Cotton Rat Placenta Anatomy and Fc Receptor Expression and Their Roles in Maternal Antibody Transfer

Abstract

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral pneumonia in infants and young childrenworldwide. Currently no vaccine is available to prevent RSV infection, but virus-neutralizing monoclonal antibodies can begiven prophylactically, emphasizing the protective potential of antibodies. One concept of RSV vaccinology is mothers’ immunization to induce high antibody titers, leading to passive transfer of high levels of maternal antibody to the fetus throughthe placenta and to the neonate through colostrum. Cotton rats are an excellent small animal model for RSV infection andhave been used to test maternal immunization. To mechanistically understand antibody transfer in the cotton rat model, wecharacterized the cotton rat placenta and Fc receptor localization. Placentas from cotton rats at midgestation (approximately day 14) and at late gestation (approximately day 25) and neonatal (younger than 1 wk) gastrointestinal tracts were collected for light microscopy, immunohistochemistry, and transmission electron microscopy. The cotton rat placenta is hemotrichorial and has 5 distinct layers: decidua, junctional zone, labyrinth, chorionic plate, and yolk sac. Consistent with the transfer of maternal antibodies, the majority of the Fc receptors are present in the yolk sac endoderm and fetal capillary endothelium of the chorionic plate, involving 10% of the cells within the labyrinth. In addition, Fc receptors are present on duodenal and jejunal enterocytes in cotton rats, similar to humans, mice, and rats. These findings provide the structural basis for the pre and postnatal transfer of maternal antibodies described in cotton rats.

The trophoblast giant cells of cricetid rodents

“…The placenta of cricetid rodents is haemotrichorial as has been shown in a variety of species by transmission electron microscopy (Figure 2A) (Enders, 1965;Carpenter, 1972;King and Hastings, 1977;Favaron et al, 2011;Martinez et al, 2020). The layer facing the maternal blood sinuses is made up of cytotrophoblasts that only recently were recognized to be giant cells.…”

“…The interhaemal barrier has been described at the ultrastructural level in four subfamilies of cricetid rodent. In addition to our work, species examined are the golden hamster (Cricetinae) ( Carpenter, 1972 , 1975 ); the Eastern deer mouse ( Peromyscus maniculatus ) (Neotominae) ( King and Hastings, 1977 ); Norway lemming ( Lemmus lemmus ), collared lemming ( Dicrostonyx groenlandicus ), red-backed vole ( Clethrionomys rutilus ) and Taiga vole ( Microtus xanthognathus ) (Arvicolinae) ( King and Hastings, 1977 ); and hispid cotton rat ( Sigmodon hispidus ) ( Martinez et al, 2020 ). The overall picture is that gaps or lacunae occur in the outermost layer of trophoblast.…”

Immunopathology of RSV: An Updated Review

“…Interestingly, the BAL fluid of CRs is primarily comprised of eosinophils, and challenge with RSV does not increase these cell numbers [296]. Moreover, CRs can be used in maternal antibody studies, as RSV antibodies transfer from dames to pups via the placenta and breast milk [297][298][299][300]. Further, CX3CR1 is a receptor used by RSV for infection of CRs [301].…”