Effects of activin A on M1 macrophage effector functions. Panels A and B show growth-inhibitory activity. (A) Proliferation of K562 cells exposed for 96 hours to activin A (25 ng/mL) or to GM-CSF–free M1 macrophage–conditioned medium (GM-CSF–free M1 SN) in the presence of a blocking anti–activin A antibody (α-ActA, 100 ng/mL), an isotype-matched antibody (IgG, 100 ng/mL), 10 μM SB431542, or a similar amount of vehicle (DMSO) as a control. Results show the means and SD of the effects of 3 independent preparations of GM-CSF–free M1 (GM-CSF)–conditioned medium and are expressed relative to the proliferation measured in untreated cells (Relative cell proliferation). (B) Cell volume of K562 cells after exposure for 96 hours to either activin A (25 ng/mL) or to GM-CSF–free M1 macrophage–conditioned medium (M1 SN) in the absence or presence of a blocking anti–activin A monoclonal antibody. The means and SD of triplicate determinations are shown; *P < .005; **P < .05. Panels C and D show the LPS-induced cytokine profile. (C) Determination of IL-12p40, IL-6, IL-10, and TNFα release by ELISA in culture supernatants of M1 and M2 macrophages either untreated or stimulated with LPS (10 ng/mL) for 24 hours. The means and SD of triplicate determinations are shown. (D) Determination of IL-10 and TNFα release by ELISA in the culture supernatant of M2 macrophages differentiated in the absence (M2) or presence of activin A (M2 ActA) either unstimulated or stimulated with LPS (10 ng/mL) for 24 hours in the presence or absence of activin A. The means and SD of triplicate determinations are shown; *P < .005; **P < .05.