VI . Recogni t ion o f I - E Molecules by I - J - bearing Suppressor Factors BY CARL WALTENBAUGH , L 1 ZHE SUN , AND HUAN - YAO

I-A and I-E gene products of the murine histocompatibility complex (H-2) are expressed by most B cells and to varying degrees by macrophages and T cells (1, 2). I-J products are intimately involved in immune regulation and are expressed by Ts cells and their factors (TsF), 1 as well as by some Th cells and macrophages (3, 4). A great deal is known about the function, serology, and biochemistry of the I-A and I-E molecules, due in part, to a large number of cells expressing these molecules in high density on their cell membranes. The paucity of I-J products has limited their characterization mainly to functional studies (3, 5). I-J-bearing TsF have been shown in several antigen systems, including KLH (6), Ars (7), GAT (8), and poly(GluS°Tyr ~°) (GT) (9). Moreover, in the KLH and Ars systems, I-J identity between the TsF donor and recipient is required for suppression (7, 10). No such restriction pattern has been shown for the GATor GT-TsF1 (first-order suppressor factor) (8, 1 1, 12). Sorensen and Pierce (13), however, reported an I-J-restricted GAT-TsF2 derived from responder mice. In the GT system, there is not a complete lack of allogenic restriction (1 1). Injection of H-2 b'd'k haplotype mice with GT produces GT-TsF1 that suppress PFC responses of H-2 a'd'k mice to the immunogenic form of GT, GTMBSA (GT coupled to methylated bovine serum albumin [MBSA]) (1 1, 12). H-2 b'q's haplotype mice are not suppressed by GT-TsF1 (reference 1 1 and this paper). The present study shows that I-E molecules must be expressed in order for the recipient strain to be suppressed by I-J-bearing GT-TsF 1. We show that GTTsF 1 is presented in the context of I-E molecules and that GT-TsF 1 presentation is blocked by anti-I-E, but not anti-I-A, antibodies. Our results indicate recognition between I-J and I-E molecules.