A binding site for the T-cell co-receptor CD8 on the alpha 3 domain of HLA-A2

Adhesion measurements between CD8 and 48 point mutants of HLA-A2.1 show that the CD8 alpha-chain binds to the alpha 3 domain of HLA-A2.1. Three clusters of alpha 3 residues contribute to the binding, with an exposed, negatively charged loop (residues 223-229) playing a dominant role. CD8 binding correlates with cytotoxic T-cell recognition and sensitivity to inhibition by anti-CD8 antibodies. Impaired alloreactive T-cell recognition of an HLA-A2.1 mutant with reduced affinity for CD8 is not restored by functional CD8 binding sites on an antigenically irrelevant class I molecule. Therefore, complexes of CD8 and the T-cell receptor bound to the same class I major histocompatibility complex molecule seem to be necessary for T-cell activation.     

Thermodynamic study and methanothermal temperature-programmed reaction synthesis of molybdenum carbide

Nanostructured molybdenum carbide (Mo₂C) was successfully prepared from molybdenum trioxide (MoO₃) using methanothermal temperature-programmed reaction. Thermodynamic analysis indicated that in presence of methane, the formation of Mo₂C from MoO₃ occurs through the path of MoO₃ → MoO₂ → Mo₂C. The carburized MoO₃ was characterized using X-ray diffraction (XRD), CHNS/O analysis, Brunauer–Emmett–Teller (BET) analysis, and field-emission scanning electron microscopy (FESEM). At final carburization temperatures of 700 and 800℃ and at methane contents ranging from 5vol% to 20vol%, Mo₂C was the only solid product observed in the XRD patterns. The results indicated that the effect of methane content on the formation of the carbide phase is substantial compared with the effect of carburization time. Elemental analysis showed that at a final temperature of 700℃, the carbon content of carburized MoO₃ is very close to the theoretical carbon mass percentage in Mo₂C. At higher carburization temperatures, excess carbon was deposited onto the surface of Mo₂C. High-surface-area Mo₂C was obtained at extremely low heating rates; this high-surface-area material is a potential electrocatalyst.