Th2 immune response correlates inversely with the egg load in S. mansoni infection

Question Infection with Schistosoma mansoni, a worm parasite, results in deposition of parasitic eggs in the liver where they cause granuloma formation. Adult worms induce a hepatic Th1 immune response, shifting towards a Th2 immune response after egg production. We aimed to investigate whether the hepatic Th2 immune response is correlated with egg infestation.

Methods Twenty-two female hamsters were infected with S. mansoni bisex (both sexes), ten with monosex cercariae (control without egg deposition), and six were not infected (super control). After 6-8 weeks, liver tissue was examined by qRT-PCR for expression of Th2 inflammatory interleukins, such as IL-4, IL 5, and IL-13. The extent of hepatic infection with S. mansoni eggs and worms was determined by counting.

Results The mRNA expression of IL-4, IL-5, and IL-13 were significantly upregulated in bisex-infected hamsters. Within the bisex-infected group, expression of IL-4, IL-5, and IL-13 correlated inversely with the number of eggs. There was no strong correlation between the examined inflammatory markers and the total number of worms.

Conclusion The increased expression of Th2 interleukins in bisex-infected animals confirms that Th2 response is triggered by the parasitic eggs. The inverse correlation of egg load with Th2 response, however, remains elusive. The connection between a decrease in the Th2 immune response and an increasing egg load has never been described before. A possible explanation could be an acquired immune tolerance due to severe infection. Understanding the underlying mechanisms in detail could help to provide new therapeutic approaches.

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Artikel online veröffentlicht:
26. Januar 2022