Histomorphometric characteristics of immune cells in small intestine of pigs perorally immunized with vaccine candidate F18ac nonenterotoxigenic E. coli strain.

Colidiarrhea and colienterotoxemia caused by F4(+) and/or F18(+) enterotoxigenic E. coli (ETEC) strains are the most prevalent infections of suckling and weaned pigs. Here we tested the immunogenicity and protective effectiveness of attenuated F18ac(+) non-ETEC vaccine candidate strain against challenge infection with F4ac(+) ETEC strain by quantitative phenotypic analysis of small intestinal leukocyte subsets in weaned pigs.We also evaluated levamisole as an immune response modifier (IRM) and its adjuvanticity when given in the combination with the experimental vaccine. The pigs were parenterally immunized with either levamisole (at days -2, -1 and 0) or with levamisole and perorally given F18ac(+) non-ETEC strain (at day 0), and challenged with F4ac(+) ETEC strain 7 days later.At day 13 the pigs were euthanatized and sampled for immunohistological/histomorphometrical analyses. Lymphoid CD3(+), CD45RA(+), CD45RC(+), CD21(+), IgA(+) and myeloid SWC3(+) cell subsets were identified in jejunal and ileal epithelium, lamina propria and Peyer's patches using the avidin-biotin complex method, and their numbers were determined by computer-assisted histomorphometry. Quantitative immunophenotypic analyses showed that levamisole treated pigs had highly increased numbers of jejunal CD3(+), CD45RC(+) and SWC3(+) cells (p<0.05) as compared to those recorded in nontreated control pigs.In the ileum of these pigs we have recorded that only CD21(+) cells were significantly increased (p<0.01). The pigs that were treated with levamisole adjuvanted experimental vaccine had significantly increased numbers of all tested cell subsets in both segments of the small intestine. It was concluded that levamisole adjuvanted F18ac(+) non-ETEC vaccine was a requirement for the elicitation of protective gut immunity in this model; nonspecific immunization with levamisole was less effective, but confirmed its potential as an IRM.

Histopathological features in the small intestine of pigs infected with F4ac+ non-enterotoxigenic or enterotoxigenic strains of Escherichia coli.

Four porcine strains of Escherichia coli were examined for their effects on the small intestine of 4-week-old weaned pigs infected orogastrically. The strains used experimentally were: strain 1467 (adhesin negative, non-toxigenic); strains 2407 and 1466 (adhesin positive, non-toxigenic), derived by genetical engineering from strain 1467 and containing a wild type plasmid and a recombinant plasmid, respectively, encoding the F4 antigen (adhesin); and strain M1823 (adhesin positive, toxigenic). In addition, 2-week-old pigs that died from natural colibacillosis associated with two strains ("Ihan 1 and 2"; adhesin positive, toxigenic) were examined. Strain M1823 and the Ihan strains produced moderate and marked lesions, respectively. Strain 1467 did not cause mucosal damage or an inflammatory response. Strains 1466 and 2407 caused a mild to moderate leucocyte (mononuclear and polymorphonuclear) infiltration in the jejunal (but not ileal) lamina propria. However, unlike strain 1466, strain 2407 did not cause damage to the small intestinal mucosa and should be further studied as a potential oral vaccine strain for post-weaning E. coli diarrhoea.

In vivo modulating effects of bacterial peptidoglycans on PHA-induced responses of porcine PBL and splenocytes.

The modulating effect of Brevibacterium divaricatum cell wall derivatives, i.e. peptidoglycan monomer (PGM) and peptidoglycan polymer (PGP) on phytohemagglutinin (PHA)-induced responses of peripheral blood lymphocytes (PBL) and spleen lymphocytes (SPL) from neonatal pigs farrowed to gilts or sows was tested. Both, PBL from progeny of sows and SPL from progeny of gilts responded significantly lower (P < 0.01) when PGM (14 mg/kg) was given by intraperitoneal (IP) route at Day 0 and Day 7 after farrowing as compared to the respective controls. When the same amount of PGM was given i.p. at Day 7 and Day 14, the responses of PBL and SPL from offspring of gilts were much higher (P < 0.01) than those of nontreated controls. The treatment with PGP (2.5 mg/kg) by the same route at Day 7 and Day 14 strongly stimulated (P < 0.01) the responses of PBL and SPL of pigs originating from litters of either gilts or sows, respectively.