FIG 4.

Reduced sensitivity of Kappa, Delta, and B.1.618 to neutralization of convalescent-phase sera. (A to C) MLV particles pseudotyped with the indicated spike proteins of Kappa, Delta, and B.1.618 or mutations as indicated were preincubated with serially diluted convalescent-phase sera, respectively. HeLa-ACE2 cells were incubated with these preincubated mixtures and analyzed 48 h later by measuring luciferase activity to calculate the plasma dilution factor leading to 50% reduction in spike protein-driven cell entry (50% neutralizing titer [NT₅₀]). The NT₅₀ of each serum against each pseudovirion (pvNT50) is presented, and identical serum samples are connected with lines. Statistical significance of differences between WT and variant spike proteins was analyzed by two-sided Friedman test with Dunn’s multiple comparison. *, P < 0.05; **, P < 0.01. The pVNT50 of each sample was tested with two repeats.