Ex vivo bactericidal activity against group C Neisseria meningitidis in seronegative subjects

Background: To determine the anti-meningococcal C immunological activity by adding functional tests (opsonophagocytosis) to the classical serology tec hniques. Subjects and Methods: 42 adult volunteers were screened using serological m ethods (determination of total and bactericidal antibodies). Seronegative s ubjects were tested by opsonophagocytosis, Results: 24 subjects (57%) showed serological evidence of previous contact with Neisseria meningitidis group C antigens: 19 subjects had both total an d bactericidal antibodies, two subjects had only total antibodies and three subjects had only bactericidal antibodies. Of the 18 seronegative subjects , five showed ex vivo activity in killing curves with or without polymorpho nuclear cells: two subjects exhibited only complement-mediated bactericidal activity, one subject only opsonophagocytosis, and two subjects exhibited both activities. Conclusion: The addition of functional tests to the classical serological d etermination increases the evidence of previous contact with N. meningitidi s antigens by 12%.