Studies of the Reticuloendothelial Mass and Sequestering Function of Rat Bone Marrow.

IT IS BELIEVED that bone marrow contains a relatively large mass of reticuloendothelial (RE) cells. These provide a lining for the marrow sinusoidss 3 and are potentially capable of phagocytosing injected foreign particles such as carbon and electronegative colloidal dyes, much as do the RE cells of liver and spleen.4 However, there is little quantitative information concerning this population of RE cells or the ability of the marrow to sequester defective red cells, a function conspicuously evident in the spleen and liver.5 Expression of marrow RE function in quantitative terms has been delayed because the inherent structure of marrow makes accurate sampling difficult.#{176}9 Previous publications from this laboratory have described the sequestration by spleen and liver of Cr51-labeled rat red cells that have been coated in vitro with rabbit antirat red cell antibody.'#{176}'' This red cell preparation was used to evaluate the capacity of bone marrow to sequester cells. Other measurements were made with Fe59-labeled, immature, isologous red cells and with colloidal suspensions of carbon particles. Comparisons were made between normal rats and animals whose marrow was made hypocellular by protein deprivation, by hypertransfusion, or by treatment with either mechlorethaminc (nitrogen mustard) or 6-mercaptopurine. A preliminary report of the findings has been published.12 METHOD General Procedures Caesarian-derived male rats of the Sprague-I)awley strain0 were used. Animals of uniform age were divided randomly into the desired number of groups; each group initially contained 4 or more animals, but occasionally accidental death occurred during experimental procedures which resulted in groups of unequal nunibers. Injections were made into tail veins in the following volumes: (a) 2 ml. of a 40 per cent suspension in normal saline of Cr51-labeled antil)ody-treated red cells; (b) 2 ml. of a serum suspension of Fe59-labeled immature erythrocytes, which usually contained about 100 x 106 nucleated cells; (c) 1 ml. of rat serum containing less than 1 g. of added ferric iron and 5-7 jj c. of Fe59; and (d) mechlorethamine hydrochloride. f about 0.5 ml. of a solution containing 1 mg. per ml. The mechlorethamine was injected within 15 minutes after dissolving the dry powder in saline. The close per animal was 1 mg/Kg. 158 KEENE AND JANDL body weight unless specifically stated otherwise. Experiments were made with mechlo-rethamine-treated animals 48 hours later at which time the treated animals were usually 10 to 15 Gm. lighter than controls, white blood counts were 5000 per mm.3 or less, and …