Delayed isotype switching in Dirofilaria immitis infection

Area of Science:

• Veterinary Immunology
• Parasitology
• Immunoglobulin Isotype Switching

Background:

• Dirofilaria immitis infection, commonly known as heartworm disease, affects canines worldwide.
• The canine immune response to microfilariae, the larval stage of D. immitis, is complex and not fully understood.
• Understanding immunoglobulin (antibody) responses is crucial for developing effective treatments and vaccines.

Purpose of the Study:

• To serially investigate the anti-microfilarial immunoglobulin response in a naturally infected dog.
• To characterize the role of IgM and IgG antibodies in the clearance of D. immitis microfilariae.
• To determine the timeline of immunoglobulin isotype switching during chronic D. immitis infection in dogs.

Main Methods:

• Serial blood sampling from a naturally infected dog over a 6- to 11-month period.
• In vitro assays to assess microfilariae killing by canine granulocytes, with and without specific immunoglobulin isotypes (IgM, IgG) and complement (fresh non-immune serum).
• Quantification of anti-microfilarial immunoglobulin levels and functional activity.

Main Results:

• Spontaneous clearance of microfilariae correlated with the presence of IgM opsonizing antibodies.
• IgM antibodies promoted in vitro killing of microfilariae by granulocytes.
• A shift from a predominantly IgM to an IgG response was observed over the study period (6-11 months).
• Fresh non-immune serum significantly enhanced microfilariae killing mediated by both IgM and IgG antibodies.

Conclusions:

• The study documents a conversion from IgM to IgG isotype response during chronic canine D. immitis infection.
• Isotype switching in canine heartworm infection appears to be delayed compared to typical responses seen in bacterial or viral infections.
• The findings highlight the sequential role of different immunoglobulin isotypes in controlling D. immitis infection and suggest potential targets for immunomodulatory therapies.