Impaired apoptotic cell clearance in the germinal center by Mer-deficient tingible body macrophages leads to enhanced antibody-forming cell and germinal center responses.
Germinal centers (GCs) are specialized microenvironments that generate high-affinity Ab-forming cells (AFCs) and memory B cells. Many B cells undergo apoptosis during B cell clonal selection in GCs. Although the factors that regulate the AFC and GC responses are not precisely understood, it is widely believed that dysregulated AFCs and GCs contribute to autoimmunity. The Mer receptor tyrosine kinase (Mer) facilitates macrophage clearance of apoptotic cells. The Tyro-3, Axl, and Mer receptors, including Mer, suppress TLRs and cytokine-mediated inflammatory responses. We report in this study that tingible body macrophages (TBMφs) in GCs express Mer. Compared to C57BL/6 (B6) controls, Mer-deficient (Mer(-/-)) mice had significantly higher AFC, GC, and Th1-skewed IgG2 Ab (especially IgG2c) responses against the T cell-dependent Ag (4-hydroxy-3-nitrophenyl) acetyl-chicken γ globulin. Mer(-/-) mice had a significantly higher percentage of GC B cells on days 9, 14, and 21 postimmunization compared with B6 controls. Significantly increased numbers of apoptotic cells accumulated in Mer(-/-) GCs than in B6 GCs, whereas the number of TBMφs remained similar in both strains. Our data are the first, to our knowledge, to demonstrate a critical role for Mer in GC apoptotic cell clearance by TBMφs and have interesting implications for Mer in the regulation of B cell tolerance operative in the AFC and GC pathways.
Rahman
Ziaur S M
ZS
Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA 19107-5541, USA. zrahman@mail.jci.tju.edu
Shao
Wen-Hai
WH
Khan
Tahsin N
TN
Zhen
Yuxuan
Y
Cohen
Philip L
PL
D000818:Animals; D000917:Antibody Formation / Q000276:immunology; D000921:Antibody-Producing Cells / Q000276:immunology* / Q000378:metabolism; D017209:Apoptosis / Q000276:immunology*; D002469:Cell Separation; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D018858:Germinal Center / Q000166:cytology / Q000276:immunology; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011518:Proto-Oncogene Proteins / Q000276:immunology* / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology* / Q000378:metabolism; D013154:Spleen / Q000166:cytology / Q000276:immunology; D000076202:c-Mer Tyrosine Kinase
D011518:Proto-Oncogene Proteins; C490767:Mertk protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase