Expression of immunoglobulin and scavenger receptor superfamily domains as chimeric proteins with domains 3 and 4 of CD4 for ligand analysis.

One approach to the analysis of leucocyte cell surface proteins is to express their domains with part of another protein as a carrier. We report the use of two immunoglobulin superfamily (IgSF) domains from rat CD4 (CD4d3 + 4) in producing domains from various superfamilies as chimeric proteins in Chinese hamster ovary cell lines. Four types of construct were successfully expressed containing: (i) the two IgSF domains of CD48; (ii) the IgSF domain of mb-1 which is part of the B cell antigen recognition complex; (iii) a T cell receptor V domain; and (iv) the N-terminal domain of CD5 which belongs to the scavenger receptor superfamily. This CD5 chimeric protein was antigenic for a panel of CD5 mAbs showing that mAbs with functional effects reacted with the N-terminal domain of CD5. The CD48 chimeric protein has been used both as multivalent complexes produced by cross-linking with mAbs recognizing CD4 and in a monomeric form to analyse the kinetics of the interaction between CD48 and CD2 [van der Merwe et al. (1993) EMBO J., 12, 4945-4954].