Dietary conjugated linoleic acid modulates phenotype and effector functions of porcine CD8+ lymphocytes

In vivo vaccination and challenge studies have demonstrated that CD8(+) lymphocytes are essential for the development of cell-mediated protection against intracellular pathogens and neoplasic cells. Depletion of peripheral blood CD8(+) cells interferes with clearance of viruses and intracellular fungi, induction of delayed type hypersensitivity responses and antitumoral activity. In contrast to humans or mice, porcine peripheral CD8(+) lymphocytes are characterized by a heterogeneous expression pattern (i.e., CD8 alpha beta and CD8 alpha alpha) that facilitates the study of distinctive traits among minor CD8(+) cell subsets. A factorial (2 X 2) arrangement within a split-plot design, with 16 blocks of two littermate, pigs as the experimental units for immunization treatment (i.e., unvaccinated or vaccinated with a proteinase-digested Brachyspira hyodysenteriae bacterin) and pig within block as the experimental unit for dietary treatment (soybean oil or conjugated linoleic acid) were used to investigate the phenotypic and functional regulation of CD8(+) cells by dietary conjugated linoleic acid (CLA). Dietary CLA supplementation induced in vivo expansion of porcine CD8(+) cells involving T-cell receptor (TCR)-gamma delta CD8 alpha alpha T lymphocytes, CD3(-)CD16(+)CD8 alpha alpha (a porcine natural killer cell subset), TCR alpha beta CD8 alpha beta T lymphocytes and enhanced specific CD8(+)-mediated effector functions (e.g., granzyme activity). Expansion of peripheral blood TCR alpha beta CD8 alpha beta cells was positively correlated (r = 0.89, P < 0.01) with increased percentages of CD8 alpha beta (+) thymocytes. Functionally, CLA enhanced the cytotoxic potential of peripheral blood lymphocytes and proliferation of TCR gamma delta CD8 alpha alpha cells. Collectively, these results indicate that dietary CLA enhances cellular immunity by modulating phenotype and effector functions of CD8(+) cells involved in both adaptive and innate immunity.