Immunological and biochemical studies of meningococcal C polysaccharides isolated by diethylaminoethyl chromatography

Detection of Neisseria meningitidis group A, Haemophilus influenzae type b, and Streptococcus pneumoniae antigens in cerebrospinal fluid specimens by antigen capture enzyme-linked immunosorbent assays

Antigen capture enzyme-linked immunosorbent assay was compared to coagglutination and counterimmunoelectrophoresis for the detection of meningococcal, Haemophilus, and pneumococcal antigens. Enzyme-linked immunosorbent assay detected 1 ng of purified meningococcal and Haemophilus polysaccharides per ml and 5 ng of pneumococcal polysaccharide per ml; coagglutination detected 20, 25, and 30 ng/ml, respectively, of these polysaccharides; and counterimmunoelectrophoresis detected 10, 50, and 60 ng/ml. Double-antibody sandwich-antiglobulin enzyme-linked immunosorbent assays, which employed antibodies produced in two animal species, differentiated 100% of the cerebrospinal fluid (CSF) specimens from meningococcal meningitis patients and 95% of the CSFs from Haemophilus patients from heterologous control CSFs. Double-antibody sandwich procedures, which use the same antiserum preparation for coating the wells of microtiter plates and for alkaline phosphatase-conjugated immunoglobulin, differentiated meningococcal CSFs from control specimens but were unable to effectively differentiate the Haemophilus or pneumococcal specimens from control CSFs. Coagglutination detected specific antigen in 92% of the meningococcal CSFs, 80% of the Haemophilus CSFs, and 92% of the pneumococcal specimens. The comparable percentages for counterimmunoelectrophoresis were 76, 95, and 71%.

Opsonization of encapsulated Cryptococcus neoformans by specific anticapsular antibody

Antisera prepared in rabbits against either whole encapsulated cells of Cryptococcus neoformans or purified cryptococcal polysaccharide were opsonic for the encapsulated yeast. The opsonic activity was removed by absorption with whole cryptococci and was inhibited by free polysaccharide. As little as 0.13 microgram of cryptococcal polysaccharide produced a 50% inhibition of opsonization. Various degrees of neutralization by polysaccharides from the four cryptococcal serotypes suggested that the opsonins were type specific. Fractionation of antiserum on Bio-Gel A-5m (Bio-Rad Laboratories) and diethylaminoethyl cellulose showed that the opsonins were antibodies of the immunoglobulin G class. These opsonizing antibodies did not require heat-labile serum components for optimal phagocytosis of the yeast. Inhibition studies using 2-deoxy-D-glucose demonstrated that ingestion of encapsulated cryptococci opsonized with anticapsular antibody was a 2-deoxy-D-glucose-inhibitable process. This result differed from similar studies with non-encapsulated cryptococci which showed that ingestion of non-encapsulated cryptococci opsonized with normal serum was not inhibited by 2-deoxy-D-glucose.

Homogeneity of protein serotype antigens in Neisseria meningitidis group A

Serotype antigens (STA), which have been shown to be constituents of outer-membrane protein, were extracted from group A meningococci with 0.2 M LiCl and pelleted by centrifugation at 150,000 X g. The STAs from 100 group A strains, which had been isolated from cases and carriers in various geographical locations, were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Every STA produced three major protein bands with molecular weights of approximately 35,000, 39,000, and 45,000, respectively. This SDS-PAGE pattern is clearly distinct from that produced by the serotype of group B and C meningococci most commonly isolated from cases (group B type 2 and group C type 2). The group A STAs were also indistinguishable by immunodiffusion. However, differences in bactericidal reactions were demonstrated, suggesting that there are other antigens that play a role in antibody response.