Immune cell populations in the equine corpus luteum throughout the oestrous cycle and early pregnancy: an immunohistochemical and flow cytometric study

• Published in: Journal of reproduction & fertility Vol. 117; no. 2; pp. 281 - 290
• Main Authors: Lawler, D F, Hopkins, J, Watson, E D
• Format: Journal Article
• Language: English
• Published: England Society for Reproduction and Fertility 01-11-1999
• Subjects: Animals; B-Lymphocytes - immunology; CD4-Positive T-Lymphocytes - immunology; CD8-Positive T-Lymphocytes - immunology; Cell Count - drug effects; Corpus Luteum - drug effects; Corpus Luteum - immunology; Dinoprost - pharmacology; Eosinophils - immunology; Estrus - immunology; Female; Flow Cytometry; Histocompatibility Antigens Class II - metabolism; Horses - immunology; Immunohistochemistry; Macrophages - immunology; Pregnancy; Pregnancy, Animal - immunology; T-Lymphocyte Subsets - immunology
• ISSN: 1470-1626; 0022-4251; 1741-7899
• DOI: 10.1530/jrf.0.1170281

Recent evidence indicates that the cells of the immune system and their large network of secretory products, or cytokines,
play an active role in the ovary throughout the oestrous cycle. In the present study, immune cell populations (T and B lymphocytes,
macrophages, granulocytes and eosinophils) and expression of major histocompatibility complex (MHC) class II were investigated
in corpora lutea from mares in early (days 2–4), mid- (days 7–10) and late (days 12–14) dioestrus, the post-luteolytic phase
(days 16–17) and early pregnancy. The number of T lymphocytes within the corpus luteum increased in the late luteal phase.
CD4+ cells did not increase until day 16, whereas the number of CD8+ cells increased before functional luteolysis; an apparently
selective luteal infiltration of CD8+ cells was observed. MHC class II expression by non-steroidogenic cells was increased
in samples from days 16–17, as was the number of infiltrating macrophages. Flow cytometry revealed very low expression of
MHC class II by large luteal cells at all stages of the oestrous cycle. In early pregnancy, the number of CD4+ and CD8+ cells
and macrophages decreased, as did MHC class II expression, compared with mid-dioestrous samples. B cells were present in very
small numbers in all samples examined. Eosinophils were similarly sparsely distributed and numbers decreased further in pregnancy.
After exogenous PGF 2α administration, populations of CD4+ cells and non-specific esterase staining cells were significantly smaller than after
natural luteolysis, whereas eosinophil numbers were increased compared with samples from days 16–17. However, the number of
CD8+ and CD5+ cells and MHC class II expression were not significantly different from those observed after natural luteolysis.
These findings indicate that populations of immune cells in the equine corpus luteum vary during its lifespan. The selective
increase in CD8+ cells before functional luteolysis indicates that they have a physiological role in the regression of the
corpus luteum.