These T cell subsets secrete a distinct set of cytokines which influence cytolytic function and antibody isotype production (1C3)

These T cell subsets secrete a distinct set of cytokines which influence cytolytic function and antibody isotype production (1C3). (which bind to the major histocompatibility complex [MHC] class II molecule I-Au with increasing affinities) given intravenously activates T cells, rendering cells hyperresponsive in vitro for at least two days after injection. Concomitantly, T cells apoptose in the periphery, the degree of which correlates SR1001 with the affinity of the peptide for the MHC. In addition, a shift in the T helper phenotype of the surviving T cells occurs such that the low affinity peptide, Ac1-11, induces primarily a Th1 response, whereas the highest affinity peptide, Ac1-11[4Y], induces primarily a Th2 type response. These data show that both the nature and the presumed number of the peptideCMHC complexes formed during specific peptide therapy affect both the degree of peripheral programmed cell death as well as the outcome of the T helper subset response in vivo, leading to amelioration of disease. In an immune response, encounter with a foreign antigen may trigger an inflammatory cellCmediated or a primarily humoral response, each of which is characterized by a subset of CD4+ T helper cells, Th1 and Th2, respectively. These T cell subsets secrete a distinct set of cytokines which influence cytolytic function and antibody isotype production (1C3). Many organ-specific autoimmune diseases are thought to be initiated by Th1 responses, whereas protection, or recovery, is SR1001 thought to be mediated by SR1001 Th2 responses (4). Experimental autoimmune encephalomyelitis (EAE)1 is a Th1-mediated rodent model of multiple sclerosis that can be induced with the NH2-terminal peptide of myelin basic protein (MBP) Ac1-11, in PL/J or (PL/J SJL/J)F1 mice (5). EAE has been successfully treated with the immunodominant epitope of MBP, Ac1-11, as well as analogues in which position four is changed from the native lysine to an alanine (Ac1-11[4A]) or tyrosine (Ac1-11[4Y]) (6C9). Ac1-11[4A] and Ac1-11[4Y] bind to the MHC with 50 BCL2L and 1,500 times higher affinity than does Ac1-11, and both peptides stimulate most Ac1-11Cspecific T cells more efficiently than does Ac1-11 (10, 11). The affinities of these peptides for I-Au correlate with the half-lives of each of the peptides complexed to I-Au; Ac1-11/I-Au has an immeasurably short half-life, Ac1-11[4A] has a half-life of 10 min, and Ac1-11[4Y]/I-Au can be detected for as long as 10 h (6, 12). The efficacy of treatment of EAE with these three peptides correlates with the affinity of the peptides for I-Au. The mechanism of this treatment may be due to anergy, deletion, a switch in Th subset, or a combination of these phenomena (6C9, 13, 14). In other systems, soluble superantigen or peptide has been shown to activate T cells whose initial expansion is followed by massive deletion (15C17), whereas administration of soluble antigen has been shown to induce Th2 type responses (18C21). To explore more fully the mechanism of peptide therapy in SR1001 EAE, we developed transgenic mice expressing a TCR specific for Ac1-11 and restricted to I-Au, which was derived from an encephalitogenic T cell clone (22). In two lines of transgenic mice that were established, the CD4/ CD8 ratio is increased at least fivefold, and at least 60% of CD4+ T cells express the Ac1-11Cspecific -TCR. Injection of Ac1-11, Ac1-11[4A], or Ac1-11[4Y] into TCR transgenic mice SR1001 induces thymic deletion and peripheral activation and apoptosis, the degree of which correlates directly with the affinity of the peptide for I-Au. Materials and Methods Mice. DNA encoding a genomic construct was derived by amplifying cDNA from the 1934.4 hybridoma, which expresses V4 and V8.2 (10), and slotting the cDNAs into genomic shuttle vectors for the and chains as described (23). Transgenic mice were established in (B10.S SJL/J)F1 embryos by using standard techniques (24). Two founders were backcrossed to PL/J mice (purchased from (30). IL-4 was provided by Dr. Anne O’Garra (DNAX Research Institute). AntiCclass II antibody 10-3.6 was used to block peptide-MHC-TCR interactions in in vitro cultures (31). T Cell Stimulation In Vitro. To determine the in vitro proliferative response, 2.5 104 lymph node cells from PBS- or peptide-injected TCR transgenic mice were incubated with 3 105 irradiated (30 Gy) nontransgenic syngeneic splenocytes, or 3 105 splenocytes from naive or peptide-injected TCR transgenic mice were incubated in flat-bottom 96-well plates in 0.2 ml/well of RPMI 1640 medium (and AICD, activation-induced cell death; APL, altered peptide ligands; DP, double positive; EAE, experimental.