Immunoglobulin Class of Influenza Antibodies Investigated by Radioimmunoassay (RIA)

Abstract

Influenza antibodies were quantitated by radioimmunoassay (RIA) binding of immunoglobulin (Ig) class-specific antibodies labeled with 125-iodine as indicators. Indicator binding values by RIA were tested by chi-square for association with hemagglutination inhibition (HI) and complement fixation (CF) titers. IgG-specific indicators for RIA had binding values which appeared to be more closely associated with HI titers than with CF titers. IgM-specific indicators appeared to be more closely related to CF titers than with HI titers. RIA indicators with combined Ig heavy chain specificity proved to be more sensitive and had a higher chi-square value when tested against both HI and CF test results than did either IgG- or IgM-specific indicators. RIA with Ig class-specific indicators has made HI and CF tests more useful in ascertaining the phase of the immune response to viral antigens. Class-specific indicators exhibited a high degree of accuracy for detecting 7S and 19S viral antibodies fractionated by sucrose density gradient ultracentrifugation. Variations in the strain of viral antigen in the RIA test revealed a predominant 7S (IgG) class of antibodies against an influenza virus which was prevalent 7 to 8 years previously. However, a predominant 19S (IgM) class of antibodies was evident when a more recent influenza strain was used for the assay. Precisely distinguishing the major Ig class of viral antibody by RIA should be helpful in determining how recently a viral infection occurred or how antigenically variable viral strains are.