Natural killer (NK) cells are key components of innate immune responses to tumors and viral infections. NK cell function is regulated by NK cell receptors that recognize both cellular and viral ligands, including MHC, MHC-like, and non-MHC molecules. These receptors include Ly49s, KIRs, LILRs, and NKG2A/CD94, which bind MHC class I molecules, and NKG2D, which binds MHC class I paralogs such as the stress-induced proteins MICA and ULBP. In addition, certain viruses have evolved MHC-like immunoevasins, such as UL18 and m157 from cytomegalovirus, that act as decoy ligands for NK receptors. A growing number of NK receptor–ligand interaction pairs involving non-MHC molecules has also been identified, including, NKp30–B7-H6, KLRG1–cadherin, and NKp80–AICL. Here we describe crystal structures determined to date of NK cell receptors bound to MHC, MHC-related, and non-MHC ligands. Collectively, these structures reveal the diverse solutions that NK receptors have developed to recognize these molecules, thereby enabling the regulation of NK cytolytic activity by both host and viral ligands.
The reaction mechanism of HCHO with HO2 radical has been studied at CBS-QB3 level of theory. Three direct hydrogen abstraction processes, one double hydrogen transfer mechanism, three cooperative hydrogen abstraction processes, and one additional channel have been identified for HCHO + HO2 reaction. The calculated results indicate that the additional mechanism of HOCH2OO formation as well as the direct hydrogen abstraction process of HOC + H2O2 formations is dominant. Other channels may be negligible due to the high barrier heights. Rate constants and branching ratios have been estimated by means of the conventional transition state theory with zero-curvature tunnelling over the temperature range of 275–1800 K. The calculation shows that the overall rate constant in the temperature of 275–1800 K is mainly dependent on the channel of HOCH2OO formation. The three-parameter expression for the total rate constant is fitted to be cm3 molecule−1 s−1 between 275 and 1800 K.
Abstract The three HLA class II alleles of the DR2 haplotype, DRB1*1501, DRB5*0101, and DQB1*0602, are in strong linkage disequilibrium and confer most of the genetic risk to multiple sclerosis. Functional redundancy in Ag presentation by these class II molecules would allow recognition by a single TCR of identical peptides with the different restriction elements, facilitating T cell activation and providing one explanation how a disease-associated HLA haplotype could be linked to a CD4+ T cell-mediated autoimmune disease. Using combinatorial peptide libraries and B cell lines expressing single HLA-DR/DQ molecules, we show that two of five in vivo-expanded and likely disease-relevant, cross-reactive cerebrospinal fluid-infiltrating T cell clones use multiple disease-associated HLA class II molecules as restriction elements. One of these T cell clones recognizes >30 identical foreign and human peptides using all DR and DQ molecules of the multiple sclerosis-associated DR2 haplotype. A T cell signaling machinery tuned for efficient responses to weak ligands together with structural features of the TCR-HLA/peptide complex result in this promiscuous HLA class II restriction.
The multifunctional hydraulic drill QK-100 was designed to meet the requirement of sampling in thick mulch area. The main technical parameter, performance specialty, main structure and test results of it was introduced.
In order to make the valveless piezoelectric pump with Y-shape tubes meet well with the needs of transporting blood and fluid in such areas as medical treatment and sanitation,theoretical analysis are applied to the pump and the governing equations of the pump are established,and the finite element method is employed to simulate the fluid flowing state in Y-shape tube and the whole pump.The pressure loss coefficients derived from the simulation results show a little difference from the experimental data,thus the correctness of the simulation is proved.The simulation results reveal that the pressure in the pump chamber varies calmly,and the pressure in the tubes eases off when the separation angel of two branch tubes increases, and there exists small vortex area at the intersections of the tubes and the pump chamber.Therefore,larger separation angel of two branch tubes should be employed and round corner should be made at the intersections of the tubes and the chamber during the process of making valveless piezoelectric pump with Y-shape tubes to decrease the votex in the pump.
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