Macrophage M1/M2 Polarization Dynamically Adapts to Changes in Cytokine Microenvironments in Cryptococcus neoformans Infection

ABSTRACT The outcome of cryptococcal pneumonia correlates with local macrophage polarization status, as M1 andM2 polar-izationmarks protective and nonprotective responses, respectively. Overall, pulmonary macrophage polarization status changes over time during a cryptococcal infection. This could have been caused by repolarization of individual macrophages or by a re-placement of M2-polarized cells by newM1-polarized cells. To explore the ability of macrophages to change between polariza-tion states, we conducted a series of experiments using in vitromacrophages. Coculture of macrophages with Cryptococcus neo-formans resulted in development of a weakM1-like phenotype, with modestly increased inducible nitric oxide synthase (iNOS) but lacking interleukin 6 (IL-6) induction. The C. neoformans-induced M1-like polarization state was plastic, as macrophages stimulated first with C. neoformans and then with gamma interferon (IFN-) or IL-4 expressed mRNA polarization patterns similar to those stimulated with cytokines alone. To further evaluate macrophage polarization plasticity, cytokine stimulatory conditions were established which fully polarized macrophages. IFN- and IL-4 stimulation differentially induced complete M1 andM2 polarization, defined by differential expression of marker mRNA panels, surface marker expression, and tumor necrosis factor alpha (TNF-) protein production. Switching IFN-- to IL-4-stimulating conditions, and vice versa, resulted in uniform changes in profiles of polarizationmarker genes consistent with the most recent cytokine environment. Furthermore, the ability of sequentially stimulated macrophages to inhibit C. neoformans reflected the most recent polarizing condition, independent of previous polarization. Collectively, these data indicate that M1/M2macrophage polarization phenotypes are highly plastic t