Characterization of MAX.3 antigen, a glycoprotein expressed on mature macrophages, dendritic cells and blood platelets: identity with CD84

MAX.3 is a monoclonal antibody that preferentially reacts with mature macrophages (MAC), monocyte-derived dendritic cells, megakaryocytes and platelets. In this study, we describe the characterization, purification and identification of the MAX.3 antigen. Immunoprecipitation and SDS/PAGE revealed different molecular masses of MAX.3 antigen in MAC (60-90 kDa) and platelets (58-64 kDa), whereas a similar size (45 kDa) was observed in both cell types after digestion with N-glycosidase F. Lectin affinity and sequential treatment with different glycosidases suggests complex type glycosylation of MAX.3 antigen in MAC and hybrid type glycosylation in platelets. Amino acid sequencing led to the identification of a corresponding cDNA clone and showed its identity to the sequence of the CD84 antigen, a member of the CD2 family of cell surface molecules. MAX.3/CD84 was further studied by immunohistochemistry and a variable expression was found on tissue MAC, confirming this antigen to be mainly a marker for MAC in situ.