The present invention concerns a family of nucleic acids, polypeptides and cloning vectors which direct expression of fusion proteins that can mimic aggregated IgG (AIG) and immune complex function with respect to their interactions with Fc.gamma.R and which allow for the inclusion and targeting of a second protein domain to cells expressing Fc.gamma.R. This was accomplished by expressing multiple linear copies of the hinge and CH2 domains (HCH2) of human IgG.sub.1 fused to the framework region of human IgG.sub.1. Convenient restriction sites allow for the facile introduction of additional amino-terminal domains. Methods for treating patients using fusion proteins are also disclosed. The HCH2 polymers described here represent a new strategy in the design of recombinant proteins for the therapeutic targeting of Fc.gamma.R in autoimmune disorders.