Localization of ISG15 and TLR4 as potential immune modulators at the bovine uteroplacental interface during early...

Microanatomical changes and immune profiles at the bovine uteroplacental interface may contribute to early gestational failure. Previous studies noted that immunological status of the intrauterine environment shifts during and post-implantation. However, localization of specific immune markers at implantation sites throughout early pregnancy in cattle remains to be elucidated. To address this, we aimed to localize interferon-stimulated gene (ISG) 15 and Toll-like receptor (TLR) 4 at the uteroplacental interface during early gestation in beef cattle.

Ipsilateral uterine horn cross-sections from pregnant crossbred beef cows (n = 63) were collected on day (d) 20, d26, and d32 of gestation. Immunofluorescence analyses were performed to colocalize ISG15 with epithelial-cadherin (E-Cad), and TLR4 with E-Cad.

Interferon-stimulated gene 15 gene expression differed between days, while TLR4 did not. On d20 and d26, ISG15 localized to the stratum compactum stroma beneath the uterine luminal epithelium (LE) proximal to conceptus (embryo and associated placental membranes) attachment sites. On d20, TLR4 localized to uterine LE, glandular epithelium, and tunica media of blood vessels, and additionally conceptus trophoblast and extraembryonic endoderm on d26 and d32. As predicted, E-Cad localized in a scattered pattern in uterine and conceptus epithelia.

This study is one of the first to identify cell-type specific protein localization at bovine implantation sites on this series of gestational days and the first to localize ISG15 and TLR4 at the uteroplacental interface during multiple days of bovine early gestation. These data provide key insights into the intricacies of establishment and maintenance of early gestation in cattle.