This work was undertaken to characterise the interaction of the leukocyterestricted integrin LFA-1 (CD1la/CD18) with its ligands. LFA-1 function is critical for an immune response and, for example, allows leukocyte binding and transmigration across the endothelium, antigen presentation and cytotoxic T lymphocyte-mediated killing. The ligands for LFA-1 are the Intercellular Adhesion Molecules (ICAMs), with ICAM-1, ICAM-2 and ICAM-3 being the best characterised. The binding sites on ICAM-1 and ICAM-3 for LFA-1 were investigated with the use of antibodies and mutated proteins. The following regions were found to have a role in binding LFA-1: the CFG face of ICAM-3 domain 1; domain 2 of ICAM-1; a residue in domain 1 of ICAM-1 that is mutated at high frequency in African populations and is associated with susceptibility to cerebral malaria. Binding of Mg2+ or Mn 2+ to the extracellular region of LFA-1 and intracellular signalling can both stimulate LFA-1 to adhere to ICAM-1, but by different processes. The former mechanism induces a high affinity form of LFA-1, which was shown to be achieved by an inter-domain movement involving the I domain of the LFA-1 a subunit. This is the first physical evidence for a conformational change occurring in an integrin upon activation. The mechanism by which intracellular signalling activates LFA-1 was demonstrated to involve calpaindependent clustering of LFA-1 in the membrane, thus increasing the avidity of LFA-1 for ICAM-1. Leukocyte Adhesion Deficiency-1 and Glanzmann's Thrombasthenia are genetic disorders in which mutations in the integrin genes result in absence of expression or expression of a non-functional integrin. The defects in function of leukocytes from a patient with clinical features of both disorders were studied. The results suggest that the patient has a novel form of integrin dysfunction in which integrins are expressed at normal levels, can be induced to bind their ligands by mechanisms which increase the affinity of interaction, but cannot be stimulated to bind ligand by intracellular signalling pathways.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:340735 |
| Date | January 2000 |
| Creators | McDowall, Alison Jane |
| Publisher | Open University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oro.open.ac.uk/58066/ |
Page generated in 0.0017 seconds