Hermann von Grafenstein

Inhibition of diabetes by an insulin-reactive CD4 T-cell clone in the nonobese diabetic mouse.

A cloned Thl cell line was isolated from pancreatic lymph nodes of NOD mice that carries a T-cell receptor encoding Vβ14 and proliferates in response to NOD islets, islet supernatant, and crystalline bovine and rat insulin, specifically to a B-chain peptide bound to IAg7. The response to islet supernatant was reduced by 75% by anti-insulin antibody treatment. The insulin-reactive clone reduced insulitis and totally blocked the development of spontaneous diabetes in NOD mice (n = 8) as well as the adoptive transfer of diabetes into irradiated NOD mice following the injection of splenocytes from diabetic mice (n = 13). Trafficking of the adoptively transferred cells was assessed by labeling the clone or diabetic splenocytes with a fluorescent marker (Dil). The labeled clone was detected in the islet periphery, whereas labeled splenocytes alone invaded the islets by 3 days. In contrast, the protective clone dramatically delayed and reduced the number of labeled diabetic splenocytes infiltrating the islet, although their appearance in the spleen was unaffected. In vitro, the clone as well as supernatant derived from the clone blocked the proliferation of diabetic NOD splenocytes to islets. This inhibitory effect was diminished by anti–transforming growth factor-β. In conclusion, an insulin-specific Thl cell was isolated from NOD mice that traffics to the islet and prevents the spontaneous development and the adoptive transfer of diabetes. It appears to act locally by releasing transforming growth factor-β and/or other factors that inhibit homing to and/or proliferation of diabetic splenocytes within the islet. These findings may provide insights into and suggest mechanisms for the protective effects of insulin therapy against diabetes.

Structural prediction of peptides binding to MHC class I molecules

Peptide binding to class I major histocompatibility complex (MHCI) molecules is a key step in the immune response and the structural details of this interaction are of importance in the design of peptide vaccines. Algorithms based on primary sequence have had success in predicting potential antigenic peptides for MHCI, but such algorithms have limited accuracy and provide no structural information. Here, we present an algorithm, PePSSI (peptide‐MHC prediction of structure through solvated interfaces), for the prediction of peptide structure when bound to the MHCI molecule, HLA‐A2. The algorithm combines sampling of peptide backbone conformations and flexible movement of MHC side chains and is unique among other prediction algorithms in its incorporation of explicit water molecules at the peptide‐MHC interface. In an initial test of the algorithm, PePSSI was used to predict the conformation of eight peptides bound to HLA‐A2, for which X‐ray data are available. Comparison of the predicted and X‐ray conformations of these peptides gave RMSD values between 1.301 and 2.475 Å. Binding conformations of 266 peptides with known binding affinities for HLA‐A2 were then predicted using PePSSI. Structural analyses of these peptide‐HLA‐A2 conformations showed that peptide binding affinity is positively correlated with the number of peptide‐MHC contacts and negatively correlated with the number of interfacial water molecules. These results are consistent with the relatively hydrophobic binding nature of the HLA‐A2 peptide binding interface. In summary, PePSSI is capable of rapid and accurate prediction of peptide‐MHC binding conformations, which may in turn allow estimation of MHCI‐peptide binding affinity. Proteins 2006.