ELISA protocol
IgG was prepared by chromatography on Protein A
Sepharose. Puri®ed BS1-IgG was coupled to biotin; the
BS1-IgG was separated from the free biotin by gel ®ltration
(Guesdon et al. 1979).
One hundred microlitre volumes were used in each well
for the ELISA, unless stated otherwise, with samples
loaded in duplicate and incubation stages carried out in a
humid chamber at 37 C. Samples and standards were
diluted in PBST (005 mol l
ÿ1 phosphate, 015 mol l
ÿ1
NaCl, 001% Tween 20, pH 74), which was supplemented
with 1% bovine serum albumin (BSA) for the dilution of
BS1-IgG-biotin and streptavidin-alkaline phosphatase. In
between each stage, plates (Dyrex Technologies,
Billinghurst, UK) were washed three times with PBST.
Plates were coated with BS1-IgG diluted to 5 mg mlÿ1 in