Ad binding to human serum components. Alexa Fluor 532-labelled (a+b) Ad5 or (c) Ad5T* (1 × 109 vp) was incubated at room temperature for 90 min in human sera −/+ 40 μg ml−1 Xbp (25 μl final volume). (a) Sera Group A=sensitive to neutralisation in the absence of FX (1 × representative of this group, serum sample #5, shown here), (b) Group B=not sensitive to neutralisation in the absence of FX (1 × representative of this group, serum sample #24 presented here). Samples were diluted in 1.5 ml phosphate-buffered saline and injected into the Nanosight. Each result is representative data from minimum three separate experiments with ~700 completed tracks. Mean±s.e.m. compared by one-way analysis of variance, Tukey’s post hoc test, *P<0.05 vs matched control or serum–Xbp conditions.