The role of macrophages in homeostatic conditions and the immune system range from clearing debris to
recognizing and killing pathogens. While classically activated macrophages (CAMacs) are induced by T helper type 1
(Th1) cytokines and exhibit microbicidal properties, Th2 cytokines promote alternative activation of macrophages
(AAMacs). AAMacs contribute to the killing of helminth parasites and mediate additional host-protective processes such
as regulating inflammation and wound healing. Yet, other parasites susceptible to Th1 type responses can exploit
alternative activation of macrophages to diminish Th1 immune responses and prolong infection. In this review, we will
delineate the factors that mediate alternative activation (e.g. Th2 cytokines and chitin) and the resulting downstream
signaling events (e.g. STAT6 signaling). Next, the specific AAMac-derived factors (e.g. Arginase1) that contribute to
resistance or susceptibility to parasitic infections will be summarized. Finally, we will conclude with the discussion of
additional AAMac functions beyond immunity to parasites, including the regulation of inflammation, wound healing and
the regulation of metabolic disorders.
Keywords: Alternatively activated macrophage, helminth, metabolism, parasite, protozoan, Th2 inflammation.
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