engleski

De novo differentiation of intestinal villous M cells in weaned pigs immunized with levamisole-adjuvanted vaccine candidate F4ac+ or F18ac+ non-enterotoxigenic Escherichia coli strains

Active immunization against porcine postweaning colidiarrhea (CD) and/or colienterotoxemia (CE) caused by F4+ and/or F18+ enterotoxigenic Escherichia coli (ETEC) is still an unsolved problem. The intestinal microfold (M) cells play role in entry/invasion of intraluminal pathogens (such as ETEC strains), in antigen sampling, and in facilitating induction of immunity to gut infections. Just as ETEC strains can exploit M cells as the portal of entry for infections such as CD and/or CE, their high transcytotic ability make them an attractive target for mucosally delivered vaccines, adjuvants and therapeutics. The objective of our study was to evaluate the effects of levamisole-adjuvanted vaccine candidate F4ac+ and F18ac+non-ETEC strains on incidence/fequency of ileal M cells and up-regulation of antigen delivery by de novo formation of these cells in weaned pigs. Conventionally reared 4-weeks-old pigs were divided into three groups of which two were parenterally and orally immunized with levamisole (at Days -2, -1 and 0) in combination with either vaccine candidate non-ETEC strain (at Day 0), respectively. The third group of pigs received saline as a placebo. Challenge was performed (at Day 7) with F4ac+ ETEC strain, and the pigs were euthanatized (at Day 13) and sampled for immunohistology. Distribution patterns of cytokeratin 18 positive M cells revealed that they are rather solitary interspersed between enterocytes than as small clusters, and most of them were found to be located at the apex of villi in the ileum of 6-weeks-old pigs. Morphometric quantification of M cells in the ileal mucosa showed that levamisole-pretreated F18ac+non-ETEC-immunized and challenged pigs had significantly increased numbers (p<0.01) of ileal M cells as compared to the values obtained in the control nonprimed and challenged pigs. The proportion of these cells in this group of pigs was increased for 145%. In the levamisole-pretreated F4ac+ non-ETEC-immunized and challenged pigs only slightly increased (for 7%) proportion of M cells was recorded. However, this increase was not significantly different from the numerical values obtained for control pigs. Our finding that levamisole-adjuvanted F18ac+non-ETEC vaccine may affect de novo differentiation of antigen-sampling M cells by increasing their number in the ileum, indicated that the vaccine probably utilizes these cells as a target for entry/delivery to the nerby lymphocytes and induces protective immunity against CE. On the other hand, the failure of levamisole-adjuvanted F4ac+non-ETEC vaccine to produce a similar effect on M cells remains to be elucidated.

M stanice; adjuvantnost levamisola; E. coli vakcine; odbijena prasad

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