Exosomes are nanometer‐sized vesicles secreted by various cells, with potentially diverse roles in physiology. Although emphasis has been placed on their involvement in immune modulation, their potential for more wide‐ranging biological effects has not been appreciated. A common exosome feature is the expression of adhesion molecules, which include the integrin family. We have for the first time addressed the possible function of B cell‐derived exosome‐integrins by examining adhesive interactions of exosomes (immobilized onto beads) with extracellular matrix (ECM) components and cytokine‐treated fibroblasts. Integrin (β1 and β2) expression was demonstrated by Western blotting and flow cytometry. Binding studies (with blocking antibodies) demonstrated their function in adhesion to collagen‐I, fibronectin, and tumor necrosis factor (TNF)‐α‐activated fibroblasts. Exosome adhesion to TNF‐α‐activated fibroblasts also triggered integrin‐dependent changes in cytosolic calcium, measured by single cell imaging. Thus, B cell‐derived exosomes express functional integrins, which are capable of mediating anchorage to ECM and cell‐surface adhesion molecules, and may be a novel mode of delivering adhesion signals at distances beyond that of direct cell‐cell contact during inflammation.

Fibroblast to myofibroblast differentiation drives effective wound healing and is largely regulated by the cytokine transforming growth factor-β1 (TGF-β1). Myofibroblasts express α-smooth muscle actin and are present in granulation tissue, where they are responsible for wound contraction. Our previous studies show that fibroblast differentiation in response to TGF-β1 is dependent on and mediated by the linear polysaccharide hyaluronan (HA). Both the HA receptor, CD44, and the epidermal growth factor receptor (EGFR) are involved in this differentiation response. The aim of this study was to understand the mechanisms linking HA-, CD44-, and EGFR-regulated TGF-β1-dependent differentiation. CD44 and EGFR co-localization within membrane-bound lipid rafts was necessary for differentiation, and this triggered downstream mitogen-activated protein kinase (MAPK/ERK) and Ca²⁺/calmodulin kinase II (CaMKII) activation. We also found that ERK phosphorylation was upstream of CaMKII phosphorylation, that ERK activation was necessary for CaMKII signaling, and that both kinases were essential for differentiation. In addition, HA synthase-2 (HAS2) siRNA attenuated both ERK and CaMKII signaling and sequestration of CD44 into lipid rafts, preventing differentiation. In summary, the data suggest that HAS2-dependent production of HA facilitates TGF-β1-dependent fibroblast differentiation through promoting CD44 interaction with EGFR held within membrane-bound lipid rafts. This induces MAPK/ERK, followed by CaMKII activation, leading to differentiation. This pathway is synergistic with the classical TGF-β1-dependent SMAD-signaling pathway and may provide a novel opportunity for intervention in wound healing.

Patients with sepsis commonly develop leukocytosis, which is presumed to reflect a host response to infection. Effective phagocytosis by neutrophils is crucial in the clearance of invading microbes. However, efficacy of phagocytosis in sepsis is controversial. We hypothesized that host phagocytic capacity in sepsis can be affected by immature neutrophils that are released into the circulation. Circulating neutrophils were evaluated in 16 patients with severe sepsis and 5 healthy donors. Immature neutrophils were identified by the cell morphology. Phagocytosis was evaluated by micromanipulation technique and simultaneous cytosolic-free Ca2+ imaging. Leukocytosis was present in 12 of 16 patients. Nine of the 12 patients with leukocytosis and 3 of 4 patients with normal white blood cell counts had increased circulating immature neutrophils (mean, 39.3% +/- 20.7%; normal