Asymptomatic carriage of Pneumocystis jirovecii and cytomegalovirus in lungs of immunocompetent patients

Colonization Density of the Upper Respiratory Tract as a Predictor of Pneumonia-Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, and Pneumocystis jirovecii

Background.

There is limited information on the association between colonization density of upper respiratory tract colonizers and pathogen-specific pneumonia. We assessed this association for Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, and Pneumocystis jirovecii.

Methods.

In 7 low- and middle-income countries, nasopharyngeal/oropharyngeal swabs from children with severe pneumonia and age-frequency matched community controls were tested using quantitative polymerase chain reaction (PCR). Differences in median colonization density were evaluated using the Wilcoxon rank-sum test. Density cutoffs were determined using receiver operating characteristic curves. Cases with a pathogen identified from lung aspirate culture or PCR, pleural fluid culture or PCR, blood culture, and immunofluorescence for P. jirovecii defined microbiologically confirmed cases for the given pathogens.

Results.

Higher densities of H. influenzae were observed in both microbiologically confirmed cases and chest radiograph (CXR)–positive cases compared to controls. Staphylococcus aureus and P. jirovecii had higher densities in CXR-positive cases vs controls. A 5.9 log₁₀ copies/mL density cutoff for H. influenzae yielded 86% sensitivity and 77% specificity for detecting microbiologically confirmed cases; however, densities overlapped between cases and controls and positive predictive values were poor (<3%). Informative density cutoffs were not found for S. aureus and M. catarrhalis, and a lack of confirmed case data limited the cutoff identification for P. jirovecii.

Conclusions.

There is evidence for an association between H. influenzae colonization density and H. influenzae–confirmed pneumonia in children; the association may be particularly informative in epidemiologic studies. Colonization densities of M. catarrhalis, S. aureus, and P. jirovecii are unlikely to be of diagnostic value in clinical settings.

The role of microRNAs in respiratory viral infection: friend or foe?

MicroRNAs (miRNAs) have emerged as a class of regulatory RNAs in host-pathogen interactions. Aberrant miRNA expression seems to play a central role in the pathology of several respiratory viruses, promoting development and progression of infection. miRNAs may thus serve as therapeutic and prognostic factors for respiratory viral infectious disease caused by a variety of agents. We present a comprehensive review of recent findings related to the role of miRNAs in different respiratory viral infections and discuss possible therapeutic opportunities aiming to attenuate the burden of viral infections. Our review supports the emerging concept that cellular and viral-encoded miRNAs might be broadly implicated in human respiratory viral infections, with either positive or negative effects on virus life cycle. Copyright © 2016 John Wiley & Sons, Ltd.

Anti-CD20 antibody therapy and susceptibility to Pneumocystis pneumonia

Anti-CD20 antibody therapy has been a useful medication for managing non-Hodgkin's lymphoma as well as autoimmune diseases characterized by autoantibody generation. CD20 is expressed during most developmental stages of B lymphocytes; thus, CD20 depletion leads to B-lymphocyte deficiency. As the drug has become more widely used, there has been an increase in the number of case reports of patients developing Pneumocystis pneumonia. The role of anti-CD20 in Pneumocystis jirovecii infection is under debate due to the fact that most patients receiving it are on a regimen of multiple immunosuppressive medications. To address the specific role of CD20 depletion in host immunity against Pneumocystis, we examined a murine anti-CD20 depleting antibody. We demonstrated that anti-CD20 alone is permissive for Pneumocystis infection and that anti-CD20 impairs components of type II immunity, such as production of interleukin-4 (IL-4), IL-5, and IL-13 by whole-lung cells, in response to Pneumocystis murina. We also demonstrated that CD4(+) T cells from mice treated with anti-CD20 during Pneumocystis infection are incapable of mounting a protective immune response when transferred into Rag1(-/-) mice. Thus, CD20(+) cells are critical for generating protective CD4(+) T-cell immune responses against this organism.