Locally dividing macrophages in normal and inflamed mammary glands

Goat mammary macrophage division in vivo was assessed by detection of mitotic figures, by autoradiographic measurement of the uptake of 3H thymidine, and by a 96-well proliferation assay. Autoradiography revealed that 3.74 +/- 0.77% of nonstimulated mammary macrophages were actively synthesizing DNA. Eight days of sterile inflammation, induced by lipopolysaccharide or thioglycollate, increased mammary macrophage division (10.9 +/- 2.1%). The division increased within 2 h after inducing inflammation with thioglycollate. After 1 day, the rate of division decreased, and another increase occurred 3-4 days later. The high rate of division was maintained for greater than 60 days after the induction of sterile inflammation. Division was further shown to occur by injecting 3H-thymidine directly into the mammary gland, harvesting the macrophages 1.5 h later, and determining incorporation by autoradiography. The results of all assays of division were in agreement, suggesting they reflected the same event. The dividing cells were nonspecific esterase-positive, adherent, motile, phagocytic, and had morphological characteristics of macrophages.