CD4 and Zika virus infectious disease: An in vitro ADE assay with K562 cells was performed to measure ZIKV infection-enhancing antibodies in DENV2-immune macaque serum from 90 days p.i. Sera from both CD4-depleted and undepleted animals exhibited similar ZIKV infection activity at the lowest serum dilution, ranging from 40 to 50% (Figure 4).