Opportunistic fungal infection

Pneumocystis pneumonia (PCP) is a life-threatening opportunistic fungal infection with a high mortality rate in immunocompromised patients, ranging from 20 to 80%. However, current understanding of the variation in host immune response against Pneumocystis across different timepoints is limited.

In this study, we conducted a time-resolved single-cell RNA sequencing analysis of CD45⁺ cells sorted from lung tissues of mice infected with Pneumocystis. The dynamically changes of the number, transcriptome and interaction of multiply immune cell subsets in the process of Pneumocystis pneumonia were identified according to bioinformatic analysis. Then, the accumulation of Trem2^hi interstitial macrophages after Pneumocystis infection was verified by flow cytometry and immunofluorescence. We also investigate the role of Trem2 in resolving the Pneumocystis infection by depletion of Trem2 in mouse models.

Our results characterized the CD45⁺ cell composition of lung in mice infected with Pneumocystis from 0 to 5 weeks, which revealed a dramatic reconstitution of myeloid compartments and an emergence of PCP-associated macrophage (PAM) following Pneumocystis infection. PAM was marked by the high expression of Trem2. We also predicted that PAMs were differentiated from Ly6C⁺ monocytes and interacted with effector CD4⁺ T cell subsets via multiple ligand and receptor pairs. Furthermore, we determine the surface markers of PAMs and validated the presence and expansion of Trem2^hi interstitial macrophages in PCP by flow cytometry. PAMs secreted abundant pro-inflammation cytokines, including IL-6, TNF-α, GM-CSF, and IP-10. Moreover, PAMs inhibited the proliferation of T cells, and depletion of Trem2 in mouse lead to reduced fungal burden and decreased lung injury in PCP.

Our study delineated the dynamic transcriptional changes in immune cells and suggests a role for PAMs in PCP, providing a framework for further investigation into PCP's cellular and molecular basis, which could provide a resource for further discovery of novel therapeutic targets.

BACKGROUND Candida prosthetic valve endocarditis is a rare disease that is increasing in incidence with the rising rates of fungemia and increased use of intracardiac devices. Chronic antifungal prophylaxis is used after primary treatment to prevent recurrence, but the optimal duration of prophylaxis is currently unknown. This case report is of a woman with a history of mitral valve replacement due to Candida endocarditis presenting 2 years later with prosthetic valve and native aortic valve Candida albicans endocarditis. CASE REPORT A 32-year-old woman with a history of intravenous drug abuse, Staphylococcus and Candida endocarditis, and 2 mitral valve replacements 2 years ago on long-term oral fluconazole presented with fevers, weight loss, and dyspnea. She had stopped taking her oral antifungals prior to presentation. She was found to have vegetations on her prosthetic mitral valve and on her native aortic valve. She was started on ceftriaxone, vancomycin, and micafungin, and blood cultures grew C. albicans. She also developed a C. albicans metatarsal abscess and a splenic infarct. She underwent redo mitral valve replacement and aortic valve debridement successfully and was continued on intravenous micafungin for 8 weeks. CONCLUSIONS This case highlights the association between prosthetic valve endocarditis, intravenous drug abuse, and opportunistic fungal infections. Lifelong oral fluconazole can be considered for all patients with C. albicans prosthetic valve endocarditis, especially in the setting of the presence of other risk factors, such as intravenous drug abuse, as demonstrated in our case. Further studies are needed to determine differences in outcomes.

Opportunistic infections are common in transplant recipients, but gastrointestinal bleed is rarely reported to be due to opportunistic fungal infections, and hence could present as a diagnostic challenge. We report a case of disseminated histoplasmosis in a kidney transplant recipient whose initial presentation was acute lower gastrointestinal bleeding with no other symptoms. The colonoscopy showed scattered punchout circular colonic ulcers with biopsy revealing budding yeasts consistent with a diagnosis of histoplasmosis. The patient was successfully treated with a prolonged course of intravenous amphotericin B followed by oral itraconazole.