Hematopoiesis in hereditarily athymic mice

Hematopoiesis was studied in hereditarily athymic (nude) mice and athymic mice given congeneic thymus cells. Athymic and reconstituted mice had mild anemia which resulted from both hypoplasia of the bone marrow erythrocytic series and decreased iron incorporation in erythroid precursors. Untreated nude mice had hypoplastic marrows due to decrease of both erythrocytic and lymphocytic precursors. The latter was associated with a marked peripheral lymphopenia. Transplantation of thymocytes caused the number of bone marrow and peripheral lymphocytes to return to normal whereas the granulocytic series decreased. Mice reconstituted with thymocytes had marked neutrophilia, eosinophila, and monocytosis compared with either normal or athymic siblings. The number of granulocytic colonies produced by bone marrow cells in agar was very similar in normal and athymic mice with neutrophilia, thus reflecting a normal functioning granulocytic series in a marrow with decreased lymphocytic and erythrocytic cells. The transplantation of thymocytes into athymic mice had no effect on the number of colonies produced by bone marrow cells and the number of spleen colony forming units. It was postulated that maturation of the additional thymocytes permits them to interact with the few endogenous thymocyte precursors present in the nude mice for promotion of bone marrow erythrocytic and lymphocytic proliferations. Alternatively, mature thymocytes may produce factors that were responsible for the effect on lymphoid and erythroid cells.