title: T lymphocyte proliferative capacity and CD4+/CD8+ ratio in primiparous and pluriparous lactating cows.
abstract: T cells play a central role in specific immunity; their populations and phenotypes could be affected by number of lactation in high-yielding dairy cows. To investigate the effects of parity on the dynamics of T lymphocytes, lymphoproliferative capacity, T lymphocyte subsets and CD4+/CD8+ ratio were studied in peripheral blood of primiparous and pluriparous dairy cows during mid-late lactation. A non-radioactive technique was also adapted for a detailed lymphoproliferation assay. Compared with the primiparous cows, the pluriparous cows exhibited weaker lymphoproliferative activity, larger number of CD4+ cells and substantially greater CD4+/CD8+ ratio in their blood circulation. The increase of the CD4+/CD8+ ratio in the blood of pluriparous dairy cows was mainly due to the rise in the proportion of CD4+ cells and decline in the proportion of CD8+ cells. This increase of the CD4+/CD8+ ratio coincided with the decrease of mitogen-induced proliferation capacity of T lymphocytes. Of four lymphocyte divisions or generations during the lymphoproliferation assay, maximal lymphocyte proliferation capacity at generation 3 in primiparous cows was markedly greater than in pluriparous cows. With an alternatively safer, faster and more reproducible assay (compared with 3H-thymidine scintillation assay) we showed for the first time that aging in dairy cows leads to a decreased mitogen-induced lymphoproliferation and disturbed proportion between CD4+ and CD8+ T cells. This CD4+-CD8+ imbalance together with diminished lymphoproliferative capacity may lead to a weaker T cytotoxic-mediated immunity and increased susceptibility to infectious diseases in pluriparous lactating cows. Our study also emphasizes further application of the methods in farm animals.
authors.affiliation: Ferdowsi University of Mashhad, Faculty of Veterinary Medicine, Department of Pathobiology, Section Immunology, P.O. Box 917751793, Mashhad, Iran.
authors.forename: Jalil
authors.initials: J
authors.lastname: Mehrzad
authors.forename: Xin
authors.initials: X
authors.lastname: Zhao
mesh_terms: D000818:Animals; D016516:CD4-CD8 Ratio; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology; D003601:Cytotoxicity Tests, Immunologic / Q000662:veterinary; D004198:Disease Susceptibility; D005260:Female; D007109:Immunity; D007239:Infections / Q000453:epidemiology / Q000662:veterinary; D007774:Lactation / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology*; D010298:Parity / Q000276:immunology; D011247:Pregnancy; D013601:T-Lymphocytes / Q000276:immunology*