Acidic protein in macrophages.

Abstract

An antiserum to unstimulated rat peritoneal macrophages was produced in rabbits. The antibodies were directed against an acidic protein with a molecular weight of 35,000 and with an isoelectric point at 4.6. The macrophage acidic protein (MAP) was purified by gel filtration of rat lung soluble proteins, followed by preparative isoelectric focusing. The preparation of MAP was pure as assayed by agar gel electrophoresis and showed one precipitation peak in crossed immunoelectrophoresis against the crude antiserum directed against peritoneal macrophages. The purified MAP was used for immunization of rabbits, and the antiserum obtained was monospecific, assayed by crossed immunoelectrophoresis and Grabar-Williams immunoelectrophoresis. The titre was 4 times higher in the anti-MAP antiserum (1:80) than in the crude antimacrophage antiserum (1:20), tested against MAP by counter-current immunoelectrophoresis. The antigen (MAP) was demonstrated by direct and indirect immunofluorescence microscopy in rat blood monocytes, in spleen and lung monocytic cells, in clusters of cells in the thymus, and in adventitial macrophages around larger blood vessels in liver, kidney, lung and brain. Scattered meningeal macrophages showed fluorescence in the normal, brain. In stab-wounded areas of rat brain MAP was localized to perivascular and perineuronal macrophages with a morphology similar to that of microglial cells. The localization of the fluorescence was the same both for the antiserum against MAP and for the antiserum raised against crude peritoneal macrophages.