G. Malizia

Expression of leukocyte adhesion molecules by mucosal mononuclear phagocytes in inflammatory bowel disease

Leukocyte adhesion molecules are important in cell-cell interactions of the immune system. Lymphocyte function-associated antigen 1 (cluster designation 11a) mediates interactions between T cells and mononuclear phagocytes through its ligand, the intercellular adhesion molecule 1 (CD54), whereas complement receptors 3 (CD 11b) and 4 (CD11c) are involved in complement-mediated phagocytosis. Expression of CD11 molecules and intercellular adhesion molecule 1 was studied in colonic biopsy specimens from 20 patients with inflammatory bowel disease and 10 normal controls. In normal colon, few mononuclear phagocytes expressed lymphocyte function-associated antigen 1 and intercellular adhesion molecule 1 at high densities. The major adhesion molecule was CD11c. Thus, the largest population of normal colonic mononuclear phagocytes was represented by quiescent, resident macrophages with likely phagocytic function. In inflammatory bowel disease, mononuclear phagocytes showed only a slight increase in CD11a expression and no significant change in expression of CD11b and CD11c. By contrast, the percentage of mononuclear phagocytes expressing intercellular adhesion molecule 1 was increased from 6.9% +/- 3.9% in controls to 69.2% +/- 12.8% in ulcerative colitis (P less than 0.001) and to 45.7% +/- 22.8% in Crohns disease (P less than 0.01), showing a close relationship with histological activity. The increased expression of intercellular adhesion molecule 1 in inflammatory bowel disease indicates a state of immunological activation induced by local release of inflammatory cytokines. Such induction of intercellular adhesion molecule 1 on mononuclear phagocytes may be important in the maintenance of chronic inflammation by facilitating interactions with T cells and T-cell antigen recognition.

Expression of leukocyte adhesion molecules in the liver of patients with chronic hepatitis B virus infection

Virus-specific T-cell responses are believed to be involved in the pathogenesis of liver cell injury secondary to hepatitis B virus infection. In this study, liver biopsy specimens from patients with chronic hepatitis B virus infection were analyzed for expression of two major pathways of adhesion used by cytotoxic T cells to interact with target cells. The lymphocyte function-associated antigen 3 was found preferentially expressed on hepatocytes of patients with active hepatitis B virus replication, whereas the expression of the intercellular adhesion molecule 1 on hepatocytes seemed more closely related with inflammatory activity. Adhesion molecules were also highly expressed on T lymphocytes found in areas of piecemeal and spotty necrosis, indicating the presence of antigen-specific memory T cells at the site of hepatocellular injury. This study suggests that the expression of the lymphocyte function-associated antigen 3 on hepatocytes may be important for viral elimination. The coordinate expression of the intercellular adhesion molecule 1 may regulate inflammatory response and enhance viral antigen presentation to T cells. Conversely, the absence of hepatocyte adhesion molecules might be a favorable factor for viral persistence.

Leucocyte adhesion molecules in inflammatory bowel disease: expression by colonic macrophages

Recent interest has focused on intercellular adhesion molecules and their ligands (the “integrins”), which mediate cell-cell interactions (1). Three leukocyte adhesion glycoproteins share a common β-chain (CD18); the a-chains are LFA-1 (“Lymphocyte Function-associated Antigen-1”; CD11a), MAC-1 (CD11b) and pl50,95 (CD11c), respectively. ICAM-1 (“Intercellular Adhesion Molecule-1”; CD54) is the ligand/receptor for LFA-1. The LFA-l/ICAM-1 interaction of T cells and mononuclear phagocytes is central for antigen presentation, antigen priming and for the mediation of inflammatory responses (2). CD11b and CD11c are receptors for complement C3bi and mediate phagocytosis of opsonized particles and cell binding to endothelium.