Comparison of different approaches to measuring influenza A virus-specific hemagglutination inhibition antibodies in the presence of serum inhibitors.

The A/Los Angeles/2/87 (H3N2) (A/LA/2/87) virus is sensitive to inhibitors of hemagglutination present in certain human sera. It was found that the effect of these inhibitors could be removed by treating sera with high-concentration receptor-destroying enzyme or trypsin-periodate or by using inhibitor-resistant viruses in the hemagglutination inhibition (HAI) test. Inhibitor-resistant viruses were not effective for detecting rises in antibody titers in the sera of volunteers infected with the A/LA/2/87 wild-type virus, while rises in antibody titer were readily detected in sera treated with trypsin-periodate and tested against A/LA/2/87 wild-type virus in an HAI test. It is therefore suggested that chemical or enzymatic methods be used to inactivate serum inhibitors and that standard virus be used in the HAI test for the currently circulating H3N2 viruses.