Delayed hypersensitivity in guinea pigs was produced by immunization. with a conjugate prepared by coupling diazotized arsanilic acid to polytyrosine. The resulting sensitivity could be demonstrated by skin test with conjugates prepared from a wide variety of tyrosine-containing proteins. Definite but smaller degrees of sensitivity could be induced with conjugates of proteins containing little or no tyrosine. The apparent absence of carrier-specificity is considered to be due to the narrowed range of immunologic response produced by immunization with polytyrosine-azobenzenearsonate.

Injections of the hapten N-acetyltyrosine-azobenzenearsonate was found to suppress completely the delayed reaction attributable to the tyrosine-azobenzenearsonate group. The same hapten was only slightly effective in suppressing reactions in guinea pigs immunized with guinea pig serum albumin-azobenzenearsonate, suggesting that a broader range of specificities is involved with such antigens.

Confirmation of such increased range of specificity attributable to antigenic determinants contributed by the carrier protein was obtained by desensitization studies with N-acetyltyrosine-azobenzenearsonate and guinea pig serum albumin-azobenzoate. While separately these materials produced only a slight decrease in skin reactivity to guinea pig serum albumin-azobenzenearsonate, the combination was found to give almost complete suppression.

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