Functional derivatives of ICAM-1 which are substantially capable of binding to LFA-1 but are substantially incapable of binding to MAC-1

An ICAM-1 functional derivative which is substantially incapable of binding to MAC-1 but is substantially capable of binding to LFA-1, wherein said functional derivative comprises domains 1-3 of ICAM-1 and said functional derivative further contains a substitution or deletion of one or more of the amino acid residues from about residues 229 to 231 and from about 254 to 256 within domain 3 of ICAM-1 or an insertion of one or more amino acid residues within the region from about residues 229 to 231 and from about 254 to 256 within domain 3 of ICAM-1.