Both stem cells and mast cells express c-kit and proliferate after exposure to c-kit ligand. Mutations in c-kit may enhance or interfere with the ability of c-kit receptor to initiate the intracellular pathways resulting in cell proliferation. These observations suggested to us that mastocytosis might in some patients result from mutations in c-kit. cDNA synthesized from peripheral blood mononuclear cells of patients with indolent mastocytosis, mastocytosis with an associated hematologic disorder, aggressive mastocytosis, solitary mastocytoma, and chronic myelomonocytic leukemia unassociated with mastocytosis was thus screened for a mutation of c-kit. This analysis revealed that four of four mastocytosis patients with an associated hematologic disorder with predominantly myelodysplastic features had an A-->T substitution at nt 2468 of c-kit mRNA that causes an Asp-816-->Val substitution. One of one patient examined who had mastocytosis with an associated hematologic disorder had the corresponding mutation in genomic DNA. Identical or similar amino acid substitutions in mast cell lines result in ligand-independent autophosphorylation of the c-kit receptor. This mutation was not identified in the patients within the other disease categories or in 67 of 67 controls. The identification of the point mutation Asp816Val in c-kit in patients with mastocytosis with an associated hematologic disorder provides insight not only into the pathogenesis of this form of mastocytosis but also into how hematopoiesis may become dysregulated and may serve to provide a means of confirming the diagnosis, assessing prognosis, and developing intervention strategies.

Pre-clinical data demonstrate a pivotal role for interleukin (IL)-13 in the development and maintenance of asthma. This study assessed the effects of tralokinumab, an investigational human IL-13-neutralising immunoglobulin G4 monoclonal antibody, in adults with moderate-to-severe uncontrolled asthma despite controller therapies.194 subjects were randomised to receive tralokinumab (150, 300 or 600 mg) or placebo subcutaneously every 2 weeks. Primary end-point was change from baseline in mean Asthma Control Questionnaire score (ACQ-6; ACQ mean of six individual item scores) at week 13 comparing placebo and combined tralokinumab dose groups. Secondary end-points included pre-bronchodilator lung function, rescue β2-agonist use and safety. Numerical end-points are reported as mean±sd.At week 13, change from baseline in ACQ-6 was -0.76±1.04 for tralokinumab versus -0.61±0.90 for placebo (p=0.375). Increases from baseline in forced expiratory volume in 1 s (FEV1) were 0.21±0.38 L versus 0.06±0.48 L (p=0.072), with a dose-response observed across the tralokinumab doses tested. β2-agonist use (puffs per day) was decreased for tralokinumab -0.68±1.45 versus placebo -0.10±1.49 (p=0.020). The increase in FEV1 following tralokinumab treatment remained evident 12 weeks after the final dose. Safety profile was acceptable with no serious adverse events related to tralokinumab.No improvement in ACQ-6 was observed, although tralokinumab treatment was associated with improved lung function.

Asthma is a complex, persistent, inflammatory disease characterised by airway hyperresponsiveness in association with airway inflammation. Studies suggest that regular use of high-dose inhaled corticosteroids and long-acting bronchodilators or omalizumab (a humanised monoclonal antibody that binds to immunoglobulin E and is often used as next-step therapy) may not be sufficient to provide asthma control in all patients, highlighting an important unmet need. Interleukin-4, interleukin-13, and the signal transducer and activator of transcription factor-6 are key components in the development of airway inflammation, mucus production, and airway hyperresponsiveness in asthma. Biological compounds targeting these molecules may provide a new therapeutic modality for patients with uncontrolled severe asthma. The purpose of this review is to summarise current studies of compounds targeting the interleukin-4/interleukin-13 pathway and to provide a rationale for the development of such compounds for this use.

The plasminogen activator inhibitor type 1 (PAI-1) has an essential role in tissue remodeling. The PAI-1 gene was induced by a combination of phorbol ester and calcium ionophore at the highest level among the inducible human mast cell genes that we have analyzed on a DNA microarray. PAI-1 was secreted by both a human mast cell line (HMC)-1 and primary cultured human mast cells upon stimulation, whereas PAI-1 was undetectable in either group of unstimulated cells. The secretion of PAI-1 was due to de novo synthesis of PAI-1 rather than secretion of preformed PAI-1. The functional significance of PAI-1 secretion was demonstrated by complete inhibition of tissue-type plasminogen activator activity with supernatants of stimulated HMC-1 cells. Furthermore, we were able to regulate PAI-1 gene expression in HMC-1 cells by known therapeutic agents. High-dose (1 μM) dexamethasone induced PAI-1 mRNA expression. Cyclosporin down-regulated the expression of the PAI-1 gene. Cycloheximide abrogated PAI-1 mRNA expression, suggesting that transcription of the PAI-1 gene requires de novo synthesis of early gene products, including transcription factors. Finally, we demonstrated PAI-1 in lung mast cells from a patient with asthmatic attack by double-immunofluorescence study. This is the first report demonstrating that activated human mast cells release a striking amount of functionally active PAI-1. These results suggest that PAI-1 could play an important role in airway remodeling of asthma, and inhibition of PAI-1 activity could represent a novel therapeutic approach in the management of airway remodeling.