Functional and phenotypic analyses of porcine gut immune cells immunized by oral administration of F4ac<sup>+</sup>nonenterotoxigenic Escherichia coli strains

Abstract

The aim of this study was to determine the priming effect of experimentally inoculated non-ETEC strains (2407, 1466) on gastrointestinal mucosal lymphocytes. Five 4-week-old pigs per group were orally inoculated with either F4ac<sup>+</sup>(1466 or 2407) or F4– (1467) non-ETEC strains. The control pigs were given broth containing 1.2% sodium bicarbonate. At postinoculation Day 6 the pigs were killed, their gut lymphocytes were isolated, and their responsiveness was tested in vitro with F4 antigen, peptidoglycan monomer (PGM), pokeweed mitogen (PWM), phytohemagglutinin (PHA) and lipopolysaccharide (LPS). Additionally, the patterns of cluster of differentiation (CD) antigen expression on T and B cells in the single cell suspensions from JLP, IPP, and MLN were determined by flow cytometry using anti-swine CD-specific monoclonal antibodies. F4ac+ non-ETEC strain 2407 and, to a lesser extent 1466, activated lymphocytes from PP and MLN to respond better to common mitogens (PHA, PWM, LPS), purified fimbrial (F4ac) antigen or immunologic response modifier (PGM). An increase of CD2a<sup>+</sup>and CD8a<sup>+</sup>T cells in JLP, and species-specific SWC1<sup>+</sup>T cells in MLN (P < 0.05) was detected in 2407-treated pigs. In conclusion, inoculation with non-ETEC strain 2407 exhibited stimulatory properties to porcine gut immune cells, and thus, could be used in the vaccination programs to control the postweaning colibacillosis in pigs.