Anti-CD18 Antibody [M18/2] (A86478)

Tissue-specific silencing of genes may be used for genetic engineering in mice and has possible therapeutic applications in humans. Current strategies in mice rely on Cre/loxP technology requiring the generation of multiple transgenic lines and breeding strategies. Here, we describe the selective silencing of CD18, a leukocyte-specific integrin in neutrophils using a micro RNA (miRNA) strategy that requires the generation of one transgenic line. CD18-specific miRNA hairpin driven by the myeloid specific human MRP8 promoter resulted in the generation of transgenic lines with 75% to 95% reduction in CD18 protein levels in neutrophils and monocytes. Minimal decreases in T cells and a partial diminution in macrophages were observed. Neutrophil CD18 silencing resulted in neutrophilia, splenomegaly, and significant defects in neutrophil trafficking with the degree of alterations correlating with the extent of CD18 silencing. Thus, our data demonstrate the utility of using miRNA approaches to silence genes in neutrophils, which are terminally differentiated cells with a short half-life that largely precludes their genetic manipulation in vitro. Furthermore, the mouse models provide a valuable tool to examine the contribution of CD18 on neutrophils to leukocyte adhesion deficiency type I (LAD-I), a complex inherited disorder in which reduced or absent CD18 expression in multiple leukocyte subsets leads to impaired innate and adaptive immune responses.

Leukocyte infiltration of synovial fluid and tissues is the hallmark of inflammatory arthritis. Selectins and beta2 integrins have been implicated in the multistep process of leukocyte adhesion to vascular endothelium. However, previous work has revealed disparate requirements for leukocyte recruitments to specific anatomic locales. Moreover, the mechanisms regulating recruitment of leukocytes to the joint in inflammatory arthritis models are not fully understood. We hypothesized that beta2 integrins, expressed on leukocytes, might play a pathogenic role in synovial inflammation. Using mice deficient in all beta2 integrins (CD18 null mice), we demonstrate that expression of these heterodimeric adhesion molecules is critical for arthritis induction in the K/B x N serum transfer model. Using null-allele mice and blocking mAbs, we demonstrate specifically that CD11a/CD18 (LFA-1) is absolutely required for the development of arthritis in this model. Blocking mAbs further revealed an ongoing requirement for LFA-1 I-domain adhesive function in disease perpetuation. These findings suggest that the LFA-1 I-domain forms an attractive target for treatment of human inflammatory arthritis.

We have previously identified a 16-kDa protein with a pI of 5.1 (P16/5.1) that is associated with macrophage CR3. Microsequencing of P16/5.1 indicated exclusive homology to the beta-galactoside-binding lectin, galectin-1. Abs specific to a galectin-1 unique peptide reacted with P16/5.1. The association of P16/5.1 with CR3 was specifically inhibited by lactose, which binds with high affinity to galectin-1. These data together with similarities in molecular mass and pI suggest that P16/5.1 is galectin-1. Two-color immunofluorescence staining revealed the expression of galectin-1 on the macrophage surface and its colocalization with CR3. However, a surplus of CR3 was free of galectin-1, and some galectin-1 molecules were associated with cell surface receptors other than CR3. Based on these results we propose two models depicting the functional significance of CR3-galectin-1 association: 1) homodimeric galectin-1 possessing a divalent sugar binding site may act as an extracellular adapter molecule that cross-links CR3 with other receptors; and 2) association of galectin-1 with beta-galactosides on the extracellular domain of CR3 may modify the binding affinity of the receptor to its ligand. These possibilities are not mutually exclusive and can clarify the mode by which CR3 transmits signals in macrophages.