Ecotin-Like ISP of L. major Promastigotes Fine-Tunes Macrophage Phagocytosis by Limiting the Pericellular Release of Bradykinin from Surface-Bound Kininogens: A Survival Strategy Based on the Silencing of Proinflammatory G-Protein Coupled Kinin B2 and B1 Receptors

Abstract EN

Inhibitors of serine peptidases (ISPs) expressed by Leishmania major enhance intracellular parasitism in macrophages by targeting neutrophil elastase (NE), a serine protease that couples phagocytosis to the prooxidative TLR4/PKR pathway.

Here we investigated the functional interplay between ISP-expressing L.

major and the kallikrein-kinin system (KKS).

Enzymatic assays showed that NE inhibitor or recombinant ISP-2 inhibited KKS activation in human plasma activated by dextran sulfate.

Intravital microscopy in the hamster cheek pouch showed that topically applied L.

major promastigotes (WT and Δ i s p 2 / 3 mutants) potently induced plasma leakage through the activation of bradykinin B2 receptors (B2R).

Next, using mAbs against kininogen domains, we showed that these BK-precursor proteins are sequestered by L.

major promastigotes, being expressed at higher % in the Δ i s p 2 / 3 mutant population.

Strikingly, analysis of the role of kinin pathway in the phagocytic uptake of L.

major revealed that antagonists of B2R or B1R reversed the upregulated uptake of Δ i s p 2 / 3 mutants without inhibiting macrophage internalization of WT L.

major.

Collectively, our results suggest that L.

major ISP-2 fine-tunes macrophage phagocytosis by inhibiting the pericellular release of proinflammatory kinins from surface bound kininogens.

Ongoing studies should clarify whether L.

major ISP-2 subverts TLR4/PKR-dependent prooxidative responses of macrophages by preventing activation of G-protein coupled B2R/B1R.