The avidity of specific IgM detected in primary rubella and reinfection

Abstract

SUMMARYAn IgM capture enzyme-linked immunosorbent assay for rubella-specific IgM was used to assess the avidity of specific IgM by comparing the results obtained with and without a mild protein denaturant in the washing fluid used after incubation of IgM with rubella haemagglutinating antigen. An avidity index (Al) was calculated with AIs < 50% considered to indicate low avidity. Sera from recent primary rubella, rubella reinfection and from patients persistently reactive for specific IgM were tested. Urea and diethylamine (DEA) were compared as the protein denaturants. Twenty-six of 28 sera from cases of primary rubella gave an Al < 50% with DEA, compared with 25 of 28 with urea. Seventeen of 20 sera from cases of reinfection gave an Al > 50 % with DEA whereas only 14 of 20 had a similarly high avidity with urua. Eight of 10 sera from 4 cases of persistent specific IgM reactivity gave AIs > 50 % with DEA, although this was reduced to 5 when urea was used. Thus a difference has been demonstrated between the avidity of specific IgM in primary infection from that demonstrated after a secondary antigenic challenge (reinfection). This may help in serologically distinguishing primary infection from reinfection.

Reliability of low-avidity IgG and of IgA in the diagnosis of primary infection by rubella virus with adaptation of a commercial test

“…With regard to low-avidity IgG in the control group, 2% of cases had low-avidity antibodies at a fairly low level (50.4%). With the exception of a slightly higher sensitivity (92.8%; 100%) (12,13), these results are comparable to others for the diagnosis of primary infection. However, they indicate less sensitivity in detecting a past infection or reinfection.…”

The diagnosis of toxoplasmosis using IgG avidity

“…Adaptation of the IgG ELISA for the measurement of antibody avidity Toxoplasma specific avidity was measured using the 'bind and break' method and the calculation of an avidity index [8]. Various concentrations of the hydrogen-bond disrupting agent, urea and diethylamine, were used to elute the IgG from the immobilized antigen.…”

“…It has been shown that the strength of the bond between antibody and individual epitopes increases with the duration of infection [7]. Measurement of the avidity of the antibody/antigen interaction has been applied to viral infections including rubella [8] and Puumala virus [9]. Recently avidity maturation has been demonstrated in patients infected with toxoplasma [10,11].…”

High-resolution structures of the IgM Fc domains reveal principles of its hexamer formation

“…To compensate for the reduced binding efficiency of the monomers, IgM forms oligomers ( Fig. 1) whose multiple antigenbinding sites confer high overall avidity (4). Moreover, the complex structure of IgM makes it especially effective in activating the complement system (5).…”