Influence of age on surfactant isolated from healthy horses maintained on pasture.

BACKGROUND: Surfactant alterations are described in horses after exercise, anesthesia, and prolonged transport, in horses with recurrent airway obstruction, and in neonatal foals. The effect of horse age or bronchoalveolar lavage fluid (BALF) sample characteristics on surfactant is unknown. OBJECTIVES: To evaluate surfactant phospholipid composition and function in healthy horses, and to investigate the influence of age and BALF sample characteristics on surfactant. ANIMALS: Seventeen healthy horses 6-25 years of age maintained on pasture year-round. METHODS: BALF was collected by standard procedures and was assessed for recovery volume, nucleated cell count (NCC), and cytology. Cell-free BALF was separated into crude surfactant pellet (CSP) and surfactant supernatant (Supe) by ultracentrifugation. Phospholipid and protein content were determined from both fractions. CSP phospholipid composition was analyzed by high-performance liquid chromatography with an evaporative light scatter detector. Surface tension of CSP was evaluated with a pulsating bubble surfactometer. Regression analysis was used to evaluate associations between age, BALF sample characteristics, and surfactant variables. RESULTS: Results and conclusions were derived from 15 horses. Increasing age was associated with decreased phospholipid content in CSP but not Supe. Age did not affect protein content of CSP or Supe, or surfactant phospholipid composition or function. Age-related surfactant changes were unaffected by BALF recovery percentage, NCC, and cytological profile. CONCLUSIONS AND CLINICAL IMPORTANCE: Older horses have decreased surfactant phospholipid content, which might be because of age-related pulmonary changes. Surfactant composition is unaffected by BALF sample characteristics at a BALF recovery percentage of at least 50%.

Role of lung surfactant in respiratory disease: current knowledge in large animal medicine.

Lung surfactant is produced by type II alveolar cells as a mixture of phospholipids, surfactant proteins, and neutral lipids. Surfactant lowers alveolar surface tension and is crucial for the prevention of alveolar collapse. In addition, surfactant contributes to smaller airway patency and improves mucociliary clearance. Surfactant-specific proteins are part of the innate immune defense mechanisms of the lung. Lung surfactant alterations have been described in a number of respiratory diseases. Surfactant deficiency (quantitative deficit of surfactant) in premature animals causes neonatal respiratory distress syndrome. Surfactant dysfunction (qualitative changes in surfactant) has been implicated in the pathophysiology of acute respiratory distress syndrome and asthma. Analysis of surfactant from amniotic fluid allows assessment of fetal lung maturity (FLM) in the human fetus and exogenous surfactant replacement therapy is part of the standard care in premature human infants. In contrast to human medicine, use and success of FLM testing or surfactant replacement therapy remain limited in veterinary medicine. Lung surfactant has been studied in large animal models of human disease. However, only a few reports exist on lung surfactant alterations in naturally occurring respiratory disease in large animals. This article gives a general review on the role of lung surfactant in respiratory disease followed by an overview of our current knowledge on surfactant in large animal veterinary medicine.

Lung lymphocyte elimination by apoptosis in the murine response to intratracheal particulate antigen.

Pulmonary immune responses are suited to determine mechanisms of lymphocyte elimination, as lung inflammation must be regulated tightly to preserve gas exchange. The self-terminating response of primed C57BL/6 mice to intratracheal challenge with the T cell-dependent Ag sheep erythrocytes (SRBC) was used to test the importance of lung lymphocyte apoptosis in pulmonary immunoregulation. Apoptosis of alveolar and interstitial lymphocytes was demonstrated morphologically, by three independent methods to detect DNA fragmentation, and by surface expression of phosphatidylserine. Apoptotic lymphocytes were exclusively CD4-, CD8-, B220-, but many were CD3+ and Thy 1+. Inhibiting apoptosis by in vivo cyclosporine treatment prolonged lung lymphocyte accumulation following SRBC challenge. Experiments using mice homozygous for the lpr or gld mutations showed that pulmonary lymphocyte apoptosis depended on expression of Fas (CD95) and its ligand (Fas-L). Pulmonary inflammation increased on repeated intratracheal SRBC challenge of lpr/lpr mice, in contrast to the waning response in normal mice. These results confirm that in situ lymphocyte apoptosis contributes to termination of immune responses in nonlymphoid organs, probably because of activation-induced cell death, and may be important in inducing tolerance to repeated antigen exposure.

The pathogenesis of chronic obstructive pulmonary disease of horses.

Present evidence suggests that chronic obstructive pulmonary disease (COPD) of horses is a delayed hypersensitivity response to inhaled antigens, particularly the thermophilic moulds and actinomycetes that grow in damp hay. Within several hours of exposing COPD-susceptible horses to such hay, neutrophils invade the lung and accumulate in the lumens of airways, particularly bronchioles. The inflammatory response is accompanied by increased levels of histamine in bronchoalveolar lavage fluid, increased plasma levels of the inflammatory mediators thromboxane and 15-hydroxyeicosatetraenoic acid (15-HETE), and a decrease in the production of prostaglandin (PG) E2 by the airway mucosa. During acute exacerbations of COPD, airways exhibit nonspecific hyperresponsiveness and become obstructed as a result of bronchospasm and the accumulation of mucus and exudates. Bronchospasm is due largely to activation of smooth muscle muscarinic receptors by acetylcholine (ACh). Because the in vitro response of smooth muscle to ACh is unaltered, the increase in airway smooth muscle tone is probably a result of activation of airway reflexes by inflammatory mediators and decreases in inhibitory mechanisms such as the intrapulmonary nonadrenergic noncholinergic nervous system and the production of PGE2 in affected horses. The diffuse airway obstruction leads to uneven distribution of ventilation, ventilation/perfusion mismatching, and hypoxaemia. As a result of the increased respiratory drive caused by hypoxaemia and the presence of airway obstruction, horses adopt a characteristic breathing strategy in which very high peak flows at the start of exhalation rapidly diminish as exhalation proceeds.

Adhesion receptor phenotypes of murine lung CD4+ T cells during the pulmonary immune response to sheep erythrocytes.

Understanding the molecular mechanisms of pulmonary lymphocyte recruitment is a crucial step toward selective control of immune lung diseases and infections in immunocompromised hosts. To dissect these mechanisms, we are studying the response induced in primed C57BL/6 mice by intratracheal challenge with the T cell-dependent antigen, sheep red blood cells (SRBC). This study used four-parameter flow cytometry to examine expression by CD4+ murine T cells in peripheral blood and lungs of receptors known to be differentially expressed on primed human lymphocytes (CD2, CD11a, CD44, CD45RB, CD49d, and L-selectin). Compared with peripheral blood, more lung CD4+ T cells recovered by bronchoalveolar lavage (BAL) showed a primed phenotype. Judged by low expression of CD45RB or L-selectin, 76 to 90% of BAL CD4+ T cells were primed at all times. Adhesion receptor phenotype of CD4+ T cells in BAL and lung interstitium agreed closely, although BAL contained a greater percentage of primed cells. The percentage of CD4+ T cells with high expression of CD44+ and CD49d increased late in the response. However, when considering only upregulated adhesion receptors which might mediate recruitment, 22 to 52% of CD4+ T cells in BAL did not have increased adhesion receptor expression. Longer duration between priming and challenge did not increase adhesion receptor upregulation. High adhesion receptor expression was least evident during the periods of maximal lymphocyte influx, suggesting that factors other than increased surface density of organ-nonspecific adhesion receptors contribute to lymphocyte recruitment during pulmonary immune responses.