Abstract
Integrin alpha IIb beta 3 is expressed in mast cells as well as in megakaryocytes/platelets. A recent study has shown that surface expression levels of integrin alpha V beta 3 are elevated in integrin alpha IIb-deficient bone marrow-derived mast cells (BMMCs) as compared with wild-type (WT) counterparts, but the underlying mechanism remains obscure. Here we demonstrate by transducing integrin alpha IIb into integrin alpha IIb-deficient BMMCs that surface expression levels of integrin alpha V beta 3 are inversely related to those of integrin alpha IIb beta 3. Thus, competitive association of integrin beta 3 with integrin alpha IIb or integrin alpha V determines surface expression levels of integrin alpha IIb beta 3 or alpha V beta 3 in mast cells. We compared WT and integrin alpha IIb-deficient BMMCs as well as integrin alpha IIb-deficient BMMCs transduced with integrin alpha IIb(WT) or non-functional alpha IIb(D163A) mutant and found that enhancement of proliferation, degranulation, cytokine production, and migration of BMMCs through interaction with fibrinogen (FB) depended on integrin alpha IIb beta 3. In addition, elevated surface expression of integrin alpha V beta 3 failed to compensate for loss of FB-associated functions in integrin alpha IIb-deficient BMMCs while enhancing adhesion to vitronectin or von Willebrand factor. Importantly, integrin alpha IIb deficiency strongly suppressed chronic inflammation with the remarkable increase of mast cells induced by continuous intraperitoneal administration of FB, although it did not affect acute allergic responses or mast cell numbers in tissues in steady states. Interestingly, soluble FB promoted cytokine production of BMMCs in response to Staphylococcus aureus with FB-binding capacity, through integrin alpha IIb beta 3-dependent recognition of this pathogen. Collectively, integrin alpha IIb beta 3 in mast cells plays an important part in FB-associated, chronic inflammation and innate immune responses.
Highlights
Mast cells play a critical role in IgE-associated allergic disorders, but recent advances have delineated the involvement of mast cells in IgE-independent physiological and pathological processes, including certain innate immune responses
Surface Expression Levels of Integrin ␣V Are Elevated in Integrin ␣IIb-deficient bone marrow-derived mast cells (BMMCs)—To investigate the role of integrin ␣IIb in mast cells, bone marrow cells from WT and integrin ␣IIbϪ/Ϫ mice were cultured in the presence of IL-3 for 5 weeks to generate comparable numbers of morphologically pure (Ͼ95%) mast cells
Experiments using blocking Abs specific for integrins demonstrated that adhesion to FB, VN, or von Willebrand factor (vWF) was mediated through integrin ␣IIb3, integrin ␣V3, or both, respectively [9]
Summary
Mice—All experimental mice were sex- and age-matched (6 –16 weeks old). Balb/c mice were purchased from Charles River Japan (Tokyo, Japan). 5 ϫ 104 cells of IgEsensitized BMMCs in Tyrode buffer (10 mM HEPES buffer (pH 7.4), 130 mM NaCl, 5 mM KCl, and 5.6 mM glucose) containing 0.1% BSA, 1 mM CaCl2, and 0.5 mM MgCl2 were stimulated with the indicated concentration of TNP-BSA in BSA- or FB-coated 96-well plates for 1 h at 37 °C. The amounts of extravasated dye were measured after 30 min by extracting ears In another type of experiment, mice received anti-DNP IgE intravenously. Quantitation of Tissue Mast Cells—Tissue mast cells in ear skin, back skin, peritoneal wall, and intestine were quantified by light microscopy at ϫ400 by an observer who was unaware of the identity (i.e. mouse genotype) of the individual specimens, in Giemsa-stained sections, as previously described [28, 35, 36]. Statistical significance was determined by Student’s t test, with p Ͻ 0.01 (**) and p Ͻ 0.05 (*) taken as being statistically significant
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