Intercellular adhesion molecule-2 (ICAM-2) and Pseudomonas aeruginosa ocular infection

Identification of unique proteins in vitreous fluid of patients with noninfectious uveitis

PURPOSE

Uveitis is a cause for concern in the developing countries like India. Its poor diagnosis and lack of proper therapeutics often cause blindness in children and young adults. Moreover, the exact mechanism of pathogenesis of different types of uveitis is still elusive. Modern proteomic techniques are found to be advantageous for an in-depth understanding of the ocular physiology using proteomic diversity. Our aim was to identify unique proteins involved in the pathogenesis of autoimmune or noninfectious uveitis.

METHODS

Vitreous fluid samples (n = 90) were obtained from infectious (N = 34) and noninfectious (N = 56) uveitis patients, and their protein profiles were compared by analysing sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and 2D electrophoresis. Unique proteins were identified through matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and further studied for pathway analysis.

RESULTS

Protein spots having different molecular weights were observed in noninfectious vitreous fluid samples. Enzymatic digestion of these spots after MALDI-TOF MS analysis revealed different proteins. We identified 25 different proteins through SDS-PAGE and 22 through 2D electrophoresis. 50% of the proteins from SDS-PAGE were associated with heterotrimeric G-protein signalling pathway-rod outer segment phototransduction. 50% proteins from SDS-PAGE and 20% from 2D electrophoresis revealed association with de novo purine biosynthesis. Carbonic anhydrase 1 and serpin B3 were found to be common in both analyses.

CONCLUSION

High-throughput proteomic and pathway analyses have exposed the potential association of these proteins with autoimmune pathogenesis in uveitis. The exact role of most of the proteins in autoimmune uveitis is yet to be unfurled.

The regulation of transendothelial migration: new knowledge and new questions

Leucocyte transendothelial migration (TEM) involves a co-operative series of interactions between surface molecules on the leucocyte and cognate counter-ligands on the endothelial cell. These interactions set up a cascade of signalling events inside the endothelial cell that both allow for the junctions to loosen and for membrane to be recruited from the lateral border recycling compartment (LBRC). The LBRC is thought to provide an increased surface area and unligated receptors to the leucocyte to continue the process. The relative importance of the individual adhesion/signalling molecules that promote transmigration may vary depending on the type of leucocyte, the vascular bed, the inflammatory stimulus, and the stage of the inflammatory response. However, the molecular interactions between leucocyte and endothelial cell activate signalling pathways that disengage the adherens and tight junctions and recruit the LBRC to the site of transmigration. With the exception of disengaging the junctions, similar molecules and mechanisms promote transcellular migration as paracellular migration of leucocytes. This review will discuss the molecular interactions and signalling pathways that regulate transmigration, and the common themes that emerge from studying TEM of different leucocyte subsets under different inflammatory conditions. We will also raise some unanswered questions in need of future research.

Neutrophil and monocyte recruitment by PECAM, CD99, and other molecules via the LBRC

The recruitment of specific leukocyte subtypes to the site of tissue injury is the cornerstone of inflammation and disease progression. This process has become an intense area of research because it presents several possible steps against which disease-specific therapies could be targeted. Leukocytes are recruited out of the blood stream by a series of events that include their capture, rolling, activation, and migration along the endothelium. In the last step, the leukocytes squeeze between adjacent endothelial cells to gain access to the inflamed tissue through a process referred to as transendothelial migration (TEM). Although many of the molecules, such as PECAM and CD99, that regulate these sequential steps have been identified, much less is understood regarding how they work together to coordinate the complex intercellular communications and dramatic shape changes that take place between the endothelial cells and leukocytes. Several of the endothelial cell proteins that function in TEM are localized to the lateral border recycling compartment (LBRC), an interconnected reticulum of membrane that recycles selectively to the endothelial borders. The recruitment of the LBRC to surround the migrating leukocyte is required for efficient TEM. This review will focus on the proteins and mechanisms that mediate TEM and specifically how the LBRC functions in the context of these molecular interactions and membrane movements.

Complement component C5a activates ICAM-1 expression on human choroidal endothelial cells

PURPOSE

The complement system plays a crucial role in the progression of age-related macular degeneration (AMD). In this study, the authors sought to evaluate the pathophysiologic roles of complement components C3a and C5a in the human choroid in AMD.

METHODS

Human RPE/choroid was assayed for the presence of C3a and C5a receptors (C3aR and C5aR) using RT-PCR and immunohistochemistry. Choroidal endothelial cell migration and proliferation were evaluated in the presence of C5a. Organ cultures of human choroid were incubated in C5a or bovine serum albumin (BSA) followed by quantitative immunohistochemistry and quantitative PCR for ICAM-1. AMD patients and controls were genotyped at SNPs in the C5R1 and C3AR1 genes.

RESULTS

C5aR, but not C3aR, was detected in human choroid. C5a did not promote endothelial cell migration or proliferation. However, choriocapillaris endothelial cells in organ culture responded to C5a by increasing ICAM-1 mRNA and protein. No significant association of SNP genotypes was detected in AMD patients at the C3AR1 and C5R1 genes.

CONCLUSIONS

The generation of C5a peptides may lead to activation of choriocapillaris endothelial cells in AMD. Activation of the choroidal endothelium may affect the progression of AMD by recruitment of monocytes, leading to additional sequelae of AMD pathogenesis.

Endothelial cell activation leads to neutrophil transmigration as supported by the sequential roles of ICAM-2, JAM-A, and PECAM-1

Leukocyte transmigration is mediated by endothelial cell (EC) junctional molecules, but the associated mechanisms remain unclear. Here we investigate how intercellular adhesion molecule-2 (ICAM-2), junctional adhesion molecule-A (JAM-A), and platelet endothelial cell adhesion molecule (PECAM-1) mediate neutrophil transmigration in a stimulus-dependent manner (eg, as induced by interleukin-1beta [IL-1beta] but not tumor necrosis factor-alpha [TNF-alpha]), and demonstrate their ability to act in sequence. Using a cell-transfer technique, transmigration responses of wild-type and TNF-alpha p55/p75 receptor-deficient leukocytes (TNFR(-/-)) through mouse cremasteric venules were quantified by fluorescence intravital microscopy. Whereas wild-type leukocytes showed a normal transmigration response to TNF-alpha in ICAM-2(-/-), JAM-A(-/-), and PECAM-1(-/-) recipient mice, TNFR(-/-) leukocytes exhibited a reduced transmigration response. Hence, when the ability of TNF-alpha to directly stimulate neutrophils is blocked, TNF-alpha-induced neutrophil transmigration is rendered dependent on ICAM-2, JAM-A, and PECAM-1, suggesting that the stimulus-dependent role of these molecules is governed by the target cell being activated. Furthermore, analysis of the site of arrest of neutrophils in inflamed tissues from ICAM-2(-/-), JAM-A(-/-), and PECAM-1(-/-) mice demonstrated that these molecules act sequentially to mediate transmigration. Collectively, the findings provide novel insights into the mechanisms of action of key molecules implicated in leukocyte transmigration.

Lymphocyte function-associated antigen-1-dependent inhibition of corneal wound healing

Abrasion of murine corneal epithelium induces neutrophil emigration through limbal vessels into the avascular corneal stroma, peaking within 12 to 18 hours after wounding. A central corneal wound closes within 24 hours by epithelial cell migration and division, and during wound closure corneal epithelial cells express intercellular adhesion molecule (ICAM)-1 (CD54). We investigated the contributions of lymphocyte function-associated antigen (LFA)-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) by analyzing wound closure in mice with targeted deletions of CD11a (CD11a-/-) or CD11b (CD11b-/-). In contrast to CD11a-/- mice, CD11b deficiency revealed a much greater delay in epithelial wound closure with >90% inhibition of epithelial cell division at a time when neutrophil accumulation in the cornea was approximately threefold higher than normal. Treating CD11b-/- mice with anti-CD11a monoclonal antibody at the time of epithelial abrasion resulted in significant reductions in neutrophils and significant increases in corneal epithelial cell division and migration. Treating CD11b-/- mice with anti-ICAM-1 significantly increased measures of healing but marginally reduced neutrophil influx. In conclusion, wound healing after corneal epithelial abrasion is disrupted by the absence of CD11b. The disruption is apparently linked to excessive neutrophil accumulation at a time when epithelial division is essential to wound repair, and neutrophils appear to be detrimental through processes involving LFA-1 and ICAM-1.

ICAM-2 mediates neutrophil transmigration in vivo: evidence for stimulus specificity and a role in PECAM-1-independent transmigration

ICAM-2 has been implicated in leukocyte transmigration in vitro, but there is little in vivo evidence to support this. To address this, neutrophil migration was investigated in ICAM-2-deficient mice (KO) and in wild-type (WT) mice treated with an anti-ICAM-2 blocking monoclonal antibody (mAb) (3C4). In a peritonitis model, IL-1beta-induced accumulation of neutrophils was significantly reduced in mice treated with 3C4 (51% inhibition) and in KO mice (41% inhibition). In contrast, TNF-alpha- or thioglycolate-induced responses were not suppressed in KO mice. Analysis of IL-1beta-induced leukocyte responses in cremasteric venules of KO animals by intravital microscopy indicated a defect in transmigration (44% inhibition) but not rolling or adhesion. As found before, TNF-alpha-induced leukocyte transmigration was unaltered in the KO mice. WT mice treated with the anti-ICAM-2 mAb also exhibited a selective reduction in leukocyte transmigration in response to IL-1beta while an anti-ICAM-1 mAb inhibited both leukocyte adhesion and transmigration. Interestingly, mAb 3C4 significantly suppressed IL-1beta-induced neutrophil transmigration in PE-CAM-1 KO animals in the peritonitis model but not in the cremaster muscle. The findings provide direct evidence for the involvement of ICAM-2 in neutrophil transmigration in vivo, though this role appears to be stimulus specific. Furthermore, ICAM-2 appears capable of mediating PECAM-1-independent leukocyte transmigration.