Functional Expression of IgG-Fc Receptors in Human Airway Smooth Muscle Cells

Abstract

IgE-Fc receptors and IgG-Fc receptors are expressed on hematopoietic cells, but some evidence suggests that these receptors are also found on nonhematopoietic cells, including human airway smooth muscle (hASM) cells. Our study characterizes the expression of IgE-Fc receptors (FcεRI/CD23) and IgG-Fc receptors (FcγRs-I, -II, and -III) in cultured hASM cells by flow cytometry and Western blotting, and the functional activity of receptors was determined through quantification of cell proliferation and released cytokines. Expression of Fc receptor-linked intracellular signaling proteins and phosphorylation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1/2 and p38(MAPK) in hASM cells was examined by Western blotting. Expression of FcεRI and CD23 was not detectable in hASM cells. However, FcγRI and FcγRII were shown to be expressed on these cells. Specific antibodies, validated using transfected cell lines, revealed that the inhibitory IgG receptor, FcγRIIb, was the most abundant Fc receptor subtype expressed. Although cross-linking FcγR with heat-aggregated γ globulin (HAGG) did not induce detectable cell stimulation, pretreating hASM cells with HAGG significantly inhibited IL-1α-induced increases in cytokine levels and basic fibroblast growth factor-induced cell proliferation. This inhibitory effect of HAGG was abrogated by preincubation of cells with an anti-FcγRIIb antigen-binding fragment (Fab). Expression of proteins involved in the canonical FcγRIIb inhibitory signaling pathway was established in hASM cells. Pretreatment of hASM cells with HAGG significantly inhibited IL-1α- and basic fibroblast growth factor-induced extracellular signal-regulated kinase 1/2 and p38(MAPK) phosphorylation. This study identifies functional expression of FcγRIIb in hASM cells, with the potential to suppress their remodeling and immunomodulatory roles.

Secreted Factors from Human Mast Cells Trigger Inflammatory Cytokine Production by Human Airway Smooth Muscle Cells

“…hASM cells basally secrete IL-8 and IL-6 and the cells produced similar levels of the measured cytokine after treatment with hIgE/antigen (fig. 1a), consistent with previous findings that there is no functional IgE receptor expression on cultured hASM cells [31,37]. …”

“…We recently showed expression of the Src kinase Lyn in hASM cells [37]. Another study also reported Lyn expression in hASM cells alongside a number of other Src kinases including Fyn, YES, and c-SRC [60].…”

“…This argues against HMCα-derived IL-1β, TNFα, and INFγ being responsible for the hASM cell activation. It may be that there are multiple mast cell-derived factors differentially regulating IL-8 and IL-6 production from hASM cells or, alternatively, that there are different signaling pathways differentially controlling IL-8 and IL-6 production in hASM cells [37]. Src kinases are known to activate numerous signaling cascades [62], and further studies are thus required to reveal the pathway important for the ability of the HMCα-derived active factor/factors to induce IL-8 production from hASM cells.…”

Symphony of Vascular Contraction

“…76-79 In an analogous way necrotic cell death is increased in hypertension giving rise to DAMPs. Various DAMPs are associated with hypertension (e.g.…”

Direct evidence for functional smooth muscle myosin II in the 10S self-inhibited monomeric conformation in airway smooth muscle cells

“…This raises the possibility that a significant amount of 10S myosin may exist in this muscle type. The cultured hASMCs used here (10)(11)(12)(13)(14)(15)(16)(17)(18)(19) are defined as smooth muscle cells because (i) they express smooth muscle restricted genes, i.e., SMM, calponin, smooth muscle tropomyosin, α and γ smooth muscle actins, SM22, and smoothelin; (ii) growth arrest of proliferating cells by serum deprivation in the presence of TGF-β further up-regulates expression of these genes in the so-called "contractile" phenotype; (iii) they express many different functionally coupled receptors and activation of these receptors causes changes in cell Ca 2+ and RLC phosphorylation as in intact airway muscle; (iv) they contract when embedded in a 3D collagen matrix and relax in response to agents that increase cAMP; and (v) they synthesize the same cytokines and chemokines as primary airway smooth muscle cells. These molecular and functional characteristics are all shared with intact smooth muscle tissue.…”