Association of SPOP Expression with the Immune Response to Salmonella Infection in Chickens

SIMPLE SUMMARY: Salmonella frequently causes human illness via the consumption of contaminated meat or eggs. At present, studies about how the host immune response against Salmonella is regulated are limited. Speckle-type POZ (poxvirus and zinc finger) protein (SPOP) is a specific adaptor of Cul3-based ubiquitin ligase, which catalyzes the ubiquitination and degrades the substrates. However, its role in the immune response is still unknown. Therefore, this study measured expression of SPOP and the proinflammatory cytokines interleukin-1β and interleukin-8 in chicken macrophage cells stimulated with a bacterial substitute and assessed their relationship using the quantitative polymerase chain reaction. We then validated the results in chickens infected with Salmonella. Notably, SPOP expression gradually decreased and then gradually increased in cells after challenging the bacterial substitute, indicating its potential involvement in the regulation of the immune response. Additionally, SPOP expression was negatively correlated with expression of interleukin 1β and interleukin-8 both in vivo and in vitro. More importantly, SPOP expression was related to immunoglobulin (Ig) A production and bacterial loads in chickens infected with Salmonella. These results indicate that SPOP could be a potential marker of the immune response in chickens. ABSTRACT: Salmonellosis is a zoonosis that is not only harmful to the health of poultry but also poses a threat to human health. Although many measures have been put in place to reduce morbidity, they have not provided satisfactory results. Therefore, it is necessary to clarify the immune mechanisms involved in improving the resistance of chickens against Salmonella. BTB (Broad-complex Tramtrack and Bric-a-brac) Speckle-type POZ (poxvirus and zinc finger) protein (SPOP) regulates protein expression by promoting substrate ubiquitination and degradation. The correlation between SPOP expression and the immune response has not been fully described. Therefore, the aim of this study was to clarify this relationship. In vitro, we stimulated chicken macrophage cells (HD11) with lipopolysaccharide, then analyzed the correlation between SPOP and IL1β or IL8 expression using quantitative real-time polymerase chain reaction (qRT-PCR). In vivo, we infected 7-days-old chickens with Salmonella Typhimurium, then analyzed the association between SPOP expression and the immune response, including IL1β and IL8 expression, IgA production, and bacterial loads. We found that SPOP may participate in the regulation of the immune response in macrophage cells. SPOP expression was negatively correlated with IL-1β and IL-8 expression both in vivo and in vitro. SPOP expression was also negatively related to bacterial loads and immunoglobulin (Ig) A production. These results indicate that SPOP may have important functions in the response to Salmonella infection.