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Opsonization modulates Rac-1 activation during cell entry by Leishmania amazonensis
J Morehead1, I Coppens, N W Andrews
1Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut 06536, USA.
Abstract:
Lesions caused by Leishmania amazonensis normally heal, but relapses occur due to parasite persistence in host tissues. It has been proposed that infection of fibroblasts plays an important role in this process by providing the parasites with a safe haven in which to replicate. However, most previous studies have focused on the entry of Leishmania into macrophages, a process mediated by serum opsonins. To gain insight into a possible role of nonopsonic entry in the intracellular persistence of amastigotes, we examined the invasion of Chinese hamster ovary (CHO) cells. Amastigotes entered CHO cells by a cytochalasin D, genistein, wortmannin, and 2,3-butanedione monoxime-sensitive pathway and replicated within phagolysosomes. However, unlike most phagocytic processes described to date, amastigote internalization in CHO cells involved activation of the GTPases Rho and Cdc42 but not Rac-1. When uptake was mediated by fibronectin or when amastigotes were opsonized with immunoglobulin G and internalized by Fc receptor-expressing CHO cells, Rac-1 activation was restored and found to be required for parasite internalization. Given the essential role of Rac in assembly of the respiratory burst oxidase, invasion through this nonopsonic, Rac-1-independent pathway may play a central role in the intracellular survival of Leishmania in immune hosts.
Insights
Leishmania amazonensis persists in host tissues by invading fibroblasts through a nonopsonic pathway. This invasion, independent of Rac-1, may be key to intracellular survival and disease relapse.
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.
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