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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)

Previous in vitro findings suggest a critical role for the polymorphonuclear leukocyte (PMN) membrane glycoprotein complex CD18 in PMN adherence and chemotaxis. We examined the effect of the murine monoclonal antibody (MoAb) 60.3, recognizing CD18, on induced PMN accumulation in vivo. Rabbits were pretreated with MoAb 60.3, and the chemotactic factors fMLP, leukotriene (LT)B4, and C5a, as well as histamine, were injected intradermally; 4 hours later, plasma leakage (125I-albumin) and the PMN accumulation (myeloperoxidase) were determined. Both PMN accumulation and PMN-dependent plasma leakage were abolished in the inflammatory skin lesions of rabbits pretreated with MoAb 60.3 as compared with control animals, whereas histamine-induced PMN-independent plasma leakage was unaffected. Intravital microscopy of the rabbit tenuissimus muscle revealed that MoAb 60.3 inhibited both PMN adherence in the venules and migration into the tissue following application of LTB4 and zymosan-activated serum (ZAS). Rolling of PMNs along the venular endothelium was unaffected. Thus, these experiments confirm and extend earlier in vitro findings of the critical role of the membrane glycoprotein complex, CD18, in PMN adherence and chemotaxis.

Haemorrhagic mucosal lesions are produced during intestinal ischaemia and after reperfusion probably mediated by oxygen radicals. Oxygen radicals react with cell membrane lipids and induce cell damage by peroxidation and induce accumulation of polymorphonuclear leucocytes in the tissue. The aim ofthe study was to elucidate the involvement of polymorphonuclear leucocytes in postischaemic intestinal damage. Intestinal ischaemia was induced in cats by partial occlusion of the superior mesenteric artery. Samples from the small intestine were excised before and at the end of the two hour hypotensive period as well as 10 minutes and 60 minutes after reperfusion. Conjugated dienes, myeloperoxidase, and the purine metabolites were determined in the samples. The tissue was also examined histologically. Seven cats were treated before reperfusion with a monoclonal antibody (IB4) which inhibits leucocyte adherence to endothelial cells and its subsequent activation. After reperfusion myeloperoxidase activity increased and the ischaemic mucosal lesions worsened significantly. IB4 treatment prevented an increase in posthypotensive myeloperoxidase activity and attenuated the normally observed severe mucosal lesions. We conclude that the severe postischaemic lesions are induced by polymorphonuclear leucocytes. Such mucosal injury may be appreciably reduced by blocking leucocyte adherence with IB4.