[Human anti-immunoglobulins. Presence of anti IGD and anti IgA in human sera]

Particle counting immunoassay (PACIA). II. Automated determination of circulating immune complexes by inhibition of the agglutinating activity of rheumatoid sera

Antigen--antibody complexes were detected in patients' sera by inhibition of the agglutinating activity of rheumatoid sera toward IgG coated particles (latex). Precision, sensitivity (1--10 microgram/ml equivalents of heat-aggregated IgG), and reproducibility (maximum coefficient of variation of 11%) were obtained by measuring agglutination with an instrument counting the residual free particles. Automation allowed testing of 20 to 40 samples per hour. The inhibitory activity of spontańeously agglutinating sera was determined after inactivating endogenous rheumatoid factor by reduction with dithiothreitol. Non-aggregated IgG did not significantly interfere. The agglutinating activity of 6 rheumatoid sera was tested after incubation with the various immunoglobulin classes and subclasses polymerized by coupling to agarose, and all were found to be readily absorbed by IgG1, but poorly by IgG3, IgA1 and IgM. Reactivity with IgG2, IgG4 and IgA2 clearly differed for different rheumatoid sera. Among 70 sera from blood donors, 7 had abnormally high inhibitory activity. Six of these had also an abnormal protein profile, suggesting existence of latent disease. High inhibitory activity in 15 sera out of 18 from patients with systemic lupus erythematosus, and in 23 sera out of 46 from patients with breast cancer suggested that the rheumatoid factor inhibition test has a discriminatory capacity comparable with that of more sophisticated techniques requiring radioisotopes and/or cellular material.

Naturally occurring human antibodies with specificity for light chains of immunoglobulins

Human sera of different categories were screened for antibodies against IgA. A surprisingly high incidence of antibodies was observed. All of these antibodies were of restricted specificity, i.e. able to react with one or a few individual IgAs from a panel of eight myeloma proteins used in the screening. In one serum of a patient with selective IgA deficiency an antibody against the allotype A2m(1) was found. Some of the antibodies were shown to belong to the IgG class. The IgA, IgG and IgM content of the antibody-containing sera was generally increased. Two different antibodies which both reacted with the same individual IgA were studied in detail. The antigen involved could not be detected in normal Caucasian sera but was detectable in some sera of patients with IgA, IgG, IgM or IgD paraproteinemia. The antigenic site was located on the light chain of the Ig molecule but no correlation with either the light chain type or the genetically determined Inv factor was evident.