Takashi K. Kishimoto

The leukocyte integrins.

Publisher Summary This chapter focuses on the molecular biology of the leukocyte integrins, LFA-1, Mac-1, and p150,95, and on their role in mediating inflammation. Three recent developments have underscored the importance of the leukocyte integrins as adhesion receptors of the immune system: The recognition that the leukocyte integrins are evolutionarily related to other integrins; Identification of intercellular adhesion molecule-1 (ICAM-l), a ligand for LFA-1, which is induced during inflammation, and may regulate leukocyte migration and localization; and discovery and characterization of immunodeficiency patients who are genetically deficient in their expression of the leukocyte integrins. Researchers have found a class of immune-deficient patients who suffer from recurrent, life-threatening bacterial and fungal infections, and who have neutrophils deficient in chemotaxis and phagocytosis. Infected, necrotic lesions in these patients contain few leukocytes, despite the observation that these patients have chronic leukocytosis. The leukocyte integrins are α 1 β 1 heterodimers, in which the α subunit is noncovalently associated with the β subunit. The α subunits of LFA-1, Mac-1, and p150, 95 are 1,80,000, 1,70,000, and 1,50,000 Da, respectively. The α subunits have been shown to be distinct by MAb reactivity, antigen-preclearing studies, and tryptic peptide mapping. In contrast, the β subunit, M r = 95,000, has been shown to be identical in all three proteins by the same criteria. There is also substantial evidence that other ligands for LFA-1, Mac-1, and p150, 95 exist. Rational strategies must be designed to identify these ligands and to assess their contributions in different phases of the immune response. Multiple ligands may provide quite distinct signals and positional information to leukocytes.

Cloning of the β subunit of the leukocyte adhesion proteins: Homology to an extracellular matrix receptor defines a novel supergene family

We have isolated cDNA clones encoding the beta subunit of the human LFA-1, Mac-1, and p150,95 family of leukocyte adhesion proteins. The deduced 769-amino-acid sequence defines a cysteine-rich polypeptide with the characteristic features of an integral membrane protein. Peptide sequence data, Northern blot analysis, and Southern blot analysis suggest that a single gene encodes the beta subunit of all three leukocyte adhesion proteins. There is 45% homology between the beta subunit sequence and band III of integrin, a chick fibronectin and laminin receptor. This homology defines a new supergene family of cellular adhesion proteins.

Heterogeneous mutations in the β subunit common to the LFA-1, Mac-1, and p150,95 glycoproteins cause leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is a heritable disease involving deficient expression of three related leukocyte adhesion glycoproteins: LFA-1, Mac-1, and p150,95. These proteins are alpha beta heterodimers containing identical 95,000 dalton beta subunits. Here we demonstrate that the primary defect in LAD is in the beta subunit gene. We identified five distinct beta subunit phenotypes in LAD patients: undetectable beta subunit mRNA and protein precursor; low levels of beta subunit mRNA and precursor; an aberrantly large beta subunit precursor, probably due to an extra glycosylation site; an aberrantly small precursor; and a grossly normal precursor. Mutant beta subunit precursors from LAD patients failed to associate with the LFA-1 alpha subunit. In family studies, inheritance of the aberrant precursors correlates with the known inheritance of the LAD defect.

Expression and Regulation of L-Selectin on Eosinophils from Human Adults and Neonates

ABSTRACT: L-Selectin, previously known as LEC. CAM-1, LECAM-1, LAM1, and as the MEL-14, Leu-8, TQ1, and DREG-56 antigens, is a leukocyte membrane protein that participates in adhesion to endothelium. We studied its expression on eosinophils using flow cytometry and the MAb Dreg-56 and Leu-8. Unstimulated peripheral blood eosinophils from healthy adults expressed about one third the level of L-selectin as neutrophils (mean ± SD specific fluorescence: 20.9 ± 3.2 versus 54.5 ± 8.4, p = 0.0001, n = 18). After stimulation with A23187, L-selectin expression on eosinophils was rapidly lost. This was temporally correlated with increased expression of Mac-1 (CD11b/CD18); the kinetics on eosinophils and neutrophils were similar. Eosinophil expression of L-selectin decreased modestly after stimulation with platelet activating factor, but was minimally affected by N-formyl-methionyl-leucyl-phenylalanine, leukotriene B4, or C5a compared with their effects on neutrophils. Eosinophils from cord blood of healthy neonates born at term expressed less L-selectin than adult eosinophils (10.4 ± 3.8 versus 19.4 ± 2.7, p = 0.0001, n = 9); the relative reduction was the same as on cord blood neutrophils (36.4 ± 8.2 versus 55.5 ± 4.8, p = 0.0001, n = 9). Relative to baseline expression, the responses of neonatal and adult cells to stimulation did not differ. We conclude that neonatal eosinophils have abnormalities in L-selectin expression similar to neonatal neutrophils and suggest that decreased expression of L-selection and a diminished responsiveness to direct stimulation with chemotactic factors are possible mechanisms that may limit the exudation of eosinophils.