Caspase-1 deficiency impairs neutrophils recruitment and bacterial clearance in Streptococcus equi ssp. zooepidemicus infected mice.

Streptococcus equi ssp. zooepidemicus (S. zooepidemicus, SEZ) is a zoonotic bacterial pathogen that can cause various inflammation, including pneumonia. As the most abundant leukocytes in the circulation, neutrophils are the first wave of leukocytes to arrive in the lung upon infection. This study aims to evaluate the effect of caspase-1 on the host response to SEZ infection in a mouse model. Intranasal exposure to SEZ induced the expression of caspase-1 in wild-type mice lung, and increased the number of neutrophils in the alveolar cavity and alveolar wall. In addition, caspase-1 deficiency reduced the transcription levels of IL-1α, IL-1β, IL-6, and TNF-α in the lungs of infected mice, which was accompanied by decreased recruitment of pulmonary neutrophils. Moreover, knocking out caspase-1 decreased the bactericidal activity of neutrophils and promoted the pulmonary bacterial load. In line with this, the mortality of caspase-1-/- mice infected with SEZ was significantly increased compared with those of caspase-1+/+ mice. Collectively, recruiting neutrophils and enhancing the bactericidal ability of neutrophils are important means for caspase-1 to promote bacterial clearance.