The Nature of Blocking Antibodies in Human Brucellosis

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Abstract
Summary: Agglutinating antibodies were found in γ-and β-globulins of the sera of patients with brucellosis. “Blocking” antibodies were found to appear later than the agglutinating antibodies. They were seen first in the γ-globulins but soon shifted to the β-globulins. They persisted after the agglutinating antibodies subsided. The “blocking” and prozone phenomena seem to be related. The prozone phenomenon does not represent the effect of antibody excess. A combination of equal volumes of “blocking” fractions resulted in a “blocking” titer corresponding approximately to the algebraic sum of the titers of the constituent fractions. Extraction with ether or incubation with Salmonella typhi failed to eliminate the “blocking” effect, but absorption with Brucella abortus did so. This suggests that the “blocking” substance in the β-globulins is a specific antibody.