Occurrence of Eosinophilic Granulocytes in the Decidua of Placentas With Perinatal Clinical Findings.

Introduction: Inflammatory and immunologic homeostasis in the basal plate of the placenta is essential for the fetal development and growth, since the fetus immunologically constitutes a semi-allograft. Bone marrow derived eosinophilic granulocytes are usually not found in the basal plate.

Materials and methods: We retrospectively analyzed the occurrence of eosinophilic granulocytes in the basal plate of singleton placentas and investigated clinical and pathologic-anatomic associations.

Results: In 5 singleton placentas (0.3% of all investigated cases from the archive) eosinophilic granulocytes were detectable. All these cases also displayed chronic deciduitis. Two cases had a clinical history of substitution therapy with methadone, in 2 instances the mothers had a history of atopic diseases, and 1 mother had a SARS-CoV-2-infection during pregnancy.

Conclusions: The infiltration of eosinophilic granulocytes in the decidua is a rare feature of placentas with perinatal clinical findings. Strikingly, all 5 affected cases also presented with chronic deciduitis. This may hint at a contribution of the eosinophilic infiltrate to a non-infectious pathologic inflammatory process with an increased risk for perinatal complications.