The objective of this study was to evaluate the immune effects and the dynamics of intestinal integrity in broilers challenged with Salmonella Enteritidis (SE) and treated continuously with yeast cell wall (YCW). At 4 D posthatch (2 D postinfection [dpi] and poststart of treatment), challenged animals presented the highest intestinal permeability (P < 0.05). The number of circulating leukocytes was highest in the non–SE-challenged groups (P < 0.005). Despite this, challenged broilers consistently presented higher numbers of various cell subtypes, especially at 14 D (Kul01−MHC class II+, Kul01+MHC class II+, Kul01+MHC class II− cells, and the series of CD4+ and CD8+ cells). Treatment was effective in evading the reduction of total leukocytes and in preventing some of the immune subset fluctuations provoked by the challenge, such as for Kul01−MHC II+ and CD8+ cells. The number of phagocytic cells was increased by challenge at 6 dpi, while the YCW decreased this effect (P < 0.05). The test group presented the highest number of anti–salmonella IgA–reactive animals, as well as the highest level of IgA (P = 0.053). The challenge induced marked inflammatory responses in the intestine and liver (assessed by lymphocyte counts, section area, goblet cell counts, and tissue architecture). Treatment was effective in improving inflammatory tissue signs such as lymphocyte infiltration in the cecum (P < 0.05), but not in the liver. The challenge with SE induced changes in all evaluated systems; however, intestinal integrity and some immune parameters were improved with the presence of the YCW.
