title: Interaction of HLA-DR with actin microfilaments.
abstract: Capping of HLA-DR on the surface of a human lymphoblastoid cell line (RAJI) and a transfectant human fibroblast cell line (M1DR1) was studied by confocal microscopy. Capping was induced at 22 degrees C after treating cells with an HLA-DR specific monoclonal antibody, L243, followed by a secondary antibody conjugated with FITC. Cytoskeletal actin filaments (F-actin) accumulated under the caps were detected by rhodamine-phalloidin fluorescence. Two processes appear to take place: in the round lymphoblastoid cells, actin, initially distributed uniformly at the cell periphery, redistributes and becomes concentrated underneath HLA-DR patches or caps. In the non-round, substrate-attached fibroblasts, actin was organized in tightly packed filaments along the plasma membrane. It was observed that crosslinked HLA-DR receptors were associated with these filaments and were dragged toward the perinuclear area of the cells, where they coalesce to form a cap. The cytoskeleton-disrupting drugs that inhibit actin polymerisation were used to investigate the mechanism of capping of HLA-DR molecules. Sodium nitroprusside, a nitric oxide releasing agent, cytochalasin D both inhibited the percentage of capping in a dose-dependent manner. These data suggest that on antigen presenting cells, such as B cells and fibroblasts, actin microfilaments acts as a regulator of the movement and capping of HLA-DR receptors.
authors.affiliation: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, UK.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Fernández
authors.forename: Peter J
authors.initials: PJ
authors.lastname: O'Toole
authors.forename: Ian E G
authors.initials: IE
authors.lastname: Morrison
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cherry
authors.forename: Nelson
authors.initials: N
authors.lastname: Fernández
mesh_terms: D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000954:Antigens, Surface / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism; D002460:Cell Line; D002465:Cell Movement; D015638:Cytochalasin D / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006684:HLA-DR Antigens / Q000187:drug effects / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology; D011940:Receptor Aggregation / Q000187:drug effects; D013696:Temperature
chemical_list: D000199:Actins; D000954:Antigens, Surface; D006684:HLA-DR Antigens; D009599:Nitroprusside; D015638:Cytochalasin D