title: Estimating the relative avidity of mucosal IgA for antigen.
abstract: This report concerns the application of a method to estimate the relative avidity of mucosal IgA for casein and beta-lactoglobulin. The chaotropic ion, thiocyanate, was used to disrupt antigen-antibody binding in an enzyme immunoassay. The resultant proportional decrease in optical density of the enzyme immunoassay was directly related to the proportion of IgA eluted from the solid phase-bound antigen. The relative avidity was expressed as the molarity of KSCN resulting in a particular reduction in optical density. The measurement of avidity, the avidity index, was independent of the concentration of mucosal IgA. For anti-casein IgA the interassay coefficient of variation of the index was 14-18%, and the intra-assay coefficient of variation was 6%. For anti-beta-lactoglobulin IgA the interassay coefficient of variation was 10-13% and the intra-assay coefficient of variation was 6%. The method is simple and free of complicated calculations.
authors.affiliation: Department of Paediatrics, Royal Children's Hospital, Melbourne, Australia.
authors.forename: C L
authors.initials: CL
authors.lastname: Jones
authors.forename: R A
authors.initials: RA
authors.lastname: Macdonald
authors.forename: C S
authors.initials: CS
authors.lastname: Hosking
authors.forename: D M
authors.initials: DM
authors.lastname: Roberton
mesh_terms: D000915:Antibody Affinity; D002364:Caseins / Q000276:immunology; D006801:Humans; D007124:Immunoenzyme Techniques; D007071:Immunoglobulin A, Secretory / Q000276:immunology*; D007782:Lactoglobulins / Q000276:immunology; D009061:Mouth Mucosa / Q000276:immunology; D012463:Saliva / Q000276:immunology; D013861:Thiocyanates
chemical_list: D002364:Caseins; D007071:Immunoglobulin A, Secretory; D007782:Lactoglobulins; D013861:Thiocyanates