The present invention discloses a method of assaying Fc-function in an immunoglobulin containing sample by contacting the sample, in the presence of a complement, with red blood cells modified to incorporate a F-S-L peptide- lipid construct. The F-S-L peptide construct comprises a functional group (F) that is a target antigen for a complement activating immunoglobulin, a spacer group (S) covalently linking F to L and a lipid group (L). The present invention further discloses a specific construct, DOPE-Ad-CMG(2)-hCMV2 (see below) where the F group is an antigen of cytomegalovirus, that is used in assaying the Fc function of an intravenous immunoglobulin (IVIG) product.
