Idiotypic networks and nature of molecular mimicry: an overview.
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Animals↗
Biomedical subjects
S Kaveri
Publications and source records attributed to S Kaveri.
Revised immune network concepts.
The idiotype network concept needs to be revised in order to be in agreement with current data on protein/protein interactions, with the phenomenon of T and B cell recognition of idiotopes, and with the failure of certain anti-idiotypes to stimulate a given immune response. It is proposed that the distinction among Ab2 alpha, beta, and gamma is abandoned, as well as the concept of an internal image idiotope which mimics the three-dimensional shape of nominal antigen. In place of these definitions, the concept of "network antigen" is introduced. Network antigens are potentially the entire repertoire of anti-idiotypes. However, their biological effectiveness is controlled and established by two factors: (i) the affinity to the idiotype Ig receptor; and (ii) the preexisting regulatory network segment that controls the outcome of immune stimulation or suppression. Screening for effective idiotype therapeutic agents has to be done with panels of anti-idiotype and idiotype antibodies in order to establish correlations between idiotope expression and disease progression. Recognizing the importance of network segments will be the first step in the direction toward a rational design of idiotype-based therapies.
Humans↗
Internalization of beta-adrenergic receptor in A431 cells involves non-coated vesicles.
To characterize the mechanism of internalization of beta-adrenergic catecholamine receptors on human epidermoid A431 carcinoma cells, their distribution was analyzed by immunocytochemistry using the monoclonal anti-receptor antibody BRK2. In preconfluent cultures, the receptors appeared to be randomly distributed on the cell surface. Exposure to the agonist isoproterenol induced an overall decrease in the number of cell surface receptors as determined by binding experiments and visualized by immunofluorescence. When cells were incubated at 4 degrees C with BRK2 and anti-mouse IgG-gold and then transferred at 37 degrees C, non-coated invaginations and vesicles were labeled. The addition of isoproterenol resulted in an increased rate of internalization of the receptor-BRK2-anti-IgG-gold complex. When incubation with the two antibody reagents was prolonged (with or without isoproterenol), non-coated vesicles fused in the endosomal compartment, and receptors were transferred to multivesicular bodies and lysosomes. At no stage in this process was there any indication that clathrin-coated pits or vesicles participated. Furthermore, we found that an intracellular potassium depletion treatment known to inhibit endocytosis, did not affect the normal pattern of desensitization of beta-adrenergic receptors.
Antibodies, Monoclonal↗
The beta 2-adrenergic receptors of human epidermoid carcinoma cells bear two different types of oligosaccharides which influence expression on the cell surface.
The beta 2-adrenergic receptors of the human epidermoid carcinoma A431 cells reside on two polypeptide chains revealed by photoaffinity labelling with [125I]iodocyanopindolol-diazirine. These proteins correspond to two distinct populations of N-asparagine-linked glycoproteins: the 55-52 kDa molecules are associated with complex carbohydrate chain(s), the 65-63 kDa component with polymannosidic carbohydrate chain(s). Both types of receptors are present in preconfluent cells, but only the polymannosidic type is found in the postconfluent cells. Moreover, complex chains appear to be associated with the receptors with the highest affinity for (-)-isoproterenol and polymannosidic chains with the receptors with the lowest affinity for this agonist. the carbohydrate moiety of the beta-adrenergic receptor is involved in the expression and function of the beta 2-adrenergic receptors at the surface of the A431 cells, since tunicamycin and monensin, complete and partial inhibitors of glycosylation respectively, diminish the number of binding sites at the cell surface and increase the total number of sites in the cell. In these conditions a diminution of cyclic AMP accumulation is also observed.
Adrenergic beta-Antagonists↗
Catecholaminergic nerves in the embryonic chick ovary: co-localization with beta 2-adrenoceptor-bearing steroidogenic cells.
The present study investigates the innervation of the embryonic chick ovary with regard to (i) development and compartmentalization of catecholaminergic nerves, and (ii) presence of adrenoceptors on steroidogenic target cells of catecholaminergic nerve terminals. Catecholaminergic nerve fibers visualized by glyoxylic acid-induced histofluorescence first appeared at embryonic day (E) 13. From E15 through E21 the density of fluorescent aminergic nerves increased markedly in parallel with the concentration of catecholamines and numbers of nerve bundles and single axons seen at the electron-microscopic level. Catecholaminergic nerves were confined to the ovarian medulla and closely associated with interstitial cells. Nerve terminals approached interstitial cells up to a distance of 20 nm and, in their majority, exhibited uptake of the false adrenergic transmitter 5-hydroxydopamine. Although adrenaline amounted to 14% of the total catecholamine content at E21, adrenaline immunoreactivity was only detected in adrenal chromaffin cells, but not in nerve fibers or cell bodies within the ovary. Interstitial cells structurally matured between E15 and E21 as documented by an increase of smooth endoplasmic reticulum and tubular mitochondria. Monoclonal antibodies mAB 120 and BRK 2 raised against avian beta 1- and mammalian beta 2-adrenergic receptors revealed the presence of beta 2-adrenoceptor-like immunoreactivity on the surface of interstitial cells, but not on any other cell type. The results are consistent with the notion of a dense adrenergic innervation of the embryonic chick ovarian medulla and its steroidogenic interstitial cells, and suggest the chick ovary as an excellent model for elucidating the functional role of a neural input to steroidogenic cells during development.
Animals↗
Immunology of muscarinic acetylcholine and beta-adrenergic catecholamine receptors.
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Animals↗
Biochemical and immunochemical analysis of avian beta 1 and mammalian beta 2-adrenergic receptors.
We have studied the molecular properties of avian beta 1-adrenergic receptor and human beta 2-adrenergic receptor. The turkey erythrocytes beta 1-receptor has been solubilized in active form by digitonin and has been purified to homogeneity by affinity chromatography followed by electroelution from polyacrylamide gel. The photoactivable ligand, iodocyanopindololdiazirine, labels specifically a major 45 kDa and minor 55 kDa polypeptide in turkey erythrocytes, whereas in A431, it labels two polypeptides of molecular weights 65 kDa and 55 kDa. Both types of receptors are N- and possibly O-glycosylated but the turkey beta 1 receptor has only complex carbohydrates whereas the human beta 2 receptor has in addition oligo mannosidic polysaccharidic moiety. Polyclonal and monoclonal antibodies were raised against the beta 1- and beta 2-adrenergic receptors. Polyclonal antibodies were found to mimic beta-adrenergic agonists by stimulating adenylate cyclase upon binding to the receptors. The monoclonal antibodies precipitated both intact and affinity labeled receptors which they also revealed on immunoblots.
Animals↗
Immunochemical studies of the muscarinic acetylcholine receptor.
Muscarinic receptors have been purified from calf forebrain plasma cell membranes by affinity chromatography on a dexetimide-agarose gel. SDS-PAGE analysis showed a single 70 kDa band. Monoclonal antibodies have been prepared against these affinity purified 70 kDa protein(s). One antibody, M-35, immunoprecipitated up to 80% of digitonin-solubilized muscarinic receptors. M-35 had agonist-like effects on guinea-pig myometrium: it increased the intracellular cyclic GMP content, decreased prostaglandin-induced cyclic AMP accumulation and caused muscle contractions. The two first effects were inhibited by atropine. M-35 was used to visualize muscarinic receptors at the surface of human fibroblastic cells. In the particular cell line used, the receptors have a low affinity for pirenzepine, were negatively coupled to adenylate cyclase and mediated increase in the phosphatidyl-inositol breakdown.
Acetylcholine↗