prozone

In the case of agglutination and of precipitation, the phenomenon in which visible reaction does not occur in mixtures of specific antigen and antibody because of antibody excess. SYN: prezone.

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pro·zone 'prō-.zōn n the portion of the range of concentration of antibody-antigen mixtures in which one of them although present in excess does not produce its characteristic effect (as agglutination or precipitation)

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pro·zone (proґzōn) [pro- + zone] in an agglutination or precipitin reaction, the zone of higher antibody concentrations within which no reaction occurs. As the antibody concentration is lowered below the prozone, the reaction occurs. This phenomenon may be due simply to antibody excess (such as in the precipitin reaction), or it may be due to blocking antibody or to nonspecific inhibitors in serum. Called also prezone.