As the amount of MAb increases, infectivity decreases, and there are significant differences in the neutralization of inoculum and purified infectious virus. EV71 infectious virus preincubated with MAb 22A12 (red line) was incapable of infecting HeLa cells at all but one tested concentration of antibody, indicating efficient neutralization of purified virus. However, the EV71 inoculum (a mixture of infectious virus and procapsid) preincubated with the same amount of MAb 22A12 (blue line) readily infected cells, causing severe CPE and death. The data were collected from two independent experiments that contained five replicates each. The error bars denote standard errors.