Ultrastructural similarities between epidermal Langerhans cell Birbeck granules and the surface-connected canalicular system of EDTA-treated human blood platelets.
Birbeck granules characterize under the electron microscope epidermal Langerhans cells. These distinctive pentalaminar organelles are indeed not detectable in the possible precursors of human Langerhans cells and tend to disappear in cultured human Langerhans cells. The mechanisms that lead to the appearance of Birbeck granules in epidermal Langerhans cells and to their later disappearance still remain unknown. In the present study we show that the more or less dilated elements of the surface-connected canalicular system of human blood platelets collapse after EDTA treatment. Made up of two parallel limiting membrane and central irregular striated density, these elements show great ultrastructural similarities with the Birbeck granules of human epidermal Langerhans cells. These platelet morphologic changes i) are directly dependent on the EDTA-induced dissociation of the glycoprotein GP IIb-IIIa, the platelet-specific calcium-dependent heterodimer complex, member of the beta 3 integrin subfamily (alpha IIb beta 3) and ii) apparently result from a cross-linking of the dissociated glycoproteins. These findings lead us to propose that in the same manner cells of the Langerhans lineage, on reaching the epidermis, will find themselves in contact with an epidermal specific ligand. Interactions between this epidermal ligand and Langerhans cell receptors could then induce, all along the circuit taken by the ligand-receptor complexes, morphologic modifications, i.e., appearance of structures of Birbeck granule type.
Hanau
D
D
Laboratoire d'Histocompatibilité, Faculté de Médecine, Université Louis Pasteur, Strasbourg, France.
Gachet
C
C
Schmitt
D A
DA
Ohlmann
P
P
Brisson
C
C
Fabre
M
M
Cazenave
J P
JP
D001792:Blood Platelets / Q000187:drug effects / Q000648:ultrastructure*; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D004492:Edetic Acid / Q000494:pharmacology*; D000078404:Epidermal Cells; D006801:Humans; D007801:Langerhans Cells / Q000648:ultrastructure*
D004492:Edetic Acid