The role of LSP1 in microvascular hyperpermeability during neutrophil recruitment in vivo

Leukocyte-specific protein 1 (LSP1) is an F-actin- and Ca2+-binding, intracellular cytoskeletal and nuclear phosphoprotein expressed in hematopoietic lineage and endothelial cells. It has been shown to play an important role in leukocyte motility and recruitment during inflammation when leukocytes interact with matrix proteins or the endothelial cells of postcapillary venules at the site of infection or injury. The role of LSP1 in microvascular hyperpermeability during neutrophil recruitment is the focus of this study. To induce neutrophil recruitment in the cremasteric microvasculature, mouse cremaster muscle was treated by superfusion with CXC chemokine KC (Keratinocyte-derived chemokine, CXCL1), MIP-2 (Macrophage inflammatory protein-2, CXCL2) or intrascrotal injection with the cytokine tumor necrosis factor-α (TNFα). Neutrophil recruitment was visualized and determined by intravital microscopy that measures neutrophil adhesion and emigration. The changes of microvascular permeability after chemokines or cytokine are simultaneously measured by the use of fluorescent intravital microscopy. I observed that both KC and TNFα induced similar increases in microvascular permeability in wild-type and LSP1-deficient mice. The emigration of neutrophils was significantly lower in response to KC and TNFα in LSP1-deficient mice than in wild-type mice. However, the permeability increases induced by each emigrated neutrophil in LSP1-deficient mice were significantly higher compared with that in wild-type mice. When the circulating neutrophils were depleted by >98% by using anti-neutrophil antibodies, neutrophil rolling, adhesion and emigration and microvascular hyperpermeability in response to KC and TNFα were completely inhibited to the basal level in the inflamed venules. I conclude that neutrophil-endothelial cell interactions dictate the increases of microvascular permeability in inflamed tissues, and LSP1-deficient neutrophils contribute much more to the permeability increases than wild-type neutrophils do