Effect of phospholipase A₂ inhibitors on mouse T lymphocytes. I. Phospholipase A₂ inhibitors exert similar immunological activities as glycosylation inhibiting factor

Since our previous experiments suggested that gtycosylation-inhibiting factor (GIF) is a phosphorylated derivative of a phosphollpase inhibitory protein, we determined whether other well-known phosphollpase inhibitors may have similar biological activities. The results showed that phosphollpase A₂ (PLA₂) inhibitors, such as recombinant human lipocortin I and ONO-RS-082, could switch T cell hybridoma 12H5 cells from the formation of glycosylated IgE-binding factors (IgE-BF) to the formation of unglycosylated IgE-BF, whereas neomycin, a phospholipase C inhibitor, failed to affect the nature of IgE-BF formed by the cells. The minimum concentrations of lipocortin I and ONO-RS-082 required for switching the 12H5 cells to the formation of unglycosylated IgE-BF were comparable to or less than IC₅₀ of the inhibitors for PLA₂ The ability of partially purified GIF to switch the 12H5 cells to the formation of unglycosylated IgE-BF was markedly enhanced by treatment of the preparation with alkaline phosphatase. It was also found that lipocortin I and ONO-RS-082, but not neomycln, facilitated the generation of GIF-producing T cells. When spleen cells of ovalbumin (OVA)-primed BDF1 mice were stimulated with homologous antigen and the activated T cells were propagated by recombinant IL-2 in the presence of GIF, Iipocortin I, or ONO-RS-082, I cells obtained In the cultures constltutively produced their own GIF. Antigenic stimulation of the T cells Induced the formation of unglycosylated IgE-BF and GIF with an affinity for OVA. In contrast, the same antigen-activated T cells which had been propagated in the absence of PLA₂ Inhibitor constitutively secreted glycosylatation-enhancing factor and formed glycosylated IgE-BF upon antigenic stimulation. The results Indicate that PLA₂ Inhibitory activity of GIF is responsible for its immunological activities.