Endocytosis and intracellular transport of meningococci-laden vacuoles mediate the passage of these organisms to the submucosa. To survive and multiply in the intravascular space, the meningococci must evade nonspecific and specific humoral and complement-mediated immune defenses. The observation that overt meningococcal infection is primarily a disease of infants and young children implies that immunity is acquired with increasing age. Immunity has been correlated with the presence of bactericidal antibody in serum, and the age-specific attack rate of meningococcal disease is reciprocally related to the presence of serum bactericidal activity against groups A, B, and C meningococci. Furthermore, among military recruits, the risk of meningococcal disease is highest in the absence of bactericidal activity against the prevalent pathogenic strain.
Natural immunity is initiated and expanded by meningococcal colonization of the nasopharynx.
Among susceptible children, colonization by avirulent meningococci and other Neisseria species results in an immune response that cross-reacts with virulent strains. Among adolescents and adults, bactericidal antibody to potentially pathogenic meningococci is reinforced and extended by sporadic nasopharyngeal carriage of groupable as well as avirulent nongroupable strains. The bactericidal activity of the complement system is important in preventing primary and recurrent invasive Neisseria infections. A striking correlation observed between complement-deficiency states and meningococcal infection underscores this fact. Approximately 50 percent of terminal complement-deficient individuals have at least one episode of meningococcal infection, and 20 to 25 percent have more than one episode.