Despite substantial attention given to the development of osteoregenerative biomaterials, severe deficiencies remain in current products. These limitations include an inability to adequately, rapidly, and reproducibly regenerate new bone; high costs and limited manufacturing capacity; and lack of surgical ease of handling. To address these shortcomings, we generated a new, synthetic osteoregenerative biomaterial, hyperelastic "bone" (HB). HB, which is composed of 90 weight % (wt %) hydroxyapatite and 10 wt % polycaprolactone or poly(lactic-co-glycolic acid), could be rapidly three-dimensionally (3D) printed (up to 275 cm(3)/hour) from room temperature extruded liquid inks. The resulting 3D-printed HB exhibited elastic mechanical properties (~32 to 67% strain to failure, ~4 to 11 MPa elastic modulus), was highly absorbent (50% material porosity), supported cell viability and proliferation, and induced osteogenic differentiation of bone marrow-derived human mesenchymal stem cells cultured in vitro over 4 weeks without any osteo-inducing factors in the medium. We evaluated HB in vivo in a mouse subcutaneous implant model for material biocompatibility (7 and 35 days), in a rat posterolateral spinal fusion model for new bone formation (8 weeks), and in a large, non-human primate calvarial defect case study (4 weeks). HB did not elicit a negative immune response, became vascularized, quickly integrated with surrounding tissues, and rapidly ossified and supported new bone growth without the need for added biological factors.

T lymphocytes have a central regulatory role in the pathogenesis of asthma. We delineated the participation of lymphocytes in the acute allergic and chronic tolerant stages of a murine model of asthma by characterizing the various subsets of lymphocytes in bronchoalveolar lavage and lung tissue associated with these responses. Acute (10-day) aerosol challenge of immunized C57BL/6J mice with ovalbumin resulted in airway eosinophilia , histological evidence of peribronchial and perivascular airway inflammation, clusters of B cells and TCR␥␦ cells in lung tissue, increased serum IgE levels , and airway hyperresponsiveness to methacholine. In mice subjected to chronic (6-week) aerosol challenge with ovalbumin, airway inflammation and serum IgE levels were significantly attenuated and airway hyperresponsiveness was absent. The marked increases in lung B and T cell populations seen in the acute stage were also significantly reduced in the chronic stage of this model. Thus , acute ovalbumin challenge resulted in airway sensitization characteristic of asthma, whereas chronic ovalbumin challenge elicited a suppressed or tolerant state. The transition from antigenic sensitization to tolerance was accompanied by shifts in lymphocyte profiles in the lung and bronchoalveolar lavage fluid. Asthma is the most common chronic illness in developed countries. Our current understanding of the pathophysiology of allergic asthma is that it occurs from a breakdown of the normal tolerance to inhaled antigens, as a result of complex interactions between host and environmental factors. Emerging evidence suggests that the development of clinical sensitivity versus normal tolerance to inhaled antigens involves the establishment of a dominant population of CD4 ϩ T lymphocytes that are either classified as Th2-like (sensitization) or Th1-like (tolerance).1 Th2 responses are characterized by secretion of the cytokines interleukin (IL)-4 and IL-13, which induce the production of IgE by B cells, 2-5 and IL-5, which regulates the growth, differentiation, and activation of eosinophils.6 Conversely, Th1 responses are characterized by secretion of IL-2, tumor necrosis factor (TNF)-␤, and interferon (IFN)-␥. IFN-␥ has been shown to stimulate low-level IgG production and to potently inhibit IL-4-mediated IgE responses both in vivo and in vitro.7 The mechanisms that control CD4 ϩ T lymphocyte polarization into either Th1 or Th2 phenotypes are incompletely understood but appear to involve genetic predispositions, local factors such as existing cytokine concentrations and inflammation, and antigenic factors such as the potency, dose, and duration of exposure of the eliciting antigen. In susceptible individuals, antigen sensitization results in specific local and systemic IgE production and airway eosinophilia, which in turn induce the airway inflammation, airway hyperresponsiveness, and reversible airway obstruction characteristic of asthma.The factors influencing antigen sensitization or tolerance can be better studied in mice, given their well defined...

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The role of lymphocytes bearing alphabeta or gammadelta T-cell receptors (TCRs) was assessed during the acute allergic response in a mouse model of asthma. The inflammatory immune response to ovalbumin (OVA) was characterized in wild-type C57BL/6J mice and congenic TCRbeta(-/-) and TCRdelta(-/-) mice by evaluation of airway eosinophilia, histopathology, serum immunoglobulin (Ig)E levels, and in vivo airway responsiveness to methacholine. OVA-challenged wild-type mice demonstrated marked pulmonary inflammation, evidenced by airway eosinophilia (68 +/- 7 x 10(4) cells), peribronchial lympho-plasmocytic infiltration, and elevated serum IgE (4.9 +/- 0.6 microg/ml). These responses were markedly attenuated in TCRdelta(-/-) animals (5.0 +/- 1.0 x 10(4) eosinophils and 1.6 +/- 0. 3 microg/ml IgE) and were completely absent in TCRbeta(-/-) mice (< 1 x 10(3) eosinophils and 0.38 +/- 0.21 microg/ml IgE). Similar results were observed in mice treated with anti-TCRgammadelta or anti-TCRalphabeta monoclonal antibodies. Airway responsiveness to aerosolized methacholine was also reduced in challenged TCRdelta(-/-) animals relative to challenged wild-type mice. These results demonstrate that acute allergic airway responses are dependent upon intact TCRalphabeta and TCRgammadelta lymphocyte function and that TCRgammadelta cells promote acute airway sensitization.