Current understanding of Pneumocystis immunology

Abstract

Pneumocystis jirovecii is the opportunistic fungal organism that causes Pneumocystis pneumonia (PCP) in humans. Similar to other opportunistic pathogens, Pneumocystis causes disease in individuals who are immunocompromised, particularly those infected with HIV. PCP remains the most common opportunistic infection in patients with AIDS. Incidence has decreased greatly with the advent of HAART. However, an increase in the non-HIV immunocompromised population, noncompliance with current treatments, emergence of drug-resistant strains and rise in HIV(+) cases in developing countries makes Pneumocystis a pathogen of continued interest and a public health threat. A great deal of research interest has addressed therapeutic interventions to boost waning immunity in the host to prevent or treat PCP. This article focuses on research conducted during the previous 5 years regarding the host immune response to Pneumocystis, including innate, cell-mediated and humoral immunity, and associated immunotherapies tested against PCP.

Figure 1. Gomori’s methenamine-silver stain of Pneumocystis cysts in lung tissue

Cysts contain one to eight sporozoites within. Arrow shows cyst containing two sporozoites.

Figure 2. Chest radiograph of Pneumocystis pneumonia

A 23-year-old male with 3-week history of fever, cough and shortness of breath. Chest x-ray shows bilateral ground glass infiltrates. Bronchoscopy revealed Pneumocystis jirovecii. Patient was found to be HIV⁺ on hospital admission.