Macrophages with immunoregulatory activity in the absence of STAT6 signaling

Macrophages readily change their phenotype in response to exogenous stimuli. In this work, macrophages were stimulated under a variety of experimental conditions, and alterations in mRNA levels were analyzed. We identified three transcriptionally related populations of macrophages with immunoregulatory activity. They were generated by stimulating cells with TLR ligands, in the presence of three different “reprogramming” signals; high density immune complexes (IC), prostaglandin E2 (PGE2), or adenosine (Ado). All three of these cell populations produced higher levels of transcripts for IL-10, and growth and angiogenic factors. They also secreted reduced levels of inflammatory cytokines IL-1Beta, IL-6, and IL-12. All three macrophage phenotypes could partially rescue mice from lethal endotoxemia, and therefore we consider each to have immunoregulatory activity. This immunoregulatory activity occurred equally well in macrophages from stat6-deficient mice. The lack of STAT6 did not affect macrophages’ ability to reciprocally change cytokine production or to rescue mice from lethal endotoxemia. Furthermore, treatment of macrophages with IL-4 failed to induce similar phenotypic or transcriptional alterations. This work demonstrates that there are multiple ways to generate macrophages with immunoregulatory activity. These immunoregulatory macrophages are transcriptionally and functionally related, and quite distinct from macrophages treated with IL-4.

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Fleming BD, Chandrasekaran P, Dillon LA, Dalby E, Suresh R, Sarkar A, El-Sayed NM, Mosser DM