Observations on the accumulation of mononuclear cells and the activities of reticulum cells in bone marrow of guinea-pigs recovering from whole body gamma irradiation.

Abstract

A study was made of the activities of reticulum cells, especially evidence of their proliferation, at an early stage in the final recovery from irradiation, and of whether the small mononuclear cells which accumulate in the irradiated marrow are a homogeneous group and whether some of them are formed in situ. The guinea pigs studied were irradiated with sublethal (150-200 rad), whole-body doses of Co/sup 60/ gamma rays. Quantitative studies of the proliferating bone marrow cells at an early stage of recovery did not show marked reticulum cell proliferation. However, at this time fat storage and phagocytosis, including lymphocyte ingestion, were commonly seen in reticulum cells, also an accumulation of small mononuclear cells in irradiated marrow. Some of these cells were small lymphocytes and appeared in large numbers in marrow. Others resembled small lymphocytes but the pattern of their nuclear chromatin was different. These cells can synthesize DNA, divide, and are comparable with cells previously termed micromyeloblasts and hematogones. Their small size could result from frequent divisions in larger precursors; but irrespective of the origin of the lymphocyte progenitors, these experiments indicate lymphocyte production in irradiated bone marrow. The observed phagocytosis of erythrocytes by reticulum cells and fat storage, atmore » a time when erythropoietic and granulopoietic recovery are imminent on a large scale, suggests that reticulum cells may have an important metabolic role. By making stored lipid and protein available to regenerating cells at an important stage during recovery from irradiation, reticulum cells may contribute to an environment favoring the growth of hemopoietic cells. This may promote the localization of bone marrow injected into irradiated animals. Although in irradiated marrows there was little evidence that reticulum cells serve as stem cells, in a metabolic capacity their role may be equally vital. (BBB)« less