Abstract
Citrobacter freundii (C. freundii) is responsible for a number of significant opportunistic infections. The present research was aimed to estimate the immune response of rabbits immunized with whole cell sonicated antigen (WCSA), lipopolysaccharide (LPS), and DNA antigens (Ag) extracted from C. freundii. Twenty-four Albino rabbits of both sexes, with 2-3 kg body weight, were divided randomly into four groups (6 rabbits for each). Two types of tests were performed including ELISA and skin test (delayed type hypersensitivity, DTH)). The 1st group was immunized with WCSA (1000 μg/mL). The 2nd group was immunized with LPS Ag at the same dose. The 3rd group was immunized with DNA extracted Ag (0.083 μg/mL). The 4th group (negative control) was injected with 1 mL PBS (pH 7.2) subcutaneously. After 14 days, rabbits were given booster doses of same Ag. The immunized animals showed significant increase of IgG and IL-6 concentration (P<0.05) following 28, 32, 46, 50 and 60 days of immunization in comparison with the negative control group. Concerning DTH, it showed an increase in the means of induration and erythema, with significant differences (P˂0.05) exerted by the concentrated antigens in all immunized groups after 24 h and 48 h compared with diluted Ag and negative control group. In conclusion, WCSA and LPS Ag, in comparison to DNA Ag, were observed to promote stronger humoral (IgG) and cellular (DTH and IL-6) immune responses. DNA Ag, on the other hand, elicited a weaker humoral and cellular immune response than other Ag.
Highlights
Citrobacter spp. are potential zoonotic pathogens and opportunistic nosocomial bacteria that may lead to infection of the respiratory tract, septicemia and encephalitis in sheep [1, 2]
The results of IL-6 were elevated in all immunized groups that may be due to the production of inflammatory cytokines and the inhibition of microbicidal activities of macrophages, neutrophils, and neutralizing IL-6 in infected laboratory animals which may decrease mortality [16]
Dann et al (2008) [17] recorded an increase of colonic IL-6 expression after Citrobacter rodentium infection to investigate the role of IL-6 in mucosal host defense against C. rodentium, and the expression of the cytokine during the course of infection
Summary
Citrobacter spp. are potential zoonotic pathogens and opportunistic nosocomial bacteria that may lead to infection of the respiratory tract, septicemia and encephalitis in sheep [1, 2]. The antigenic structure of Citrobacter spp. is closely related to the antigens of many species such as Salmonella and E. coli, where the three antigenic species possess the flagellum H, somatic O, and capsular antigen K [3] They produce potent toxins (Shiga like toxin), lipopolysaccharide (LPS), and outer membrane protein [4,5,6], cause pediatric diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS) [7]. Infection with this bacterium leads to stimulating the systemic and local immune response as it leads to stimulating the production of CD4+ T cells, which play an important role in stimulating the humoral immune response and production of immunoglobulins from B cells including both IgM and IgG. T cells play a role in the production of cytokines, including: IFN γ, άTNF-, IL-12, IL-17, and IL-6, whose role is
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