Mouse mast cell tryptase mMCP-6 is a critical link between adaptive and innate immunity in the chronic phase of Trichinella spiralis infection

New developments in mast cell biology

Mast cells can function as effector and immunoregulatory cells in immunoglobulin E-associated allergic disorders, as well as in certain innate and adaptive immune responses. This review focuses on exciting new developments in the field of mast cell biology published in the past year. We highlight advances in the understanding of FcvarepsilonRI-mediated signaling and mast cell-activation events, as well as in the use of genetic models to study mast cell function in vivo. Finally, we discuss newly identified functions for mast cells or individual mast cell products, such as proteases and interleukin 10, in host defense, cardiovascular disease and tumor biology and in settings in which mast cells have anti-inflammatory or immunosuppressive functions.

Genetic inversion in mast cell-deficient (Wsh) mice interrupts corin and manifests as hematopoietic and cardiac aberrancy

Mast cells participate in pathophysiological processes that range from antimicrobial defense to anaphylaxis and inflammatory arthritis. Much of the groundwork for the understanding of mast cells was established in mice that lacked mast cells through defects in either stem cell factor or its receptor, Kit. Among available strains, C57BL/6-Kit(W-sh) (W(sh)) mice are experimentally advantageous because of their background strain and fertility. However, the genetic inversion responsible for the W(sh) phenotype remains poorly defined, and its effects beyond the mast cell have been incompletely characterized. We report that W(sh) animals exhibit splenomegaly with expanded myeloid and megakaryocyte populations. Hematopoietic abnormalities extend to the bone marrow and are reflected by neutrophilia and thrombocytosis. In contrast, mast cell-deficient WBB6F1-Kit(W)/Kit(W-v) (W/W(v)) mice display mild neutropenia, but no changes in circulating platelet numbers. To help define the basis for the W(sh) phenotype, a "DNA walking" strategy was used to identify the precise location of the 3' breakpoint, which was found to reside 67.5 kb upstream of Kit. The 5' breakpoint disrupts corin, a cardiac protease responsible for the activation of atrial natriuretic peptide. Consistent with this result, transcription of full-length corin is ablated and W(sh) mice develop symptoms of cardiomegaly. Studies performed using mast cell-deficient strains must consider the capacity of associated abnormalities to either expose or compensate for the missing mast cell lineage.

The mouse mast cell-restricted tetramer-forming tryptases mouse mast cell protease 6 and mouse mast cell protease 7 are critical mediators in inflammatory arthritis

OBJECTIVE

Increased numbers of mast cells (MCs) that express beta tryptases bound to heparin have been detected in the synovium of patients with rheumatoid arthritis (RA). The corresponding tryptases in mice are mouse MC protease 6 (mMCP-6) and mMCP-7. Although MCs have been implicated in RA and some animal models of arthritis, no direct evidence for a MC-restricted tryptase in the pathogenesis of inflammatory arthritis has been shown. We created transgenic mice that lack heparin and different combinations of mMCP-6 and mMCP-7, to evaluate the roles of MC-restricted tryptase-heparin complexes in an experimental model of arthritis.

METHODS

The methylated bovine serum albumin/interleukin-1beta (mBSA/IL-1beta) experimental protocol was used to induce inflammatory monarthritis in different mouse strains. Mice were killed at the time of peak disease on day 7, and histochemical methods were used to assess joint pathology.

RESULTS

Arthritis was induced in the knee joints of mBSA/IL-1beta-treated mMCP-6(+)/mMCP-7(-) and mMCP-6(-)/mMCP-7(+) C57BL/6 mice, and numerous activated MCs that had exocytosed the contents of their secretory granules were observed in the diseased mice. In contrast, arthritis was markedly reduced in heparin-deficient mice and in mMCP-6(-)/mMCP-7(-) C57BL/6 mice.

CONCLUSION

MC-derived tryptase-heparin complexes play important roles in mBSA/IL-1beta-induced arthritis. Because mMCP-6 and mMCP-7 can compensate for each other in this disease model, the elimination of both tryptases is necessary to reveal the prominent roles of these serine proteases in joint inflammation and destruction. Our data suggest that the inhibition of MC-restricted tryptases could have therapeutic potential in the treatment of RA.

A negative regulator of delayed prostaglandin D2 production in mouse mast cells

We have previously shown that maturation of mouse bone marrow-derived mast cells (BMMCs) into connective tissue mast cells (CTMCs) upon coculture with fibroblasts in the presence of stem cell factor (kit ligand) is accompanied by marked induction of a panel of genes, one of which was identified as NLRP3. Here we report that NLRP3 acts as a novel negative regulator of delayed prostaglandin (PG) D(2) production in BMMCs. We found that, apart from its cell maturation-associated induction, NLRP3 expression was markedly induced in BMMCs several hours after FcepsilonRI crosslinking or cytokine stimulation. Ectopic expression of NLRP3 in BMMCs resulted in marked attenuation of cyclooxygenase (COX)-2-dependent delayed PGD(2) generation, whereas it had no effects on other effector functions, including degranulation, COX-1-dependent immediate PGD(2) generation and cytokine/chemokine expression. The suppression of delayed PGD(2) generation by NLRP3 was preceded by a transient decrease of NF-kappaB activation and a marked reduction in the expression of COX-2, but not that of cytosolic phospholipase A(2) alpha (cPLA(2)alpha), COX-1 and hematopoietic PGD(2) synthase. Moreover, in CTMC-like differentiated cells in which endogenous NLRP3 expression was induced, cytokine-stimulated induction of COX-2 and attendant delayed PGD(2) generation were markedly reduced. Our results suggest that, in mouse mast cells, NLRP3 counter-regulates COX-2-dependent sustained production of PGD(2), a prostanoid that exhibits both pro- and anti-allergic effects, thereby potentially influencing the duration of allergic and other mast cell-associated inflammatory diseases.

Immunomodulatory mast cells: negative, as well as positive, regulators of immunity

Mast cells can promote inflammation and other tissue changes in IgE-associated allergic disorders, as well as in certain innate and adaptive immune responses that are thought to be independent of IgE. However, mast cells can also have anti-inflammatory and immunosuppressive functions. Here, we review the evidence that mast cells can have negative, as well as positive, immunomodulatory roles in vivo, and we propose that mast cells can both enhance and later suppress certain features of an immune response.