Comparative analysis of decidual and peripheral immune cells and immune-checkpoint molecules during pregnancy in wild-type and PACAP-deficient mice.

PROBLEM: PACAP is a neuropeptide having a major relevance in the nervous system and in several peripheral organs including those of the reproductive system. PACAP-deficient mice have several morphological, biochemical, behavioral defects, and show reduced fertility. Female reproductive functions such as fertility, mating behavior, maternal behaviors, and implantation alterations have been widely investigated, but no comparative immune analyses are available in pregnant wild-type (WT) and PACAP knockout (KO) mice.

METHODS OF STUDY: Therefore, we performed a detailed immunophenotyping of decidual and peripheral immune cells and investigated the expression of two immune-checkpoint molecules by immune cells together with immunohistochemistry detecting Galectin-9 in placental tissues. We investigated the percentage of numerous immune cell populations in the periphery and in the decidua of pregnant mice.

RESULTS: We demonstrated a significant increase in the frequency of decidual Gal-9+ Th cells obtained from PACAP KO mice compared to the decidua of WT mice. We could not determine statistical differences in TIM-3 and programmed cell death-1 expression by different immune cells in the decidua and in the periphery between WT and KO mice. In conclusion, we could not find any significant alteration either in the distribution or in the cytotoxicity of the investigated decidual immune cells which could elucidate any reproductive alterations in PACAP KO mice.

CONCLUSION: The only remarkable finding is the recruitment of Gal-9+ Th cells to the decidua promoting local immune homeostasis in PACAP KO mice, which nevertheless cannot explain the reduced fertility observed in these mice.