Histochemistry of dipeptidyl aminopeptidase (DAP) II and IV in reactive lymphoid tissues and malignant lymphoma

A modified histochemical method was used to show the presence of dipeptidyl aminopeptidase (DAP) II and IV in fixed, freeze dried, cryostat sections of tonsils, lymph nodes, and skin. In 14 reactive tonsils and lymph nodes both enzyme reactions were largely confined to T dependent areas where scattered positive lymphocytes were shown in the paracortical zones, while lymphocytes of germinal centres (B dependent areas) were negative. In either site some macrophages showed strong positivity for both enzymes. In 23 lymph node and two skin biopsy specimens of non-Hodgkin's lymphoma the neoplastic lymphocytes of 12 B cell lymphomas were completely unstained, whereas in the 13 cases of T cell lymphoma the neoplastic lymphocytes showed variable reactions with positivity for DAP II in eight and for DAP IV in seven, both reactions being positive in four and negative in two. Touch imprints of a lymph node from a case of Hodgkin's disease showed that the Reed-Sternberg cells were unreactive for both enzymes. The histochemistry of DAP II and IV may supplement other histochemical and immunological markers in the cytological classification of lymphomas.