FcRγ promotes contact hypersensitivity to oxazolone without affecting the contact sensitisation process in B6 mice.

The process of sensitisation by specific contact allergens is indispensable for the induction of allergic contact dermatitis. Oxazolone is a well-characterised contact allergen. Previous studies suggested that immune cells bearing the FcRγ subunit are essential for oxazolone-induced contact hypersensitivity, but the biological functions of the FcRγ subunit in the process of sensitisation to oxazolone remain unknown. In this study, we show that FcRγ deficiency decreases ear-swelling responses to oxazolone in mice. However, we found that oxazolone-sensitised FcRγ(-/-) mice and oxazolone-sensitised wild-type (WT) mice have comparable numbers of CD11c(+) MHCII(hi) dendritic cells (DCs) in their draining lymph nodes (LNs). In addition, oxazolone-sensitised LN cells from both FcRγ(-/-) and WT mice showed considerable production of interferon-gamma (IFNγ), interleukin-4 (IL-4) and IL-17A upon oxazolone-keyhole limpet haemocyanin loading. Consistent with these data, oxazolone-sensitised FcRγ(-/-) and FcRγ(+/+) LN cells conferred contact hypersensitivity to WT naïve mice challenged with the hapten. Our findings clearly indicate that, in an experimental mouse model, the FcRγ subunit positively regulates contact hypersensitivity to oxazolone without affecting the contact sensitisation process.

Double expression of CD34 and CD117 on bone marrow progenitors is a hallmark of the development of functional mast cell of Callithrix jacchus (common marmoset).

Mast cells (MCs) are developed from hematopoietic progenitor cells and play an important role in inflammation. Study of the kinetics of development and accumulation of primate MC in vivo is crucial for the control of human inflammatory diseases, as evolution of the immune system is quite rapid and inflammation including MC response is considered to be different between mouse and human. In the present study, we examined the development of MC from hematopoietic progenitors of Callithrix jacchus (common marmoset), an experimental animal of nonhuman primates. Bone marrow cells were fractionated for the expression of CD34 and CD117 by cell sorting. MCs were developed in vitro or by transplanting the cells to NOD/SCID/IL-2γc knockout (NOG) mice. In vitro culture of CD34(+)CD117(+) (double positive, DP) cells with stem cell factor could generate high-affinity Fc epsilon receptor (FcεR)-expressing CD117(+) cells with typical granules. The developed MC released ß-hexosaminidase and produced leukotriene C(4) after the stimulation of FcεRI. Transplantation of DP cells gave rise to a marked expansion of CD34(-)CD45(+)CD117(+)FcεR(+) cells in NOG mice. They expressed transcripts encoding chymase 1 and tryptase ß. Differentiation of CD34(-)CD117(+) cells to MCs was relatively limited compared with the DP cells, similarly to human MCs. These results suggest that this marmoset system provides a good model for human MC development.

Fc receptor beta chain deficiency exacerbates murine arthritis in the anti-type II collagen antibody-induced experimental model.

OBJECTIVE: Fc receptor ß chain (FcRß) acts as a signaling component of FcγRIII in immune cells such as mast cells (MCs) or basophils. Recent studies reported that FcγRIII contributes to the development of arthritic inflammation. These findings suggest that FcRß may play a pivotal role in the pathogenesis of arthritic inflammation. To address this possibility, we examined the function of FcRß in arthritic inflammation employing a mouse model. METHODS: For the induction of arthritis, we injected 2 mg of a cocktail of anti-type II collagen (CII) monoclonal antibodies (mAbs) into C57BL/6J mice (FcRß(+/+)) and FcRß(-/-) mice intravenously. Three days later, 100 µg lipopolysaccharide (LPS; Escherichia coli 055:B5) was intraperitoneally injected. Joint swelling was evaluated by inspection. Histopathology of joint tissues was examined by hematoxylin and eosin (H&E) or tartrate-resistant acid phosphatase staining. RESULTS: Here, we demonstrate in a well-established experimental arthritis model induced by LPS and anti-CII mAbs that FcRß(-/-) mice exhibit exacerbated arthritic inflammation manifested in paw swelling, leukocyte infiltration into the knee joint, and bone erosion and tissue cytokine expression. CONCLUSION: Our findings clearly indicate that FcRß negatively regulates arthritic inflammation in an experimental arthritis model.

Protease-mediated house dust mite allergen-induced reactive oxygen species production by neutrophils.

A growing body of evidence indicates that neutrophils may play an important role in the pathogenesis of asthma. However, the involvement of the house dust mite (HDM) in neutrophil activation associated with the pathogenesis of asthma is not fully understood yet. To address this situation, we harvested neutrophils isolated from 15 HDM-sensitized asthmatic subjects and 18 HDM-sensitized nonasthmatic subjects and measured the amounts of neutrophil reactive oxygen species (ROS) production in response to the major HDM allergens Der-f and Der-f1. Der-f and Der-f1 significantly increased ROS production in neutrophils isolated from asthmatic subjects versus nonasthmatic subjects. To assess the involvement of Der-f-specific IgE antibodies binding to their receptors in HDM allergen-induced ROS production, we examined whether neutrophils produce ROS by cross-linking of cell-bound IgE antibodies with anti-IgE. Treatment with anti-IgE antibodies did not induce ROS production by neutrophils isolated from 6 asthmatic subjects. On the other hand, pretreatment of Der-f with E-64, a cysteine protease inhibitor, eliminated Der-f-induced ROS production. These results suggest that HDM-allergen exposure may result in greater production of ROS in asthmatic patients and may be involved in the pathogenesis of asthma.

Lipoteichoic acid improves the capability of mast cells in the host defense system against bacteria.

OBJECTIVES AND DESIGN: We investigated the effects of microbial components on the uptake of microbes by mast cells (MCs), and studied the change in cytokine production in MCs after bacterial uptake. MATERIAL OR SUBJECTS: LAD2 human mast cells, cord-blood and peripheral-blood derived MCs were employed to analyze their surface molecule expression and cytokine generation by flow cytometry. Bacterial internalization in these MCs was observed by confocal microscopy and flow cytometry. RESULTS: Complement receptor 3 expression was augmented by LTA but not by PGN or 3CpG-oligodeoxynucleotide. LTA also enhanced the uptake of opsonized bacteria (over twofold augmentation). After bacterial uptake, MCs augmented the production of chemoattractant cytokines for neutrophils, while Th1 and Th2 cytokine production showed little or no change. CONCLUSIONS: LTA increases the capability of the MC as a sentinel in the host immune response, and some bacterial components direct human MC function towards innate immunity after pathogen infection.

Human cathelicidin CAP18/LL-37 changes mast cell function toward innate immunity.

The antimicrobial peptide LL-37 is generated from skin keratinocytes during infection of Gram-negative bacteria and exerts a microbicidal effect. LL-37 also causes functional changes in mast cells. Mast cells in the skin are involved in the innate immune system response against microbial infections via Toll-like receptors (TLRs), such as TLR4, which that is known to recognize lipopolysaccharide (LPS), a bacterial component. Thus, in the present study, we examined the effects of LL-37 on the expression of TLRs and the generation of cytokines on mast cells, and considered functional changes in the host defense system against bacteria. We observed that LL-37 increased the level of TLR4 mRNA and TLR4 protein, and that LL-37 induced the release of IL-4, IL-5 and IL-1beta from mast cells. Cross-interaction between LL-37-triggered TLR4 augmentation and LL-37-inducible cytokine generation was also examined. Although the up-regulation of LL-37-inducible Th2 cytokines was cancelled by LPS, the augmentation of pro-inflammatory cytokine production was still observed. These findings indicate that LL-37 co-existing with the bacterial component switches mast cell function and directs human mast cells toward innate immunity. In conclusion, LL-37 may be a candidate modifier of the host defense against bacterial entry by serving as an alarm for sentinels such as mast cells.

Lipoteichoic acid downregulates FcepsilonRI expression on human mast cells through Toll-like receptor 2.

BACKGROUND: FcepsilonRI on the surface of mast cells (MCs) plays a central role in allergic responses. Recent evidence shows that exposure to microbial components corresponds with a significant reduction in the risk for allergic diseases. Although many reports suggest that this is due to changes in T-cell functions, how MC functions are altered by bacterial infection remains unknown. OBJECTIVE: We sought to elucidate the effect of bacterial infection on MC function and expression of Fc receptors, such as FcepsilonRI. METHODS: Isolated human pulmonary MCs and a human MC line (LAD2) were stimulated with bacterial components, and the function and surface expression of Fc receptors were measured. RESULTS: Lipoteichoic acid (LTA) and peptidoglycan, but not LPS, flagellin, or 3CpG-oligodeoxynucleotide, reduced the expression of FcepsilonRI on LAD2 cells. An antibody to Toll-like receptor (TLR) 2 partially blocked the effect of LTA but not peptidoglycan. Both LTA and peptidoglycan reduced MC degranulation caused by an antigen-specific IgE. Furthermore, exposure of pulmonary MCs to LTA reduced both FcepsilonRI expression and IgE-induced degranulation. None of the bacterial components affected the expression of other Fc receptors, such as Fcgamma receptors or Fcalpha receptor I. CONCLUSIONS: Our results indicate that LTA reduces the surface expression of FcepsilonRI through TLR2 and suggests that TLR2 ligands could be used as a novel therapy for controlling allergic disorders. CLINICAL IMPLICATIONS: By knowing how bacterial components modulate MC function, we can expand our possibilities for therapeutic interventions of allergic diseases.