Figure 4. Diagnostic and therapeutic applications.

(a) Detection of immobilized HA via lateral flow on nitrocellulose paper strips using either a Tri-HSB variant for capture and the stem-region binding design HB36.6²⁷ (coupled to streptavidin-gold via biotinylation) for detection, or vice versa. Tri-HSB.2 readily binds to nitrocellulose and can be directly used as an immobilization reagent for HA. HB36.6 was immobilized through biotinylation followed by nitrocellulose-binding streptavidin. For detection via the head-region binder, Tri-HSB.2 was conjugated to HRP for signal amplification. (b) Inhibition of infection of MDCK-SIAT1-CMV-PB1 cells by H3N2 HK68 virus at indicated concentrations. Values are reported as percent infectivity compared to untreated, infected cells averaged over triplicate measurements. TriHSB.2 has an IC₅₀ of 0.15 nM for HK68 neutralization, and Tri-HSB.1C an IC₅₀ of 19 nM for neutralization of H1 NewCal; both values are close to their apparent K_d, consistent with a simple receptor blocking mechanism. (c) Mice (n=10) treated with a single dose of 3 mg/kg TriHSB.2/body weight either before (prophylactically) or after (therapeutically) intranasal challenge of H3N2 (X-31) virus show substantial protection from weight loss (P < 0.00001) following influenza challenge compared to PBS or non-binding Tri-HSB.2ko-treated controls. Mean values are plotted for each group and with s.e.m.as error bars.