Delayed hypersensitivity to hapten-protein conjugates. I. The effect of carrier protein and site of attachment to hapten.

Further data have been presented showing that the specificity of the delayed hypersensitivity reaction in the guinea pig to hapten-protein conjugates involves to a considerable degree a contribution by the protein carrier. The carrier contribution is such that sensitization to guinea pig albumin-m-azobenzenesulfonate, for example, does not result in cross-reaction with conjugates of the same hapten with unrelated proteins such as ovalbumin or human gamma globulin, nor were cross-reactions observed between conjugates prepared with the same hapten, coupled to the same protein, but by two different chemical routes, such that the point of attachment of the hapten to the protein differed. It thus appears that in this system both hapten and carrier protein are necessary, but that neither alone is in general sufficient to stimulate the delayed sensitive cell. Desensitization experiments with cross-reacting hapten-protein conjugates have suggested the presence of a multiplicity of antigenic determinants participating in the elicitation of the delayed lesion, and of a concomitant development of a heterogeneity of specificities in the population of delayed sensitive cells in the sensitized animal. The data are discussed in terms of the apparent requirement of the delayed sensitivity mechanism for a larger functional antigenic determinant than that required for interaction with circulating antibodies. Some possible explanations for this difference, and some of its consequences, are discussed.