Membrane exposure of novel constructs and recognition by bnMAbs. 293 T cells were transfected with equal masses of pcDNA3.1(+) expression plasmids containing envelope genes and stained 48 h p.tr. with AlexaFluor647-labelled 2F5 or 4E10 bnMAbs and Fluorescein-labeled anti-HA antibody. (A) Comparison gp41CTM to gp145. MFI for all constructs was normalized to those of gp41CTM(89.6). (B) Detection of gp41 derivatives of clades B (89.6), C (96ZM651) and SIVmac239 by extracellular staining with anti-HA antibody, normalized to gp41CTM(89.6). (C, D) 2F5 and 4E10 binding to gp41 variants, normalized to the fluorescence intensity of their simultaneous anti-HA staining. Error bars indicate the standard deviation of three independent experiments.