Luteal Microenvironment Directs Resident T Lymphocyte Function in Cows

The corpus luteum (CL) is a transient endocrine organ composed of a heterogeneous mixture of cells. Functional interactions exist between peripheral T cells and luteal cells in vitro; however, the precise role of resident T cells (RTC) remains unknown. The goals of the present study were to isolate RTC from within the CL and determine if alteration of luteal function resulted in changes in RTC phenotypes. Functional lymphocyte phenotypes identified in the bovine CL by using quantitative flow cytometric analysis were clearly different from those in the peripheral circulation. The proportion of CD8(+) RTC was greater than CD4(+) RTC. These proportions were opposite in peripheral blood. The proportion of gamma delta(+) lymphocytes was not different in the CL compared to that in peripheral blood nor was it altered during luteal regression. There was a significant increase in CD8 alpha alpha(+) and gamma delta(+)CD8 alpha alpha(+) RTC during luteal regression. The proportion of FOXP3(+) lymphocytes in the CL was greater than that isolated from peripheral blood, and this proportion of lymphocytes was dramatically reduced by induction of luteolysis. Within the CL of early pregnancy, there was an increase in the CD8 alpha beta(+) and gamma delta(+)CD8 alpha beta(+) populations compared to those in the CL of nonpregnant animals. Based on these data, we concluded that the functional state of the CL creates a microenvironment that regulates the recruitment of or differentiation into specific lymphocyte types. Understanding the interactions between steroidogenic cells and ovarian lymphocytes within CL will not only enhance understanding of reproductive function but may provide vital clues to lymphocyte regulation within tissues.