Er are rabbit red blood cells which have been washed free of rabbit plasma proteins, but they are not coated with antibodies as is done with EA. These cells have traditionally been used as cells that spontaneously activate the human alternative complement pathway in serum samples (Morgan, B.P. (2000; Dodds, A.W. and Sim, R.B. (1997)). Most human serum samples have small amounts of natural antibodies (usually IgG) to rabbit antigens and at high concentrations of serum these will agglutinate Er. This will activate the classical pathway if not blocked. Blocking the classical pathway is usually accomplished with 3 to 13 mM MgEGTA (CompTech 0.1 M MgEGTA #B106).
Er are supplied at assay-ready concentrations in the traditional buffer used for APH50 assays (GVBo) which lacks metal ions. They are prepared fresh every Monday morning and need to be ordered by Friday in order to receive them the next week. They are shipped Monday afternoon by overnight courier for delivery Tuesday (or Wednesday for most international shipments). They can usually be used for 2 weeks after preparation. They are shipped cold, but are not harmed by extended periods at room temperature (note that they circulate 60+ days at 37oC in vivo). They should be washed once before each use (3-5 min at 500 to 1000 x g at 4oC) and resuspended in GVBo to reduce background and readjust their concentration. This procedure may also be used to concentrate the cells.
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