Neutrophils Are Essential for Containment of Vibrio cholerae to the Intestine during the Proinflammatory Phase of Infection

Cholera is classically considered a noninflammatory diarrheal disease, in comparison to invasive enteric organisms, although there is a low-level proinflammatory response during early infection with Vibrio cholerae and a strong proinflammatory reaction to live attenuated vaccine strains. Using an adult mouse intestinal infection model, this study examines the contribution of neutrophils to host defense to infection. Nontoxigenic El Tor O1 V. cholerae infection is characterized by the upregulation of interleukin-6 (IL-6), IL-10, and macrophage inflammatory protein 2 alpha in the intestine, indicating an acute innate immune response. Depletion of neutrophils from mice with anti-Ly6G IA8 monoclonal antibody led to decreased survival of mice. The role of neutrophils in protection of the host is to limit the infection to the intestine and control bacterial spread to extraintestinal organs. In the absence of neutrophils, the infection spread to the spleen and led to increased systemic levels of IL-1 beta and tumor necrosis factor alpha, suggesting the decreased survival in neutropenic mice is due to systemic shock. Neutrophils were found not to contribute to either clearance of colonizing bacteria or to alter the local immune response. However, when genes for secreted accessory toxins were deleted, the colonizing bacteria were cleared from the intestine, and this clearance is dependent upon neutrophils. Thus, the requirement for accessory toxins in virulence is negated in neutropenic mice, which is consistent with a role of accessory toxins in the evasion of innate immune cells in the intestine. Overall, these data support that neutrophils impact disease progression and suggest that neutrophil effectiveness can be manipulated through the deletion of accessory toxins.