Migration of marrow neutrophils under basal conditions and their mobilization, following subcutaneous implantation of cover slips, were investigated in groups of protein-deficient rats, using 3HTdR with sequential autoradiography of the peripheral blood smears. Animals fed a protein-rich diet served as controls. The pattern of appearance of labeled neutrophils in the blood was identical in the two groups under basal conditions. However, a higher percentag of labeled neutrophils appeared earlier in the blood following cover slip implantation in the deficient rats as compared to controls. The inflammatory exudate on the cover slips was low throughout the period of observation in deficient animals, with a delay in the appearance of monocytes. A pool of mature neutrophils resides in the bone marrow. It is proposed that in PCM there is atrophy of all neutrophil compartments, including that of the marrow pool, associated with a proportionate reduction in the efflux of cells from one compartment to another. This proportionate reduction in efflux would explain the normal kinetics of migration of neutrophils under basal conditions in the deficient rats in spite of a reduction in the marrow pool. On the other hand, in cover slip-implanted deficient rats, appearance of larger numbers of labeled neutrophils in the blood is attributed to a reduction in size of the marrow pool. This hypothesis is substantiated by the experiments in protein-deficient monkeys in which estimation of the marrow pool of neutrophils revealed a marked reduction in the deficient animals. It is further proposed that a diminuation of the marrow pool of neutrophils and retarded mobilization of cells at the site of inflammation are important mechanism responsible for the increased susceptibility of the malnourished host to infections.

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