title: Nonspecific cytotoxic cells in fish (Ictalurus punctatus). IV. Target cell binding and recycling capacity.
abstract: The morphology of nonspecific cytotoxic cells (NCC) was identified. NCC were purified by target cell conjugate formation and density gradient separation. NCC are monocyte-like. They have reniform nuclei and a low nucleus/cytoplasm ratio. Cytoplasmic granules were not seen after giemsa staining. Scanning electron microscopy demonstrated moderate surface villi and target cell attachment occurred via long membraneous filament-like surface projections extending to the target cell membranes. Transmission electron microscopy of effector:target cell conjugates revealed membrane contact areas without fusion or fragmentation. The nucleus of the NCC had accentuated peripheral chromation and a prominent Golgi apparatus; the cytoplasm contained osmiophilic granules. Michaelis-Menten and Lineweaver-Burk transformation of target cell binding revealed a Vmax of 11-15,000 and a Km of 40,000. The percentage of NCC bound to target cells was 16-18%. Results of these studies were combined with the conjugate experiment to obtain an estimated percentage of active NCC (5-7%). A maximum recycling capacity of .16-.30 indicated that once attachment by NCC to the target cell occurred (and a lethal signal delivered by an effector cell), either the NCC did not recycle or a long lag period was required to restore its cytotoxic capability.
mesh_terms: D000818:Animals; D001665:Binding Sites; D003602:Cytotoxicity, Immunologic; D005260:Female; D005399:Fishes / Q000033:anatomy & histology / Q000276:immunology*; D007111:Immunity, Cellular; D066298:In Vitro Techniques; D007694:Killer Cells, Natural / Q000276:immunology / Q000648:ultrastructure; D008297:Male; D008855:Microscopy, Electron, Scanning