Immunoglobulin complex

Abstract: An ultrastructural immunostaining method that uses silver-intensified gold was combined with another procedure that uses biotin peroxidase conjugates to allow simultaneous identification of two neurotransmitter-related antigens in the central nervous system. Tyrosine hydroxylase-immunoreactive neurons labeled with silver-intensified gold could be differentiated at both light and electron microscopic levels from glutamate decarboxylase-immunoreactive neurons labeled with peroxidase. Cross reactivity of the second group of immunoreagents with the first group was reduced by the heavy metal silver shell formed around the colloidal gold immunoglobulin complex. With this dual pre-embedding method, peroxidase-stained axons containing the inhibitory neurotransmitter gamma-aminobutyric acid were found to synapse directly on silver-stained dopamine neurons in the rat dorsomedial hypothalamus. This approach can be used in combination with a post-embedding immunocytochemical colloidal gold procedure, allowing ultrastructural identification of three neurotransmitter-related antigens in the same tissue section.

Abstract: Immune responses taking place in mucosal tissues are typified by secretory immunoglobulin A (S-IgA) molecules, which are assembled from proteins expressed in two cell lineages. The heavy and light chains as well as the J chain are produced in plasma cells, whereas the secretory component (SC) is associated to the immunoglobulin complex during transcytosis across the epithelial layer. S-IgA antibodies represent the predominant immunoglobulin class in external secretions, and the best defined entity providing specific immune protection for mucosal surfaces by blocking attachment of bacteria and viruses. S-IgA constitutes greater than 80% of all antibodies produced in mucosa-associated lymphoid tissues in humans. The existence of a common mucosal immune system permits immunization on one mucosal surface to induce secretion of antigen-specific S-IgA at distant sites. In addition, S-IgA antibodies not only function in external secretions, but also exert their antimicrobial properties within the epithelial cell during transport across the epithelium. Passive mucosal delivery of monoclonal IgA molecules neutralizes pathogens responsible for gastrointestinal and respiratory infections. Mucosal and systemic immunity can be achieved by orally administered recombinant S-IgA molecules carrying a protective bacterial epitope within the SC polypeptide primary sequence.

Abstract: Background As an essential step of adaptive immune response, the recognition between antigen and antibody triggers a series of self-protection mechanisms. Therefore, the prediction of antibody-binding sites (B-cell epitope) for protein antigens is an important field in immunology research. The performance of current prediction methods is far from satisfying, especially for conformational epitope prediction. Here a multi-perspective analysis was carried on with a comprehensive B-cell conformational epitope dataset, which contains 161 immunoglobulin complex structures collected from PDB, corresponding to 166 unique computationally defined epitopes. These conformational epitopes were described with parameters from different perspectives, including characteristics of epitope itself, comparison to non-epitope surface areas, and interaction pattern with antibody. Results According to the analysis results, B-cell conformational epitopes were relatively constant both in the number of composing residues and the accessible surface area. Though composed of spatially clustering residues, there were sequentially linear segments exist in these epitopes. Besides, statistical differences were found between epitope and non-epitope surface residues with parameters in residual and structural levels. Compared to non-epitope surface residues, epitope ones were more accessible. Amino acid enrichment and preference for specific types of residue-pair set on epitope areas have also been observed. Several amino acid properties from AAindex have been proven to distinguish epitope residues from non-epitope surface ones. Additionally, epitope residues tended to be less conservative under the environmental pressure. Measured by topological parameters, epitope residues were surrounded with fewer residues but in a more compact way. The occurrences of residue-pair sets between epitope and paratope also showed some patterns. Conclusions Results indicate that, certain rules do exist in conformational epitopes in terms of size and sequential continuity. Statistical differences have been found between epitope and non-epitope surface residues in residual and structural levels. Such differences indicate the existence of distinctiveness for conformation epitopes. On the other hand, there was no accordant estimation for higher or lower values derived from any parameter for epitope residues compared with non-epitope surface residues. This observation further confirms the complicacy of characteristics for conformational epitope. Under such circumstance, it will be a more effective and accurate approach to combine several parameters to predict the conformation epitope. Finding conformational epitopes and analysing their properties is an important step to identify internal formation mechanism of conformational epitopes and this study will help future development of new prediction tools.