Fibrocytes contribute to the fibrotic changes most frequently observed in forms of asthma where inflammation is driven by T helper type 2 (Th2) cells. The mechanisms that regulate the profibrotic function of asthmatic fibrocytes are largely unknown. We isolated circulating fibrocytes from patients with allergen-exacerbated asthma, who showed the presence of fibrocytes, together with elevated concentrations of interleukin (IL)-4 and IL-13 and slightly increased concentrations of the Th17 cell-derived IL-17A, in induced sputum. Fibrocytes stimulated with IL-4 and IL-13 produced high levels of collagenous and non-collagenous matrix components and low levels of proinflammatory cytokines. Conversely, fibrocytes stimulated with IL-17A proliferated and released proinflammatory factors that may promote neutrophil recruitment and airway hyperresponsiveness. IL-17A also indirectly increased α-smooth muscle actin but not collagen expression in fibrocytes. Thus, fibrocytes may proliferate and express a predominant profibrotic or proinflammatory phenotype in asthmatic airways depending on the local concentrations of Th2- and Th17-derived cytokines.

The fibrocytes are thought to serve as a source of newly deposited collagens I and III during reparative processes and in certain fibrotic disorders, but their matrix remodelling properties are incompletely understood. We evaluated their ability to produce several extracellular matrix (ECM) components, in comparison with fibroblasts, and to participate in collagen turnover. The collagen gene expression profile of fibrocytes differed from that of fibroblasts because fibrocytes constitutively expressed relatively high levels of the mRNA encoding collagen VI and significantly lower levels of the mRNA encoding collagens I, III and V. The proteoglycan (PG) gene expression profile was also different in fibrocytes and fibroblasts because fibrocytes constitutively expressed the mRNA encoding perlecan and versican at relatively high levels and the mRNA encoding biglycan and decorin at low and very low levels, respectively. Moreover, fibrocytes expressed the mRNA for hyaluronan synthase 2 at higher level than fibroblasts. Significant differences between the two cell populations were also demonstrated by metabolic labelling and analysis of the secreted collagenous proteins, PGs and hyaluronan. Fibrocytes constitutively expressed the scavenger receptors CD163 and CD204 as well as the mannose receptors CD206 and Endo180, and internalized and degraded collagen fragments through an Endo180-mediated mechanism. The results of this study demonstrate that human fibrocytes exhibit ECM remodelling properties previously unexplored, including the ability to participate in collagen turnover. The observed differences in collagen and PG expression profile between fibrocytes and fibroblasts suggest that fibrocytes may predominantly have a matrix-stabilizing function.

We present an analysis of queues with the dropping function and infinite buffer. In such queues, the arriving packet (job, customer, etc.) can be dropped with the probability which is a function of the queue size. Currently, the main application area of the dropping function is active queue management in routers, but it is applicable also in many other queueing systems. So far, queues with the dropping function have been analyzed with finite buffers only, which led to complicated, computationally demanding formulas. Assuming infinite buffers enabled us herein to obtain formulas in compact, easy to use forms. Moreover, a model with the infinite buffer can often be used as a good approximation of the real queue, in which the buffer is large. We start with noticing that the classic stability condition, ρ<1, cannot be used for queues with the dropping function and infinite buffer. For this reason, we prove a few new, easy to use conditions, which guarantee system stability or instability. Then we prove several theorems on popular performance characteristics, including the queue size, busy period, loss ratio, output rate, and system response time. Additionally, we derive a special, very important characteristic called the burst ratio, which may influence severely the quality of real-time multimedia transmissions. All the theorems are illustrated with numerical examples, demonstrating in particular how the system stability may be tested and how the shape of the dropping function may affect different performance characteristics.

Idiopathic pulmonary fibrosis is a progressive fibrosing disorder for which there is no cure and no pharmacological treatment capable of increasing in a meaningful way the survival rate. Lung transplantation remains the only possible treatment for patients with advanced disease, although the increase in 5-year survival is only 45 %. Some preclinical studies have generated promising results about the therapeutic potential of exogenous stem cells. However, two initial clinical trials involving the endobronchial or systemic delivery of autologous adipose tissue-derived or unrelated-donor, placenta-derived mesenchymal stem cells have not convincingly demonstrated that these treatments are acceptably safe. The results of other ongoing clinical trials may help to identify the best source and delivery route of mesenchymal stem cells and to estimate the risk of unwanted effects related to the mesenchymal nature of the transplanted cells. Considering that most of the therapeutic potential of these cells has been ascribed to paracrine signaling, the use of mesenchymal stem cell-derived secretome as an alternative to the transplantation of single cell suspension may circumvent many regulatory and clinical problems. Technical and safety concerns still limit the possibility of clinical applications of other promising interventions that are based on the use of human amnion stem cells, embryonic stem cells or induced pluripotent stem cells to replace or regenerate the dysfunctional alveolar epithelium. We summarize the current status of the field and identify major challenges and opportunities for the possible future integration of stem cell-based treatments into the currently recommended clinical management strategy for idiopathic pulmonary fibrosis.

No abstract