Allocation of Interferon Gamma mRNA Positive Cells in Caecum Hallmarks a Protective Trait Against Histomonosis

Abstract

Histomonosis is a parasitic disease of gallinaceous birds characterized by necrotic lesions in cacum and liver that usually turns fatal in turkeys while it is less severe in chickens. Vaccination using in vitro attenuated Histomonas meleagridis has been experimentally shown to confer protection against histomonosis. The protective mechanisms that underpin the vaccine-induced immune response are not resolved so far. Therefore, the actual study aimed to evaluate the location and quantitative distribution patterns of signature cytokines of type 1 [interferon gamma (IFN-γ)] or type 2 [interleukin (IL)-13] immune responses in vaccinated or infected hosts. An intergroup and interspecies difference in the spatial and temporal distribution patterns of cytokine mRNA positive cells was evident. Quantification of cells showed a significantly decreased percentage of IFN-γ mRNA positive cells at 4 days post-inoculation (DPI) in caeca of turkeys inoculated exclusively with the attenuated or the virulent inocula, compared to control birds. The decrement was followed by a surge of cells expressing mRNA for IFN-γ or IL-13, reaching a peak of increment at 10 DPI. By contrast, turkeys challenged following vaccination showed a slight increment of cecal IFN-γ mRNA positive cells at 4 DPI after which positive cell counts became comparable to control birds. The increase in infected birds was accompanied by an extensive distribution of positively stained cells up to the muscularis layer of cecal tissue whereas the vaccine group maintained an intact mucosal structure. In chickens, the level of changes of positive cells was generally lower compared to turkeys. However, control chickens were found with a higher percentage of IFN-γ mRNA positive cells in cecum compared to their turkey counterparts indicating a higher resistance to histomonosis, similar to the observation in immunized turkeys. In chickens, it could be shown that the changes of cytokine-positive cells were related to variations of mononuclear cells quantified by immunofluorescence. Furthermore, gene expression measured by reverse transcription quantitative real time PCR confirmed variations in organs between the different groups of both bird species. Overall, it can be concluded that a proportionally increased, yet controlled, allocation of IFN-γ mRNA positive cells in caeca hallmarks a protective trait against histomonosis.

Cytokine production and phenotype of Histomonas meleagridis-specific T cells in the chicken

“…Powell et al [9] found overall higher levels of IL-13 than IFN-γ mRNA in the liver of chickens while our studies did not show a significant increase in frequencies of IFN-γ or IL-13-producing liver cells from infected birds. In another study, which analyzed cytokine mRNA expression by ISH, spleens and livers of infected chickens showed no distinct elevated levels of IFN-γ or IL-13 mRNA in comparison to controls [12]. On the contrary, we found significant differences in IFN-γ-producing CD4 + and CD4 − CD8β − splenocytes comparing infected and control chickens.…”

“…Infected compared to vaccinated and challenged turkeys showed a delayed increase of IFN-γ mRNA + cells in the cecum coinciding with severe tissue damage. Hence, an early rise in IFN-γ mRNA + cells following vaccination could be protective by a rapid activation of effector memory T cells in turkeys [12].…”

Unravelling the Immunity of Poultry Against the Extracellular Protozoan Parasite Histomonas meleagridis Is a Cornerstone for Vaccine Development: A Review

“…Specific detection of the parasite in tissue sections was described to be accompanied with infiltrations of mononuclear and polymorphonuclear cells in the infected organs cecum and liver ( 58 , 59 ). In recent studies, quantitative analyses using specific markers against chicken macrophages/monocytes revealed that significantly higher amounts of this cell population were present in the blood ( 52 ) and the cecum ( 53 ) of infected chickens from the early stage of infection until the time period when most severe lesions were observed. The ability of macrophages to incorporate cells by phagocytosis indicates efforts to contain the parasite during the initial stage of infection in chickens.…”

“…until 10 days p.i. ( 53 ). In contrast, chickens that were vaccinated showed a similar range of the above mentioned cell population in the cecum compared to control birds even after challenge.…”

“…Recently, Kidane et al ( 53 ) investigated the abundance of Th1 and Th2 cytokines, IFN-γ, respectively IL-13 mRNA positive cells by in situ hybridization in vaccinated and/or infected chickens and turkeys. It was demonstrated that changes in the abundance of positive cells following infection or vaccination were less pronounced in chickens compared to turkeys.…”