Degeneracy of the immune response to sheep red cells.

We found that some mice immunized with sheep red blood cells (SRBC) made antibodies that agglutinated horse RBC (HRBC). Absorption studies indicated that the cross-reacting antibodies were highly avid. They appeared either late in a primary response, in secondary responses, or after multiple immunizations. Thus, the antibody response to SRBC loses specificity with time and is a further example of the degeneracy of the immune response. The similarities between the system we described and previously studied examples of degeneracy suggest that their bases may be the same; reactions of high affinity antibodies with related determinants. This interpretation was strengthened by the observation that antibodies made by mice which had recently escaped from tolerance were particularly deficient in cross-reacting subsets. The possible pitfalls of using hyperimmune serum in tests requiring high degrees of immunological specificity were emphasized.