Proliferative activity of macrophages in the greater omentum of the mouse in relation to the early postnatal development of the vascular structures.

The rudimental omentum in newborn mice presents itself as a thin, poorly vascularized membrane covering the stomach. Imprints and whole mounted preparations of the omental membrane of mice from seven different inbred strains, aged 1-10 days, were made and sequential morphological changes were described. It was found that omentum of suckling mice contains numerous foci or colonies of mononuclear phagocytes (omental macrophages). These cells reveal a high proliferative activity when examined 1 hr after exposure of tritiated thymidine. The labeling index in the population of omental macrophages is variable, ranging in individual mice from less than 5% to 25%. This wide variation is a nonrandom phenomenon. It was found in all seven strains of mice and depends mainly on the age of the mouse. Two possible interpretations are as follows: Some interrelation exists between the intensity of the proliferative activity of omental macrophages and the development of vascular and lymphoid structures that are characteristic for the omentum of adult mice. Omental macrophages originate from local precursors that are not dependent on the bone marrow.