes in massive lymphadenopathy showed very weak staining with anti-Ia-like serum, strong Ia expression seems to be restricted to a subclass of mesenchymal cells which might be involved in the regulation of T cell function.