Activin A is a member of the transforming growth factor-␤ superfamily, which we have identified as having a role in inflammatory responses. We show that circulating levels of activin increase rapidly after LPS-induced challenge through activation of Toll-like receptor 4 and the key adaptor protein, MyD88. Treatment with the activin-binding protein, follistatin, alters the profiles of TNF, IL-1␤, and IL-6 after LPS stimulation, indicating that activin modulates the release of several key proinflammatory cytokines. Further, mice administered one 10-g dose of follistatin to block activin effects have increased survival after a lethal dose of LPS, and the circulating levels of activin correlate with survival outcome. These findings demonstrate activin A's crucial role in the inflammatory response and show that blocking its actions by the use of follistatin has significant therapeutic potential to reduce the severity of inflammatory diseases.lipopolysaccharide ͉ cytokines ͉ Toll-like receptor ͉ MyD88 ͉ innate immunity

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Recent evidence suggests a role for activin A, and its binding protein, follistatin, in inflammatory pathways. However, whether activin is released systemically during inflammation is not known. In this study, a release of activin A into the circulation occurred in sheep within 1 hour of injection of lipopolysaccharide. This rapid peak in activin A preceded the release of the key inflammatory cytokines, tumor necrosis factor-alpha and interleukin-6. Follistatin release into the circulation occurred some 4 hours after the peak of activin A and continued out to 24 hours from lipopolysaccharide treatment. These data are the first to document a circulatory response of activin A to an inflammatory stimulus, and together with previous findings, suggest that activin A may have both pro- and anti-inflammatory actions in regulating cytokine-driven pathways.

A series of experiments were conducted in adult ewes to delineate the release profile of activin A and its relationship to other cytokines following an i.v. injection of the bacterial cell wall component, lipopolysaccharide (LPS). Following this challenge, plasma activin A increased rapidly and appeared to be released in a biphasic manner, slightly preceding the release of tumour necrosis factor-(TNF ) and before elevation of interleukin (IL)-6 and follistatin levels. The concentration of activin A was correlated with body temperature during the response to LPS. A second experiment compared cytokine concentrations in matched blood and cerebrospinal fluid (CSF) samples. This revealed that activin A was not released centrally in the CSF following a peripheral LPS injection, nor was TNF or the activin binding protein, follistatin, but IL-6 showed a robust elevation. In a third experiment, the stimulus for activin A release was examined by blocking prostaglandin synthesis. Flurbiprofen, a prostaglandin synthesis inhibitor, effectively attenuated the fever response to LPS and partly inhibited cortisol release, but the cytokine profiles were unaffected. Finally, the bioactivity of TNF and/or IL-1 was blocked using soluble receptor antagonists. These treatments did not affect the initial release of activin A, but blockade of TNF depressed the second activin peak. These studies define more rigorously the release of activin A into the circulation following acute inflammatory challenge. The response is rapid and probably biphasic, independent of prostaglandinmediated pathways and does not depend upon stimulation by TNF or IL-1. The data suggest that activin A release is an early event in the inflammatory cascade following the interaction of LPS with its cellular receptor.

Recent evidence suggests a role for activin A, and its binding protein, follistatin, in inflammatory pathways. However, whether activin is released systemically during inflammation is not known. In this study, a release of activin A into the circulation occurred in sheep within 1 hour of injection of lipopolysaccharide. This rapid peak in activin A preceded the release of the key inflammatory cytokines, tumor necrosis factor-alpha and interleukin-6. Follistatin release into the circulation occurred some 4 hours after the peak of activin A and continued out to 24 hours from lipopolysaccharide treatment. These data are the first to document a circulatory response of activin A to an inflammatory stimulus, and together with previous findings, suggest that activin A may have both pro- and anti-inflammatory actions in regulating cytokine-driven pathways.

Serum-free culture conditions to generate immature human monocyte-derived DC (Mo-DC) were optimized, and the parameters that influence their maturation after exposure to lipopeptides containing CD4(+) and CD8(+) T-cell epitopes were examined. The lipopeptides contained a single CD4(+) helper T-cell epitopes, one of a number of human leucocyte antigen (HLA)-A2-restricted cytotoxic T-cell epitope and the lipid Pam2Cys. To ensure complete maturation of the Mo-DC, we examined (i) the optimal lipopeptide concentration, (ii) the optimal Mo-DC density and (iii) the appropriate period of exposure of the Mo-DC to the lipopeptides. The results showed that a high dose of lipopeptide (30 microm) was no more efficient at upregulating maturation markers on Mo-DC than a low dose (6 microm). There was an inverse relationship between Mo-DC concentration and the mean fluorescence intensity of maturation markers. In addition, at the higher cell concentrations, the chemotactic capacity of the Mo-DC towards a cognate ligand, CCL21, was reduced. Thus, high cell concentrations during lipopeptide exposure were detrimental to Mo-DC maturation and function. The duration of exposure of Mo-DC to the lipopeptides had little effect on phenotype, although Mo-DC exposed to lipopeptides for 48 rather than 4 h showed an increased ability to stimulate autologous peripheral blood mononuclear cells to release interferon-gamma in the absence of exogenous maturation factors. These findings reveal conditions for generating mature antigen-loaded DC suitable for targeted immunotherapy.

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