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.


TLR9 Induced Macrophage Activation Syndrome Is Driven by IFN Produced by Lymphocytes and Natural Killer Cells but Is Dampened by Lymphocyte Produced IL-10.

Behrens2,  Edward M., Slade3,  Katharine, Rao3,  Sheila, Kreiger1,  Portia A., Paessler3,  Michele, Kambayashi5,  Taku, Koretzky4,  Gary A.

A.I. DuPont Hospital for Children
Childrens Hospital of Phil, Philadelphia, PA
The Children's Hospital of Philadelphia
University of Pennsylvania, Philadelphia, PA
University of Pennsylvania

Purpose:

Macrophage Activation Syndrome (MAS) is a clinical entity consisting of massive inflammation, cytopenia, and multi-system organ failure associated with an overproduction of IFNg. Previous murine models implicate genetic defects in CD8+ T-cell cytotoxicty as the cause of the syndrome. However, this model does not explain the link of MAS with genetically normal patients having rheumatologic disease or Epstein Barr Virus (EBV) infections. To investigate the pathoetiology of MAS in inflamed, genetically normal animals, we utilized a system of chronic inflammation driven by Toll-like receptor (TLR) stimulation.

Methods:

Mice treated with every other day i.p. injection of CpG (TLR9 agonist) for 10 days. Cytokines were measured by ELISA, cell surface markers by flow cytometry, and organs were taken for histology. Natural killer (NK) cells were depleted using the PK136 anitbody (100 mg i.p. every day).

Results:

CpG treated mice develop pancytopenia, splenomegaly, microthrombosis, hepatitis, hyperferritinemia, and elevated serum IFNg consistent with MAS. None of these changes occur in PBS injected control mice. Only a small population of CD8+ T-cells are activated by the CpG treatment as measured by CD69 levels. In contrast, Natural Killer (NK) cells show a more robust CD69 upregulation. Consistent with previous MAS models, disease is dependent on IFNg as IFNg-/- CpG treated mice are protected from disease. Unlike previous models, CpG treated b2m-/- mice lacking CD8+ T-cells develop disease to the same extent as wild type mice showing that CD8+ T-cells are not required. Furthermore, Rag-/- mice develop CpG induced disease, showing that all B- and T-cells are dispensable. NK cell depleted mice develop disease suggesting NK cells are dispensable. However, Rag/common gamma chain (Rag/cgc -/-) doubly deficient mice missing B-, T- and NK cells have greatly reduced disease. Thus, in the absence of adaptive immunity, NK cells are required for full disease expression. Interestingly, consistent with incomplete protection, Rag/cgc -/- CpG treated mice produce half as much IFNg as Rag-/- mice suggesting that an IFNg producing myeloid cell also contributes to disease. IL-10 is also produced by CpG treated mice, but is reduced in IFNg-/- mice suggesting it is produced in response to IFNg induced inflammation. IL-10 is also reduced in CpG treated Rag-/- mice, which develop enhanced liver disease, suggesting both that the source of IL-10 is from lymphocytes, and that its production is protective.

Conclusions:

Our novel mouse model shows that MAS can result from TLR stimulation. This provides a rationale for the link between MAS and rheumatic diseases such as Still's Disease and lupus, both of which are associated with TLR activation, as well as the association of MAS with EBV, a TLR9 stimulating virus. We show that NK cells are important mediators of disease, a cell population implicated in the etiology of Still's Disease. We show that IFNg is critical for driving disease, but that IL-10 from a lymphocyte origin is protective. Interestingly, these studies also suggest a role for an IFNg producing myeloid cell, a population whose relevance has been controversial, in driving this disease process.

To cite this abstract, please use the following information:
Behrens, Edward M., Slade, Katharine, Rao, Sheila, Kreiger, Portia A., Paessler, Michele, Kambayashi, Taku, et al; TLR9 Induced Macrophage Activation Syndrome Is Driven by IFN Produced by Lymphocytes and Natural Killer Cells but Is Dampened by Lymphocyte Produced IL-10. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1354
DOI: 10.1002/art.29120

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