MURAMIDASE - A USEFUL MONOCYTE MACROPHAGE IMMUNOCYTOCHEMICAL MARKER IN SWINE, OF SPECIAL INTEREST IN EXPERIMENTAL CARDIOVASCULAR-DISEASE/

The reliability of a rabbit polyclonal antibody against muramidase to identify monocytes/macrophages in swine was evaluated by immunostainin g of cell smears and formaldehyde-fixed, paraffin-embedded tissue sect ions. Blood in tissue sections, cell smears (peripheral blood, buffy c oat, and isolated mononuclear cells), and cultured mononuclear cells ( adherent monocytes) contained positively stained cells with a morpholo gy and in a number corresponding to that expected for a monocyte marke r. Polymorphonuclear leukocytes (PMN), lymphocytes, and platelets were negative. In normal organs and tissues, mesenchymal cells with a dist ribution similar to that expected for macrophages were found to stain positively for muramidase. In pathologic tissues, positively stained i nflammatory cells were identified in wounds, infected lungs, recently infarcted myocardium, and acute (variable numbers), organizing (often many), and healed (usually few) arterial thrombi. Enzymatic unmasking of antigenic determinants by trypsinization was necessary to achieve s trong and consistent staining of monocytes/macrophages in tissue secti ons. A variety of epithelial cells of no differential diagnostic signi ficance for monocyte/macrophage identification (e.g., renal proximal t ubular cells) also stained positive for muramidase. The staining patte rn of muramidase in swine corresponds to that described in humans, in whom muramidase has been shown to be a valuable marker of monocytes/ma crophages. Swine PMN were, however, not stained or only weakly stained , whereas human PMN reportedly are strongly positive. As in humans, sw ine cardiac myocytes, smooth muscle cells, endothelial cells, lymphocy tes, and platelets were consistently negative. This antibody against m uramidase is a useful immunohistochemical marker for swine monocytes/m acrophages in formaldehyde-fixed, paraffin-embedded tissues.