engleski

Levamisole synergizes a live attenuated Escherichia coli oral vaccine in recruiting and activating T cells in the gut mucosa of weaned pigs

We have reported recently that levamisole appears as a candidate mucosal adjuvant for experimental F4ac+ Escherichia coli oral vaccine in weaned pigs. In the present study we aimed 1) to test the hypothesis that levamisole exerts its adjuvant activity in the vaccinated pigs by priming T lymphocytes in the gut mucosa, e.g. ileal Peyer’ ; ; ; s patch (IPP), a primary lymphoid organ generating B lymphocytes, or intestinal lamina propria (LP) and 2) to evaluate the possibility that this form of its adjuvant activity may be required to abrogate the inefficacy of vaccination against porcine post-weaning colibacillosis (PWC) induced by the vaccine alone. Experimental group of weaned pigs was primed with levamisole in immunostimulatory dose of 2.5 mg/kg given daily, in 3 consecutive days, and controls received saline according to the same schedule. Both groups were orally vaccinated with the vaccinal E. coli strain on day 0 and challenged with the virulent E. coli strain 7 days later. All pigs were sacrificed on post-challenge day 6. The health status of the two groups upon virulent challenge was evaluated by clinical observations for signs of PWC. Expression of CD3 and CD6 antigens by IPP and LP T cells was tested using flow cytometry and immunohistochemistry. Our clinical data show that priming by levamisole significantly contributed to the effectiveness of a live attenuated oral vaccine against porcine PWC, as evidenced by a good health status of primed vaccinated vs un-primed vaccinated pigs upon virulent challenge. By the quantitative phenotypic analysis of isolated lymphocytes, CD3+ and CD6+ IPP but not LP T cells increased in experimental vs control pigs, implying that levamisole exerts its adjuvant activity in the IPP by augmenting both recruitment and activation of cells that participate in cell-mediated immunity. The results of the quantitative phenotypic analysis of isolated cells were confirmed by immunohistochemical in situ staining. Moreover, immunohistochemical analysis of the gut mucosa revealed the presence of numerous CD3+ and CD6+ cells within the villous epithelium ; however, T cells were rarely present in the LP in the primed-vaccinated pigs. Our overall data would suggest that levamisole appeared to stimulate the effector sites of the gut immune system in the vaccinated weaned pigs, serving as critical component in the establishment of protective immunity against enterotoxigenic E. coli-induced clinical disease.

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