Background: Presence of cholesterol in hydatid cyst fluid is associated with cyst degeneration through its
immunomodulatory effect as a non-immune inducer of inducible nitric oxide synthase (iNOS) expression.
Objective: To investigate the association of cholesterol crystals (CCs) in hydatid fluid, viability of
protoscoleces and iNOS expression in hydatid cyst wall.
Patients and Methods: Cases were divided into two groups; group (1) included six patients with CCs
in their hydatid cyst fluid and group (2) included 12 patients without CCs in their hydatid cyst fluid.
Protoscoleces' viability was assessed and correlated with iNOS expression in the hydatid cyst walls in
both groups by immunohistochemistry.
Results: Protoscoleces' viability was significantly decreased in G1 containing CCs. High expression
levels of iNOS were recorded in sections from the hydatid cyst walls of G1, as compared to minimal iNOS
expression observed in sections from G2. A significant negative correlation was recorded between the
degree of iNOS tissue expression and viability percentage of hydatid protoscoleces.
Conclusion: The decreased viability of protoscoleces suggests a role for cholesterol in immunomodulation,
possibly through the involvement of the nitric oxide pathway.