Neil M. Ampel, MD reviewing Eddens T et al. Am J Respir Crit Care Med 2016 Oct 1. Shah A and Armstrong-James D. Am J Respir Crit Care Med 2016 Oct 1.

In a mouse model, Pneumocystis infection is associated with an allergic-type reaction in the lung; humans with severe asthma have elevated antibody levels to Pneumocystis antigen.

Pneumocystis is a fungus with a limited host range whose human species, P. jirovecii, is a cause of pneumonia in highly immunosuppressed patients, particularly those with HIV-1 infection and very low CD4+ lymphocyte counts. Considerable evidence indicates that humans are exposed to Pneumocystis at a very early age and then throughout life through airborne spread.

Hypothesizing that Pneumocystis could be a cause of asthma, investigators at the University of Pittsburgh exposed mice to P. murina, the murine species of the fungus. They noted an increase in expression of type II allergic cytokines, such as interleukin (IL)-4 and IL-5, in lung tissue. Depletion of CD4+ lymphocytes blocked these responses.

Subsequently, in human patients, the researchers found that levels of IgG antibodies to Pneumocystis were significantly higher in those with severe asthma than in healthy controls. Moreover, asthma symptom scores and spirometry scores were worse in those with elevated versus lower IgG antibody levels.

CITATION(S):

Eddens T et al. A novel CD4+ T cell–dependent murine model of Pneumocystis-driven asthma-like pathology. Am J Respir Crit Care Med 2016 Oct 1; 194:807. 

Shah A and Armstrong-James D.Opportunist turns allergen: Double life of Pneumocystis jirovecii in asthma. Am J Respir Crit Care Med 2016 Oct 1; 194:779. 

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