Another observation was that all three isolated Abs have a narrower and partially different neutralization spectrum relative to the corresponding plasma in the extended incubation PBMC and TZMbl PV assays. Results with the HJ16 mAb from the PBMC, TZMbl and GHOST assays show good correspondence while for the HGN194 mAb the GHOST neutralization responses are broader. The HK20 mAb shows little to no neutralization in either the TZMbl or GHOST assays. Neutralization breadth across subtypes is unlikely to be due to endotoxin since plasma are negative in conventional assays where absorption phases (and therefore contact between plasma and cells) are longer [21] .