#43 Fungal colonization by Pneumocystis is highly frequent in the human placenta at birth.
Authors: Vargas Sergio L 
Published: June 2022

Background

Pneumocystis is well-known as a pathogen of the severily immunocompromised host. However, this fungus is also, a frequent colonizer of immunocompetent hosts inducing subclinical characteristic histologic features of Th2-type lung inflammation, and is associated to asthma. The pathology that Pneumocystis induces in the lung of non-severily immunocompromised hosts warrants exploring whether it colonizes and induces pathology in other organs. Physiologically immunosupressed pregnant women display increased nasal carriage of Pneumocystis and, of interest, Pneumocystis pneumonia were reported in neonates or still-born infants before the AIDS epidemic, and Pneumocystis-DNA has recently been identified in formalin fixed fetal organs. In addition, transplacental transmission has been documented in rabbit does that have an hemo-monochorial placenta similar to humans. Moreover, fungal species are a frequent cause of chorioamnionitis and fetal death in farm cattle. Motivated by these observations, we undertook a search for Pneumocystis in the placenta of full term pregnancies in Santiago, Chile.

Method

106 prospective volunteer mothers were approached during early labor at the San Jose Maternity Hospital in Santiago. After signed informed consent, the placenta of 91 full-term deliveries (37-42 weeks) was collected in a sterile bag and transported at 4°C to the research laboratory for immediate surgical removal of 0.5 cm of surface of each cotyledon at the maternal side in a laminar flow hood before sampling. The exposed cotyledons were then dissected to obtain approx 2 g (1.02-2.2 g) tissue from each cotyledon and samples from 3-4 cotyledons were pooled in two samples of approx. 7 (5.34-8.06) grams per each placenta. A 2 gram aliquot from each sample was homogeneized and DNA was extracted using QIAmp DNA extraction kit (QIAGEN) with an additional bead beating step. Pneumocystis was diagnosed by nested-PCR amplifying the mtLSUrRNA and the beta-tubulin loci of P. jirovecii. Pneumocystis was additionally examined by microscopy immunofluorescence in a subset of DNA-positive samples using immunofluorescence kit (Meridian).

Results

Pneumocystis jirovecii-DNA was detected by amplification of the two loci in 35 (38.5%) of 91 placentas; In 25 after analysis of the first sample tissue pool, and the other 10 after analysis of the second pooled sample. Characteristic Pneumocystis cyst forms were documented by IF microscopy in 4 P. jirovecii DNA positive samples.

Conclusion

Pneumocystis colonization of the placenta at full term is highly frequent and can be detected by DNA amplification and, more laboriously, by immunofluorescence microscopy. Placental colonization is focal, similar to what occurs in the lung during primary infection. Data suggests transplacental as a route of transmission of Pneumocystis in addition to the aerial route in humans. It also warrants exploring placental inflammation associated to Pneumocystis as documented in the colonized lung. Further studies are needed to determine the significance of placental colonization by Pneumocystis in the placental unit.