Plant lectins ConBr and CFL modulate expression toll-like receptors, pro-inflammatory cytokines and reduce the bacterial burden in macrophages infected with Salmonella enterica serovar Typhimurium

Abstract

Background: Plant lectins have long been used in biomedical research as immunomodulators against tumor cells and microbial infections.

Purpose: To test the ability of plant lectins ConBr (Canavalia brasiliensis) and CFL (Cratylia argentea) to activate antimicrobial and immunomodulatory activities of murine peritoneal macrophages (pMØ) infected with a virulent strain of Salmonella enterica serovar Typhimurium (STm).

Methods: We incubated pMØ with non-toxic amounts of ConBr and CFL either before (preventive schedule) or after (curative schedule) exposure to STm.

Results: In uninfected pMØ, ConBr and CFL greatly increased levels of mRNA transcripts for IL-1β, TNF-α and IL-6 and the inducible nitric oxide synthase (iNOs), but not IL-10 and IL-12. Exposure to naïve splenocytes of culture supernatants of pMØ previously stimulated with CFL resulted in expression of IL-12 and IFN-γ. Both preventive and curative treatment schedules significantly reduced the intracellular load of Salmonella. Experiments in infected macrophages exposed to lectins in the preventive schedule showed that mRNA transcripts for IL-6 and TNF-α were increased by CFL, whereas ConBr enhanced IL-12 (subunit p40). In the curative schedule, CFL induced significant expression of IL-12 (p40) whereas ConBr enhanced expression IL-1β and TNF-α genes. The lectin treatments did not influence on iNOs expression in pMØ infected with STm C5 regardless of the treatment schedule. Curative treatments with CFL increased approximately 130-fold expression of TLR-4 whist expression of TLR-9 was increased by treatments with ConBr.

Conclusion: We conclude that lectins ConBr and CFL have immunomodulatory properties that are beneficial on control of cells infected by Salmonella.

Keywords: C. argentea; C. brasiliensis; Immunomodulators; Mannose-binding.