Milk fat globule EGF factor 8 in the serum of human patients of systemic lupus erythematosus

Hiroshi Yamaguchi^*^,, Junichi Takagi, Takako Miyamae, Shumpei Yokota, Takashi Fujimoto^||, Shinobu Nakamura^||, Shiro Ohshima^¶^,#, Tetsuji Naka^¶^,** and Shigekazu Nagata^*^,^,^,1

^* Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Kyoto, Japan;
Laboratory of Genetics, Integrated Laboratories, Graduate School of Frontier Biosciences and
^¶ Department of Molecular Medicine, Graduate School of Medicine, and
Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, Osaka, Japan;
Department of Pediatrics, Yokohama City University School of Medicine, Yokohama, Japan;
^|| Department of General Medicine, Nara Medical University, Nara, Japan;
^# Department of and Rheumatology and Clinical Research, National Hospital Organization Osaka Minami Medical Center, Osaka, Japan;
^** Laboratory for Immune Signal, National Insutitute of Biomedical Innovation, Osaka, Japan; and
Solution Oriented Research for Science and Technology, Japan Science and Technology Corporation, Kyoto, Japan

¹Correspondence: Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo, Kyoto 606-8501, Japan. E-mail: snagata{at}mfour.med.kyoto-u.ac.jp

ABSTRACT

Mouse milk fat globule epidermal growth factor 8 (MFG-E8), whichis secreted by a subset of activated macrophages, binds to apoptoticcells by recognizing phosphatidylserine and promotes their engulfment.Many apoptotic cells are left unengulfed in the germinal centersof the spleen in MFG-E8^–/– mice, and these micedevelop an autoimmune disease resembling human systemic lupuserythematosus (hSLE). Here, we report that hMFG-E8 bound tophosphatidylserine and an integrin ${alpha}$ _vβ₃ complex. Increasingconcentrations of MFG-E8 generated a bell-shaped response curvefor the efficiency of phagocytosis. That is, in NIH3T3 and MFG-E8^–/–thioglycollate-elicited peritoneal macrophages that do not expressMFG-E8, hMFG-E8 enhanced engulfment at low concentrations butinhibited it at high concentrations. On the other hand, hMFG-E8dose-dependently inhibited the engulfment of apoptotic cellsby MFG-E8^+/+ thioglycollate-elicited peritoneal macrophages,indicating that an excess of MFG-E8 has an inverse effect onthe engulfment of apoptotic cells. To investigate the role ofMFG-E8 in human disease, we generated two mAb against MFG-E8and screened human blood samples for MFG-E8 using an ELISA.We found that some childhood-onset and adult SLE patients carrieda significant level of MFG-E8 in their blood samples. Theseresults suggested that the aberrant expression of MFG-E8 isinvolved in the pathoetiology of some cases of hSLE.

Key Words: apoptosis • clinical immunology • macrophages • autoimmunity • integrin