CYTOKINE EXPRESSION FROM BONE-MARROW-DERIVED MACROPHAGES

Monocytes and macrophages show marked phenotypic variation dependent o n their tissue of origin. Peripheral blood monocytes have been found t o be sources of a variety of cytokines, but isolated marrow macrophage s have not been characterized in this regard. Marrow macrophages form a predominant component of murine adherent Dexter stromal cells and ca n be isolated by sequential explant culture in colony-stimulating fact or-1 (CSF-1). We have studied murine (Balb/c) bone marrow macrophage ( BMM) cytokine production in the presence or absence of CSF-1, the lect in pokeweed mitogen (PWM) or interleukin-3 (IL-3). Biologic activity i n conditioned media (cm) from control and induced BMM was assessed usi ng the factor-dependent cell lines 32D, NFS-60, T1165, MC-6 and FDC-P1 . Cell line stimulation and antibody blocking indicated the presence o f c-kit ligand, interleukin-6 (IL-6) and granulocyte colony-stimulatin g factor (G-CSF). This stimulatory activity was increased by exposure to PWM or the combination of CSF-1 and PWM or CSF-1 and IL-3. CSF-1, a s determined by radioimmunoassay (RIA), was essentially undetectable i n baseline cm and induction was not seen with PWM or CSF-1. Baseline o r ''constitutive'' expression of BMM mRNA for CSF-1 and c-kit ligand w as seen. Uninduced BMM did not express mRNA for G-CSF, granulocyte-mac rophage CSF (GMCSF), IL-6 or IL-3. CSF-1 induced increased expression of IL-6 mRNA, PWM induced increased expression of G-CSF and IL-6 mRNA and the combination of PWM and CSF-1 induced expression of CSF-1, G-CS F and IL-6 mRNA. Varying levels of CSF-1 had differential effects on c ytokine production. Increasing levels of CSF-1 increased IL-6 mRNA and downmodulated CSF-1 mRNA expression. There was a biphasic response of c-kit ligand mRNA expression to CSF-1 exposure; low levels of CSF-1 ( 50 U/mL) induced, while higher levels (2000 U/mL) inhibited, expressio n.