A chemiluminescence dot-blot (CLDB) method was developed to quantify RSPs. Briefly, 40 ml of supernatant of either HeLa-prME cell line or purified E protein solution at known concentration were blotted onto PVDF membrane through a Dot Blot 96 System (Biometra, Goettingen, Germany). The membrane was blocked overnight in 5% milk in PBST solution, incubated with anti-E antibody (4E11, 1:10,000) for 1 hour and then for 1 additional hour with a peroxidase-labeled goat anti mouse IgG polyclonal antibody (1:10,000; ZYMED). ECL Western blot detection reagents (Invitrogen), diluted five times, were mixed and added to the membrane and the luminescence intensity was measured using the Microbeta luminometer (PerkinElmer, Waltham, MA, USA).