Immune and non-immune precipitation of human sera with gonococci and meningococci

Sera from 218 healthy humans were examined by double-diffusion and counter-electrophoresis against the ultrasonically-disrupted N. gonorrhoeae strain 8551 and the group B N. meningitidis strain Ne 15. All the sera examined contained precipitins against one or more antigens common to the bacteria. On immunodiffusion analysis, the sera formed a precipitation line, called the curved line, close to the gonococcal antigen basin but not the meningococcal antigen basin. It was not formed after digestion of serum with pepsin. IgG prepared from human serum by DEAE cellulose chromatography or the F(ab')2 fragment of IgG did not produce the line. The serum component involved was separated from IgA, IgG, and IgM by gel filtration, and was eluted in fractions suggestive of a molecular weight close to that of albumin. Presumably, the curved line resulted from non-immune interaction of a constituent of the gonococcus with a human serum component of unknown identity.