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The ability of microfilariae to evade in vitro cell-mediated cytotoxicity
Abstract:
When microfilariae (Mf) of Dirofilaria immitis, both uterine and systemic, were incubated in an in vitro cytotoxicity assay with neutrophils and sera from dogs with occult infections, some Mf remained free of adherent cells and consequently evaded cytotoxicity. The ability to evade cytotoxicity could not be related to the age of the Mf, and host albumin was not detected on any Mf, either uterine or systemic. However, it was shown that some Mf failed to bind IgM, IgG and C3 when incubated with occult sera. It is suggested that the ability of some Mf to evade serum-dependent, neutrophil-mediated cytotoxicity in vitro was related to differences in their antigenicity.
Insights
Some Dirofilaria immitis microfilariae evade immune attack by neutrophils. This evasion is linked to their inability to bind certain antibodies and complement proteins in infected dog serum, suggesting altered antigenicity.
Area of Science:
- Veterinary Parasitology
- Immunology
- Canine Infectious Diseases
Background:
- Dirofilaria immitis causes heartworm disease in dogs.
- Microfilariae (Mf) are the larval stage of the parasite.
- Immune evasion is a key factor in parasite survival.
Purpose of the Study:
- To investigate the mechanisms by which Dirofilaria immitis microfilariae evade neutrophil-mediated cytotoxicity.
- To determine if Mf antigenicity plays a role in evading the host immune response.
Main Methods:
- In vitro cytotoxicity assay using neutrophils and sera from dogs with occult heartworm infections.
- Incubation of uterine and systemic Mf with immune components.
- Assessment of Mf adherence to neutrophils and binding of antibodies (IgM, IgG) and complement (C3).
Main Results:
- Some Mf evaded neutrophil-mediated cytotoxicity by remaining free of adherent cells.
- This evasion was not correlated with Mf age or the presence of host albumin.
- A subset of Mf failed to bind IgM, IgG, and C3 when incubated with sera from infected dogs.
Conclusions:
- The ability of Dirofilaria immitis microfilariae to evade serum-dependent, neutrophil-mediated cytotoxicity is likely due to differences in their surface antigenicity.
- This suggests a mechanism of immune evasion employed by the parasite to survive within the host.