Eosinophil and IgE responses of IL-5 transgenic mice experimentally infected with Nippostrongylus brasiliensis.

Eosinophil and IgE responses of interleukin (IL)-5 transgenic and normal C3H/HeN mice were studied after experimental infection with Nippostrongylus brasiliensis (Nb). Intestinal worms were recovered at day 5 post-infection (PI), and numbers of total white blood cells (WBC) and eosinophils, and total serum IgE and anti-hapten (dinitrophenyl) (DNP) specific IgE titers, were measured at days 0, 14 and 21 PI. IL-5 mice appeared resistant to Nb infection showing a significantly lower worm recovery rate than normal mice (P < 0.05). Total WBC and eosinophil counts (/mm3) were significantly increased in Nb infected normal mice (P < 0.05), but unchanged (total WBC) or decreased (eosinophils) in IL-5 mice at day 21 PI. The total serum IgE level remarkably increased in normal mice, but only a little in IL-5 mice at days 14 and 21 PI. Priming with DNP brought about more remarkable increases of the total and anti-DNP specific IgE in normal mice than in IL-5 mice. The results show that IL-5 mice are resistant to Nb infection, and that eosinophil and IgE responses in these mice are not augmented by Nb infection.

Protective roles of eosinophils in Nippostrongylus brasiliensis infection.

Nippostrongylus brasiliensis infection is characterized by blood and tissue eosinophilia induced by interleukin (IL)-5 secreted from CD4+ T cells. However, it is still obscure whether eosinophils play an important role in the protection against N. brasiliensis infection. In this study we attempted to determine whether the in vivo environment of IL-5 transgenic mice, characterized by high eosinophil production, could affect the worm burden after N. brasiliensis infection. Kinetic studies on the infection demonstrated a significantly lower worm recovery from the intestine of IL-5 transgenic mice compared to age-matched background controls. This tendency was also observed at the lung stage of the infection. Furthermore, with respect to elevation of the serum IgE concentration, the peak level was observed at 2 weeks after infection in infected background control mice with four times higher concentrations than those of uninfected mice. In contrast, the increase of IgE concentration in IL-5 transgenic mice was very limited and low. The adoptive transfer of eosinophils from IL-5 transgenic mice into background control animals resulted in the reduction of worm recovery from the lungs, suggesting that eosinophils play a key role in the protection against migrating larvae of N. brasiliensis. These results indicate that the innate high level of eosinophils due to constitutive production of IL-5 augments immunity against N. brasiliensis infection.