Naturally Occurring Isoantibodies of the S Blood Group System in Cattle

Abstract

Several normal sera with naturally occurring antibodies reactive with cattle cells possessing the subtype factors U₁ and U₂ are described and two representative ones are more fully characterized by absorption analyses. It was shown that these sera detect a new specificity called U′, possessed by U₂ and not by U₁ cells. The results indicate strongly that the antigenic specificity called U₂ is qualitatively different from U₁. The new U′ reagents are useful in distinguishing cells containing U₁ and U₂ from those containing U₁ only. The naturally occurring antibodies exhibit a marked prozone, which is a distinctive feature that may have contributed to the failure to detect this specificity before now. A development of general interest is the illustration that differences in specificity between two reagents can not always be detected by their patterns of reactivity with even a large panel of known cells.