IgM-Dependent Phagocytosis in Microglia Is Mediated by Complement Receptor 3, Not Fcα/μ Receptor.
Microglia play an important role in receptor-mediated phagocytosis in the CNS. In brain abscess and other CNS infections, invading bacteria undergo opsonization with Igs or complement. Microglia recognize these opsonized pathogens by Fc or complement receptors triggering phagocytosis. In this study, we investigated the role of Fcα/μR, the less-studied receptor for IgM and IgA, in microglial phagocytosis. We showed that primary microglia, as well as N9 microglial cells, express Fcα/μR. We also showed that anti-Staphylococcus aureus IgM markedly increased the rate of microglial S. aureus phagocytosis. To unequivocally test the role of Fcα/μR in IgM-mediated phagocytosis, we performed experiments in microglia from Fcα/μR(-/-) mice. Surprisingly, we found that IgM-dependent phagocytosis of S. aureus was similar in microglia derived from wild-type or Fcα/μR(-/-) mice. We hypothesized that IgM-dependent activation of complement receptors might contribute to the IgM-mediated increase in phagocytosis. To test this, we used immunologic and genetic inactivation of complement receptor 3 components (CD11b and CD18) as well as C3. IgM-, but not IgG-mediated phagocytosis of S. aureus was reduced in wild-type microglia and macrophages following preincubation with an anti-CD11b blocking Ab. IgM-dependent phagocytosis of S. aureus was also reduced in microglia derived from CD18(-/-) and C3(-/-) mice. Taken together, our findings implicate complement receptor 3 and C3, but not Fcα/μR, in IgM-mediated phagocytosis of S. aureus by microglia.
Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98195; jweinste@u.washington.edu.
Jonathan R
http://orcid.org/0000-0001-6080-9758
JR
Weinstein
Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98195;
Yi
http://orcid.org/0000-0003-2572-8893
Y
Quan
Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98195;
Josiah F
JF
Hanson
Division of Rheumatology, Department of Medicine, School of Medicine, University of Washington, Seattle, WA 98195; and.
Lucrezia
L
Colonna
Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98195;
Michael
M
Iorga
Department of Immunology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575, Japan.
Shin-ichiro
S
Honda
Department of Immunology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575, Japan.
Kazuko
K
Shibuya
Department of Immunology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575, Japan.
Akira
A
Shibuya
Division of Rheumatology, Department of Medicine, School of Medicine, University of Washington, Seattle, WA 98195; and.
Keith B
KB
Elkon
Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98195;
Thomas
T
Möller
D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D039481:CD11b Antigen / Q000276:immunology; D018821:CD18 Antigens / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D003176:Complement C3 / Q000235:genetics / Q000276:immunology*; D007075:Immunoglobulin M / Q000276:immunology*; D016177:Macrophage-1 Antigen / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D011961:Receptors, Fc / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D013203:Staphylococcal Infections / Q000276:immunology / Q000382:microbiology; D013211:Staphylococcus aureus / Q000276:immunology
D019138:Antibodies, Blocking; D039481:CD11b Antigen; D018821:CD18 Antigens; D003176:Complement C3; C526791:Fcalpha-mu protein, mouse; D007075:Immunoglobulin M; D016177:Macrophage-1 Antigen; D011961:Receptors, Fc