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Variations in complement activation of Brugia patei, B. malayi and B. pahangi microfilariae
U R Rao1, A C Vickery, J K Nayar
1College of Public Health, Department of Environmental and Occupational Health, University of South Florida, Tampa 33612.
Abstract:
The complement of fresh normal heterozygotic BALB/C (nu/+) and nude (nu/nu) mice was activated by sheathed microfilariae (Mf) of Brugia malayi and B. pahangi but not by B. patei. Mouse C3 was detected by immunofluorescence on the sheathed surface of B. malayi and B. pahangi Mf but not on B. patei Mf. The bound complement promoted macrophage and neutrophil mediated adherence and cytotoxicity to these Mf. However, BALB/C nu/+ or nu/nu mouse macrophages and neutrophils adhered to exsheathed Mf of B. patei and killed them in the presence of fresh normal mouse serum (NMS). C3 molecules were detected on the cuticle of exsheathed Mf of B. patei and B. malayi. Fresh NMS (nu/+ or nu/nu) depleted of complement factors by heating or by zymosan or anti-mouse C3, failed to promote cell adherence to these parasites. EDTA but not EGTA abolished the adherence activity to sheathed and exsheathed Mf of B. malayi, whereas both EGTA and EDTA abolished the adherence activity to exsheathed Mf of B. patei and sheathed Mf of B. pahangi suggesting the different pathways of complement activation by these closely related species. Macrophages and neutrophils from peritoneal exudate cells of nu/+ or nu/nu were equally potent in adherence and killing of Mf. Transfused B. patei but not B. malayi or B. pahangi Mf were recovered from the peritoneal cavity of BALB/C mice with no cell adherence and cytotoxicity.
Insights
Complement activation by microfilariae (Mf) differs between Brugia species. Mouse complement (C3) binds to sheathed B. malayi and B. pahangi Mf, promoting immune cell killing, but not to B. patei Mf.
Area of Science:
- Immunology
- Parasitology
- Molecular Biology
Background:
- The complement system is crucial for innate immunity, mediating pathogen clearance.
- Microfilariae (Mf) are the larval stage of filarial nematodes, causing diseases like lymphatic filariasis.
- Understanding host-parasite interactions involving complement is key to developing therapeutic strategies.
Purpose of the Study:
- To investigate the role of mouse complement activation in the interaction with different species of Brugia microfilariae.
- To determine the specific complement components involved and the pathways utilized.
- To assess the impact of complement activation on immune cell-mediated parasite clearance.
Main Methods:
- Activation of complement in normal and nude BALB/C mouse serum using sheathed and exsheathed microfilariae (Mf) of Brugia malayi, B. pahangi, and B. patei.
- Detection of mouse complement component C3 deposition on Mf using immunofluorescence.
- Assay of macrophage and neutrophil adherence and cytotoxicity to Mf in the presence of normal mouse serum (NMS) or complement-depleted serum.
- Use of EDTA and EGTA to chelate divalent cations and investigate complement activation pathways.
Main Results:
- Fresh normal mouse serum activated complement on sheathed B. malayi and B. pahangi Mf, but not B. patei Mf, with C3 deposition observed on the former.
- Bound complement promoted adherence and cytotoxicity of macrophages and neutrophils to sheathed B. malayi and B. pahangi Mf.
- Exsheathed B. patei and B. malayi Mf were killed by macrophages and neutrophils in NMS, with C3 detected on their cuticle, suggesting alternative complement activation.
- Complement depletion (heat, zymosan, anti-C3) or chelation (EDTA, EGTA) abrogated adherence and killing, indicating complement-dependent mechanisms.
- Different divalent cation requirements (EDTA vs. EGTA) suggested distinct complement activation pathways for different Brugia species.
Conclusions:
- Complement activation pathways differ significantly among closely related Brugia species, influencing host immune responses.
- Mouse complement, particularly C3, plays a vital role in mediating immune cell recognition, adherence, and killing of microfilariae.
- The state of the microfilariae (sheathed vs. exsheathed) and species-specific surface properties dictate complement deposition and subsequent immune effector functions.