Serum Antibodies Protect against Intraperitoneal Challenge with Enterotoxigenic Escherichia coli
Figure 3
Evaluation of protective immunity induced by a low dose of CFA/I fimbriae. BALB/c mice (6–8/group) were i.m. immunized with (a) 30, (b) 10, and (c) 0 μg detoxed CFA/I fimbriae with or without CT on day 0. (a, b) Elevated serum IgG and mucosal IgA anti-CFA/I Ab fimbriae responses were induced by 2 wks after immunization (c), but not by control mice. Depicted is the mean ± SD as ** and *** versus 10 μg CFA/I fimbriae-immunized mice. (d) Assessment of the protective efficacy by the low-dose CFA/I fimbriae-immunized mice. The CFA/I fimbriae-immunized and sPBS-dosed mice (a)–(c) were i.p. challenged with CFUs of wt ETEC H10407 at 4 wks after immunization. Mouse survival rates were determined for 14 days. Both 30 μg CFA/I + 2.5 μg CT-immunized mice and 10 μg CFA/I + 2.5 μg CT-immunized mice survived (8/8); the survival rates for 30 μg CFA/I- and 10 μg CFA/I-immunized mice were 87.5% (7/8) and 62.5% (5/8), respectively; the 2.5 μg CT-immunized mice showed 25% (2/8) survival; and the sPBS-dosed mice all succumbed to challenge (0/6). Survival fractions obtained from 30 μg CFA/I + 2.5 μg CT-immunized mice and 10 μg CFA/I + 2.5 μg CT-immunized mice were compared to sPBS-dosed mice and were determined, * and †, respectively.
