Avirulence and lysozyme secretion in Paneth cells after infection of BALB/c mice with oocysts of Toxoplasma gondii strains TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9)

Toxoplasma gondii has a complex life cycle and pathogenic mechanisms. Acute T. gondii infections in mice often result in death, whereas in chronic infections, the parasites may persist in the host tissues as intraneuronal or intramuscular cysts. However, the virulence of T. gondii strains in mice varies with its genetic background. The present study investigated the pathogenicity and pathological lesions of two T. gondii isolates from China: namely, TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9). The virulent (ToxoDB#216) and avirulent (VEG) strains were employed as controls. Toxoplasmosis was induced by inoculating BALB/c mice with oocysts of the strains of T. gondii VEG, ToxoDB#216, TgCatCHn2 (ToxoDB#17), and TgCatCHn4 (ToxoDB#9), respectively. As a result, one oocyst of ToxoDB#216 could kill a mouse within 10 days post inoculation (DPI). The survival time of the mice for T. gondii TgCatCHn2 and TgCatCHn4 was >60 DPI for 106/mL oocysts, but this concentration (106/mL oocysts) of VEG strain could kill mice within 11 DPI. Compared with the strains of T. gondii ToxoDB#216 and VEG, the lesions in the small intestines of the strains of TgCatCHn2- and TgCatCHn4-infected mice were significantly smaller (P < 0.01). The positive area of T. gondii antigen in the ileum of mice infected with the strains of T. gondii VEG, TgCatCHn2 and TgCatCHn4 were significantly lower than that T. gondii ToxoDB#216 at 8 DPI (P < 0.01). Paneth cells (PCs) in the small intestines was eliminated by ToxoDB#216 (5–6 DPI) (P < 0.05). The strains of T. gondii TgCatCHn2-, TgCatCHn4- and VEG-infected mice, the number of PCs and granules decreased in the intestines, compared to T. gondii free mice, but the difference was not significant (8 DPI, P > 0.05). However, the granules in the PCs showed negative lysozyme expression in the intestines of mice infected with T. gondii TgCatCHn2 and TgCatCHn4. Thus, T. gondii strains of TgCatCHn2 (ToxoDB#17) and TgCatCHn4 (ToxoDB#9) were avirulent strains, they triggered an inhibition of lysozyme expression in the granules of PCs of the mouse intestine. These effects may in turn lead to intestinal dysbiosis, which may be related to further parasitic invasion of the intestines. The findings of the present study further expand the spectrum of the pathogenic features of various Chinese isolates of T. gondii.