Heteroclitic proliferative responses and changes in cytokine profile induced by altered peptides: implications for autoimmunity

Abstract

Productive engagement of T cell receptors (TCRs) by cognate ligand (major histocompatibility complex plus peptide) leads to proliferation, differentiation, and the elaboration of effector functions. Altered peptides generated by single amino acid substitutions in the antigenic peptide have diverse effects on the outcome of the T cell response. We have generated an altered peptide (Q144) from an autoantigenic peptide of myelin proteolipid protein 139-151 by a single amino acid substitution (from tryptophan to glutamine) in the primary TCR contact at position 144 that is capable of inducing CD4(+) T cell responses in H-2(s) mice. By using a Q144-specific T cell clone (Q1.1B6), we see a hierarchy in T cell proliferation and cytokine production with various position 144 substituted peptides and have identified a peptide (L144) that hyperstimulates this T cell clone. In contrast to Q144, L144 induces maximal proliferation at 7 logs lower antigen concentration, induces greater cell death at higher antigen dose, and induces the secretion of cytokines not detected following stimulation with the cognate ligand. This heteroclitic T cell response associated with changes in cytokine profile was observed with several other T cell clones of different specificities. The L144 peptide also induces costimulation independent proliferation and cytokine production from the Q1.1B6 T cell clone. We describe this as a superagonist response. Such responses may have a role in the initiation of autoimmunity by promoting a proinflammatory environment following ligation of a cross-reactive TCR on autoreactive T cells.

Figure 1

Hierarchy of the T cell proliferative response of the T cell clone Q1.1B6 to different altered peptide ligands: L144 > R144 > Q144 >W144 ≥ A144 ≫ L144/R147. T cell clones were activated with peptide antigens at the concentrations shown. Proliferation was assessed 48 h after activation.

Figure 2

TCR utilization by the Q1.1B6 clone. TCR V, D, and J segments and the predicted amino acid sequence of V(D)J regions of TCR-α and -β chains from T cell clone Q1.1B6 are shown. Assignments to V, D, and J segments are based on Arden et al. (40).

Figure 3

Dose response of Q1.1B6 with agonist peptide (Q144), superagonist peptide (L144), and anti-TCR antibodies (H57.597). (A) L144 and Q144 differ in proliferation and pattern of cytokines produced from the Q1.1B6 clone over a wide dose range, following activation by antigen and APCs. (B) The proliferation and cytokine production to anti-TCR antibody most closely resembles the response to the cognate Q144 ligand. All samples in each set were tested on the same plate. Background proliferation was <400 cpm. Background cytokine production was below the limit of detection of the assays. One representative experiment of at least four is shown.

Figure 4

Q1.1B6 is less costimulation dependent when activated with L144 compared with Q144. (A) Syngeneic splenic APCs were irradiated and an aliquot of cells was fixed with ECDI. Washed ECDI-fixed and unfixed-APCs were used to activate the Q1.1B6 T cell clone in a proliferation assay with 100 μg/ml of the L144 or Q144 peptides. The data are the mean of four experiments. (B) The Q1.1B6 was activated by syngeneic splenic APCs in the presence of human CTLA4-Ig or a control fusion protein at a concentration of 10–25 μg/ml, to determine percent inhibition. The data are the mean of two experiments.