1010 - Expression of Caspase 8 in Dendritic Cells Is More Potent Than in Myeloid Cells in the Prevention of SLE-Like Disease Onset

Monday, November 7, 2011: 9:00 AM-6:00 PM
Hall F2 - Poster Hall (McCormick Place West)
Carla M. Cuda1, Jaime Chowaniec1, Jack Hutcheson2, G. Kenneth Haines III3, Chandra Mohan2 and Harris R. Perlman4, 1Northwestern University Feinberg School of Medicine, Chicago, IL, 2University of Texas Southwestern Medical Center, Dallas, TX, 3Yale University, New Harven, CT, 4Northwestern University, Chicago, IL
Presentation Number: 1010

Background/Purpose:  Caspase 8 has been referred to as the initiator caspase of the death receptor mediated extrinsic apoptotic pathway.  The death receptor Fas can trigger the extrinsic apoptotic pathway, and loss of Fas in macrophages and dendritic cells (DCs) results in autoimmunity.  Deletion of caspase 8 revealed non-apoptotic roles for this molecule in regulating embryonic development, lymphocyte activation and proliferation, and NFκB activation, though its effect on non-proliferating immune cells such as macrophages or DCs remains unknown.  Due to caspase 8’s involvement in the activation of apoptosis triggered by multiple death receptors as well as signaling via non-apoptotic pathways, it was of interest to assess how loss of caspase 8 in either macrophages or DCs would affect development of systemic autoimmunity.

Method:  Mice with caspase 8 flanked by loxP sites (Casp8flox/flox) were crossed with mice expressing Cre under control of either the lysozyme M gene promoter (CreLysM), which functions in mature lysozyme-expressing cells of the myelomonocytic lineage, or the CD11c gene promoter (CreCD11c), which is expressed by dendritic cells.  Both CreLysMCasp8flox/flox and CreCD11cCasp8flox/flox mice were verified by RT-PCR.  Flow cytometric analysis was employed to characterize both myeloid and lymphoid cell distribution and activation in bone marrow, blood, lymph node, and spleen.  Luminex-based assays and ELISAs were used to detect serum cytokine and Ig levels.  Immunohistochemical staining revealed kidney pathology.

Result:  With age, both CreCD11cCasp8flox/flox and CreLysMCasp8flox/flox mice presented with a break in tolerance, as indicated by splenomegaly, lymphadenopathy, and autoantibody production, though these phenotypes were more exaggerated in CreCD11cCasp8flox/flox mice.  While central and peripheral lymphoid organ analysis revealed that this break occurs via peripheral mechanisms, it also strikes early in development.  Peripherally, both myeloid cell and DC-specific loss of caspase 8 not only increased circulating granulocytes and Gr-1+ monocytes, as well as splenic and lymph node antigen presenting cells.  Additionally, increased peripheral effector T cells coincided with decreased peripheral naïve T cell populations.  Moreover, not only did loss of caspase 8 in DCs and myeloid cells intrinsically amplified DC and macrophage activation, respectively, while affecting activation of other immune cells in a paracrine fashion.  In an in vitro antigen-specific MLR, CreCD11cCasp8flox/flox DCs induced T cell proliferation, while CreLysMCasp8flox/flox macrophages inhibited proliferation.  Elevated serum IL-12, TNFα, sRANKL levels were common to both strains, though CreCD11cCasp8flox/flox mice presented with heightened IgG2b levels and more severe kidney pathology.

Conclusion:  These results demonstrate that while loss of caspase 8 in both DCs or myeloid cells initiates inflammatory phenotypes, intact caspase 8 signaling appears to be more crucial in DCs than in myeloid cells to prevent systemic autoimmunity.  These data have implications for autoimmunity by elucidating previously unknown functions of a potentially useful target for therapy.

Keywords: apoptosis, autoantibodies, dendritic cells, lupus nephritis and macrophages

Disclosure: C. M. Cuda, None; J. Chowaniec, None; J. Hutcheson, None; G. K. Haines III, None; C. Mohan, None; H. R. Perlman, None.