Heterogeneity of macrophages evidenced by variability in their glycoconjugates

Staining rat tissues with a battery of 15 lectin-horseradish peroxidase conjugates showed that macrophages contain glycoconjugates possessing terminal alpha, beta-galactose, N-acetylgalactosamine, fucose, and N-acetylneuraminic acid, plus two terminal disaccharides. Dissimilar binding of lectins by different phagocyte populations in the same or different organs evidenced variability in glycoconjugates according to the location of the macrophages. With a group of four lectins, macrophages stained most intensely in lung, next strongest in splenic red pulp and lymph node sinuses, and weakest in skin and liver. Two populations of macrophages were newly recognized in spleen on the basis of content of fucose-rich glycoconjugate. These included a necklace-like band of macrophages at the border between marginal zone and germinal center and distinctive macrophages dispersed throughout the marginal zone. In lymph nodes, phagocytes stained strongly in the germinal centers and weakly in sinuses for glycoconjugate with N-linked oligosaccharides and conversely for glycoconjugate with terminal beta-galactose. Variable lectin binding indicated heterogeneity of thymic macrophages. Lectin cytochemistry offers increased sensitivity for detecting macrophages in tissue sections, provides selective staining that shows the prevalence and distribution of the phagocytes and differentiates macrophages into separate subtypes.