Rabbit bone marrow suppressor cells block the production or release of a soluble bone marrow growth factor.

Fc gamma-receptor (Fc gamma R)-bearing cells from normal rabbit bone marrow suppressed the constitutive proliferation rates of the remaining, Fc gamma R-, cells. In the absence of the suppressive influences of Fc gamma R+ cells, cells in the Fc gamma R- population spontaneously elaborated a soluble growth factor (GF) which induced the proliferation of unseparated bone marrow cells. To examine regulation by Fc gamma R+ bone marrow cells, graded numbers of the Fc gamma R+ cells were mixed with constant numbers of the FcR- cells. At 24 hr, supernates were collected and tested for GF activity. The Fc gamma R+ suppressor cells efficiently and in a dose-dependent fashion blocked GF production or release. The GF was nondialyzable and relatively heat stable. Supernates with GF activity also had colony-stimulating factor activity, but were negative in assays modified from murine interleukin 1 (IL-1) and IL-2 assays. Regulation of GF production or release represents a new function for bone marrow suppressor cells.