Naso-oropharyngeal Brucella Infections and Mucosal Immune Protection

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ABSTRACT Human brucellosis ranks third among 8 neglected zoonotic diseases, and is contracted as a result of ingesting unpasteurized dairy products. The Gram-negative Brucella is highly infectious, and is believed that less than 2000 CFUs are needed for pulmonary infection. Infection primarily occurs following a mucosal exposure causing a systemic disease manifested by its flu-like symptoms. Despite aggressive antibiotic treatment, it can still persist in a recurring sequelae evident as undulant fever and arthritis. Brucellae survival within the host is linked to its ability to evade intracellular recognition, thus, allowing them to sequester in various tissues. Although human disease is mostly acquired via a mucosal exposure, few studies have examined mucosal immunization for brucellosis. In part, this is attributed to the inefficiency of oral gavage methods requiring an enormous amount of brucellae to induce an infection. Bearing this, we have devised an oral infection method, termed ad bibitum, that retains the infection to the oral mucosa and draining head and neck lymph nodes (HNLNs) recapitulating natural human infections. Hence, we hypothesize that mucosal immunization of the naso-oropharyngeal tissues will derive the required correlates of protective immunity using our novel attenuated Brucella melitensis (BM) strain. Such approaches will allow for the comparison of which immune cell types are needed for protection and to reverse wild-type (wt) BM infection from mounting regulatory responses in order to evade detection. Subsequent to immunization, the attenuated BM mutant stimulates increases in IFN-g- and TNF-a-producing CD4+ and CD8+ T cells, which can effectively eliminate the brucellae. To further these studies, three Specific Aims are proposed. Studies in Specific Aim 1 will establish a mucosal naso-oropharyngeal vaccination regimen that confers protection against mucosal challenge with virulent Brucella. Studies in Specific Aim 2 will determine which T cell subsets are responsible for protection in the mucosal and systemic compartments. Studies in Specific Aim 3 will establish the role for mucosal memory CD8+ T cells in augmenting protection against virulent Brucella challenge more effectively than CD4+ T cells. These studies will further our understanding of how to induce immunity in the naso- oropharyngeal mucosa, and will aid in devising strategies to circumvent BM' evasion methods. This work will ultimately define what constitutes protection and which T cells are needed to guard against wt BM challenges.