Zone phenomena in the Kahn precipitation test for syphilis.

Abstract

The precipitation test for syphilis described by Kahn 1 is carried out with three tubes containing equal amounts of serum and diminishing amounts of antigen.

Three types of positive test are observed: In one, a strong precipitation occurs in the first tube, and progressively weaker reactions in the second and third; in the second type of positive test an equally strong precipitation occurs in all three tubes; in the third type, the precipitation is strongest in the third tube, and weaker in the second and first.

Zone phenomena in the Wassermann reaction were described in 1912 by Coca and L'Esperance 2 and more recently by Kahn and Johnson. 3 We have not observed zones similar to those described by these authors in which the strength of fixation increased as the antigen was diluted. We have, however, observed that very strongly positive sera when progressively diluted fixed with smaller amounts of antigen up to a certain maximum and in still higher dilution only with concentrated antigen.

The significance of such zone phenomena in precipitation and complement fixation reactions was carefully studied by Gay 4 and Dean 5 . Their findings have been confirmed by Parker 6 and by others who have studied the question. Dean pointed out that as a serum is diluted it is necessary to dilute the antigen correspondingly in order to obtain maximum fixation or precipitation and that consequently a serum which fixed or precipitated only with concentrated antigen, as a rule, had a higher antibody content than one which fixed with highly diluted antigen.

That the phenomena observed in the Kahn test follow this rule is shown by experiments such as that given in Table 11, in which increasing dilutions of serum are tested with increasing dilutions of antigen.