Anti-idiotypic antibody probes of neuronal nicotinic receptors

Decreased protein levels of nicotinic receptor subunits in the hippocampus and temporal cortex of patients with Alzheimer's disease

Deficits of cortical nicotinic acetylcholine receptors (nAChRs) have been observed in Alzheimer's disease (AD) by receptor binding assays. Little is known about the receptor subunit specificity influenced by AD, and it might be of importance for therapeutic strategies. In the present study, the protein levels of nAChR alpha3, alpha4, alpha7, and beta2 subunits were investigated using western blot analysis on postmortem brains of patients with AD and age-matched controls. The results showed that in human postmortem brain samples, bands with molecular masses of 52, 42, and 50 kDa were detected by anti-alpha4, anti-alpha7, and anti-beta2 antibodies, respectively. When anti-alpha3 antibody was used, one major band of 49 kDa and two minor bands of 70 and 38 kDa were detected. In AD patients, as compared with age-matched controls, the alpha4 subunit was reduced significantly by approximately 35 and 47% in the hippocampus and temporal cortex, respectively. A significant reduction of 25% in the alpha3 subunit was also observed in the hippocampus and a 29% reduction in the temporal cortex. For the alpha7 subunit, the protein level was reduced significantly by 36% in the hippocampus of AD patients, but no significant change was detected in the temporal cortex. In neither the hippocampus nor the temporal cortex was a significant difference observed in the beta2 subunit between AD patients and controls. These results reveal brain region-specific changes in the protein levels of the nAChR alpha3, alpha4, and alpha7 subunits in AD.

Polyclonal anti-idiotypic antibodies to idazoxan and their interaction with human brain imidazoline binding sites

Polyclonal antibodies were raised in rabbits against purified polyclonal anti-idazoxan antibodies. The anti-idiotypic antibodies thus obtained, proved able to inhibit [3H]idazoxan specific binding to anti-idazoxan antibodies. Applied to human nucleus reticularis lateralis membrane preparations, these antibodies (20 micrograms) inhibited about 50 and 70% of the imidazoline specific binding of [3H]idazoxan and [3H]clonidine, respectively. Furthermore, they specifically immunoprecipitated 50% of [3H]idazoxan binding activity of imidazoline binding sites solubilized from the same tissue. [3H]Rauwolscine binding to alpha 2-adrenoceptors in rat cortex was not significantly affected by these antibodies. The antibodies labeled a 43 kDa protein in Western blots of partially purified imidazoline binding sites from human brain. In conclusion, these anti-idiotypic antibodies recognize imidazoline binding sites from human brain and allow the detection of a 43 kDa binding protein associated with or representing the imidazoline receptor expressed in human brain.

Polyclonal anti-idazoxan antibodies: characterization and purification

Amino-idazoxan coupled to hemocyanine was used to raise anti-idazoxan antibodies in the rabbit. The antibodies were affinity purified with an amino-idazoxan affinity column. Binding studies with [3H]idazoxan showed a dissociation constant of 2.2 +/- 1.4 nM. The specificity spectrum of these antibodies indicates that the imidazoline part of idazoxan is more important for recognition than the benzodioxan ring as imidazoline substances (clonidine, cirazoline) are powerful competitors of [3H]idazoxan binding on the antibodies. Catecholamines or imidazoles were unable to displace [3H]idazoxan from the antibodies. These anti-idazoxan antibodies present specificity similarities with the imidazoline receptor as did our previously obtained anti-clonidine antibodies. Affinity-purified antibodies represent useful tools for studying the imidazoline receptors particularly with an anti-idiotypic approach.

Characterization of macrophage proteins bearing the functional leukotriene D4-binding site of an anti-cysteinylleukotriene monoclonal antibody

Protein conformations of the putative cysteinylleukotriene (LT) receptor of macrophages were characterized using anti-idiotypic IgG (AIAb) against an anti-LT monoclonal Ab (LTmAb). The AIAb nature of two rabbit antisera were demonstrated with titers of up to 1:1000 against F(ab')2 from the LTmAb (in an enzyme-linked immunoassay) which also inhibit LTD4 binding to the LTmAb (in a radioimmunoassay), whereas non-immunized rabbit serum was not reactive. The specific reactivity of Fc-purified AIAb towards LTmAb was measured by two fractions obtained after passage over columns of Sepharose either coupled with LTmAb (fraction A, representing immunoglobulins not absorbed to LTmAb) or coupled with homologous immunoglobins (fraction B, representing immunoglobulins not absorbed to homologous IgG). The difference in immunoreactivity between both fractions showed that fraction B contains AIAb against a LT-recognizing domain of the LTmAb (in enzyme-linked immunoassays coated with LTmAb and homologous IgG) and AIAb against the functional LT-binding site of LTmAb (in radioimmunoassay). Using the antisera, Western-blot analysis with peritoneal cell proteins detected signals at 236, 198, 118, 99, 75, 25 and 18 kDa. Dithiothreitol-reduced proteins were detected at 25 kDa and 18 kDa. In general, this suggested recognition of a 236-kDa oligomeric protein composed of subunits with molecular masses of 25 kDa and 18 kDa, including intramolecular disulfide bridges all bearing an epitope similar to the LTmAb. From these conformations, an overlay assay with [3H]LTD4 favoured a 75-kDa protein. Immunohistochemical analysis demonstrated that the recognized proteins may be located at cell membranes, because (a) in an ELISA, enriched plasma membrane preparations from peritoneal cells showed a threefold increase in reactivity to the AIAb, compared to the original cell homogenate; (b) after Western-blot analysis, the membrane-enriched protein fraction exhibited stronger protein signals than the microsomal fraction and the original cell homogenate; (c) regions of AIAb binding on the surface of cultured mouse peritoneal macrophages were detected by indirect immunofluorescence. Taken together, this study demonstrated AIAb binding to macrophage membrane-associated proteins bearing the LTD4-binding site of LTmAb, which may include identification of the putative LT receptor.

Generation of anti-idiotypic monoclonal antibodies recognizing vasopressin receptors in cultured cells and kidney sections

To produce anti-idiotypic antibodies against receptors for the neurohypophyseal hormone vasopressin, an anti-vasopressin monoclonal antibody with a ligand specificity similar to that of vasopressin receptors was employed for immunization. Three anti-idiotypic monoclonal antibodies were obtained which induced, like vasopressin, plasminogen activator production in the renal epithelial cell line LLC-PK1 (expressing V2-receptors). Induction of plasminogen activator synthesis by the anti-idiotypic antibodies could be inhibited by coincubation with a vasopressin antagonist. In a fashion similar to that of vasopressin itself, the anti-idiotypic antibodies induced receptor down-regulation. The anti-idiotypic antibodies were employed to visualize vasopressin receptors on LLC-PK1 and A7r5 (V1-receptor-expressing) smooth muscle cells by immunofluorescence. Antibody-mediated fluorescence was not observed in receptor-deficient mutant cell lines or vasopressin-receptor-down-regulated cells. Furthermore, these antibodies were used for immunohistochemical localization of vasopressin receptors in rat and bovine kidney preparations. In accordance with earlier physiological and biochemical observations, vasopressin receptors were detected predominantly in collecting ducts in cortex and medulla. On the cellular level, a differential staining pattern was observed.

Brain nicotinic receptors isolated by a monospecific antibody against a synthetic alpha-3 subunit receptor peptide compared to a monoclonal anti-idiotypic (to nicotine) antibody

Nicotinic cholinergic receptor proteins purified from rat brain by immunoaffinity chromatography were characterized using the anti-S3 polyclonal antibody vs. the anti-idiotypic monoclonal antibody 422F11 (generated against an antibody to nicotine). Anti-S3 IgG was purified to homogeneity; anti-S3-Sepharose 4B and 422F11-Sepharose 4B each depleted 3H-nicotine binding sites from brain. Nicotinic receptors isolated from both immunoaffinity columns showed major bands (silver-stained) at 55K and 70K. Using anti-S3 serum as probe, Western blots of nicotinic receptors isolated by the two immunoaffinity gels also showed major bands at 55 and 70K. However, Western blots of fresh brain extracts revealed a major band at 80K and minor bands at 55K and 70K. These results show similar nicotinic cholinergic receptor proteins isolated by the anti-S3 and 422F11 anti-idiotypic antibodies; 80K was dominant only when fresh brain extract was subjected to Western blotting without prior immunoaffinity purification.