[show abstract][hide abstract] ABSTRACT: The Gram-positive Streptococcus pneumoniae is the leading cause of community-acquired pneumonia worldwide, resulting in high mortality. Our in vivo studies show that galectin-3(-/-) mice develop more severe pneumonia after infection with S. pneumoniae, as demonstrated by increased bacteremia and lung damage compared to wild-type mice and that galectin-3 reduces the severity of pneumococcal pneumonia in part by augmenting neutrophil function. Specifically, we show that 1) galectin-3 directly acts as a neutrophil-activating agent and potentiates the effect of fMLP, 2) exogenous galectin-3 augments neutrophil phagocytosis of bacteria and delays neutrophil apoptosis, 3) phagocytosis of apoptotic neutrophils by galectin-3(-/-) macrophages is less efficient compared to wild type, and 4) galectin-3 demonstrates bacteriostatic properties against S. pneumoniae in vitro. Furthermore, ad-back of recombinant galectin-3 in vivo protects galectin-3-deficient mice from developing severe pneumonia. Together, these results demonstrate that galectin-3 is a key molecule in the host defense against pneumococcal infection. Therapeutic strategies designed to augment galectin-3 activity may both enhance inflammatory cell function (by directly affecting neutrophil responsiveness and prolonging neutrophil longevity) and have direct bacteriostatic activity, improving clinical outcomes after severe pneumococcal infection.
American Journal Of Pathology 03/2008; 172(2):395-405. · 4.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Alternative macrophage activation is implicated in diverse disease pathologies such as asthma, organ fibrosis, and granulomatous diseases, but the mechanisms underlying macrophage programming are not fully understood. Galectin-3 is a carbohydrate-binding lectin present on macrophages. We show that disruption of the galectin-3 gene in 129sv mice specifically restrains IL-4/IL-13-induced alternative macrophage activation in bone marrow-derived macrophages in vitro and in resident lung and recruited peritoneal macrophages in vivo without affecting IFN-gamma/LPS-induced classical activation or IL-10-induced deactivation. IL-4-mediated alternative macrophage activation is inhibited by siRNA-targeted deletion of galectin-3 or its membrane receptor CD98 and by inhibition of PI3K. Increased galectin-3 expression and secretion is a feature of alternative macrophage activation. IL-4 stimulates galectin-3 expression and release in parallel with other phenotypic markers of alternative macrophage activation. By contrast, classical macrophage activation with LPS inhibits galectin-3 expression and release. Galectin-3 binds to CD98, and exogenous galectin-3 or cross-linking CD98 with the mAb 4F2 stimulates PI3K activation and alternative activation. IL-4-induced alternative activation is blocked by bis-(3-deoxy-3-(3-methoxybenzamido)-beta-D-galactopyranosyl) sulfane, a specific inhibitor of extracellular galectin-3 carbohydrate binding. These results demonstrate that a galectin-3 feedback loop drives alternative macrophage activation. Pharmacological modulation of galectin-3 function represents a novel therapeutic strategy in pathologies associated with alternatively activated macrophages.
The Journal of Immunology 03/2008; 180(4):2650-8. · 5.52 Impact Factor