Inhibition of Protein-Kinase C in Peripheral Blood Mononuclear Cells of Patients with Systemic Lupus Erythematosus: Effect on Spontaneous Immunoglobulin Production

Systemic Lupus Erythematosus (SLE) is a multisystem disease characterized by an increase in the spontaneous secretion of immunoglobulin (Ig) molecules, many of which are autoreactive. We have previously shown (Biochem & Biophys. Res. Comm. (1989) 161: 1319-1326) that normal human peripheral blood mononuclear cells (PBMCs) can be stimulated to secrete large quantities of Ig upon incubation with the protein kinase-C activator 1 oleoyl-2-acetylglycerol (OAG). Specific blockage of protein kinase C with the isoquinoline sulfonyl piperazine compound (H-7) inhibited the OAG-induced Ig production. In experiments reported here, PBMC of 5 patients with active SLE produced high levels of IgG spontaneoulsy in culture. PBMC of 6 inactive SLE patients and 7 normal control subjects produced comparable low levels of IgG spontaneously. Pokeweed mitogen (PWM) stimulation of PBMC in inactive SLE and control groups, but not active SLE patients produced markedly enhanced IgG production. The lack of response to PWM stimulation in active SLE patients is likely due to inherent maximal stimulation of active SLE B-cells. In addition, we examined the ability of H-7 to inhibit both mitogen-stimulated (normal and inactive SLE) and spontaneous (active SLE) Ig production. In other experiments, we also examined the ability of the isoquinoline sulfonamide (HA-1004), a potent inhibitor of cAMP-dependent protein kinase to regulate mitogen stimulated and spontaneous Ig production in the patient groups indicated above. H-7 significantly inhibited PWM stimulated Ig production in normal (P < 0.0001) and inactive SLE patients, (P < 0.040) suppressing PWM stimulated levels to spontaneous levels. HA-1004 inhibition of cAMP-dependent protein kinase had no inhibitory effect on Ig production in inactive and active SLE patients. These findings suggest that protein kinase C activation is critical to PWM-stimulated IgG production in normal and inactive SLE patients, and is also important in the high spontaneous IgG production found in active SLE patients. Although H-7 was also a potent inhibitor of spontaneous IgG production in active SLE patients, this did not reach statistical significance.