CD4 and infection: The IIPs of the CD4 immunoadhesin reagents (CD4Im) reflected their differences in IC50, where eCD4-Ig achieved a 1.4 log greater reduction in infection than CD4-Ig (IIP=1.6±0.7 for CD4-Ig and 3.0±1.0 for eCD4-Ig, P<0.001).