To identify the physiological role of Hck, a functionally redundant member of the Src family of tyrosine kinases expressed in myelomonocytic cells, we generated HckF/F “knock-in” mice which carry a targeted tyrosine (Y) to phenylalanine (F) substitution of the COOH-terminal, negative regulatory Y499-residue in the Hck protein. Unlike their Hck−/− “loss-of-function” counterparts, HckF/F “gain-of-function” mice spontaneously acquired a lung pathology characterized by extensive eosinophilic and mononuclear cell infiltration within the lung parenchyma, alveolar airspaces, and around blood vessels, as well as marked epithelial mucus metaplasia in conducting airways. Lungs from HckF/F mice showed areas of mild emphysema and pulmonary fibrosis, which together with inflammation resulted in altered lung function and respiratory distress in aging mice. When challenged transnasally with lipopolysaccharide (LPS), HckF/F mice displayed an exaggerated pulmonary innate immune response, characterized by excessive release of matrix metalloproteinases and tumor necrosis factor (TNF)α. Similarly, HckF/F mice were highly sensitive to endotoxemia after systemic administration of LPS, and macrophages and neutrophils derived from HckF/F mice exhibited enhanced effector functions in vitro (e.g., nitric oxide and TNFα production, chemotaxis, and degranulation). Based on the demonstrated functional association of Hck with leukocyte integrins, we propose that constitutive activation of Hck may mimic adhesion-dependent priming of leukocytes. Thus, our observations collectively suggest an enhanced innate immune response in HckF/F mice thereby skewing innate immunity from a reversible physiological host defense response to one causing irreversible tissue damage.

We measured respiratory input impedance (1–25 Hz) in mice and obtained parameters for airway and tissue mechanics by model fitting. Lung volume was varied by inflating to airway opening pressure (Pao) between 0 and 20 cmH2O. The expected pattern of changes in respiratory mechanics with increasing lung volume was seen: a progressive fall in airway resistance and increases in the coefficients of tissue damping and elastance. A surprising pattern was seen in hysteresivity (η), with a plateau at low lung volumes (Pao < 10 cmH2O), a sharp fall occurring between 10 and 15 cmH2O, and η approaching a second (lower) plateau at higher lung volumes. Studies designed to elucidate the mechanism(s) behind this behavior revealed that this was not due to chest wall properties, differences in volume history at low lung volume, time dependence of volume recruitment, or surface-acting forces. Our data are consistent with the notion that at low lung volumes the mechanics of the tissue matrix determine η, whereas at high lung volumes the properties of individual fibers (collagen) become more important.

The role of tumor necrosis factor-alpha (TNF-α), an important mediator of the inflammatory response after injury, was investigated in regenerating skeletal muscle. The pattern of expression of TNF-α during muscle regeneration was examined by immunohistochemistry in tissue sections of crush-injured or transplanted muscle autografts and in primary cultures of adult skeletal muscle. TNF-α was highly expressed in injured myofibers, inflammatory cells, endothelial cells, fibroblasts, and mast cells. Myoblasts and myotubes also expressed TNF-α in primary muscle cultures and tissue sections. The essential role of TNF-α and its homologue lymphotoxin-alpha (LT-α) during muscle regeneration was assessed by basic histology in TNF-α(–) and TNF-α(-/-)/LT-α(-/-) mice. No difference was apparent in the onset or pattern of muscle regeneration (i.e., inflammatory response, activation and fusion of myoblasts) between the two strains of null mice or between nulls and normal control mice. However, both strains of null mice appeared more prone to bystander damage of host muscle and regeneration distant from the site of injury/transplantation. Although expression of TNF-α may play an important role in muscle regeneration, the studies in the null mice show that redundancy within the cytokine system (or some other response) can effectively compensate for the absence of TNF-α in vivo. (J Histochem Cytochem 49:989–1001, 2001)

A tracking impedance estimation technique was developed to follow the changes in total respiratory impedance (Zrs) during slow total lung capacity maneuvers in six anesthetized and mechanically ventilated BALB/c mice. Zrs was measured with the wave-tube technique and pseudorandom forced oscillations at nine frequencies between 4 and 38 Hz during inflation from a transrespiratory pressure of 0-20 cmH2O and subsequent deflation, each lasting for approximately 20 s. Zrs was averaged for 0.125 s and fitted by a model featuring airway resistance (Raw) and inertance, and tissue damping and elastance (H). Lower airway conductance (Glaw) was linearly related to volume above functional residual capacity (V) between 0 and 75-95% maximum V, with a mean slope of dGlaw/dV = 13.6 +/- 4.6 cmH2O-1. s-1. The interdependence of Raw and H was characterized by two distinct and closely linear relationships for the low- and high-volume regions, separated at approximately 40% maximum V. Comparison of Raw with the highest-frequency resistance of the total respiratory system revealed a marked volume-dependent contribution of tissue resistance to total respiratory system resistance, resulting in the overestimation of Raw by 19 +/- 8 and 163 +/- 40% at functional residual capacity and total lung capacity, respectively, whereas the lowest frequency reactance was proportional to H; these findings indicate that single-frequency resistance values may become inappropriate as surrogates of Raw when tissue impedance is changing.