Inability of Kaolin Treatment to Remove Nonspecific Inhibitors from Equine Serum for the Hemagglutination Inhibition Test Against Equine H7N7 Influenza Virus

Abstract

The hemagglutination inhibition test is used by many diagnostic and surveillance laboratories for detection of antibodies to influenza viruses. It is well known that the hemagglutination inhibition test is affected by nonspecific inhibitors present in equine serum. Several serum treatments are in use to remove these inhibitors, including treatment with kaolin. Discrepant results were observed in the authors' laboratories when using kaolin treatment before testing equine sera for antibodies against equine influenza virus (EIV) subtype-1 (H7N7). It is demonstrated here that kaolin treatment leads to false positive results when testing for antibodies against EIV subtype-1, as compared to other standard serum treatments (trypsin-periodate, receptor-destroying enzyme). Against EIV subtype-2 (H3N8), however, false positive results were not evident. Trypsin-periodate and receptor-destroying enzyme (RDE) treatments appear to be superior to kaolin for removal of nonspecific inhibitors from equine serum and should be used for serological diagnosis and surveillance of equine influenza virus.

Keywords

Equine influenza virus HI test nonspecific inhibitors serum treatments

References

Anders

Hartley

Jackson

: 1990, Bovine and mouse serum beta inhibitors of influenza A viruses are mannose-binding lectins. Proc Natl Acad Sci USA 87: 4485–4489.

Anonymous: 2005, Conclusions and recommendations from the 2005 meeting of the Expert Surveillance Panel on Equine Influenza Vaccines. OIE bulletin: 26–27.

Borth

: 1992, Alpha 2-macroglobulin, a multifunctional binding protein with targeting characteristics. FASEB J 6: 3345–3353.

Connor

Kawaoka

Webster

Paulson

: 1994, Receptor specificity in human, avian, and equine H2 and H3 influenza virus isolates. Virology 205: 17–23.

Francis

Jr : 1947, Dissociation of hemagglutinating and antibody-measuring capacities of influenza virus. J Exp Med 85: 1–7.

Hierholzer

Suggs

Hall

: 1969, Standardized viral hemagglutination and hemagglutination-inhibition tests. II. Description and statistical evaluation. Appl Microbiol 18: 824–833.

Hsiung

: 1973, Diagnostic virology: An illustrated handbook, pp. 26–34, 172. Yale University Press, New Haven, CT.

Kendal

Cate

: 1983, Increased sensitivity and reduced specificity of hemagglutination inhibition tests with ether-treated influenza B/Singapore/222/79. J Clin Microbiol 18: 930–934.

Mumford

Chambers

: 1999, Textbook of influenza, pp. 146–162. Blackwell Science, Oxford, England.

10.

Pritchett

Paulson

: 1989, Basis for the potent inhibition of influenza virus infection by equine and guinea pig alpha 2-macroglobulin. J Biol Chem 264: 9850–9858.

11.

Ryan-Poirier

Kawaoka

: 1993, Alpha 2-macroglobulin is the major neutralizing inhibitor of influenza A virus in pig serum. Virology 193: 974–976.

12.

Ryan-Poirier

Kawaoka

: 1991, Distinct glycoprotein inhibitors of influenza A virus in different animal sera. J Virol 65: 389–395.

13.

Subbarao

Kawaoka

Ryan-Poirier

: 1992, Comparison of different approaches to measuring influenza A virus-specific hemagglutination inhibition antibodies in the presence of serum inhibitors. J Clin Microbiol 30: 996–999.