Project description:β-glucans, which can activate innate immune responses, are a major component in the cell wall of the cyst form of Pneumocystis. In the current study we examined whether β-1,3 glucans are masked by surface proteins in Pneumocystis, and what role β-glucans play in Pneumocystis-associated inflammation. For 3 species, including P. jirovecii, which causes Pneumocystis pneumonia (PCP) in humans, P. carinii, and P. murina, β-1,3 glucans were masked in most organisms, as demonstrated by increased exposure following trypsin treatment. Using Q-PCR and microarray techniques, we demonstrated in a mouse model of PCP that treatment with caspofungin, an inhibitor of β-1,3 glucan synthesis, for 21 days, decreased expression of a broad panel of inflammatory markers, including IFN-γ, TNF-α, IL-1β, IL-6, and multiple chemokines/chemokine ligands. Thus, β-glucans in Pneumocystis cysts are largely masked, which likely decreases innate immune activation; this mechanism presumably was developed for interactions with immunocompetent hosts, in whom organism loads are substantially lower. In immunosuppressed hosts with a high organism burden, organism death and release of glucans appears to be an important contributor to deleterious host inflammatory responses.
Project description:Pneumocystis pneumonia is an opportunistic pneumonia that has been increasing in non-HIV patients in recent years. To obtain a better understanding of the cellular and molecular mechanisms involved in disease pathogenesis, we profile the transcriptomes of mouse lungs with Pneumocystis pneumonia and from uninfected control subjects using single-cell RNA sequencing, yielding multiple populations of myeloid cells, T cells and B cells. We uncover a PCP-associated TREM2+ subpopulation of interstitial macrophages, which expands in PCP, differentiates from Ly6C+ monocytes. We also define the subsets of effector CD4+ T cells that expand after the infection of Pneumocystis. Finally, intercellular crosstalk between interstitial macrophages and effector CD4+ T cells via multiple ligand and receptor interactions reveals several anti-pneumocystis pathways. Our work dissects unanticipated aspects of the cellular and molecular basis of Pneumocystis pneumonia at a single-cell level, and provides a conceptual framework for the discovery of rational therapeutic targets in Pneumocystis pneumonia.