Receptor-ligand Reaction Research Articles

Pattern-recognition receptors in endometriosis: A narrative review.

Endometriosis is closely associated with ectopic focal inflammation and immunosuppressive microenvironment. Multiple types of pattern recognition receptors (PRRs) are present in the innate immune system, which are able to detect pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) in both intracellular and external environments. However, the exact role of PRRs in endometriosis and the underlying molecular mechanism are unclear. PRRs are necessary for the innate immune system to identify and destroy invasive foreign infectious agents. Mammals mainly have two types of microbial recognition systems. The first one consists of the membrane-bound receptors, such as toll-like receptors (TLRs), which recognize extracellular microorganisms and activate intracellular signals to stimulate immune responses. The second one consists of the intracellular PRRs, including nod-like receptors (NLRs) and antiviral proteins retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5) with helix enzyme domain. In this review, we mainly focus on the key role of PRRs in the pathological processes associated with endometriosis. PRRs recognize PAMPs and can distinguish pathogenic microorganisms from self, triggering receptor ligand reaction followed by the stimulation of host immune response. Activated immune response promotes the transmission of microbial infection signals to the cells. As endometriosis is characterized by dysregulated inflammation and immune response, PRRs may potentially be involved in the activation of endometriosis-associated inflammation and immune disorders. Toll-like receptor 2 (TLR2), toll-like receptor 3 (TLR3), toll-like receptor 4 (TLR4), nod-like receptor family caspase activation and recruitment domain (CARD) domain containing 5 (NLRC5), nod-like receptor family pyrin domain containing 3 (NLRP3), and c-type lectin receptors (CLRs) play essential roles in endometriosis development by regulating immune and inflammatory responses. Absent in melanoma 2 (AIM2)-like receptors (ALRs) and retinoic acid-inducible gene I-like receptors (RLRs) may be involved in the activation of endometriosis-associated immune and inflammation disorders. PRRs, especially TLRs, may serve as potential therapeutic targets for alleviating pain in endometriosis patients. PRRs and their ligands interact with the innate immune system to enhance inflammation in the stromal cells during endometriosis. Thus, targeting PRRs and their new synthetic ligands may provide new therapeutic options for treating endometriosis.

Modern view on the role of pattern-recognition receptors and signaling pathways in the development of innate immunity in viral infections

Features of organization and functioning of pattern-recognizing receptors and signaling pathways in induction of antiviral immune response are considered. The recognition of antigenic structures of the virus is carried out by pathogen-associated molecular patterns of innate immunity cells. These are Toll-like receptors, nucleotide-binding oligomerization domain-like receptors, lectin C-type receptors, and RIG-I-like receptors. The functioning of these receptor structures depends on protein molecules that provide activation signals. These are the adapter proteins of the primary response of myeloid differentiation 88, interleukin-1 receptor-associated kinase, nuclear factor-KB. Interactions of cellular proteins in the activation of signaling pathways are complex and receptor-ligand reactions can lead to different outcomes in a single cell, in most cases leading to a limitation of viral reproduction. An important obstacle to the effective recognition of viruses and the development of an adequate immune response is the close organization of viral antigens and receptor structures of the cell. The role of LGP2 protein molecules is associated with the peculiarities of the development of the immune response, which can be not only positive, but also negative regulators of the transmission of excitation signals from intracellular cytoplasmic helicase receptors. A number of viral proteins inhibit activation signals, which ultimately leads to various options for the development of the immune response. A special role belongs to the transmembrane protein of the endoplasmic reticulum, which increases the expression of interferon a stimulator of interferon genes that provide detection of deoxyribonucleic acid viruses. Maximum activation of this protein, ensures the effective development of a cellular antiviral immune response.

Receptor-ligand diffusion-limited reaction rates on curved membranes

We provide an expression for the diffusion-limited reaction rate on a curved surface, or membrane, in the perturbative deformation regime. This result is applied to the specific case of calculating the receptor-ligand association rate at membrane deforming, transmembrane receptor proteins, or inclusions. The dynamics of mechanochemical coupling between chemical activity and local membrane curvature is further investigated, and the effect of thermal membrane fluctuations is also discussed. It is found for transmembrane proteins, or inclusions, that their concomitant receptor-ligand reaction rates can be typically reduced by as much as 20% due to the effect of locally induced membrane curvature or geometry.

Integration of antibody-antigen and receptor-ligand reactions to establish a gold strip biosensor for detection of 33 β-lactam antibiotics

A novel lateral flow immunoassay biosensor, combining the receptor-ligand reaction and antigen-antibody reaction was developed for the detection of β-lactam antibiotics in milk. The receptor protein, the carboxy-terminal domain of β-lactam sensor-transducer mutant from Bacillus. licheniformis, served as the recognition element. Colloidal gold (CG)-labelled receptor antibody-receptor ternary complex was applied as a signal transducer probe. The presence of β-lactams was identified through a color change in the test zone, where the reaction between the complex of CG/anti-receptor antibody/receptor and β-lactam antigen on the test line could be inhibited by β-lactam residues in the sample, thus leading to a reduction in color signal. Based on the indirect labeling of the receptor with an antibody as a linker, the ability to detect 33 β-lactams was below or near the corresponding maximum residue limit. The proposed lateral flow immunoassay biosensor appears to be an excellent field-based screening tool for the qualitative screening of β-lactams in milk.

A mechano-chemo-biological model for bone remodeling with a new mechano-chemo-transduction approach.

Bone remodeling is a fundamental biological process that develops in bone tissue along its whole lifetime. It refers to a continuous bone transformation with new bone formation and old bone resorption that changes the internal microstructure and composition of the tissue. The main objectives of bone remodeling are: repair of the internal microcracks; adaptation of the macroscopic stiffness and strength to the actual changing mechanical demands; and control of the calcium homeostasis. Understanding this process and predicting its evolution is critical to reduce the effects of long-term disuse as happens during periods of reduced mobility. It is also important in the design of bone implants to avoid long-term stress shielding. Many mathematical models have been proposed from the earliest purely phenomenological to the latest that include biological knowledge. However, there still exists a lack of connection between the mechanical driving force and the biochemical and cell processes it triggers. Here, and following previous works that model independently the mechanobiological and biochemical processes in bone remodeling, we present a more complete model, useful for both cortical and trabecular bone, that uses a new mechanotransduction approach based on the effect of strains onto the bonding-unbonding rate of RANK/RANKL/OPG receptor-ligand reactions. We compare the results of this model with previous ones, showing a good agreement in similar conditions. We also apply it to realistic situations such as a femoral bone after implantation of a hip prosthesis, getting similar results to the clinical ones in the final bone density distribution. Finally, we extend this approach to the anisotropic case, getting not only the mean density, but also the directional homogenization of the microstructure. This biochemical approach permits, not only to predict the bone evolution under changes in the mechanical loads, but also, to consider anabolic and catabolic drugs to control bone density, such as those used in osteoporosis.

Adhesion Frequency Assay for <em>In Situ</em> Kinetics Analysis of Cross-Junctional Molecular Interactions at the Cell-Cell Interface

The micropipette adhesion assay was developed in 1998 to measure two-dimensional (2D) receptor-ligand binding kinetics. The assay uses a human red blood cell (RBC) as adhesion sensor and presenting cell for one of the interacting molecules. It employs micromanipulation to bring the RBC into contact with another cell that expresses the other interacting molecule with precisely controlled area and time to enable bond formation. The adhesion event is detected as RBC elongation upon pulling the two cells apart. By controlling the density of the ligands immobilized on the RBC surface, the probability of adhesion is kept in mid-range between 0 and 1. The adhesion probability is estimated from the frequency of adhesion events in a sequence of repeated contact cycles between the two cells for a given contact time. Varying the contact time generates a binding curve. Fitting a probabilistic model for receptor-ligand reaction kinetics to the binding curve returns the 2D affinity and off-rate. The assay has been validated using interactions of Fcγ receptors with IgG Fc, selectins with glycoconjugate ligands, integrins with ligands, homotypical cadherin binding, T cell receptor and coreceptor with peptide-major histocompatibility complexes. The method has been used to quantify regulations of 2D kinetics by biophysical factors, such as the membrane microtopology, membrane anchor, molecular orientation and length, carrier stiffness, curvature, and impingement force, as well as biochemical factors, such as modulators of the cytoskeleton and membrane microenvironment where the interacting molecules reside and the surface organization of these molecules. The method has also been used to study the concurrent binding of dual receptor-ligand species, and trimolecular interactions using a modified model. The major advantage of the method is that it allows study of receptors in their native membrane environment. The results could be very different from those obtained using purified receptors. It also allows study of the receptor-ligand interactions in a sub-second timescale with temporal resolution well beyond the typical biochemical methods. To illustrate the micropipette adhesion frequency method, we show kinetics measurement of intercellular adhesion molecule 1 (ICAM-1) functionalized on RBCs binding to integrin α(L)β(2) on neutrophils with dimeric E-selectin in the solution to activate α(L)β(2).

Computational analysis of adhesion force in the indentation of cells using atomic force microscopy

A mechanical model was developed to study the indentation of an atomic force microscopic (AFM) tip on a cell with adhesion mediated by receptor-ligand binding. The effects of indentation rate, indentation depth, indenter size, and the mechanical properties of cells on the adhesion force were investigated. It was found that the presence of adhesion between the cell and AFM tip may affect both the loading curve and unloading curve, which may in turn change the extracted elastic modulus values using the conventional indentation models. It was found that an increase in the receptor-ligand reaction rate may lead to a transition from a decrease of the maximum adhesion force with the indentation rate to an increase of the maximum adhesion force with the indentation rate. It was also found that factors such as indenter size, indentation depth, and cell mechanical properties influence the maximum adhesion force, and their corresponding underlying mechanisms were discussed.

Receptor-mediated binding of IgE-sensitized rat basophilic leukemia cells to antigen-coated substrates under hydrodynamic flow

The physiological function of many cells is dependent on their ability to adhere via receptors to ligand-coated surfaces under fluid flow. We have developed a model experimental system to measure cell adhesion as a function of cell and surface chemistry and fluid flow. Using a parallel-plate flow chamber, we measured the binding of rat basophilic leukemia cells preincubated with anti-dinitrophenol IgE antibody to polyacrylamide gels covalently derivatized with 2,4-dinitrophenol. The rat basophilic leukemia cells' binding behavior is binary: cells are either adherent or continue to travel at their hydrodynamic velocity, and the transition between these two states is abrupt. The spatial location of adherent cells shows cells can adhere many cell diameters down the length of the gel, suggesting that adhesion is a probabilistic process. The majority of experiments were performed in the excess ligand limit in which adhesion depends strongly on the number of receptors but weakly on ligand density. Only 5-fold changes in IgE surface density or in shear rate were necessary to change adhesion from complete to indistinguishable from negative control. Adhesion showed a hyperbolic dependence on shear rate. By performing experiments with two IgE-antigen configurations in which the kinetic rates of receptor-ligand binding are different, we demonstrate that the forward rate of reaction of the receptor-ligand pair is more important than its thermodynamic affinity in the regulation of binding under hydrodynamic flow. In fact, adhesion increases with increasing receptor-ligand reaction rate or decreasing shear rate, and scales with a single dimensionless parameter which compares the relative rates of reaction to fluid shear.

Immunochemical modeling of receptor-ligand reactions. Report II. Reaction of antibodies simulating N-choline receptor recognition with dicholine and dihomocholine dicarboxylic acid esters

Immunochemical modeling of receptor-ligand reactions. Report II. Reaction of antibodies simulating N-choline receptor recognition with dicholine and dihomocholine dicarboxylic acid esters

Experimental design optimisation: theory and application to estimation of receptor model parameters using dynamic positron emission tomography

The general framework and various criteria for experimental design optimisation are presented. The methodology is applied to the estimation of receptor-ligand reaction model parameters with dynamic positron emission tomography data. The possibility of improving parameter estimation using a new experimental design combining an injection of the beta +-labelled ligand and an injection of the cold ligand is investigated. Numerical simulations predict a remarkable improvement in the accuracy of the parameter estimates with this new experimental design and particularly the possibility of separate estimations of the association constant (k+1) and of the receptor density (B'max) in a single experiment. Simulation predictions are validated using experimental PET data in which parameter uncertainties are reduced by factors ranging from 17 to 1000.

Ligand-specific cross-inhibition of monocyte phagocytosis.

Human monocytes exposed to particles reacting with receptors of one specific type demonstrate a markedly reduced phagocytosis of particles reacting with receptors of another type. The phagocytosis of yeast particles (Saccharomyces cerevisiae) coated with C3 fragments and of uncoated ones by monocytes can inhibit the subsequent endocytosis of sheep erythrocytes sensitized with IgG antibody and vice versa. The erythrocytes were labelled with 51Cr and the yeast particles with 125I. The dependence of the receptor-ligand reaction on temperature and time of preincubation, as well as on ratio of cell and particle, suggests that this cross-inhibition may be associated with plasma membrane modulations beginning with the attachment of ligands to a receptor and followed by their endocytosis. The differences between the functions of temperature, time, and concentration in inhibition caused by different receptor-ligand reactions suggest that these membrane modulations are probably ligand-specific processes.

A receptor-ligand reaction studied by a novel analytical tool—The Isoscope ellipsometer

A receptor-ligand binding reaction, cholera toxin-ganglioside GM 1, was studied by diffusion of the ligand over a receptor-coated surface. The surface reaction was analyzed by the use of a novel analytical tool, the Isoscope ellipsometer. The thickness profile of the receptor-ligand binding reaction can be directly visualized and photographed with this instrument. Experimental thickness profiles were compared to different theoretically calculated thickness profiles assuming different kinetics of the receptor-ligand reaction. Experimental data were best fitted to theoretical calculations assuming an irreversible and diffusion rate-limited surface reaction. The use of the Isoscope ellipsometer for further studies on receptor-ligand reactions is discussed.

Kinetics of reaction zone formation with radial diffusion of ligands over a receptor-coated surface

Theoretical calculations are presented, describing the kinetics of reaction zone formation with radial diffusion of ligands over a receptor coated surface. Calculated concentration distributions of ligands diffusing radially over a receptor-coated surface are combined with different types of receptor-ligand reactions, taking place at the surface, in order to obtain theoretical relations between the initial concentration of ligand in the source, the diameter of the receptor-ligand reaction zone and reaction time. These relations are compared to experimental data, using bovine serum albumin (BSA) as immobilized receptor and anti-BSA antibodies as diffusing ligand. The theory predicts how the diffusion constant of the ligand and the detection level of the visualization method may be determined and how to discriminate between different kinetics of the receptor-ligand reaction. The practical use of the theory in experimental studies of receptor-ligand interaction is discussed.