S-100 protein detection in "follicular macrophages" of mouse lymphoid organs by ABC immunoperoxidase method

The distribution of S-100 protein was investigated in normal or reactive lymphoid organs from adult mice, rats and humans by the avidin-biotin complex ABC) immunoperoxidase method. In mouse lymph nodes and spleen the protein appeared to be confined to the "tingible-body macrophages" and occasionally in sinus histiocytes in the lymph nodes. No immunoreaction product was detected in the other cell types present inside or outside the follicles. In the thymus the immunostained cells were located in the medullary area and corresponded morphologically to mononuclear PAS-positive cells with histiocytic appearance. By contrast, in rat and human organs S-100 protein was detected in interdigitating reticulum cells and dendritic reticulum cells. The present findings indicate that S-100 protein is located differently in mouse lymphoid organs and in other mammalian species.