Host IgG in equine hydatid cyst fluid.

This study demonstrated the presence of equine immunoglobulins – IgG and IgG(T) – in the fluid of hydatid cysts caused by the Echinococcus granulosus parasite in horses. These proteins appeared to have diffused from the host into the cyst, which could provide protection for the parasite from the host’s immune system.

Methods and Findings

• The researchers were investigating the use of a micro-ELISA assay for detecting antibodies to the hydatid fluid antigen in horse serum when they found a contaminant that shared antigens with equine IgG.
• They used immunoelectrophoresis to further analyze the equine hydatid fluid (EHF) antigen preparation, which indicated the presence of host serum contaminants.
• The EHF antigen was created as a lyophilized powder, reconstituted in distilled water, and used alongside various antisera in the immunoelectrophoresis: rabbit anti-EHF, rabbit anti-horse serum (anti-HS), rabbit anti-horse IgG (anti-IgG), goat anti-horse IgG (T) (anti-IgG (T)), rabbit anti-horse IgA (anti-IgA) and rabbit anti-horse IgM (anti-IgM).
• The precipitation lines in the gel showed the presence of equine hydatid fluid components that shared antigens with horse serum.
• Apart from equine serum, these components also shared antigens with equine IgG and IgG (T), but did not react with anti-IgA or anti-IgM.
• These functions of the EHF were confirmed using double diffusion in agarose.

Historical Comparison and Findings

• The researchers compared the results to previous research which had found host-derived contaminants in sheep hydatid fluid sheep using immunoelectrophoresis.
• They noted that their findings were in-line with a previous study that also found IgG that was similar to host IgG in hydatid fluid from sheep, mice, gerbils and humans.
• This IgG appeared to bind to the membranes of the cyst, creating a protective barrier for the germinating parasite, which implies that it might regulate the movement of host macromolecules into the cyst fluid.

Conclusions and Implications

• The study detected two sub-classes of equine serum IgG in EHF antigen: IgG and IgG (T).
• They observed that these two classes of proteins were the most abundant in equine serum, further indicating that host serum macromolecules appear to be diffusing through the hydatid cyst membranes.