Effect of the Selection Pressure with Anti-VP7 and Anti-VP4 Neutralizing Monoclonal Antibodies on Reassortant Formation Between Two Human Rotaviruses

In order to study the effect of selection pressure of anti-VP4 and anti-VP7 neutralizing monoclonal antibodies(N-MAbs) on reassortant formation, 424 reassortant clones were produced from mixed cultures of human rotavirus strains Wa and HN126 and their genotypes were analysed. Reassortant selection was done with four types of N-MAb: anti-VP4 MAb to Wa and anti-VP7 MAb to HN126(selection A); anti-VP4 MAb to HN126 and anti-VP7 MAb to Wa(selection B); anti-VP7 MAb to Wa(selection C); and anti-VP4 MAb to Wa(selection D). In each selection experiment, more than 100 clones were isolated, and the parental origin of RNA segments was identified by polyacrylamide gel electrophoresis. All clones isolated by selections A and B were found to be antigenic mosaic reassortants with the VP4 gene of HN126 and the VP7 gene of Wa and antigenic mosaic reassortants with the VP4 gene of Wa and the VP7 gene of HN126, respectively. Although in reassortants of both selections, RNA segments 2, 3, 5 and 6 were selected from strain Wa at considerably high rates, selection rates of RNA segments 1, 7, 8, and 11 were significantly different between selection A and B. In reassortants from selection C and D, selection rates of RNA segments 1, 3, 6, 7, 8, and 11 from Wa were significantly lower than those in selection A and B, whereas RNA segments 2 and 5 were almost exclusively selected from Wa as observed in selection A and B. These results indicated the presence of two types of nonrandom gene selection in reassortant formation, one strongly dependent on, and another irrespective of, the selection pressure with N-MAbs.