Characteristics of a recent isolate of Sarcocystis neurona (SN7) from a horse and loss of pathogenicity of isolates SN6 and SN7 by passages in cell culture.

The research study primarily investigates the characteristics of an isolated strain of Sarcocystis neurona (SN7) from a horse. Furthermore, it explores how multiple passages in cell culture could cause a decrease in the pathogenicity of SN7 and SN6 strains.

Methodology of the Study and Characteristics of the Isolate

• The researchers isolated a strain of S. neurona (SN7) from the spine of a horse which exhibited neurological symptoms.
• This isolate was then grown in bovine monocyte cultures and equine spleen cells.
• They observed the completion of at least one asexual cycle by the parasite in the cell cultures within three days. This process involves division by a method known as endopolygeny where multiple offspring are created within a single cell before it bursts.
• The isolated parasite was maintained via subsequent passages in the bovine cells for a duration of 10 months.

Observations on Pathogenicity

• After the 10 month period, it was observed that the isolate was no longer pathogenic, or infectious, to gamma interferon knockout (KO) mice. Gamma interferon KO mice are genetically modified to remove interferon-gamma, a molecule that plays a critical role in immune response against infections.
• The researchers then tried to revive a low passage version of the isolate that was stored in liquid nitrogen for 18 months. After revival, the isolate was found to retain its pathogenic properties in KO mice.
• While the later passage isolate (22nd passage) proved to be infective for only one out of four KO mice that were exposed to it.
• A similar trend in pathogenicity reduction with multiple passages was observed in another isolate of S. neurona known as SN6.

Western Blot Analysis

• The researchers also performed Western blot analysis on both the low and high passage merozoites (a stage in the life cycle of certain parasites) from the SN7 and SN6 isolates.
• The Western blot, a standard technique used to identify proteins in a sample, did not indicate any differences in the specific antigens present in the various samples.

Conclusion

• Based on these observations, the researchers suggest that extended passage in cell culture could potentially diminish the pathogenicity of certain S. neurona isolates.