984 THE LACK OF CROSS REACTIVITY WITH ESCHERICHIA COLI K100 (K100) IN THE HUMAN ANTICAPSULAR RESPONSE TO HAEMOPHILUS INFLUENZAE TYPE B (HIB)

Abstract

The capsular polysaccharides (CP) of HIB and K100 are polymers of ribosyl ribitol phosphate differing only in one linkage and having common (as well as unique) antigenic determinants. Animal and human antibodies (Ab) to K100 are strongly cross reactive (XR) with HIB, and exposure to K100 is thought to contribute to natural immunity of humans to HIB. The converse relation heretofore has been little examined. Of 21 human adults responding to vaccination with HIB CP only 3 made K100-XR antibody; likewise only 2 of 11 responding children made XR Ab. In only 1 of 10 children convalescent from HIB systemic infection and 0 of 2 children asymptomatically colonized did the response include K100-XR Ab. K100 reactivity was observed in the naturally occurring anti-HIB Ab of only 3 of 21 adults but, in contrast, in 14 of 29 children. Thus K100-XR Ab in humans rarely results from exposure to HIB or its CP and must arise from K100 itself or other antigenically related stimuli. Further, humans appear likely to respond to the common determinants when exposed to K100 (although not when exposed to HIB). K100 immunogens may thus have a protective potential against HIB not manifest in corresponding immunogens prepared from HIB itself.