Dynamic association of L-selectin with the lymphocyte cytoskeletal matrix.

L-selectin mediates lymphocyte extravasation into lymphoid tissues through binding to sialomucin-like receptors on the surface of high endothelial venules (HEV). This study examines the biochemical basis and regulation of interactions between L-selectin, an integral transmembrane protein, and the lymphocyte cytoskeleton. Using a detergent-based extraction procedure, constitutive associations between L-selectin and the insoluble cytoskeletal matrix could not be detected. However, engagement of the L-selectin lectin domain by Abs or by glycosylation-dependent cell adhesion molecule-1, an HEV-derived ligand for L-selectin, rapidly triggered redistribution of L-selectin to the detergent-insoluble cytoskeleton. L-selectin attachment to the cytoskeleton was not prevented by inhibitors of actin/microtubule polymerization (cytochalasin B, colchicine, or nocodozole) or serine/threonine and tyrosine kinase activity (staurosporine, calphostin C, or genistein), although L-selectin-mediated adhesion of human PBL was markedly suppressed by these agents. Exposure of human PBL or murine pre-B transfectants expressing full-length human L-selectin to fever-range hyperthermia also markedly increased L-selectin association with the cytoskeleton, directly correlating with enhanced L-selectin-mediated adhesion. In contrast, a deletion mutant of L-selectin lacking the COOH-terminal 11 amino acids failed to associate with the cytoskeletal matrix in response to Ab cross-linking or hyperthermia stimulation and did not support adhesion to HEV. These studies, when taken together with the previously demonstrated interaction between the L-selectin cytoplasmic domain and the cytoskeletal linker protein alpha-actinin, strongly implicate the actin-based cytoskeleton in dynamically controlling L-selectin adhesion.

Fever-range hyperthermia enhances L-selectin-dependent adhesion of lymphocytes to vascular endothelium.

The L-selectin leukocyte adhesion molecule plays an important role in controlling leukocyte extravasation in peripheral lymph nodes and at sites of tissue injury or infection. Although febrile responses during infection and inflammation are associated with enhanced immune activity, the contribution of fever-range temperatures to controlling lymphocyte recruitment to tissues has not been previously examined. In this report we provide evidence that direct exposure of lymphocytes to fever-range temperatures (38-41 degrees C) in vitro for 9 to 24 h resulted in a >100% increase in L-selectin-dependent adhesion of these cells to lymph node high endothelial venules (HEV). Moreover, culture of lymphocytes under hyperthermia conditions markedly enhanced the ability of these cells to traffic in an L-selectin-dependent manner to peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. In contrast, febrile temperatures did not increase LFA-1 function as assessed by measuring lymphocyte adhesion to ICAM-1-3T3 transfectants. Fever-range hyperthermia further did not increase L-selectin surface density on lymphocytes or L-selectin-dependent recognition of soluble carbohydrate substrates; however, a marked increase in ultrastructural immunogold-labeling of L-selectin was observed in response to thermal stimuli. These results suggest that elevated temperatures enhance L-selectin adhesion and/or avidity through the regulation of L-selectin conformation or organization in the plasma membrane. Finally, the observed thermal effects on L-selectin adhesion were attributed to soluble factors in the conditioned medium of heat-treated cells. Taken together, these data provide new insight into the potential physiologic role of the febrile response in enhancing lymphocyte recruitment to tissues through the regulation of L-selectin adhesion.