Formation Of High Affinity Research Articles

System-Level Scenarios for the Elucidation of T Cell-Mediated Germinal Center B Cell Differentiation.

Germinal center (GC) reactions are vital to the correct functioning of the adaptive immune system, through formation of high affinity, class switched antibodies. GCs are transient anatomical structures in secondary lymphoid organs where specific B cells, after recognition of antigen and with T cell help, undergo class switching. Subsequently, B cells cycle between zones of proliferation and somatic hypermutation and zones where renewed antigen acquisition and T cell help allows for selection of high affinity B cells (affinity maturation). Eventually GC B cells first differentiate into long-lived memory B cells (MBC) and finally into plasma cells (PC) that partially migrate to the bone marrow to encapsulate into long-lived survival niches. The regulation of GC reactions is a highly dynamically coordinated process that occurs between various cells and molecules that change in their signals. Here, we present a system-level perspective of T cell-mediated GC B cell differentiation, presenting and discussing the experimental and computational efforts on the regulation of the GCs. We aim to integrate Systems Biology with B cell biology, to advance elucidation of the regulation of high-affinity, class switched antibody formation, thus to shed light on the delicate functioning of the adaptive immune system. Specifically, we: i) review experimental findings of internal and external factors driving various GC dynamics, such as GC initiation, maturation and GCBC fate determination; ii) draw comparisons between experimental observations and mathematical modeling investigations; and iii) discuss and reflect on current strategies of modeling efforts, to elucidate B cell behavior during the GC tract. Finally, perspectives are specifically given on to the areas where a Systems Biology approach may be useful to predict novel GCBC-T cell interaction dynamics.

Methylglyoxal-modified collagen promotes myofibroblast differentiation

Fibrosis is a frequent complication of diabetes mellitus in many organs and tissues but the mechanism of how diabetes-induced glycation of extracellular matrix proteins impacts the formation of fibrotic lesions is not defined. As fibrosis is mediated by myofibroblasts, we investigated the effect of collagen glycation on the conversion of human cardiac fibroblasts to myofibroblasts. Collagen glycation was modeled by the glucose metabolite, methylglyoxal (MGO). Cells cultured on MGO-treated collagen exhibited increased activity of the α-smooth muscle actin promoter and enhanced expression of α-smooth muscle actin, ED-A fibronectin and cadherin, which are markers for myofibroblasts. In cells remodeling floating or stress-relaxed collagen gels, MGO treatment promoted more contraction (p<0.025) than vehicle controls, which was MGO dose-dependent. Transwell assays showed that cell migration was increased by MGO-treated collagen (p<0.025). In shear-force detachment assays, cells on MGO-treated collagen were less adherent than untreated collagen, and the formation of high affinity, β1 integrin-dependent adhesions was inhibited. MGO-collagen-induced expression of SMA was dependent on TGF-β but not on Rho kinase. We conclude that collagen glycation augments the formation and migration of myofibroblasts, critical processes in the development of fibrosis in diabetes.

Mutation of Asn-391 within the Conserved NPXXY Motif of the Cholecystokinin B Receptor Abolishes Gq Protein Activation without Affecting Its Association with the Receptor

Among the most conserved regions in the G-protein-coupled receptors is the (N/D)PX(2-3)Y motif of the seventh transmembrane domain (X represents any amino acid). The mutation of the Asn/Asp residue of this motif in different G-protein-coupled receptors was shown to affect the activation of either adenylyl cyclase or phospholipase C. We have mutated the Asn residue (Asn-391) of the NPXXY motif in the CCKBR to Ala and determined the effects of the mutation on binding, signaling, and G-proteins coupling after expression of the mutated receptor in COS cells. The mutated receptor displayed similar expression levels and high affinity CCK binding compared with the wild type CCKBR. However, unlike the wild type CCKBR, the mutated receptor was completely unable to mediate activation of either phospholipase C and protein kinase C-dependent and -independent mitogen-activated protein kinase pathways, indicating an essential role of Asn-391 in CCKBR signaling. Coimmunoprecipitation experiments allowed us to show that the inactive mutant retains an intact capacity to form stable complexes with G(q)alpha subunits in response to CCK. These results indicate that the formation of high affinity CCK-receptor-G(q) protein complexes is not sufficient to activate G(q) and suggest that Asn-391 is specifically involved in G(q) proteins activation.

Changes in the sedimentation properties of cytosolic androgen receptors associated with activation in vitro and in vivo

In cell-free systems androgen receptor (AR) labeled with ( 3H) DHT at 0°C in the presence of 50mM molybdate remains unactivated (<3% binding to nuclei) and untransformed (7–8S on sucrose density gradients containing however, these complexes undergo activation and transformation even at 0°C, albeit, very slowly. Incubation of unactivated, untransformed AR complexes at 18°C, or at 0°C in the presence of 0.4M KCl, greatly accelerated both activation and transformation. Activation and transformation are also associated with formation of high affinity ( 3H) DHT-receptor complexes as indicated by decreased rates of ( 3H) DHT dissociation from the receptor. Cytosolic AR complexes labeled with ( 3H) DHT in tissue slices at 37°C, or in vivo, undergo rapid activation, transformation and nuclear translocation. The data suggest that activation and transformation of cytosolic AR in cellfree systems is associated with changes in the physicochemical properties of AR similar to those occurring upon hormone binding in intact cells and in vivo.