Kristy O’Donnell

SOCS-3 negatively regulates innate and adaptive immune mechanisms in acute IL-1–dependent inflammatory arthritis

RA is an autoimmune disease characterized by sustained imbalance between pro- and antiinflammatory immune mechanisms. The SOCS proteins are negative regulators of cytokine signaling, but to date there has been little information on their function in disease. The generation of Socs3(-/Delta vav) mice, which lack SOCS-3 in the hematopoietic and endothelial cell compartment, allowed us to explore the role of endogenous SOCS-3 during acute inflammatory arthritis. Joint inflammation in Socs3(-/Delta vav) mice was particularly severe and was characterized by increased numbers of neutrophils in the inflamed synovium, bone marrow, peripheral blood, and spleen. These features were most likely due to increased production of and enhanced responsiveness to G-CSF and IL-6 during arthritis in these mice. Local osteoclast generation and bone destruction were also dramatically increased in the absence of SOCS-3, as was macrophage activation. Finally, SOCS-3 was found to negatively regulate CD4+ T lymphocyte activation, including production of the pleiotropic cytokine IL-17. The absence of SOCS-3 therefore had dramatic effects in this disease model, with a broader impact on cellular responses than SOCS-1 deficiency. These findings provide direct in vivo evidence that endogenous SOCS-3 is a critical negative regulator of multiple cell types orchestrating inflammatory joint disease.

Distinct roles for the NF-κB1 (p50) and c-Rel transcription factors in inflammatory arthritis

Rheumatoid arthritis (RA) is a complex disease, with contributions from systemic autoimmunity and local inflammation. Persistent synovial joint inflammation and invasive synovial pannus tissue lead to joint destruction. RA is characterized by the production of inflammatory mediators, many of which are regulated by the Rel/NF-kappaB transcription factors. Although an attractive target for therapeutic intervention in inflammatory diseases, Rel/NF-kappaB is involved in normal physiology, thus global inhibition could be harmful. An alternate approach is to identify and target the Rel/NF-kappaB subunits critical for components of disease. To assess this, mice with null mutations in c-rel or nfkb1 were used to examine directly the roles of c-Rel and p50 in models of acute and chronic inflammatory arthritis. We found c-Rel-deficient mice were resistant to collagen-induced arthritis but had a normal response in an acute, destructive arthritis model (methylated BSA/IL-1 induced arthritis) suggesting c-Rel is required for systemic but not local joint disease. In contrast, p50-deficient mice were refractory to induction of both the chronic and acute arthritis models, showing this subunit is essential for local joint inflammation and destruction. Our data suggest Rel/NF-kappaB subunits play distinct roles in the pathogenesis of inflammatory arthritis and may provide a rationale for more specific therapeutic blockade of Rel/NF-kappaB in RA.

Severe inflammatory arthritis and lymphadenopathy in the absence of TNF.

It has been postulated that TNF has a pivotal role in a cytokine cascade that results in joint inflammation and destruction in rheumatoid arthritis (RA). To evaluate this, we examined the response of TNF-deficient (Tnf(-/-)) mice in two models of RA. Collagen-induced arthritis (CIA) was induced by injection of chick type II collagen (CII) in CFA. Tnf(-/-) mice had some reduction in the clinical parameters of CIA and, on histology, significantly more normal joints. However, severe disease was evident in 54% of arthritic Tnf(-/-) joints. Tnf(-/-) mice had impaired Ig class switching, but preserved T cell proliferative responses to CII and enhanced IFN-gamma production. Interestingly, CII-immunized Tnf(-/-) mice developed lymphadenopathy and splenomegaly associated with increased memory CD4(+) T cells and activated lymph node B cells. Acute inflammatory arthritis was also reduced in Tnf(-/-) mice, although again some mice exhibited severe disease. We conclude that TNF is important but not essential for inflammatory arthritis; in each model, severe arthritis could proceed even in the complete absence of TNF. These results call into doubt the concept that TNF is obligatory for chronic autoimmune and acute inflammatory arthritis and provide a rationale for further studies into TNF-independent cytokine pathways in arthritis.

The Zinc-finger protein ASCIZ regulates B cell development via DYNLL1 and Bim

B cell development requires the Zinc-finger protein and ATM substrate ASCIZ to signal through DYNLL1 and Bim.

c-Myb is required for plasma cell migration to bone marrow after immunization or infection

The transcription factor c-Myb plays a role in establishing long-lived plasma cell populations in the bone marrow by affecting migration responses to chemokine gradients. The absence of c-Myb results in an absence of IgG+ antigen-specific plasma cells in the bone marrow following immunization or virus infection.

The tyrosine kinase Lyn limits the cytokine responsiveness of plasma cells to restrict their accumulation in mice.

A nonreceptor tyrosine kinase inhibits cytokine signaling to prevent the persistence of antibody-secreting cells. Restricting Plasma Cell Survival Plasma cells, which are derived from B cells, are long-lived antibody-secreting cells that help to fight infections and maintain immunological memory. However, in autoimmune diseases such as systemic lupus erythematosus, excess numbers of plasma cells accumulate (plasmacytosis) and produce autoreactive antibodies. Infantino et al. examined mice deficient in the nonreceptor tyrosine kinase Lyn. Lyn-deficient mice exhibit plasmacytosis and autoimmunity. The accumulation of plasma cells in these mice did not depend on inflammation or other immune cell types, but was associated with the increased responsiveness of plasma cells to cytokines that stimulate survival. The findings suggest that Lyn inhibits cytokine signaling to restrict the accumulation of antibody-producing cells. Maintenance of an appropriate number of plasma cells, long-lived antibody-producing cells that are derived from B cells, is essential for maintaining immunological memory while limiting disease. Plasma cell survival relies on extrinsic factors, the limited availability of which determines the size of the plasma cell population. Mice deficient in the nonreceptor tyrosine kinase Lyn are prone to an autoimmune disease that is characterized by inflammation and an excess of plasma cells (plasmacytosis). We demonstrated that the plasmacytosis was intrinsic to B cells and independent of inflammation. We also showed that Lyn attenuated signaling by signal transducer and activator of transcription 3 (STAT3) and STAT5 in response to the cytokines interleukin-6 (IL-6) and IL-3, respectively, in two previously uncharacterized plasma cell signaling pathways. Thus, in the absence of Lyn, the survival of plasma cells was improved, which enabled the plasma cells to become established in excess numbers in niches in vivo. These data identify Lyn as a key regulator of survival signaling in plasma cells, limiting plasma cell accumulation and autoimmune disease susceptibility.

Congenic Nonobese Diabetic Mouse Strains Fail to Confirm Linkage of a Marginal Zone B Lymphocyte Phenotype to the Idd11 Locus on Chromosome 4

I t is well established that B lymphocytes contribute to diabetes pathogenesis in NOD mice (reviewed in Ref. 1). Interestingly, Rolf et al. (2) recently observed that NOD mice exhibit an increase in percentage of splenic marginal zone (MZ) B cells compared with C57BL/6 (B6) mice. Using a cohort of F2(NOD B6) mice, they mapped the control of NOD MZ B cell population enlargement to a region on chromosome (Chr) 4 encompassing a diabetes susceptibility locus, termed Idd11 (2). This overlap suggests that Idd11 might predispose NOD mice to diabetes by affecting this B cell subpopulation, which could prime and/or expand self-reactive T cells specific for pancreatic islet B cell Ags. Confirmation of genetic linkage is best achieved using congenic mouse strains. We have previously confirmed Idd11 on Chr4 using a panel of congenic NOD mouse strains with different Chr4, B6-derived intervals (3). Diabetes-resistant congenic NOD mice localized the Idd11 locus between, but not including, D4Mit338 and D4Mit204, placing this diabetes susceptibility locus within the region linked to the control of MZ B cell enlargement (2, 4). Similar to Rolf et al. (2), we observed the same difference between NOD and B6 mouse strains for percentage of splenic MZ B cells (Fig. 1). In contrast, our congenic NOD mouse strains did not confirm the linkage of this B cell trait to Chr4. We found that NOD mouse strains congenic for Chr4, either encompassing the Idd11 locus or the distal end of Chr4 (Table I), had similar percentages of splenic MZ B cells compared with NOD mice (Fig. 1). Chromosome linkage to a complex trait can be due to an epistatic effect of two or more genes located some distance apart on the same chromosome. For example, B6-derived alleles may be required in combination at two or more different genes on Chr4 to affect a decrease in the level of MZ B cells in NOD mice. As a further test of the Chr4 linkage, we compared NOD mice with congenic NOD mice harboring a larger Chr4, B6-derived interval (Table I). Once again, there was no significant difference between NOD and congenic mice for the percentage of splenic MZ B cells (Fig. 1). It is apparent from our results that the Idd11 locus, on its own, does not control the level of splenic MZ B cells. Although linkage to Chr4 may represent a false positive result, Rolf et al. (2) did observe suggestive linkage to regions on Chr1, 9, 19 and the proximal end of Chr4, not covered by our congenic mouse strains. It is possible that B6 alleles are required at more than one locus to affect the MZ B cell population, in which case it may prove difficult to confirm and fine map genes contributing to this phenotype. Nonetheless, it seems unlikely that the Idd11 locus contributes to diabetes pathogenesis by affecting this B Table I. Genetic intervals for Chr4 congenic mouse strains

Environmental sensing by mature B cells is controlled by the transcription factors PU.1 and SpiB

Humoral immunity requires B cells to respond to multiple stimuli, including antigen, membrane and soluble ligands, and microbial products. Ets family transcription factors regulate many aspects of haematopoiesis, although their functions in humoral immunity are difficult to decipher as a result of redundancy between the family members. Here we show that mice lacking both PU.1 and SpiB in mature B cells do not generate germinal centers and high-affinity antibody after protein immunization. PU.1 and SpiB double-deficient B cells have a survival defect after engagement of CD40 or Toll-like receptors (TLR), despite paradoxically enhanced plasma cell differentiation. PU.1 and SpiB regulate the expression of many components of the B cell receptor signaling pathway and the receptors for CD40L, BAFF and TLR ligands. Thus, PU.1 and SpiB enable B cells to appropriately respond to environmental cues.Although important for early development, PU.1 is dispensable for mature B cell function, possibly owing to compensation by the related transcription factor SpiB. Here the authors show PU.1 and SpiB are collectively required for humoral immunity, through regulation of germinal centre formation and plasma cell differentiation.

Arginine methylation catalyzed by PRMT1 is required for B cell activation and differentiation

Arginine methylation catalyzed by protein arginine methyltransferases (PRMT) is a common post-translational modification in mammalian cells, regulating many important functions including cell signalling, proliferation and differentiation. Here we show the role of PRMT1 in B-cell activation and differentiation. PRMT1 expression and activity in human and mouse peripheral B cells increases in response to in vitro or in vivo activation. Deletion of the Prmt1 gene in mature B cells establishes that although the frequency and phenotype of peripheral B cell subsets seem unaffected, immune responses to T-cell-dependent and -independent antigens are substantially reduced. In vitro activation of Prmt1-deficient B cells with a variety of mitogens results in diminished proliferation, differentiation and survival, effects that are correlated with altered signal transduction from the B cell receptor. Thus PRMT1 activity in B cells is required for correct execution of multiple processes that in turn are necessary for humoral immunity.PRMT1 is an arginine methyltransferase involved in a variety of cell functions. Here the authors delete PRMT1 specifically in mature B cells to show the importance of arginine methylation for B cell proliferation, differentiation and survival, and thereby for humoral immunity.