Mycorrhizal specificity differences in epiphytic habitat: three epiphytic orchids harbor distinct ecological and physiological specificity.

Orchidaceae has diversified in tree canopies and accounts for 68% of vascular epiphytes. Differences in mycorrhizal communities among epiphytic orchids can reduce species competition for mycorrhizal fungi and contribute to niche partitioning, which may be a crucial driver of the unusual species diversification among orchids. Mycorrhizal specificity-the range of fungi allowing mycorrhizal partnerships-was evaluated by assessment of mycorrhizal communities in the field (ecological specificity) and symbiotic cultures in the laboratory (physiological specificity) for three epiphytic orchids inhabiting Japan. Mycorrhizal communities were assessed with co-existing individuals growing within 10 cm of each other, revealing that ecological specificity varied widely among the three species, ranging from dominance by a single Ceratobasidiaceae fungus to diverse mycobionts across the Ceratobasidiaceae and Tulasnellaceae. In vitro seed germination tests revealed clear differences in physiological specificity among the three orchids, and that the primary mycorrhizal partners contributed to seed germination. In vitro compatibility ranges of three orchids strongly reflect the mycorrhizal community composition of wild populations. This suggests that differences in in situ mycorrhizal communities are not strongly driven by environmental factors, but are primarily due to physiological differences among orchid species. This study shows that the symbiotic strategy among the epiphytic orchid species varies from specialized to generalized association, which may contribute to biotic niche partitioning.

Novel phospho-specific monoclonal antibodies reveal differential regulation of tyrosine phosphorylation within the immunoreceptor tyrosine-based activation motif of the Fc receptor γ subunit leading to fine tuning of Syk activation.

The cytoplasmic region of the γ chain of the high-affinity receptor for IgE (FcεRI) contains a consensus sequence termed the immunoreceptor tyrosine-based activation motif (ITAM). Phosphorylation of the two tyrosine residues (N-terminal Y47 and C-terminal Y58) in the ITAM sequence is crucial for the recruitment and activation of Syk, a cytoplasmic tyrosine kinase with central signaling roles in mast cells. Using a reconstitution system in which individual tyrosine-to-phenylalanine substituted γ chains were expressed in γ-chain-deficient mast cells, we previously reported differential dephosphorylation of these tyrosines. Herein, we developed monoclonal antibodies highly specific to the phosphorylated Y47 and Y58 residues, which enables monitoring their phosphorylation under more physiological conditions. Using these antibodies, preferential dephosphorylation of Y58 following FcεRI stimulation was confirmed. Furthermore, Y58 is potentially more susceptible to phosphorylation than is Y47. Consistent with this, an in vitro kinase assay using these phospho-specific antibodies demonstrated that the Src family kinase Lyn, which is primarily responsible for ITAM phosphorylation, phosphorylates Y58 more efficiently than Y47. These results indicate that Y58 is more susceptible to dephosphorylation and phosphorylation than is Y47. Because a phosphate group on Y58 is more important for Syk binding than is a phosphate group on Y47, the preferential phosphorylation and dephosphorylation of Y58 may contribute to the fine tuning of Syk activity by promoting rapid recruitment and reducing excessive activation.

The mycorrhizal community of the epiphytic orchid Thrixspermum japonicum is strongly biased toward a single Ceratobasidiaceae fungus, despite a wide range of fungal partners.

PREMISE: Orchids depend primarily on mycorrhizal fungi to obtain nutrients throughout their life cycle. Epiphytic orchids account for 69% of orchid diversity. The unstable availability of water and nutrients in their arboreal habitats often results in severe water and nutrient stresses. Consequently, mycorrhizal associations may be important for the survival of epiphytic orchids, but our understanding thereof remains limited. Here, we investigated the mycorrhizal community in a single epiphytic orchid species, using more samples than in any previous study. METHODS: We assessed the mycorrhizal communities of Thrixspermum japonicum, one of the most common epiphytic orchids in the temperate region of Japan. In total, 144 individuals were collected from 28 host tree species at 20 sites across 1300 km. The mycorrhizal fungi were identified based on nuclear ribosomal DNA internal transcribed spacer sequences and assigned operational taxonomic units (OTUs) based on 97% sequence similarity. RESULTS: We obtained 24 OTUs; 9 belonged to the Ceratobasidiaceae and 15 to the Tulasnellaceae. These OTUs are widely distributed throughout the phylogenetic trees of the two fungal families. However, a single Ceratobasidiaceae OTU accounted for 49.7% of all fungal sequences and was predominant in samples from 15 host tree species and 12 sites. CONCLUSIONS: Our results imply that despite having a broad range of mycorrhizal partners, T. japonicum was predominantly associated with a single fungal taxon at most of the sites among the host-tree species investigated. These findings contribute to elucidating mycorrhizal symbiosis in epiphytic habitats.

A leafless epiphytic orchid, Taeniophyllum glandulosum Blume (Orchidaceae), is specifically associated with the Ceratobasidiaceae family of basidiomycetous fungi.

Leafless epiphytes in the Orchidaceae undergo a morphological metamorphosis in which the root has chloroplast-containing cortical cells and is the sole photosynthetic organ for carbon gain. All orchids are entirely dependent on mycorrhizal fungi for their carbon supply during seed germination, and this mycorrhizal association generally persists in adult plants. However, our knowledge of the mycorrhizal association of leafless epiphytic orchids remains limited, and the contribution of the mycorrhizal association to nutrient acquisition in these orchid species is largely unknown. In this study, the mycorrhizal fungi of a leafless epiphytic orchid, Taeniophyllum glandulosum, were identified molecularly using 68 mature plants and 17 seedlings. In total, 187 fungal internal transcribed spacer sequences were obtained, of which 99% were identified as Ceratobasidiaceae. These sequences were classified into five operational taxonomic units (OTUs) based on 97% sequence similarity. The most frequent sequence was OTU1, which accounted for 91% of all Ceratobasidiaceae sequences, although other phylogenetically distinct Ceratobasidiaceae fungi were detected. These results show that T. glandulosum is specifically associated with a particular group of Ceratobasidiaceae. All mycorrhizal fungi found in T. glandulosum seedlings belonged to OTU1, which was also found in adult plants on the same host tree. The mycorrhizal fungi from 13 host tree species were compared, and T. glandulosum was preferentially associated with OTU1 on 11 tree species. In conclusion, T. glandulosum is specifically associated with Ceratobasidiaceae fungi and this specific association remains throughout the orchid life cycle and is found on divergent host tree species.

Overexpression of RORγt under control of the CD2 promoter induces polyclonal plasmacytosis and autoantibody production in transgenic mice.

Retinoic acid related orphan receptor gamma-t (RORγt) is known to be a master regulator of Th17-cell development. In this study, we generated RORγt-overexpressing transgenic (RORγt Tg) mice in which transgene expression was driven by the CD2 promoter, and found that these mice developed polyclonal plasmacytosis and autoantibody production. RORγt Tg mice were generated on a C57BL/6 background, and also were intercrossed with BALB/c mice. BALB/c F1 (BALB/F1) RORγt Tg mice developed massive polyclonal plasma-cytosis, and had shorter life spans. Splenomegaly and infiltration of plasma cells into the lung were observed. Hyperglobulinemia, anti-double-stranded DNA antibodies, anti-erythrocyte antibodies, and anti-platelet antibodies were detected in BALB/F1 RORγt Tg mice. In the present study, polyclonal plasmacytosis in BALB/F1 RORγt Tg mice appeared to be due to the induction of excessive IL-6 production by IL-17. We detected increased numbers of CD11b(+) cells that produced IL-6. We also generatedIL-6-deficient RORγt Tg BALB/F1 background mice, which displayed high levels of serum IL-17, but did not develop severe hyperglobulinemia. Excessive IL-6 production by several cell types, including macrophages, in BALB/F1 RORγt Tg mice, might effect the development of plasma-cytosis. These results suggest that RORγt plays important roles in the development of plasmacytosis and autoantibody production.

Critical role of DNAX accessory molecule-1 (DNAM-1) in the development of acute graft-versus-host disease in mice.

Acute graft-versus-host disease (GVHD) is a life-threatening complication following bone marrow transplantation; however, no effective molecular-targeting therapy has been determined. Here, we show that mice that received allogeneic splenocytes deficient in DNAX accessory molecule-1 (DNAM-1) had significantly milder GVHD and lower mortality than those that received allogeneic WT splenocytes. Donor CD8(+) T cells deficient in DNAM-1 showed significantly less proliferation and infiltration of the liver and intestines of recipient mice and produced less IFN-γ after coculture with allogeneic splenocytes than WT CD8(+) T cells. Mice prophylactically treated with an anti-DNAM-1 antibody showed milder GVHD and lower mortality than those treated with a control antibody. Moreover, treatment with a single administration of the antibody after the overt onset of GVHD ameliorated GVHD and prolonged survival. Finally, we show that the anti-DNAM-1 antibody therapy also ameliorated the overt GVHD in lethally irradiated mice after MHC-matched, minor antigen-mismatched bone marrow transplantation. These results indicate that DNAM-1 plays an important role in the development of GVHD and is an ideal molecular target for therapeutic approaches to GVHD.

Functional analysis of Lyn kinase A and B isoforms reveals redundant and distinct roles in Fc epsilon RI-dependent mast cell activation.

Engagement of FcepsilonRI causes its phosphorylation by Lyn kinase. Two alternatively spliced variants, Lyn A and B, are expressed in mast cells, and both isoforms interact with FcepsilonRI. Unlike Lyn A, Lyn B lacks a 21-aa region in the N-terminal unique domain. In this study, we investigated the role of Lyn A and B isoforms in mast cell signaling and responses. Lyn B was found to be a poor inducer of mast cell degranulation and was less potent in both inositol 1,4,5-triphosphate production and calcium responses. Expression of Lyn B alone showed reduced phosphorylation of both phospholipase Cgamma-1 and -2 and decreased interaction of phospholipase Cgamma-1 with the phosphorylated linker for activation of T cells. Lyn B also showed increased binding of tyrosine-phosphorylated proteins, which included the negative regulatory lipid phosphatase SHIP-1. In contrast, both Lyn A and B caused similar total cellular tyrosine phosphorylation and FcepsilonRI phosphorylation and neither Lyn A nor Lyn B alone could completely restore mast cell degranulation or dampen the excessive cytokine production seen in the absence of Lyn. However, expression of both isoforms showed complementation and normalized responses. These findings demonstrate that Lyn B differs from Lyn A in its association with SHIP-1 and in the regulation of calcium responses. However, complementation of both isoforms is required in mast cell activation.

In-vitro symbiotic germination of seeds of five mycoheterotrophic Gastrodia orchids with Mycena and Marasmiaceae fungi.

We performed in-vitro germination tests on seeds from five Gastrodia orchids (G. confusa, G. elata var. elata, G. elata var. pallens, G. nipponica, and G. pubilabiata) using one Marasmiaceae and two Mycena isolates. Mycena sp. 1 promoted germination of all five Gastrodia orchids, with root and/or tuber formation observed in G. confusa, G. nipponica, and G. pubilabiata. No additional growth was observed in the other two orchids. Mycena sp. 2 induced G. confusa, G. elata var. elata, and G. nipponica germination, whereas Marasmiaceae sp. 1 induced G. nipponica and G. pubilabiata germination. Phylogenetic analyses indicated that the two Mycena isolates represent distinct lineages within the Mycenaceae. Mycena sp. 1 and Marasmiaceae sp. 1 are closely related to Mycena abramsii and Marasmiellus rhizomorphogenus, respectively. Our results imply that Mycena and marasmioid fungi play important roles in early development in Gastrodia species, and that Mycena fungi in particular may be common mycobionts of Gastrodia species. Root and/or tuber development was observed with four plant-fungus combinations, implying that these associations persist throughout the life cycle, whereas G. elata var. elata may require different associates over time. Our findings will contribute to elucidating the mycorrhizal associations of mycoheterotrophic orchids throughout their life cycle.

Divergent Total Syntheses of Isobatzellines A/B and Batzelline A.

Divergent total syntheses of isobatzellines A/B and batzelline A were accomplished. A fully substituted common indole intermediate bearing C-2 methylthio and C-5 chloro groups was constructed via ring expansion of benzocyclobutenone oxime sulfonate with NaSMe and a benzyne-mediated cyclization/functionalization sequence as the key steps. The total synthesis of isobatzelline B was achieved via formation of the iminoquinone structure by the redox-neutral acid-promoted C-5 proto-dechlorination of the common indole intermediate. The total syntheses of isobatzelline A and batzelline A were completed in a divergent manner by oxidation of the common indole intermediate using MnO2 or Mn(OAc)3, respectively.

LFA-1 decreases the antigen dose for T cell activation in vivo.

Leukocyte adhesion molecule leukocyte function-associated antigen (LFA)-1 not only mediates intercellular binding but also delivers co-stimulatory signals in T cells. LFA-1 has been shown to decrease the threshold of TCR signal and an antigen dose required for T cell activation and proliferation in vitro. However, physiological significance of the role of LFA-1 in TCR signal has remained unclear. We examined whether LFA-1 decreased the antigen dose for T cell activation in vivo. We showed here that, although collagen-induced arthritis (CIA) could not be induced by immunization and challenge with a standard amount of type-II collagen in LFA-1-deficient mice, a higher dose of the antigen did induce CIA in the absence of LFA-1. We also showed that CD4+ T cells could be primed by immunization with a high, but not low, dose of ovalbumin antigen in LFA-1-deficient mice. These results suggest that LFA-1 decreases the threshold of TCR signal for T cell activation in vivo as well as in vitro. Further studies using TCR-transgenic LFA-1-deficient mice showed that LFA-1 cooperated with TCR in sustained Erk1/2 phosphorylation. Moreover, TCR could induce sustained Erk1/2 phosphorylation in the absence of LFA-1 when T cells were stimulated with a high, but not low, dose of antigen, suggesting that LFA-1 may cooperate with TCR in sustaining Erk1/2 phosphorylation.

Total Synthesis of (+)-CC-1065 Utilizing Ring Expansion Reaction of Benzocyclobutenone Oxime Sulfonate.

An indole synthesis via ring expansion of benzocyclobutenone oxime sulfonate was developed. Utility of the indole synthesis was demonstrated by the total synthesis of (+)-CC-1065. The middle and right segments were constructed by a sequential ring expansion of the symmetrical benzo-bis-cyclobutenone. The left segment was also constructed via ring expansion of the methyl-substituted benzocyclobutenone oxime sulfonates. After condensation of these three segments, the dienone cyclopropane structure was formed to complete the total synthesis.

A method for facilitating the seed germination of a mycoheterotrophic orchid, Gastrodia pubilabiata, using decomposed leaf litter harboring a basidiomycete fungus, Mycena sp.

BACKGROUND: Mycoheterotrophic plants are one of the most difficult plant groups to conserve because they are entirely dependent on symbiotic fungi. Establishment of viable culture systems would greatly aid their conservation. We describe a simple culture system for the mycoheterotrophic orchid, Gastrodia pubilabiata, that does not require laboratory facilities. The orchid is symbiotic with leaf-litter-decomposing fungi. RESULTS: Gastrodia pubilabiata seeds were incubated in plastic boxes or glass bottles filled with leaf litter collected from the natural habitat of the species. Seed germination was observed after 35 days and seedling development followed. Fungal isolates from seedlings were identified as Mycenaceae (Basidiomycota), a leaf-litter-decomposing mycorrhizal fungus of Gastrodia species. CONCLUSION: Our method can be used to conserve endangered mycoheterotrophic plants associated with leaf litter-decomposing fungi efficiently, and can also serve as a model system for physiological and molecular studies of such plants.

Isolation and characterization of novel microsatellite loci for the endangered orchid Cypripedium japonicum (Orchidaceae).

PREMISE OF THE STUDY: Twenty-six microsatellite markers were developed for the endangered orchid Cypripedium japonicum (Orchidaceae) to estimate the clonal diversity and genetic structure of the remaining populations in Japan. METHODS AND RESULTS: Microsatellite loci of C. japonicum were isolated using Ion Personal Genome Machine (PGM) sequencing. The primer sets were tested on 55 ramets sampled from two populations in Japan. Sixteen loci showed polymorphism in at least one population, with two to five alleles per locus. Observed and expected heterozygosities for the two populations ranged from 0.00 to 0.92 and 0.00 to 0.71, respectively. CONCLUSIONS: The microsatellite markers developed here provide a useful tool to analyze clonal structure and sexual regeneration status and will help to manage the remaining genetic variation within C. japonicum.

Regulation of the tyrosine phosphorylation of Phospholipid Scramblase 1 in mast cells that are stimulated through the high-affinity IgE receptor.

Engagement of high-affinity immunoglobulin E receptors (FcεRI) activates two signaling pathways in mast cells. The Lyn pathway leads to recruitment of Syk and to calcium mobilization whereas the Fyn pathway leads to phosphatidylinositol 3-kinase recruitment. Mapping the connections between both pathways remains an important task to be completed. We previously reported that Phospholipid Scramblase 1 (PLSCR1) is phosphorylated on tyrosine after cross-linking FcεRI on RBL-2H3 rat mast cells, amplifies mast cell degranulation, and is associated with both Lyn and Syk tyrosine kinases. Here, analysis of the pathway leading to PLSCR1 tyrosine phosphorylation reveals that it depends on the FcRγ chain. FcεRI aggregation in Fyn-deficient mouse bone marrow-derived mast cells (BMMC) induced a more robust increase in FcεRI-dependent tyrosine phosphorylation of PLSCR1 compared to wild-type cells, whereas PLSCR1 phosphorylation was abolished in Lyn-deficient BMMC. Lyn association with PLSCR1 was not altered in Fyn-deficient BMMC. PLSCR1 phosphorylation was also dependent on the kinase Syk and significantly, but partially, dependent on detectable calcium mobilization. Thus, the Lyn/Syk/calcium axis promotes PLSCR1 phosphorylation in multiple ways. Conversely, the Fyn-dependent pathway negatively regulates it. This study reveals a complex regulation for PLSCR1 tyrosine phosphorylation in FcεRI-activated mast cells and that PLSCR1 sits at a crossroads between Lyn and Fyn pathways.

Establishment and characterization of a novel anti-DNAM-1 monoclonal antibody.

DNAM-1 (CD226) is expressed on the majority of NK cells, CD8(+) T cells, and CD4(+) T cells and mediates an activating signal in these cells upon binding to the ligands CD155 or CD112 expressed on target cells or antigen-presenting cells. DNAM-1 plays an important role in tumor immunity mediated by NK cells and CD8(+) T cells and the development of graft-versus-host disease (GVHD) in mice. We previously generated a monoclonal antibody against mouse DNAM-1, TX42, which inhibited DNAM-1 binding to its ligands CD155 and CD112 and inhibited activation of NK cells and CD8(+) T cells in vitro. Injection of mice with TX42 ameliorated the development of GVHD in mice. Here, we generated a new clone of anti-DNAM-1 MAb, TX92. TX92 similarly stained primary spleen cells, including CD8(+) and CD4(+) T cells and NK cells. TX92 as well as TX42 interfered with the interaction between DNAM-1 and ligands CD155 and CD112. However, TX92 recognizes a different epitope and, unlike TX42 partially, but not completely, depleted peripheral blood (PB) CD8(+) T cells in vivo. Thus, TX92 is a unique MAb that is characterized not only by inhibitory function of DNAM-1 binding to the ligands but also by function of partial depletion of PB CD8(+) T cells.

Secure and effective gene vector of polyamidoamine dendrimer pharmaceutically modified with anionic polymer.

The purpose of this study was to develop a new type of gene vector, polyamidoamine (PAMAM) dendriplex pharmaceutically modified, based on electrostatic interactions, by various anionic polymers. The γ-polyglutamic acid (γ-PGA)/PAMAM dendriplex and the α-PGA/PAMAM dendriplex formed a stable complex, although α-polyaspartic acid and heparin released pDNA from the complex. The addition of anionic polymer decreased the ζ-potential, although it did not greatly affect the size of the complex. As a result of an in vitro gene expression study of mouse melanoma cells, we found that the γ-PGA/PAMAM dendriplex showed high gene expression comparable to the PAMAM dendriplex, although the α-PGA/PAMAM dendriplex showed lower gene expression. Tail vein injection of the γ-PGA/PAMAM dendriplex into mice also led to high gene expression in the spleen and lung. The γ-PGA/PAMAM dendriplex showed no cytotoxicity and no agglutination, although severe cytotoxicity and agglutination were observed in the PAMAM dendriplex. Thus, we discovered that complexes of pDNA, PAMAM dendrimers, and γ-PGA showed higher gene expression in vitro and in vivo, and markedly lower toxicity. This complex is valuable and is expected to be a safe and effective gene vector.

Loss of TRPC1-mediated Ca2+ influx contributes to impaired degranulation in Fyn-deficient mouse bone marrow-derived mast cells.

MC degranulation requires the influx of calcium from the extracellular environment. Orai1/STIM1 is essential to MC SOCE, as shown in rat peritoneal MCs, the rat MC lines (RBL-2H3), or in Orai1 null embryo liver-derived, cultured MCs. However, minimal information exists about the role of other calcium channels expressed on these cells. Here, we demonstrate that the nonselective TRPC1 participates in FcεRI-mediated calcium entry in mouse BMMCs. We found that Fyn null MCs, which have an impaired degranulation response, expressed reduced levels of TRPC1, had normal depletion of intracellular calcium stores but an impaired calcium influx, and failed to depolymerize cortical F-actin (a key step for granule-plasma membrane fusion). Partial RNAi silencing of TRPC1 expression in WT MCs (to the level of Fyn null MCs) mimicked the Fyn null defect in calcium influx, cortical F-actin depolymerization, and MC degranulation. Ectopic expression of Fyn or TRPC1 in Fyn null MCs restored calcium responses and cortical F-actin depolymerization and increased MC degranulation. Together with our findings that expression of Orai1 is not altered in Fyn null MCs, our findings suggest that TRPC1 participates in calcium influx and other key events required for MC degranulation. This demonstrates that in addition to a role described previously for Orai1 in promoting MC degranulation, nonselective cation channels participate in promoting the exocytotic response.

Differential dephosphorylation of the FcRgamma immunoreceptor tyrosine-based activation motif tyrosines with dissimilar potential for activating Syk.

The cell surface-expressed gamma chain of the high affinity receptor for IgE (FcepsilonRI) can be phosphorylated on two tyrosine residues of the immunoreceptor tyrosine-based activation motif (ITAM), leading to recruitment and activation of spleen tyrosine kinase (Syk), a kinase that is essential for mast cell signaling and allergic responses. However, it is not known whether preferential phosphorylation or dephosphorylation of the two individual FcRgamma tyrosines (the N-terminal Tyr47 and C-terminal Tyr58) could regulate Syk activation. Herein we report that phosphorylation of only Tyr58 was able to elicit Syk phosphorylation and a weak rise in intracellular calcium, suggesting that Tyr58 phosphorylation may be distinctively important for Syk activation. In vitro and in vivo studies revealed that both Tyr47 and Tyr58 could be similarly phosphorylated. However, mass spectrometric analysis of the phosphorylated FcepsilonRgamma from bone marrow-derived mast cells showed that phosphorylation at Tyr47 was at least 2-fold greater than at Tyr58. This suggested that, once phosphorylated, Tyr58 is preferentially dephosphorylated. In vitro studies demonstrated more efficient dephosphorylation of Tyr58 (by the receptor-associated phosphatases SHP-1 and SHP-2) than of Tyr47. Analysis of Syk binding to wild type and mutant phosphorylated FcepsilonRI revealed that mutation at Tyr58 almost completely ablated Syk binding, whereas mutation at Tyr47 moderately reduced Syk binding. The findings argue for a novel regulatory mechanism, where dephosphorylation of phospho-Tyr58 is likely to promote the down-regulation of Syk activation and suppression of mast cell responses.

Accelerated tumor growth in mice deficient in DNAM-1 receptor.

Since the identification of ligands for human and mouse DNAM-1, emerging evidence has suggested that DNAM-1 plays an important role in the T cell- and natural killer (NK) cell-mediated recognition and lysis of tumor cells. However, it remains undetermined whether DNAM-1 is involved in tumor immune surveillance in vivo. We addressed this question by using DNAM-1-deficient mice. DNAM-1-deficient cytotoxic T lymphocyte (CTL) and NK cells showed significantly less cytotoxic activity against DNAM-1 ligand-expressing tumors in vitro than wild-type (WT) cells. The methylcholanthrene (MCA)-induced fibrosarcoma cell line Meth A expressed the DNAM-1 ligand CD155, and DNAM-1-deficient mice showed increased tumor development and mortality after transplantation of Meth A cells. Moreover, the DNAM-1-deficient mice developed significantly more DNAM-1 ligand-expressing fibrosarcoma and papilloma cells in response to the chemical carcinogens MCA and 7,12-dimethylbenz[a]anthracene (DMBA), respectively, than did WT mice. These results indicate that DNAM-1 plays an important role in immune surveillance of tumor development.

Cutting edge: genetic variation influences Fc epsilonRI-induced mast cell activation and allergic responses.

Mast cell responses are influenced by a diverse array of environmental factors, but little is known about the effect of genetic background. In this study, we report that 129/Sv mice had high levels of circulating IgE, increased expression of the high-affinity receptor for IgE (Fc epsilonRI), and greater sensitivity to anaphylaxis when compared with C57BL/6 mice. Bone marrow-derived mast cells (BMMCs) from 129/Sv mice showed more robust degranulation upon the engagement of Fc epsilonRI. Deficiency of the Src family kinase Lyn enhanced degranulation in 129/Sv BMMCs but inhibited this response in C57BL/6 cells. C57BL/6 lyn(-/-) BMMCs had reduced expression of the Src family kinase Fyn, and increasing its expression markedly enhanced degranulation. In human mast cells the silencing of Lyn or Fyn expression resulted in hyperdegranulation or hypodegranulation, respectively. The findings demonstrate a genetic influence on the extent of a mast cell's response and identify Fyn kinase as a contributory determinant.