Antigen induced eosinophilia protects gerbils (Meriones unguiculatus) against experimental amebic abscess of the liver.

While the normal human eosinophil is destroyed in vitro by virulent Entamoeba histolytica, notwithstanding the presence of antibodies and complement, activated eosinophils promptly destroy the parasite even though succumbing in the process as well. To study the possible in vivo participation of eosinophils in invasive amebiasis, we compared the induction of experimental amebic abscess of the liver (EAAL) in gerbils (Meriones unguiculatus) previously made eosinophilic (532 +/- 80 eosinophils/mm3) through Toxocara canis antigen injection and normal control gerbils (101 +/- 15 eosinophils/mm3). Shortly (6 and 24 h) after intraportal injection of 10(5) virulent E. histolytica, the ratio of gerbils with EAAL, as well as the number and size of the abscesses was comparable in eosinophilic and control gerbils. At 96 h post-inoculation, the ratio of animals with EAAL was still the same in both groups, yet number and size of abscesses were significantly (p < 0.05) smaller in eosinophilic gerbils. The actuarial EAAL survival curve up to 45 days post-amebic inoculation was significantly (p < 0.05) shifted to the right in eosinophilic gerbils. No significant changes in IL-5 levels were recorded throughout these experiments. The results suggest that antigen-induced eosinophilia may exert a protective effect against EAAL in gerbils. It is speculated that a less overwhelming EAAL strategy--more akin to human amebic abscesses--may reveal this protective effect more clearly.