Circulating mast cell progenitors increase during natural birch pollen exposure in allergic asthma patients.

BACKGROUND: Mast cells (MCs) develop from a rare population of peripheral blood circulating MC progenitors (MCps). Here, we investigated whether the frequency of circulating MCps is altered in asthma patients sensitized to birch pollen during pollen season, compared to out of season. METHODS: Asthma patients were examined during birch pollen season in late April to early June (May), and out of season in November-January. Spirometry measurements, asthma and allergy-related symptoms, asthma control questionnaire (ACQ), and asthma control test (ACT) scores were assessed at both time points. The MCp frequency was determined by flow cytometry in ficoll-separated blood samples from patients with positive birch pollen-specific IgE, and analyzed in relation to basic and disease parameters. RESULTS: The frequency of MCps per liter of blood was higher in May than in November (p = .004), particularly in women (p = .009). Patients that reported moderate to severe asthma symptoms (<.0001), nose or eye symptoms (p = .02; p = .01), or reduced asthma control (higher ACQ, p = .01) had higher MCp frequency in May than those that did not report this. These associations remained significant after adjusting for sex and BMI. The change in asthma control to a lower ACT score in May correlated with an increase in MCp frequency in May (p = .006, rho = 0.46). CONCLUSIONS: The data suggest that the frequency of MCps increases in symptomatic patients with allergic asthma. Our results unravel a link between asthma symptoms and circulating MCps, and bring new insight into the impact of natural allergen exposure on the expansion of MCs.

IgE cross-linking induces activation of human and mouse mast cell progenitors.

BACKGROUND: The concept of innate and adaptive effector cells that are repleted by maturing inert progenitor cell populations is changing. Mast cells develop from rare mast cell progenitors populating peripheral tissues at homeostatic conditions, or as a result of induced recruitment during inflammatory conditions. OBJECTIVE: Because FcεRI-expressing mast cell progenitors are the dominating mast cell type during acute allergic lung inflammation in vivo, we hypothesized that they are activated by IgE cross-linking. METHODS: Mouse peritoneal and human peripheral blood cells were sensitized and stimulated with antigen, or stimulated with anti-IgE, and the mast cell progenitor population analyzed for signs of activation by flow cytometry. Isolated peritoneal mast cell progenitors were studied before and after anti-IgE stimulation at single-cell level by time-lapse fluorescence microscopy. Lung mast cell progenitors were analyzed for their ability to produce IL-13 by intracellular flow cytometry in a mouse model of ovalbumin-induced allergic airway inflammation. RESULTS: Sensitized mouse peritoneal mast cell progenitors demonstrate increased levels of phosphorylation of tyrosines on intracellular proteins (total tyrosine phosphorylation), and spleen tyrosine kinase (Syk) phosphorylation after antigen exposure. Anti-IgE induced cell surface-associated lysomal-associated membrane protein-1 (LAMP-1) in naive mast cell progenitors, and prompted loss of fluorescence signal and altered morphology of isolated cells loaded with lysotracker. In human mast cell progenitors, anti-IgE increased total tyrosine phosphorylation, cell surface-associated LAMP-1, and CD63. Lung mast cell progenitors from mice with ovalbumin-induced allergic airway inflammation produce IL-13. CONCLUSIONS: Mast cell progenitors become activated by IgE cross-linking and may contribute to the pathology associated with acute allergic airway inflammation.

Localization-Specific Expression of CCR1 and CCR5 by Mast Cell Progenitors.

Mast cells are powerful immune cells found predominately in barrier tissues. They play an important role in immune surveillance and act as effector cells in allergic reactions. Mast cells develop from mast cell progenitors (MCp), which migrate to the peripheral tissues via the blood circulation. Presumably, the homing of MCp to the peripheral sites and localization is regulated by chemotactic signals. Due to the scarce abundance of these cells, chemotactic receptors have not been previously characterized on primary MCp. Here, mRNA transcripts for CCR1 and CX3CR1 were identified in mouse bone marrow and lung MCp in a gene expression screen of chemotactic receptors. However, surface expression of CCR1 was only found in the bone marrow MCp. Flow cytometry-based screening identified distinct surface expression of CCR5 by mouse peritoneal mast cells and MCp, while surface expression of CXCR2-5, CX3CR1, CCR1-3, CCR6-7, and CCR9 was not detected. Low surface expression of CCR5 was detected in mouse MCp in the bone marrow, spleen, and lung. To translate the findings to human, blood and bone marrow MCp from healthy donors were analyzed for possible CCR1 and CCR5 expression. Human MCp showed distinct surface expression of both CCR1 and CCR5. The expression levels of these chemokine receptors were higher in human bone marrow MCp than in the peripheral blood, suggesting that CCR1 and CCR5 may mediate retention in the bone marrow. In conclusion, mouse and human MCp show differential expression of CCR1 and CCR5 depending on their localization.

Circulating mast cell progenitors correlate with reduced lung function in allergic asthma.

BACKGROUND: Studies using mouse models have revealed that mast cell progenitors are recruited from the blood circulation to the lung during acute allergic airway inflammation. The discovery of a corresponding human mast cell progenitor population in the blood has enabled to study the relation of circulating mast cell progenitors in clinical settings. OBJECTIVES: To explore the possible association between the frequency of mast cell progenitors in the blood circulation and allergic asthma, we assessed the relation of this recently identified cell population with asthma outcomes and inflammatory mediators in allergic asthmatic patients and controls. METHODS: Blood samples were obtained, and spirometry was performed on 38 well-controlled allergic asthmatic patients and 29 controls. The frequency of blood mast cell progenitors, total serum IgE and 180 inflammation- and immune-related plasma proteins were quantified. RESULTS: Allergic asthmatic patients and controls had a similar mean frequency of blood mast cell progenitors, but the frequency was higher in allergic asthmatic patients with reduced FEV1 and PEF (% of predicted) as well as in women. The level of fibroblast growth factor 21 (FGF-21) correlated positively with the frequency of mast cell progenitors, independent of age and gender, and negatively with lung function. The expression of FcεRI on mast cell progenitors was higher in allergic asthmatic patients and correlated positively with the level of total IgE in the controls but not in the asthmatic patients. CONCLUSION: Elevated levels of circulating mast cell progenitors are related to reduced lung function, female gender and high levels of FGF-21 in young adults with allergic asthma.

Function and regulation of self-reactive marginal zone B cells in autoimmune arthritis.

Polyreactive innate-type B cells account for many B cells expressing self-reactivity in the periphery. Improper regulation of these B cells may be an important factor that underlies autoimmune disease. Here we have explored the influence of self-reactive innate B cells in the development of collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis. We show that splenic marginal zone (MZ), but not B-1 B cells exhibit spontaneous IgM reactivity to autologous collagen II in nai¨ve mice. Upon immunization with heterologous collagen II in complete Freund's adjuvant the collagen-reactive MZ B cells expanded rapidly, while the B-1 B cells showed a modest anti-collagen response. The MZ B cells were easily activated by toll-like receptor (TLR) 4 and 9-ligands in vitro, inducing proliferation and cytokine secretion, implying that dual engagement of the B-cell receptor and TLRs may promote the immune response to self-antigen. Furthermore, collagen-primed MZ B cells showed significant antigen-presenting capacity as reflected by cognate T-cell proliferation in vitro and induction of IgG anti-collagen antibodies in vivo. MZ B cells that were deficient in complement receptors 1 and 2 demonstrated increased proliferation and cytokine production, while Fcγ receptor IIb deficiency of the cells lead to increased cytokine production and antigen presentation. In conclusion, our data highlight self-reactive MZ B cells as initiators of the autoimmune response in CIA, where complement and Fc receptors are relevant in controlling the self-reactivity in the cells.