ANTIGENIC SPECIFICITY OF NEUTRALIZING ANTIBODY TO CHOLERA TOXIN

Selected rabbit antisera to cholera toxin antigens and convalescent cholera patient sera were analyzed using the permeability factor neutralization test and 2 sensitive in vitro serological assays specific for cholera toxin, cholera toxin A subunit and cholera toxin B subunit. Antisera to cholera toxin apparently contained toxin-neutralizing activity and antibodies specific for the A subunit and B subunit. Antisera to B subunit, devoid of significant anti-A subunit activity, neutralized the vascular permeability activity of cholera toxin. Antisera to A subunit contained neutralizing Ab and Ab to A and B subunits. Absorption with B subunit removed the toxin-neutralizing and anti-B subunit activities, while the anti-A activity was unaffected. Neutralizing Ab titers of rabbits immunized with B subunit were significantly higher than neutralizing Ab titers of sera from A subunit-immunized rabbits, despite the overall similarity in anti-B subunit titers as determined by passive hemagglutination [PHA] and radioimmunoassay [RIA] of sera from the 2 groups of rabbits. Anti-.alpha. chain sera neither neutralized cholera toxin nor possessed significant anti-toxin or anti-B subunit titers as determined by PH and RIA. The anti-.alpha. chain sera contained high levels of Ab specific for A subunit. The .alpha. chain may be part of the A subunit structure. The .gamma. chain was not antigenic. Sera from convalescent cholera patients possessed toxin-neutralizing Ab and PHA and RIA Ab against A and B subunits.