Abstract
One of the most important mechanisms of probiotics is to enhance innate immunity and temper the inflammation induced by pathogens through Toll-like receptors regulated signaling pathway. Hyperlipidemia is known to compromise the immune response. The current experiment studied the immunomodulatory impact of a single-strain probiotic (Bacillus lichniformis) at a dose of 0.2 g/kg bwt daily on hyperlipidemic New Zealand male rabbits for 2 months. The rabbits were allocated into four equal groups. G1: Control normal diet group; G2: high fat diet group; G3: normal diet probiotic supplemented group and G4: high fat diet probiotic supplemented group. Serum values of total protein, albumin, globulin, albumin-globulin ratio (A/G), total gamma globulin (TgG), immunoglobulin M (IgM), immunoglobulin G (IgG), tumor necrosis factor α (TNFα), interleukin 6 (IL6), C-reactive protein (CRP), ferritin and the value of lipid peroxidation product; malondialdehyde (MDA)], in addition; the antioxidant enzymes activities [ glutathione peroxidase (Gpx) and superoxide dismutase (SOD)], were determined. The percentage of positive staining of Toll-like receptor 4 (TLR4) expression in small intestine using the immunohistochemistry technique was also evaluated. Our findings displayed that the probiotic was able to ameliorate the negative impact of hyperlipidemia on rabbit immune response, enhancing values of total protein, globulin, A/G ratio, (TgG), IgG, IgM and decreasing ferritin, IL6, TNFα and CRP, in addition to decreasing lipid peroxidation and improving the antioxidant parameters. Moreover, the immunohistochemistry of the small intestine displayed a marked reduction in the cytoplasmic expression of TLR4 in rabbits receiving probiotic with a high-fat diet (G4) compared to rabbits receiving a high-fat diet alone (G2). In conclusion, the findings of the current study highlighted the ameliorative effect of probiotics on the negative impact of hyperlipidemia on the immune system.

Key words: antioxidant; hyperlipidemia; immune response; rabbits; Bacillus lichniformis; intestine; immunohistochemistry.