Porcine CD8(+) lymphocytes are critical for the development of cellular immune responses to bacterial (i.e. CD8alphaalpha(+)) and viral (i.e. CD8alphabeta(+) lymphocytes) pathogens. Vaccination and challenge modulate the kinetics of appearance of CD8(+) cells in peripheral blood. In addition to antigen-mediated modulation, nutritional modulation can also influence cell-mediated immunity. We had previously observed that diets supplemented with a mixture of conjugated linoleic acid (CLA) isomers expanded porcine CD8(+) peripheral blood mononuclear cells (PBMC). The present study aimed to investigate the influence of prior consumption of a nutraceutical, (i.e. dietary CLA) on phenotypes and effector functions of porcine PBMC following immunization with a bacterin or a modified-live viral vaccine. It was demonstrated that the effects of dietary CLA on immune cell phenotype (i.e. numbers of CD8alphabeta(+) cells) persisted after the compound was withdrawn from the diet (i.e. 67 days), whereas effector functions (i.e. antigen-stimulated proliferation and cytotoxicity) disappeared earlier (i.e. 25 days). Specifically, numbers of CD8alphabeta(+) PBMC in pigs that had been fed diets supplemented with CLA were greater than in pigs fed control (i.e. isoenergetic and unsupplemented) diets, regardless of the vaccination treatment. Furthermore, prior dietary CLA supplementation interacted with viral immunization (i.e. modified-live pseudorabies virus (PRV) vaccine) by enhancing both pseudorabies-specific proliferative responses of CD8alphabeta(+) PBMC and granzyme activities of PBMC.