Regulation of lipopolysaccharide-induced granulopoiesis and macrophage formation by spleen cells. I. Relationship between colony-stimulating factor release and lymphocyte activation in vitro.

Addition of bacterial lipopolysaccharide (LPS), a B cell mitogen, to mouse spleen cultures strongly stimulated production of colony-stimulating factor (CSF), the humoral regulator of granulopoiesis, and macrophage formation in vitro. Secretion of CSF from LPS-stimulated spleen cells coincided with cellualr DNA synthesis and cell transformation and both activities could be attributed to the lipid A moiety of the molecule. Different experimental approaches were used to study the relationship of CSF release and lymphocyte activation in response to LPS: a) modification of LPS with polymyxin B, an antibiotic bactericidal for most Gram-negative bacteria, caused a marked reduction in mitogenic activity, although the ability to induce CSF was not significantly altered; b)spleen cells from CBA/N mice, a mutant strain with an x-linked genetic defect in immunologic and mitogenic responses to polyclonal activators including LPS, showed diminished mitogeinc responses; however, high levels of CSF were produced; c) mitotic and DNA inhibitors (colchicine and cytosine arabinoside) did not affect CSF release although they completely inhibited mitogenicity. Thus, the spleen cell population participating in the process of LPS-induced CSF generation is probably a nondividing, terminally differentiated one without need for DNA synthesis. In addition, it was also shown that active RNA and protein synthesis are needed in this process.