Suppression of synthesis of an IgG subclass in a persistent viral infection

Comparison of immunoglobulin levels of nine horses before and after infection with equine infectious anaemia (EIA) virus demonstrated a significant depression of serum IgG(T) at 2 months (P less than 0-001) and at 1 year (P less than 0-01) after infection. In contrast, the levels of IgGa were significantly increased at both times after infection. Another sixteen horses with EIA for 1-4 months were examined and there was also significant depression (P less than 0-001) of IgG(T) when compared to pre-infection levels. No significant changes in IgG(T), IgGa and IgM were noted in fourteen normal horses housed for 2-7 months in the same manner as infected horses. Following DNP immunization there was a significant (P less than 0-02) decrease in the amount of IgG(T) antibody produced in five horses with EIA when compared to five normal horses. Metabolism studies with iodinated IgG(T) showed a significant (P less than 0-001) decrease in synthesis of this immunoglobulin in EIA-infected horses when compared to normal horses. Amounts of IgGa synthesized were similar in the two groups. Thus, persistent EIA viral infection suppresses the synthesis of IgG(T), an IgG subclass, without suppressing IgGa.