Opsonization modulates Rac-1 activation during cell entry by Leishmania amazonensis

Area of Science:

• Parasitology
• Cell Biology
• Immunology

Background:

• Leishmania amazonensis causes lesions that often relapse due to parasite persistence.
• Fibroblast infection is a proposed mechanism for parasite persistence, offering a protected replication niche.
• Previous research primarily focused on macrophage entry mediated by opsonins.

Purpose of the Study:

• To investigate the role of nonopsonic entry in the intracellular persistence of Leishmania amastigotes.
• To understand the invasion mechanisms of Leishmania amazonensis into non-professional phagocytic cells like fibroblasts.

Main Methods:

• Examined the invasion of Chinese hamster ovary (CHO) cells by Leishmania amastigotes.
• Utilized inhibitors (cytochalasin D, genistein, wortmannin, 2,3-butanedione monoxime) to characterize the entry pathway.
• Investigated the involvement of GTPases Rho, Cdc42, and Rac-1 during invasion.
• Studied invasion mediated by fibronectin and immunoglobulin G (IgG) opsonization via Fc receptors.

Main Results:

• Amastigotes entered CHO cells via a pathway sensitive to specific inhibitors and replicated within phagolysosomes.
• Parasite internalization involved activation of Rho and Cdc42 GTPases, but notably, not Rac-1.
• Rac-1 activation was restored and required when invasion was mediated by fibronectin or IgG opsonization.
• The nonopsonic pathway bypassed Rac-1, which is crucial for the respiratory burst oxidase.

Conclusions:

• Leishmania amazonensis can invade fibroblasts through a nonopsonic pathway independent of Rac-1.
• This Rac-1-independent invasion mechanism may be critical for intracellular survival within host tissues.
• Understanding this pathway offers insights into parasite persistence and potential therapeutic targets for Leishmania infections.