Role of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways in the secretion of tumor necrosis factor-alpha and interleukin-10 by the PPD antigen of Mycobacterium tuberculosis

Abstract

Here we investigated the role of the phosphatidylinositol 3-kinase (PI 3-K) and mitogen-activated protein kinase (MAPK) pathways in the secretion of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10 in human primary monocytes after stimulation with the PPD antigen of Mycobacterium tuberculosis. MAPK [extracellular signal-regulated kinase (ERK) 1/2 and p38] and Akt are rapidly phosphorylated in human monocytes stimulated with PPD. We found that the PI 3-K-Akt pathway stimulated by PPD is essential for both IL-10 and TNF-alpha production, although the inhibition of IL-10 production was more pronounced. The analysis of cytokine production using specific inhibitors of the MAPK pathway revealed that both p38 and ERK activation are essential for PPD-induced TNF-alpha production, whereas p38, but not ERK, activation is essential for IL-10 secretion. The inhibition of PI 3-K did not significantly activate p38 MAPK or ERK 1/2 in PPD-stimulated human monocytes. Further, the Src inhibitor PP2 inhibited the release of TNF-alpha but enhanced IL-10 release, suggesting the differential regulation of Src kinase in upstream signaling. Collectively, these data suggest that the PI 3-K and MAPK pathways play a central role in the regulation of both pro- and anti-inflammatory cytokines by the PPD antigen of M. tuberculosis.