Table 3.

Relative affinity, elution from CRBCs, and NA activity of H5 influenza viruses

VirusV. cholerae NA activity that abolishes hemagglutination (nmol of 4-MU/μl)aRelative affinity for CRBCsbTime to elute from CRBCs (h)cSp act of virus NA (nmol of 4-MU/μl · h)d
Chicken H5N1
 Ck/HK/220/97 (CHO158)e 0.16+120.66
 Ck/HK/258/97 (CHO158)e 0.16+60.48
 Ck/HK/728/97e 0.32++>240.88
 Ck/HK/786/97 (CHO158)e 0.16+30.8
 Ck/HK/915/97e 0.64++>241.6
Human H5N1 HK/156/97e 0.32++>244
Viruses from aquatic birds
 Dk/HK/205/77 (H5N2)e 1.3+++1.50.74
 Dk/MN/1525/81 (H5N1)e 3.2+++1.51.5
 Dk/MN/1525/81 (H5N1)3.2+++1.51.8
 Gull/PA/4175/83 (H5N1)1.3+++1.50.74
  • a Minimal activity of V. cholerae NA used for the treatment of 10% CRBCs, which completely abrogated their agglutination by a particular virus preparation. The values were calculated from the activity of the stock NA solution assayed by using 4-MU-NANA as a substrate.

  • b Relative affinity is based on the agglutination of V. cholerae-treated CRBCs (column 2), assuming that the higher the NA activity required to abolish hemagglutination, the higher the virus affinity for CRBCs (45). +, 0.16; ++, 0.32 to 0.64; +++, 1.3 to 3.2.

  • c Elution was assayed as described in Materials and Methods by monitoring desaggregation at 37°C of agglutinated CRBCs.

  • d Assayed as described in Materials and Methods for the same virus preparations that were used in the elution experiment.

  • e Inactivated with BPL . The similarity of the data for the live and inactivated preparations of dk/MN/1525/81 virus indicates that inactivation had no significant effect on the HA and NA activities.