title: Phenotype of the accessory cell necessary for mitogen-stimulated T and B cell responses in human peripheral blood: delineation by its sensitivity to the lysosomotropic agent, L-leucine methyl ester.
abstract: The lysosomotropic compound L-leucine methyl ester (Leu-OMe) was utilized to delineate the phenotype of the accessory cells involved in human B and T cell activation in vitro. Leu-OMe was shown to cause lysosomal disruption and selective death of human monocytes (M phi). After 30-45 minute incubations with this agent, human peripheral blood mononuclear cells (PBM) were nearly completely depleted of M phi. Associated with this M phi depletion, PBM were rendered unresponsive to a variety of T and B cell mitogens including the plant lectins phytohemagglutinin, concanavalin A, and pokeweed mitogen as well as the oxidative mitogens sodium periodate and neuraminidase plus galactose oxidase. Leu-OMe mediated loss of responsiveness was the result of a selective loss of an accessory cell necessary for each of these responses since reconstitution was accomplished by the addition of a M phi-enriched adherent cell population. While intact adherent cells could reconstitute responsiveness, crude M phi supernatants or highly purified human IL 1 alone were ineffective. Further identification of the Leu-OMe sensitive accessory cell indicated that it was entirely contained within the fraction of the adherent population identified by the monoclonal anti-M phi antibody, 63D3. The mechanism by which Leu-OMe Killed M phi was dependent on the lysosomal content of these cells, since agents that altered lysosomal enzyme activity such as chloroquine or NH4Cl protected M phi from Leu-OMe. Thus, the selective killing of M phi by Leu-OMe appeared to relate to the characteristically rich endowment of lysosomes within these cells. These results support the conclusion that a lysosome-rich, leucine methyl ester-sensitive, intact M phi identified by the monoclonal anti-M phi antibody 63D3 is the circulating accessory cell required for mitogen-triggered human B and T cell activation.
mesh_terms: D000328:Adult; D001402:B-Lymphocytes / Q000276:immunology; D002452:Cell Count; D006801:Humans; D007375:Interleukin-1 / Q000502:physiology; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D008211:Lymphocyte Cooperation / Q000187:drug effects*; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000648:ultrastructure; D008934:Mitogens / Q000494:pharmacology; D010641:Phenotype; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D007375:Interleukin-1; D008934:Mitogens; C030365:leucine methyl ester; D007930:Leucine