A granulocytosis-inducing tumor inhibits the production of B lymphocytes in murine bone marrow.

Mice bearing a transplantable CE mammary carcinoma have been shown to have greatly augmented rates of neutrophil production coupled with a marked diminution of bone marrow lymphocytes. The objective of the present study was to test whether the loss of lymphocytes, and especially of B cells, from the bone marrow and spleen of tumor-bearing animals was due to a reduced rate of cell production and if so, at what level this response was regulated. A modified 3H-TdR pulse and chase analysis was used to assess the rates of production of small lymphocytes and B cells (stained for c mu and s mu) at weekly intervals after CE tumor transplantation. 3H-TdR was infused continuously for 24 hr, and radioautographs were prepared of bone marrow and spleen cells 0, 24, and 48 hr after termination of the infusion. Pre-B cells (c mu+s mu-) essentially disappeared from the femoral bone marrow by the end of 1 wk of tumor growth, followed by a great reduction in the number of c mu+s mu+ cells in the marrow and s mu + cells in the spleen. Although pre-B cells appeared in the peripheral marrow (caudal vertebrae, metatarsal bones) and spleen of tumor-bearing mice, these cells could not compensate for the continued decrease in the numbers of more mature B cells. In normal mice, during the 48-hr chase period, newly formed, 3H-TdR-labeled, small lymphocytes and s mu+ cells continued to emerge from the prelabeled precursor compartment at a steady rate, but after 1 wk of tumor growth, the number of small lymphocytes and s mu+ cells emerging from the precursor compartment fell steadily during the 48-hr chase period. During the second and third weeks of tumor growth, a steady state appears to have been reached in B cell production, which was at a level approximately 10 times below that of normal. Because pre-B cells are normally maintained by a less mature precursor population (2), the initial disappearance of c mu+s mu- cells suggests that the CE mammary carcinoma exerts its modulatory influence on primary B cell production by inhibiting or eliminating the cells that eventually feed into the pre-B compartment. The nature of the regulatory factors apparently secreted by the tumor and the more precise identity of the target cells are under investigation.