Differential IgG avidity to rubella virus structural proteins

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Abstract
Avidity maturation of IgG antibody responses directed against the structural proteins of rubella virus ( E1, E2, and C) as well as whole rubella virus (RV) was assessed at sequential time intervals in 7 individuals following serologically confirmed wild rubella infection. Individual structural proteins were purified from tissue culture supernatants by differential centrifugation, followed by preparative SDS-PAGE under non-reducing conditions. Avidity of IgG anti-rubella responses was measured by using the 8 M urea elution technique and results expressed as an elution ratio [ER(%)]. A low mean ER(%) of 23% was determined for E1-specific IgG responses during the 10-20 day period following onset of clinical rubella, with subsequent maturation of avidity ER(%) values to 52%, 75%, and 84% at 3 months, 1 year, and 2 years, respectively, post-rubella. In contrast, IgG anti-E2 responses showed minimal avidity maturation with ER(%) values of 20%, 29%, 30%, and 31% over the same time intervals. Similarly, responses to the capsid protein (C) remained at low avidity ER(%) values of 21%, 29%, 36%, and 35% over the 2 year follow-up period. The avidity maturation values for IgG directed against whole RV preparations paralleled observations for E1 -specific responses with ER(%) values of 23%, 52% 85%, and 87%, respectively. These data support the need to assess individual protein-specific antibody avidities in order to more fully understand viral-specific immune responses.