Ultrastructural differences between macrophages of newborn and adult mice

Peritoneal macrophages from newborn mice were compared to those of adults by light and electron microscopy. A higher percentage of newborn mouse macrophages phagocytized turkey red blood cells as compared to macrophages derived from adult mice. Macrophages from newborn mice contained scarce rough endoplasmic reticulum in contrast to the well developed reticular structure found in adult mouse macrophages. Surface negative charge analysis, using cationized ferritin for labeling anionic groups, revealed differences in density and location of the particles. The newborn mouse macrophages contained almost twice as many anionic groups per μm² compared to those of adults. In addition, the cationized ferritin particles were contiguous with the membrane of the newborn mouse macrophages, while on the adult cells the grains were located at a distance of about 100 Å from the outer dense line of the 'unit membrane'.