Successful mammalian pregnancy requires precise modulation of normal biological processes to ensure the survival of the feto-placental tissues while preserving the good health of the mother. The original research presented in this dissertation encompasses studies in both of these areas. The first part of this work addresses the long-standing question as to how feto-placental tissues, specifically invasive trophoblast, survive in the hostile environment of the maternal immune system. The Antczak laboratory previously developed an ectopic trophoblast transplant system to facilitate studies of the maternal immune response to invasive trophoblast in the horse. Single transplants of horse chorionic girdle into the vulvar mucosa of non-pregnant horse recipients were found to have lifespans and physiologic effects upon recipients similar to endometrial cups in a normal horse pregnancy. The current studies first expanded the trophoblast transplant system to include multiple rather than single transplants in individual recipients. The objective of this was to examine ectopic trophoblast survival in an immunologically primed as compared to naïve recipient. These serial transplants had lifespans similar to the single transplants, suggesting that the mechanisms protecting the trophoblast from immune destruction are initiated by the trophoblast itself. A series of transplants then was performed using Jenny donkeys as recipients. In each donkey recipient, primary transplants had lifespans of similar length to the horse-to-horse transplants, with second and subsequent transplants having progressively shorter lifespans. This pattern suggests that the horse-to-donkey transplants were subjected to a classic destructive memory response. The second body of work addresses the question as to how normal placentation disrupts maternal anatomy and physiology without causing adverse effects. This work was initiated with the discovery of interleukin 22 (IL22) mRNA in day 34 chorionic girdle using gene expression array analysis. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) then revealed that IL22 mRNA was rapidly upregulated in the chorionic girdle between days 32 and 35 of pregnancy. This represented the first identification of IL22 expression by a non-immune cell type. Interleukin 22 receptor RA1 (IL22RA1) mRNA was identified in pregnant endometrium, and in situ hybridization localized the mRNA to both the luminal and glandular epithelia. A monoclonal antibody was then generated against horse IL22. Mice were immunized with a fusion protein containing recombinant horse IL4 and IL22. Murine splenic cells were fused with SP 2/O myeloma cells to generate hybridoma cell lines. A monoclonal antibody to equine IL22 was identified. IL22 protein was then successfully detected in day 35 chorionic girdle. Knowing that IL22 in other biological systems has a role in preserving the integrity of mucosal surfaces and in epithelial cell proliferation, it was hypothesized that IL22 produced from the chorionic girdle binds receptor in the endometrium, repairing the damage caused by trophoblast invasion and initiating endometrial gland development.