Characterization of a cyclosporin A-sensitive activation pathway in cultured T and natural killer cells

Previously, the authors have described a molecule, identified by the LD6 monoclonal antibody (MoAb), present at the cell surface of long-term cultured T and Natural Killer (NK) cells which is involved in cell triggering. In the study described here the authors used biotin surface labelling and immunoprecipitation to show that LD6 MoAb recognizes a surface protein of approximately 65 kDa. In combination with submitogenic concentrations of phorbol esters (PMA), LD6 MoAb was able to induce accumulation of mRNA specific for GM-CSF, γ-IFN and TNF-α and release of these cytokines by LD6⁺ T-cell lines. Both lymphokine production and lymphokine-specific mRNA accumulation induced by the LD6 MoAb were blocked totally by Cyclosporin A (CsA). To investigate the mechanism(s) of signal transduction through this activatory pathway, the authors performed Ca⁺⁺ mobilization experiments. The results of these experiments suggested a role for Ca⁺⁺ in signal transduction. The Ca⁺⁺ mobilization induced by LD6 MoAb cross-linking could be inhibited totally by the use of pertussis toxin, indicating a possible role for G proteins in signalling through the LD6 MoAb-reactive molecule. Western blot analysis performed with an anti-phosphotyrosine antibody did not suggest that tyrosine kinase activation has a role.