Influence of molecular size of IgA on its immunoassay by various techniques. III. Immunonephelometry.

The influence of size heterogeneity of IgA on its immunonephelometric (IN) assay was studied using highly purified preparations of monoclonal (MC) or polyclonal (PC) monomeric (M), dimeric (D), trimeric (T) and tetrameric (Q) IgA, as well as of secretory IgA (sIgA). Concentrations measured by optical density (OD) were compared to IN--concentrations obtained by using M as standards, on an equal weight basis. No significant difference was found between OD and IN concentrations of D, T, Q and sIgA were only slightly underestimated, with correction factors (CF) of 1.16, 1.20 and 1.24, respectively. The value of 1.24 for our sIgA sample (84% of 11S, 16% of 15S) could be due to the fact that secretory component represents about 20% of the mass of the sIgA molecule. IN seems a method of choice for measuring IgA concentrations in the range of microgram/ml, almost independently of the size of IgA.