A Functional Role for Circulating Mouse L-Selectin in Regulating Leukocyte/Endothelial Cell Interactions In Vivo

Abstract

L-selectin mediates the initial capture and subsequent rolling of leukocytes along inflamed vascular endothelium and mediates lymphocyte migration to peripheral lymphoid tissues. Leukocyte activation induces rapid endoproteolytic cleavage of L-selectin from the cell surface, generating soluble L-selectin (sL-selectin). Because human sL-selectin retains ligand-binding activity in vitro, mouse sL-selectin and its in vivo relevance were characterized. Comparable with humans, sL-selectin was present in adult C57BL/6 mouse sera at ∼1.7 μg/ml. Similar levels of sL-selectin were present in sera from multiple mouse strains, despite their pronounced differences in cell surface L-selectin expression levels. Adhesion molecule-deficient mice prone to spontaneous chronic inflammation and mice suffering from leukemia/lymphoma had 2.5- and 20-fold increased serum sL-selectin levels, respectively. By contrast, serum sL-selectin levels were reduced by 70% in Rag-deficient mice lacking mature lymphocytes. The majority of serum sL-selectin had a molecular mass of 65–75 kDa, consistent with its lymphocyte origin. Slow turnover may explain the relatively high levels of sL-selectin in vivo. The t1/2 of sL-selectin, assessed by transferring sera from wild-type mice into L-selectin-deficient mice and monitoring serum sL-selectin levels by ELISA, was >20 h, and it remained detectable for longer than 1 wk. Short-term in vivo lymphocyte migration assays demonstrated that near physiologic levels (∼0.9 μg/ml) of sL-selectin decreased lymphocyte migration to peripheral lymph nodes by >30%, with dose-dependent inhibition occurring with increasing sL-selectin concentrations. These results suggest that sL-selectin influences lymphocyte migration in vivo and that the increased sL-selectin levels present in certain pathologic conditions may adversely affect leukocyte migration.

L-Selectin or ICAM-1 Deficiency Reduces an Immediate-Type Hypersensitivity Response by Preventing Mast Cell Recruitment in Repeated Elicitation of Contact Hypersensitivity

“…Furthermore, ICAM-1 loss generally increased sL-selectin levels compared with wild-type littermates (Fig. 9B), as previously reported (22). This finding may be related to increased circulating leukocyte numbers by 2.9-to 4.1-fold in ICAM-1 Ϫ/Ϫ mice (4,15).…”

“…9B). Although the reasons for this remain unknown, it may be due to a decrease in the sL-selectin source since L-selectin expression levels on circulating leukocytes from ICAM-1 Ϫ/Ϫ mice were significantly reduced on day 24 compared with those found on day 0 (data not shown) and the t 1/2 of sL-selectin is estimated at ϳ25 h (22). Like the murine chronic CH model (Fig.…”

“…All serum samples were stored at Ϫ40°C until use. Serum sL-selectin levels were measured by ELISA as described previously (22). Briefly, 96-well microtiter plates (Costar, Cambridge, MA) were coated with an anti-L-selectin mAb (LAM1-102) (23) in 0.1 M borate buffer (pH 8.4) at 4°C for 18 h and were then blocked with 2% BSA and 1% gelatin in TBS for 1 h at 37°C.…”

No association between E- and L-selectin genes and SLE: soluble L-selectin levels do correlate with genotype and a subset in SLE

“…Interestingly, sL-selectin may not be a mere bystander in lupus as the soluble form of the molecule has been shown to be functional; for example, it can inhibit lymphocyte migration to peripheral lymph nodes. 15,16 Indeed, abnormal sL-selectin level may predict patients who develop pulmonary inflammation 47,48 and vascular disease including pulmonary hypertension, 49 and ischaemic heart disease. 50 The association of sL-selectin with IgG-ACA in our patients suggests that the soluble molecule may serve as a marker for vascular risk in SLE, and studies are planned to explore this possibility.…”

“…15 Physiological levels of sL-selectin may reduce lymphocyte migration to peripheral lymph nodes by 30%. 16 sE-selectin is also present in serum but at low concentrations. 17 Although a clear physiological role for this protein has not been defined, sE-selectin may be protective against murine nephritis.…”