Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


FLIP: The Novel Regulator of Macrophage Differentiation and Granulocyte Homeostasis.

Huang2,  Qi Quan, Perlman2,  Harris R., Huang3,  Zan, Birkett3,  Robert, Crispino3,  John D., Pope1,  Richard M.

Northwestern Univ Med School, Chicago, IL
Northwestern University, Chicago, IL
Northwestern University

Background and Purpose:

Macrophages are important mediators of innate immunity and chronic inflammation, and play an important pathogenic role in rheumatoid arthritis. In order to further understand the cellular mechanisms contributing to the persistence of macrophages in RA, a myeloid lineage Flip knock out mouse line has been generated. Characterization of these mice demonstrated that FLIP was necessary for macrophage differentiation and survival, that macrophages are essential for maintaining granulocyte homeostasis.

Methods:

Mice bearing floxed Flip alleles crossed with LysM-cre mice resulted in FLIP deletion in the myeloid cell lineage. The cell types in circulation and tissues were examined by morphology and by flow cytometry. Mixed chimera bone marrow reconstitution experiments were performed employing by CD45.1+ and CD45.2+ congenic C57BL/6 mice. Serum cytokines were quantified by LUMINEX 200. In vitro macrophage differentiation was performed from CD117+ bone marrow hematopoietic stem cells. Flip In vitro deletion was induced by recombinant Cre retro-virus.

Results:

In addition to postnatal growth retardation and premature death, myeloid specific FLIP deficient mice exhibited a dramatic increase of circulating neutrophils and multi-organ neutrophil infiltration, which was mediated by increased cytokines and growth factors. Mature macrophages in the spleen, lymph nodes and the peritoneal cavity were significantly reduced. Further analysis of cells in peritoneal cavity discovered a significant inverse non-linear correlation of peritoneal macrophages and granulocytes. That is if macrophages were present, neutrophils were kept in a homeostatic level. In vitro, CD117+ bone marrow progenitor cells failed to differentiate into macrophages when Flip was deleted. This defect was observed not only in the mature macrophages, and there are also decreased numbers of the less mature myeloid progenitors. The bone marrow reconstitution experiments demonstrated that the primary defect was a cell autonomous defect of the bone marrow derived cells, since these cells were capable to transferring the disease, in the absence of competitor wild type cells. Further, the mixed chimera experiments demonstrated that knockout bone marrow cells were not able to compete with the wild type cells, due to increased cytokines and growth factors induced stem cell exhaustion, prior to cell transfer from the knockout mice.

Conclusions:

These observations demonstrate that FLIP is necessary for macrophage differentiation and survival. The myeloid specific deletion of FLIP resulted in the loss of macrophages and consequently an increase of neutrophils. Neutrophilia and inflammation is secondary to the loss of macrophages and contributed by increased cytokines and growth factors. Since both macrophages and granulocytes are major inflammatory cell types involved in the pathogenesis of rheumatoid arthritis, further understanding of their homeostatic regulation will provide new insights into the mechanisms that control of inflammation.

To cite this abstract, please use the following information:
Huang, Qi Quan, Perlman, Harris R., Huang, Zan, Birkett, Robert, Crispino, John D., Pope, Richard M.; FLIP: The Novel Regulator of Macrophage Differentiation and Granulocyte Homeostasis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :854
DOI: 10.1002/art.28622

Abstract Supplement

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