Co-existence of classical and alternative activation programs in macrophages responding to Toxoplasma gondii

• We report the co-existence of M1 and M2 activation programs in Toxoplasma-elicited macrophages at the single cell level.
• The superimposition of the M1 and M2 activation is independent of parasite expression of the virulence factor ROP-16.
• The expression of M2-associated genes in Toxoplasma-activated macrophages does not require host cell expression of STAT6.

Pro-inflammatory M1 macrophages are critical for defense against intracellular pathogens while alternatively-activated M2 macrophages mediate tissue homeostasis and repair. Whether these distinct activation programs are mutually exclusive or can co-exist within the same cell is unclear. Here, we report the co-existence of these programs in Toxoplasma gondii-elicited inflammatory macrophages. This is independent of parasite expression of the virulence factor ROP16 and host cell expression of signal transducer and activator of transcription 6 (STAT6). Furthermore, this observation was recapitulated by IFN-γ and IL-4 treated bone marrow-derived macrophages in vitro. These results highlight the multi-functionality of macrophages as they respond to diverse microbial and endogenous stimuli.

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