The human upper respiratory tract is colonised by a diverse commensal flora that is tolerated by the host without inducing an aberrant inflammatory response. N. meningitidis is an opportunistic pathogen that asymptomatically colonises the nasopharyngeal epithelium of older children and adults, but infrequently causes invasive disease. N. lactamica is a closely related commensal that colonises the nasopharyngeal epithelium of young children without causing disease. Both species can colonise for prolonged periods without being cleared. We have Investigated the development of mucosal immunity to N. lactamica and compared the response with N. meningitidis to further understand how each maintains a commensal relationship with the host.