Clearance of Pneumocystis murina infection is not dependent on MyD88

Targeting β-glucans, vital components of the Pneumocystis cell wall

β-glucan is the most abundant polysaccharide in the cell wall of Pneumocystis jirovecii, which has attracted extensive attention because of its unique immunobiological characteristics. β-glucan binds to various cell surface receptors, which produces an inflammatory response and accounts for its immune effects. A deeper comprehension of the processes by Pneumocystis β-glucan recognizes its receptors, activates related signaling pathways, and regulates immunity as required. Such understanding will provide a basis for developing new therapies against Pneumocystis. Herein, we briefly review the structural composition of β-glucans as a vital component of the Pneumocystis cell wall, the host immunity mediated by β-glucans after their recognition, and discuss opportunities for the development of new strategies to combat Pneumocystis.

Pulmonary Interleukin-17-Positive Lymphocytes Increase during Pneumocystis murina Infection but Are Not Required for Clearance of Pneumocystis

Pneumocystis remains an important pathogen of immunosuppressed patients, causing a potentially life-threatening pneumonia. Despite its medical importance, the immune responses required to control infection, including the role of interleukin-17 (IL-17), which is important in controlling other fungal infections, have not been clearly defined. Using flow cytometry and intracellular cytokine staining after stimulation with phorbol myristate acetate and ionomycin, we examined gamma interferon (IFN-γ), IL-4, IL-5, and IL-17 production by lung lymphocytes in immunocompetent C57BL/6 mice over time following infection with Pneumocystismurina We also examined the clearance of Pneumocystis infection in IL-17A-deficient mice. The production of both IFN-γ and IL-17 by pulmonary lymphocytes increased during infection, with maximum production at approximately days 35 to 40, coinciding with peak Pneumocystis levels in the lungs, while minimal changes were seen in IL-4- and IL-5-positive cells. The proportion of cells producing IFN-γ was consistently higher than for cells producing IL-17, with peak levels of ∼25 to 30% of CD3+ T cells for the former compared to ∼15% for the latter. Both CD4+ T cells and γδ T cells produced IL-17. Administration of anti-IFN-γ antibody led to a decrease in IFN-γ-positive cells, and an increase in IL-5-positive cells, but did not impact clearance of Pneumocystis infection. Despite the increases in IL-17 production during infection, IL-17A-deficient mice cleared Pneumocystis infection with kinetics similar to C57BL/6 mice. Thus, while IL-17 production in the lungs is increased during Pneumocystis infection in immunocompetent mice, IL-17A is not required for control of Pneumocystis infection.