Defective particles can lead to underestimated antibody titers in virus neutralization tests.
OBJECTIVE
Stocks of RNA viruses often contain divergent mixtures of infectious and defective particles (DPs). Since the surface of both particles share the same immunoreactivity, differing ratios of these particles in stocks used for virus neutralization tests might alter the results. Here the impact of such off-target effects were measured.


METHODS
To determine the relative content of DPs in 3 stocks with high, medium and low titers of infectious virions, the amounts of nucleocapsid protein and viral RNA were quantified by Western blot and quantitative RT-PCR. Thereafter, stocks with different amount of DPs were used to determine the titer of neutralizing antibodies in serum from a convalescent Puumala virus-infected patient by a focus reduction neutralization test.


RESULTS
The relative amount of DPs was at least 5-fold higher in the stock with the lowest titer compared to the stock with the highest. Stocks with lower levels of DPs led to higher antibody titers compared to the analysis performed with stocks containing higher levels of DPs.


CONCLUSIONS
These results imply that DPs in virus stocks should be considered when performing virus neutralization tests to quantify neutralizing antibodies.
Institute of Virology, University Hospital Charité, Berlin, Germany.
Wiebke
W
Handke
Detlev H
DH
Krüger
Andreas
A
Rang
D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood / Q000276:immunology*; D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology; D015153:Blotting, Western; D002522:Chlorocebus aethiops; D003673:Defective Viruses / Q000276:immunology*; D006480:Hemorrhagic Fever with Renal Syndrome / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D006801:Humans; D009500:Neutralization Tests; D019590:Nucleocapsid Proteins / Q000235:genetics; D029262:Puumala virus / Q000235:genetics / Q000276:immunology; D012367:RNA, Viral / Q000032:analysis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D014709:Vero Cells; D014771:Virion / Q000276:immunology
D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D019590:Nucleocapsid Proteins; D012367:RNA, Viral