Activation of PI3K/Akt signaling has a dominant negative effect on IL-12 production by macrophages infected with Leishmania amazonensis promastigotes

Infection of macrophages with Leishmania parasites does not result in the production of IL-12. In addition, infection with Leishmania suppresses IL-12 production elicited by otherwise potent activators of IL-12. We provide evidence that engagement of phosphatidyl inositol-3 kinase (PI3K) signaling during Leishmania amazonensis infection leads to the prevention of IL-12 p70 production at the level of transcription of its p40 subunit in bone marrow derived macrophages (BMDMΦ). Inhibition of PI3K signaling with specific inhibitors of PI3K or the downstream kinase Akt, reverses the IL-12 blockade. Although the MAP kinase ERK (p44 and p42) was transiently activated by infection with L. amazonensis, inhibition of MEK, the kinase upstream of ERK, with PD98059, did not reverse the blockade of IL-12. Furthermore, inhibition of the other MAP kinases JNK and p38 as well as treatment of cells with pertussis toxin that blocks G protein mediated signaling, did not reverse the prevention of IL-12 production by Leishmania infection. Interestingly, activation of PI3K/Akt signaling had differential effects on ERK and p38 activation. Taken together we propose that infection of BMDMΦ with Leishmania promastigotes activates both positive and negative signaling pathways that control IL-12 production. PI3K signaling activated by the infection is the negative signaling pathway that prevents IL-12 production.