A monoclonal antibody (RH1-38) which inhibits multiple systems of cell-mediated cytotoxicity--II. Evidence that the epitope recognized is involved in a late step in the cytolytic mechanism.
A monoclonal antibody (RH1-38) which blocks multiple systems of cell-mediated cytotoxicity was functionally characterized. RH1-38 specifically blocks, in the absence of complement, natural killer (NK) activity (K562 targets) without any effect on NK-K562 conjugate formation. Kinetic studies suggested that the antibody blocks a step that occurs 30-120 min after effector populations are mixed with target cells. Single-cell cytotoxicity assays in agarose, combined with standard 51Cr release assays and Michaelis-Menten analysis revealed that RH1-38 markedly decreases Vmax and the number of active NK cells, again without any effect on the number of target-binding cells. The maximum recycling capacity was usually decreased, but in some experiments unchanged, in the presence of the monoclonal antibody. RH1-38 inhibited equally well whole peripheral blood mononuclear leukocytes (PBML), Percoll-fractionated lymphocytes enriched for NK activity, and interferon (IFN)-boosted NK activity. PBML exposed to RH1-38 and then washed mediated depressed NK activity which was partially reversed by subsequent treatment with IFN. These studies are most consistent with the hypothesis that RH1-38 inhibits a step late in the NK cytolytic mechanism rather than through an effect on conjugate formation. The primary effect is probably not on the IFN-generating or boosting mechanism, but a secondary effect on IFN-related mechanisms cannot be ruled out. Inhibition through an effect on a small lymphocyte modulator of NK activity is also unlikely but not rigorously excluded. Thus, RH1-38 appears to inhibit NK activity through a direct effect on NK effector cells, probably by interfering with a cell-surface molecule which is important in the expression of NK activity. The companion paper demonstrates that this monoclonal antibody immunoprecipitates a molecule which is very similar or identical to the LFA-1 antigen. Thus, RH1-38 recognizes either a novel epitope on the LFA-1 molecule or alternatively a distinct, functional killer cell surface molecule. The epitope appears to be involved in a late step in the cytolytic mechanism, possibly part of the effector cell lytic machinery.
R E
RE
Hall
R P
RP
Schall
L A
LA
Black
D000911:Antibodies, Monoclonal / Q000276:immunology*; D000937:Antigen-Antibody Reactions; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D004306:Dose-Response Relationship, Immunologic; D000939:Epitopes / Q000276:immunology*; D006801:Humans; D007372:Interferons / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000276:immunology*; D007700:Kinetics; D007962:Leukocytes / Q000276:immunology
D000911:Antibodies, Monoclonal; D000939:Epitopes; D007372:Interferons