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Utilizing the coughing rat model of pertussis to improve vaccine efficacy

Hall, J;

Pertussis, also known as whooping cough, is a respiratory disease caused by the highly contagious, Gram-negative pathogen _Bordetella pertussis_ (_Bp_). Infection occurs through inhalation of aerosolized droplets containing _Bp_, which then colonizes ciliated epithelial cells of the respiratory tract. Here, _Bp_ expresses toxins and virulence factors that lead to leukocyte recruitment, paroxysmal cough, and impairment of host innate responses. Currently, in developed countries, acellular pertussis vaccines (aP; DTaP; Tdap) are used to prevent _Bp_ infection and whooping cough disease. However, we currently realize that the aP vaccine efficacy quickly wanes resulting in a reemergence of pertussis. Recent work performed by the CDC illustrates that current strains are genetically divergent from the strains originally used to formulate the aP, which may be partially responsible for the short-lived aP immunity. In an effort to evaluate pathogenesis of recent circulating strains and, in turn, improve vaccine efficacy, an animal model that recapitulates clinical manifestations of pertussis is necessary. First, we reintroduced the coughing rat model of pertussis by comparing two genetically divergent strains, Tohama 1 and recent isolate D420. Seven-week-old Sprague-Dawley rats were intranasally (IN) challenged with 108 viable CFUs. We measured the hallmark signs of pertussis disease such as neutrophilia, pulmonary inflammation, paroxysmal cough using whole body plethysmography (WBP), bacterial burden of the respiratory tract and characterized the serological response to known virulence factors. Overall, rats infected with D420 had an increase in bacterial burden in the lung and nasal cavity, an increase in coughs over the course of infection, and an increase in anti-_Bp_ IgM antibody titers compared to Tohama 1 challenged rats. The coughing rat model of pertussis can further be used as a preclinical tool to evaluate vaccine efficacy, as they are more feasible than baboons while still demonstrating classical manifestations of the disease. Next, we evaluated vaccine mediated immunity induced through IN and oral gavage (OG) vaccination of DTaP in the coughing rat model of pertussis, compared to intramuscular (IM)-whole cell pertussis (wP) and IM-aP immunized rats. Following vaccination, rats were similarly IN infected with 108 CFUs of _Bp_ strain D420, cough, bacterial burden, respiratory distress, and both systemic and mucosal serological responses were analyzed over the nine-day infection. Our data show that both IN and OG vaccination protected against _Bp_ colonization in the respiratory tract and _Bp_ induced cough, similarly to IM-wP and IM-aP vaccinated rats. IN-aP and OG-aP vaccination also resulted in the production of anti-_Bp_ IgG antibody titers at day 9 post-challenge; additionally, IN-aP vaccination induced mucosal anti-_Bp_ IgA antibodies in the nasal cavity. Histology confirmed that both IN-aP and OG-aP immunization protected against acute inflammation in the lung. Altogether, these data further support that mucosal vaccination can generate a protective immune response against pertussis. Furthermore, the coughing rat model of pertussis can be used to improve our understanding of _Bp_ pathogenesis and can be used to evaluate the “next generation” of pertussis vaccines.