Serological Characterization

Immunoassays employ a range of methods to detect and quantify antigens or antibodies and to study the composition of antigens. This chapter describes four useful immunoassays for serological characterization of antigens of Neisseria meningitidis : whole-cell enzyme-linked immunosorbent assay (ELISA); dot blot, colony blot, and immunoblot. Serological characterization of N. meningitidis antigens is valuable for epidemiological studies as well as for identifying immunologically important antigens in vaccine development (1 ,2 ). Typing of N. meningitidis is based on the immunological detection of specific epitopes on the outer-membrane proteins (OMP) and lipopolysaccharides (LPS) (3 ), and panels of monoclonal antibodies (MAbs) have been developed by several laboratories to refine the serological classification system (4 –8 ). Differences in capsular polysaccharides determine the meningococcal serogroup, whereas the serotypes and serosubtypes are based on antigenic differences of the PorB OMP and PorA OMP, respectively (3 ). The PorA protein contains two variable loops (VR1 and VR2), each of which determine a dis- tinct set of serosubtypes. Thus the serosubtypes of an isolate can include two independent designations (9 –11 ). Variation in the oligosaccharide moiety of the LPS determines the immunotype, and more than one epitope can be present in the same population of a single isolate (6 ,12 ). In the current typing scheme the classification is given as [serogroup]: [serotype]: [serosubtype]: [immunotype], e.g., B: 15:P1.7,16:L3,7,9.