CHANGES IN THE DISTRIBUTION AND INTENSITY OF ALKALINE-PHOSPHATASE ACTIVITY IN RAT LYMPH-NODE AND SPLEEN-CELLS AFTER ANTIGEN STIMULATION

We investigated the reaction of the popliteal lymph nodes (PLN) to the injection of two antigens, keyhole limper hemocyanin (KLH) and lipopo lysaccharide (LPS), into the footpads of rats, as well as the changes occurring in the PLN after allogeneic cell stimulation. Changes in alk aline phosphatase (ALP) activity of the lymph nodes were examined enzy me histochemically. Paralleling with PLN weight gain, increased ALP ac tivity was observed in the medullary regions of the lymph nodes of sti mulated rats. ALP reactivity in the stimulated lymph nodes was observe d to be weak in the germinal centers and strong in the medullary regio ns. The spleens of rats subjected to systemic graft-vs.-host (GVH) rea ction were examined in a similar fashion. The ALP-positive areas of th e GVH spleens increased in size as compared with normal spleens. These positive areas of lymph node and spleen appear to correspond mainly t o areas containing OX12-positive cells. These results suggest that enz yme-histochemical analysis of ALP activity together with immunohistoch emical analysis of lymphocyte phenotypes may be a useful method for ex amining lymph node and spleen reactions to soluble and cellular antige ns in rats.