IL-12 is involved in the activation of CD3⁺ granular lymphocytes in patients with lymphoproliferative disease of granular lymphocytes

We investigated the effects of IL-12 on functional properties of CD3⁺CD8⁺ granular lymphocytes (GL) of patients with lymphoproliferative disease of granular lymphocytes (LDGL). To this aim, in 10 cases with a clonal CD3⁺ GL proliferation (nine cases with an associated TCR α/β receptor and one case with a TCR γ/δ receptor) we studied the proliferative and cytotoxic activities of resting and αCD3 monoclonal antibody (mAb) activated cells in the presence of rIL-12 and anti-IL-12 blocking antibodies. Specific mRNA for IL-12 p40 subunit was also investigated. Our results showed that rIL-12 increased the proliferation of αCD3 pre-stimulated GL (2 to 6 times). Further, anti-IL-12 antibodies partially inhibited αCD3-induced cell growth, suggesting a role for this cytokine in the αCD3-mediated GL activation. The addition of antibodies blocking the p55 and p75 chains of IL-2 receptor (IL-2R) did not inhibit the rIL-12-mediated cell proliferation, indicating that the activity of rIL-12 is independent of IL-2 in the in vivo expanded GL of patients under study. Concerning the cytotoxic activity, rIL-12 increased the αCD3-mediated NK activity against K-562 target cells and αCD3 redirected cytotoxicity against P815 target cells. Molecular analysis pointed out that, following αCD3 stimulation, patients' GL increased the expression of specific mRNA for the p40 subunit of IL-12 as compared to baseline conditions. Our data indicate that IL-12 is involved in the mechanisms of activation of clonal CD3⁺ GL in patients with LDGL; these features are consistent with the possibility that this discrete subset of GL might represent in vivo primed cytotoxic T lymphocytes.