Effect of cytokine interplay on macrophage polarization during chronic pulmonary infection with Cryptococcus neoformans

The immune response to Cryptococcus neoformans following pulmonary infection of C57BL/6 wild-type (WT) mice results in the development of persistent infection with characteristics of allergic bronchopulmonary mycosis (ABPM). To further clarify the role of Th1/Th2 polarizing cytokines in this model, we performed kinetic analysis of cytokine responses and compared cytokine profiles, pathologies, and macrophage (Mac) polarization status in C. neoformans-infected WT, interleukin-4-deficient (IL-4/), and gamma interferon-deficient (IFN-/) C57BL/6 mice. Results show that cytokine expression in the infected WT mice is not permanently Th2 biased but changes dynamically over time. Using multiple Mac activation markers, we further demonstrate that IL-4 and IFN- regulate the polarization state of Macs in this model. A higher IL-4/IFN- ratio leads to the development of alternatively activated Macs (aaMacs), whereas a higher IFN-/IL-4 ratio leads to the generation of classically activated Macs (caMacs). WT mice that coexpress IL-4 and IFN- during fungal infection concurrently display both types of Mac polarization markers. Concurrent stimulation of Macs with IFN- and IL-4 results in an upregulation of both sets of markers within the same cells, i.e., formation of an intermediate aaMac/caMac phenotype. These cells express both inducible nitric oxide synthase (impor-tant for clearance) and arginase (associated with chronic/progressive infection). Together, our data demon-strate that the interplay between Th1 and Th2 cytokines supports chronic infection, chronic inflammation, an