Origin of Different Cell Types in the Bovine Corpus Luteum as Characterized by Specific Monoclonal Antibodies 1

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Abstract
Specific monoclonal antibodies to granulosa and thecal cell surface antigens were produced and used to determine the contributions of theca and granulosa cells to the bovine corpus luteum (CL). Binding of each antibody was examined on collagenase-dispersed luteal cells from 18 cycling and 14 pregnant heifers by indirect immunofluorescence. The percent binding of the large luteal cells to granulosa antibody (GrAb) declined (P < 0.01) as the age of the CL advanced: 77 .+-. 6, 47.5 .+-. 3, and 30 .+-. 2 for Days 4-6, 10-12 and 16-18, respectively. Further reduction in binding of GrAb to large cells occurred between 50 and 100 days of pregnancy and no labeling was seen thereafter. Fourteen percent of the small luteal cells were bound by GrAb on Days 4-6 of the cycle, and none were labeled during subsequent stages. In contrast, when thecal antibody (TAb) was used, the proportions of large cells that were labeled increased (P < 0.01) between Days 4-6 (10 .+-. 1.3%) and 10-12 (46 .+-. 3%). The percentage of large cells bound by TAb then remained unchanged until midpregnancy, declined as pregnancy advanced, and disappeared during late gestation. A majority of small luteal cells were bound by TAb throughout the estrous cycle: 70 .+-. 4%, 69 .+-. 3% and 58 .+-. 6% at Days 4-6, 10-12, 16-18, respectively. Labeling of small cells by TAb occurred throughout pregnancy but declined (P < 0.05) as gestation advanced. The large cells of the early cyclic CL are derived from granulosa cells, while most of the small cells are of thecal origin. Small cells develop into large cells as the age of the CL increases. Granulosa-derived cells disappear during early pregnancy, while cells of thecal origin persist throughout pregnancy.