Pulmonary innate immune remodeling in Pneumocystis pneumonia with adaptive immunodeficiency

Pneumocystis pneumonia (PCP) is a severe fungal infection that predominantly affects individuals with compromised immune systems, specifically those with adaptive immunodeficiency. The mechanisms governing the remodeling of the innate immune system in the context of PCP, particularly in the presence of complete adaptive immunodeficiency, remain insufficiently elucidated. Here, using single-cell RNA sequencing (scRNA-seq) in a murine PCP model, we reveal how innate immune responses are remodeled in the absence of adaptive immunity, providing new mechanistic insights into PCP pathogenesis and a foundation for targeted therapy.

An experimental model of PCP was established using male CB-17 SCID mice with adaptive immunodeficiency. Mice were weight-matched into six pairs and randomly divided into a PCP group and a control (CON) group (n = 6 per group) using a computer-generated random sequence; PCP mice received an intranasal instillation of 1 × 10⁶ cysts in 100 μL sterile phosphate-buffered saline (PBS) under isoflurane anesthesia, whereas CON mice received an equal volume of sterile PBS alone. Lung tissues were collected for scRNA-seq to profile pulmonary innate immune cells. Bioinformatic analyses were employed to characterize several subsets of monocyte-derived macrophages, and immunofluorescence and quantitative reverse transcription PCR were used to validate these findings.

scRNA-seq indicated an expansion of Ccr2 ⁺ monocyte-derived Nckap5 ⁺ macrophages in PCP mice, which was associated with anti-inflammatory features and activation of pro-proliferative pathways. Inhibition of the MAPK pathway using Adezmapimod effectively reversed the induction of Nckap5 (4.463 ± 0.125 vs. 0.991 ± 0.052, P < 0.001) and the expression of anti-inflammatory cytokines, including Il10 (44.090 ± 1.246 vs. 4.131 ± 0.151, P < 0.001), Arg1 (2.455 ± 0.135 vs. 0.918 ± 0.018, P < 0.001) and Tgf β (1.147 ± 0.043 vs. 0.994 ± 0.031, P < 0.01).

This study advances understanding of PCP pathogenesis and identifies Nckap5 ⁺ macrophages as a potential therapeutic target for patients with compromised immune systems.