Effect of phorbol myristate acetate (PMA) and ionophore A23187 on interleukin-2 levels and proliferation of activated T lymphocytes from patients with lepromatous leprosy

International Journal of Leprosy and Other Mycobacterial Diseases, Mar 1997 by Fernando Alfaro-Bustamante, Gabriela Ramirez-Flores, Amado Gonzalez-Mendoza, Alfonso Islas-Rodriguez, Mary Fafutis-Morris

DISCUSSION

The immunodeficient behavior of T lymphocytes in LL patients has been characterized by a limited proliferation of T cells and a decreased activity of IL-2 (9,12,19). Because IL-2 production is, in part, dependent on the intracellular calcium levels and the generation of DAG to activate PKC, we decided to assay the effect of substances that increase cytosolic calcium levels, such as ionophore A23187, and/or substances that mimic DAG such as PMA alone or combined with PHA and ionophore. Our results indicate different kinds of lymphocyte responses from the different groups studied to the above-mentioned stimuli. The first difference is related to the response to PHA of lymphocytes from LL(NR) patients against the LL(R) and normal subjects. The remarkable point is that about 95% of LL(NR) patients become responders when their T cells are stimulated with PMA; the other 5% required the presence of PHA to respond (in the PHA PMA combination as well as in PPI). When ionophore A23187 is added to PMA their SI decreases, but when PHA PMA is used they again recover their SI. Conversely, cells from LL(R) patients respond in a mirror image related to the LL(NR) group when PMA I is used.

All of the groups (normals, responders, nonresponders) reach their highest SI when the triple combination (PPI) is used, implying that PHA, PMA, and ionophore A23187 can trigger enough transduction signals and Ca2 levels to have "the optimum conditions" for expressing the IL-2 gene, producing the adequate concentration of IL-2.

The explanation for the above-mentioned data is that in the case of cells from LL(NR) patients, PMA is activating PKC, p21 ras (guanosine triphosphate-binding protein), ERK 1 and 2 (extracellular signalregulated protein kinases), RAF (protein kinase, member of the cascade upstream ERK), and MEK (protein kinase, member of the cascade upstream ERK) that had not been activated by PHA alone, implying the expression of the fos gene (8,14). In the case of LL(R) patients, ionophore A23187 permits enough Ca2 levels to activate the JNK (c-jun NH2 terminal kinase) system in order to activate the jun gene (8.14). In these experiments, the necessary additions have been done in order that both pathways, in the case of LL(NR) patients and in the LL(R) patients, recover the production of AP-1 (regulatory protein, composed of fos and jun proteins) and, finally, the expression of the IL-2 gene (8,14,22) in order to progress from the Gl phase of the cell cycle to the S phase, G2 and mitosis. This is supported by the fact that IL-2 levels are very high when cells from LL(NR), and LL(R) patients are cultured in the presence of PHA PMA. The reason why the combination PPI induces the highest SI but not the highest IL-2 levels could be attributed to the fact that IL-2 levels have an optimum dose response effect. An excess of IL-2 does not necessarily imply the highest proliferation index because IL-2 receptors may be shedding from the plasma membrane, thus neutralizing their effect.