High and low zone antibody tolerance to bacterial flagellin can be induced in adult strain W Wistar rats by multiple injections of a cyanogen bromide (CNBr) digest of flagellin at two widely spaced dose levels. Intermediate doses of the CNBr digest produce enhanced antibody titers to flagellin rather than antibody tolerance. Studies reported in this paper revealed that both high and low zone antibody tolerance to flagellin were accompanied by heightened levels of delayed-type hypersensitivity. Conversely, when enhancement of the antibody response occurred, suppression of delayed hypersensitivity was observed.

This inverse relationship between humoral and cell-mediated immunity was very striking in strain W Wistar rats but was not quite so clear-cut in another strain of Wistar rats (strain J). Strain J rats were resistant to the induction of antibody tolerance and gave higher immunological responses to flagellin than strain W animals. In addition, it was observed that, in contrast to adult tolerance, administration of the CNBr digest to neonatal rats induced complete tolerance at the level of both humoral and cell-mediated immunity.

These findings were discussed in the light of earlier studies with flagellin and provide further evidence for a previously described hypothesis.