Jacqueline Prieto

Leukocyte‐Cell Adhesion: A Molecular Process Fundamental in Leukocyte Physiology

Leukocyte-cell adhesion is a form of physical contact characterized by fast (firm) stickiness between the cells. To analyze the biology and molecular basis of this process, an adhesion-specific assay was developed: the phorbol ester-induced aggregation of human lymphocytes. This rapid and antigen-independent intercellular adhesion requires cellular metabolism, an intact cytoskeleton and extracellular divalent cations, and is mediated by preformed cell-surface proteins referred to as CAMs. Phorbol ester also induces aggregation of monocytes and granulocytes, as well as adhesion of T lymphocytes to either B cells or monocytes and of the leukocytes to vascular endothelial cells. By using the adhesion-specific assay and blocking monoclonal antibodies, several CAMs have been identified, namely the Leu-CAM family (CD11a-c/CD18) and ICAM-1 (CD54). The Leu-CAM family is composed of Leu-CAMa (CD11a/CD18), Leu-CAMb (CD11b/CD18) and Leu-CAMc (CD11c/CD18), three glycoprotein heterodimers made of a common beta-chain and distinct alpha-chains. ICAM-1 is an adhesive ligand for Leu-CAMa. Expression and use of the various CAMs is selective in different types of leukocytes. The Leu-CAMs have been purified and partially characterized. CD18, whose gene is on human chromosome 21, contains 5-6 N-linked complex-type oligosaccharides, and CD11 binds Ca++. Another adhesion pathway is mediated by CD2 and CD58. CD2, a glycoprotein selectively expressed by T cells, is a receptor for CD58, a cell-surface adhesive ligand with broad tissue distribution. Antibodies to the latter CAMs do not block the phorbol ester-induced lymphocyte aggregation. Adhesion is involved in a large variety of leukocyte functions. Anti-Leu-CAM antibodies block induction of IL-2 production and lymphocyte proliferation. Lymphocyte-mediated cytotoxicity is also inhibited. Endogenous NK and LAK cells use Leu-CAMs, ICAM-1 and CD2, and sometimes RGD receptors, to bind and kill tumor cells. Endogenous compounds such as H2O2 and LTB4 also induce Leu-CAM-dependent adhesion in monocytoid cells and granulocytes, respectively, and degranulation of the latter cells is enhanced by the adhesion process. Homologous CAMs have been identified in rabbit and mouse. In in vivo studies in the former species, anti-Leu-CAM antibodies block adhesion of leukocytes to vascular endothelium and thereby their migration into extravascular tissues. The antibodies thus inhibit granulocyte accumulation and plasma leakage in inflammatory lesions, and induce lympho- and granulocytosis, indicating that cell-adhesion contributes to the distribution of leukocytes in the body.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of a novel adhesion molecule in human leukocytes by monoclonal antibody LB-2

Monoclonal antibody LB‐2 to a surface antigen on human B cells, lymphoblast, monocytes and vascular endothelial cells largely inhibited adhesion among Epstein Barr virus‐immortalized normal B cells (EBV‐B) and concanavalin A‐stimulated blood mononuclear cells (Con A‐BMC) before and after phorbol ester treatment. The antibody inhibited to a lesser extent phorbol ester‐induced aggregation of monocytes, U937 cells and fresh BMC and had virtually no inhibitory effect on the adhesion among enriched T cells and granulocytes. A surface glycoprotein band of 84 kDa was obtained from EBV‐B cells by immunoprecipitation and gel electrophoresis. Immunological and biochemical studies clearly distinguished this molecule from gp90 and associated glycoproteins which also mediate leukocyte adhesion.

Adhesion-mediating molecules of human monocytes

Adhesion of monocytes to each other and to T cells and substrates is increased by phorbol esters. In the presence of these compounds monocyte aggregation was almost completely inhibited (greater than 90%) by monoclonal antibody 60.3. This antibody recognizes GP90 (CD18), a leukocyte surface glycoprotein which is separately and noncovalently associated to either GP160 (CD11a), GP155 (CD11b), or GP130 (CD11c). Anti-LFA-1 antibody (CD11a) was only partially inhibitory (35%) while antibodies 60.1 (CD11b) and anti-Leu-M5 (CD11c) had a minimal inhibitory effect (10%). Antibody LB-2 recognizing a single glycoprotein distinct from the GP90-GP160 complex and expressed on activated B and T cells, monocytes, and vascular endothelial cells was partially inhibitory (22%). Monoclonal antibodies anti-C3bR (CD35), T29/33 (CD45, leukocyte common antigen 200). TA-1 (CD11a), OKM1 (CD11b), F10-44-2 (brain-leukocyte antigen), OKM5 (monocyte-endothelial cell antigen) and to class I or class II molecules exerted no inhibition on the monocyte aggregation. Fab fragments of antibody 60.3 efficiently inhibited not only monocyte aggregation in the absence or presence of phorbol esters but also adhesion of these cells to autologous or allogeneic T lymphocytes and, to a lesser extent, to plastic surfaces. It is thus concluded that GP90, either alone or associated to the larger glycoproteins, and LB-2 antigen mediate monocyte adhesion.

Rabbit leukocyte adhesion molecules CD11CD18 and their participation in acute and delayed inflammatory responses and leukocyte distribution in vivo

In humans the glycoprotein complexes CD11/CD18 mediate leukocyte adhesion to cells. Mouse monoclonal antibodies (mAb) 60.3, 7E4, and IB4 to human CD18, found to cross-react with rabbit white blood cells, were used to identify the antigen in rabbit cells and to study adherence of rabbit leukocytes in vitro and in vivo. These antibodies labeled almost all unfractionated rabbit blood leukocytes and immunoprecipitated surface glycopolypeptides with apparent molecular weights of 85,000 and 150,000 from these cells. Adhesion of purified rabbit polymorphonuclear cells (PMNs) to cultured vascular endothelial cells in the presence of phorbol ester was blocked by the antibodies in a dose-dependent manner. The acute inflammatory response characterized by local accumulation of PMNs and concomitant plasma extravasation following intradermal injections of zymosan-activated serum (ZAS) in rabbits was inhibited in animals pretreated intravenously with anti-CD18 mAb. Intravital microscopy of the rabbit tenuissimus muscle demonstrated that anti-CD18 mAb. Intravital microscopy of the rabbit tenuissimus muscle demonstrated that anti-CD18 treatment specifically blocked the adhesion of activated leukocytes to the venular endothelium and thereby the subsequent diapedesis of these cells into the extravascular space. The lymphocyte-dependent tissue swelling resulting from a delayed-type hypersensitivity reaction in the rabbit ear was partially inhibited by anti-CD18 mAb. Systemic anti-CD18 treatment induced a pronounced increase in the number of circulating mononuclear and polymorphonuclear cells with a maximum at 24 hr after injection of the antibody. It is concluded that GP150/GP85 is the rabbit homologue of human CD11/CD18, and that leukocyte-cell adhesion mediated by these glycoprotein complexes participates in acute and delayed inflammatory responses and leukocyte distribution in vivo.

Induction of intercellular adhesion molecule-1 (CD54) on isolated mouse pancreatic β cells by inflammatory cytokines

Insulin-dependent diabetes mellitus (IDDM) results from a T cell-dependent autoimmune destruction of insulin-producing pancreatic beta cells. In the present study, expression of adhesion molecule ICAM-1 (CD54) on pancreatic beta cells was studied in normal, obese hyperglycemic (ob/ob), and nonobese diabetic (NOD) mice. Freshly isolated pancreatic beta cells from ob/ob mice did not express ICAM-1, but treatment of the cells with IL-1-beta, TNF-alpha, or INF-gamma strongly induced its expression as measured by immunofluorescence flow cytometry. The cytokines acted in a dose- and time-dependent manner. Maximal induction by either cytokine occurred at 24 hr and thereafter expression decreased, except for INF-gamma. Immunoprecipitation from IL-1-beta-treated beta cells demonstrated a cell-surface glycoprotein with an apparent molecular weight of 95 kDa. ICAM-1 expression was undetectable on pancreatic beta cells of normal and ob/ob mice as measured by immunohistochemistry. In NOD mice at different ages (1 to 6 months) ICAM-1 was also undetectable on beta cells, in contrast to the strong expression on infiltrating mononuclear cells. The present study indicates that mouse pancreatic beta cells, under certain conditions, can express ICAM-1.