The present invention relates to a pharmaceutical composition comprising complement split product C4d for use in treating an inflammatory condition, such as graft rejection, graft versus host disease, an autoimmune disease or atopy. The C4d to be used may be a multimer. Accordingly, also C4d multimers and their use in medicine, like the treatment of inflammatory conditions, is provided. Furthermore, the present invention provides a protein complex comprising C4d interacting with its ILT4 receptor. This protein complex may be used in screening methods Also antibodies specifically binding to the C4d multimer or the C4d/ILT4-protein complex are subject of the present invention.
