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.


MASP-1 and Pro-Factor D Proteins Are Present in Synoviocytes and May Locally Activate the Complement Alternative Pathway To Induce Inflammatory Arthritis in Mice.

Banda4,  Nirmal K., Takahashi2,  Minoru, Glogowska4,  Magdalena J., Takahashi3,  Kazue, Stahl1,  Gregory L., Fujita2,  Teizo, Arend4,  William P.

Center for Experimental Therapeutics and Reperfusion Injury, Brigham and Women's Hospital, Boston, MA
Department of Immunology, Fukushima Medical University School of Medicine, Fukushima, Japan
Department of Immunology, Massachusetts General Hospital for Children, Boston, MA
Division of Rheumatology, University of Colorado at Denver, Aurora, CO

Purpose:

Mannose-binding lectin-associated serine proteases 1/3 (MASP-1/3) can cleave pro-factor D (pro-Df) into active factor D (Df), which is required for activation of the alternative complement pathway (AP). The AP is both necessary and sufficient for mediation of collagen antibody-induced arthritis (CAIA) in mice. We have recently shown that MASP1/3-/- mice are resistant to CAIA due to a defective AP and MASP-1/3 protein is the predominant mechanism to cleave pro-Df in vivo. The objectives of this study were to examine whether MASP-1/3 not bound to mannose-binding lectin (MBL) or ficolins (FCN) can activate the AP, and if MASP-1 and pro-Df proteins are present in the joint.

Methods:

Sera from wild type (WT), MASP-1/3-/-, MBL-/-/FCN A-/- and FCN A-/- C57BL/6 mice were used. CAIA was induced in WT and MASP-1/3-/- mice by injecting 4 anti-type II collagen (CII) mAb i.p. on day 0 and LPS i.p. on day 3. All mice were sacrificed on day 10. Sera from CAIA mice (with and without disease) and MBL-/-/FCN A-/- mice were analyzed by western blot analysis for the presence of pro-Df and Df. Immunohistochemical (IHC) analysis was performed for the presence of MASP-1/3 and pro-Df proteins in the knee joints of mice with or without CAIA. Sera from MBL-/-/FCN A-/- mice were examined for the presence of MASP-1 using a gel filtration assay followed by western blot analysis. Additionally, sera from MBL-/-/FCN A-/- and FCN A-/- mice were examined in vitro for AP activation induced by anti-CII antibodies, zymosan and mannan.

Results:

In the sera of WT and MBL-/-/FCN A-/- mice, factor D existed exclusively in its active form, indicating that pro-Df is cleaved by MASP-1 in both sera. Conversely, sera from MASP1/3-/- mice contained only pro-Df. There was no conversion of pro-Df to Df between day 0 (without disease) and day 10 (with CAIA) in MASP1/3-/- mice. MASP-1/3 proteins are normally bound to MBL or FCN; however, we detected MASP-1/3 in the sera of MBL-/-/FCN A-/- mice which might be bound to an unknown protein. Anti-CII mAb, zymosan and mannan particles all induced C3b deposition and C3a and C5a generation in vitro using sera from MBL-/-/FCN A-/- and FCN A-/- mice under conditions where only the AP was active. These results suggest that MASP-1/3 is present in the circulation of MBL-/-/FCN A-/- mice and can initiate the AP of complement in vitro. IHC analysis showed the presence of MASP-1/3 in the synovium, but not on chondrocytes, in the knee joints of WT mice with CAIA. Pro-Df was found by IHC both in the synovium and on chondrocytes in the knee joints of MASP1/3-/- mice without CAIA. These results indicate that MASP-1/3 protein is the predominant mechanism for cleavage of pro-Df in vivo and may activate the AP locally. Future studies will examine whether MASP-1 and pro-Df proteins are produced by the same cell in the synovium and whether conversion of pro-Df to Df occurs locally inside the cell or in the microenvironment.

Conclusions:

MASP-1/3 protein predominantly cleaves pro-Df in vivo in CAIA. This study demonstrated that MASP-1/3, in the absence of MBL or FCN, can act locally in the knee joint and in the circulation to initiate the AP and inflammatory disease.

To cite this abstract, please use the following information:
Banda, Nirmal K., Takahashi, Minoru, Glogowska, Magdalena J., Takahashi, Kazue, Stahl, Gregory L., Fujita, Teizo, et al; MASP-1 and Pro-Factor D Proteins Are Present in Synoviocytes and May Locally Activate the Complement Alternative Pathway To Induce Inflammatory Arthritis in Mice. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :2227
DOI: 10.1002/art.29991

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