Detection of purine nucleoside phosphorylase in paraffin sections by the immunoperoxidase method

A method is described for immunohistochemical demonstration of purine nucleoside phosphorylase (PNP: EC 2.4.2.1) in paraffin sections from routine surgical histology specimens. A peroxidase-antiperoxidase (PAP) method was employed, using specific rabbit antiserum against human PNP, which was purified from postmature human erythrocytes. In human lymph nodes, intensive staining for PNP was observed in the vast majority of small lymphocytes in paracortical areas, in many small lymphocytes in medullary cords, and in a few small-to medium-sized lymphocytes in germinal centers. Small lymphocytes in the primary follicles and those in the mantle zones of secondary follicles were negative for PNP staining. Tingible body macrophages, lymphatic sinus cells, and most of the large cells in germinal centers did not stain with anti-human PNP (hPNP) antibody. Endothelial cells of small vessels in the cortex and plasma cells did not show any constant pattern of PNP staining intensity. Histochemistry revealed that the distribution pattern of PNP activity was quite similar to that demonstrated on paraffin sections by the PAP method.