Bovine immune response to Shiga-toxigenic Escherichia coli O157:H7

Although cattle develop humoral immune responses to Shiga-toxigenic (Stx(+)) Escherichia coli O157:H7, infections often result in long-term shedding of these human pathogenic bacteria. The objective of this study was to compare humoral and cellular immune responses to Stx(+) and Stx(-) E. coli O157:H7. Three groups of calves were inoculated intrarumenally, twice in a 3-week interval, with different strains of E. coli: a Stx2-producing E. coli O157:H7 strain (Stx2(+)O157), a Shiga toxin-negative E. coli O157:H7 strain (Stx(-)O157), or a nonpathogenic E. coli strain (control). Fecal shedding of Stx2(+)O157 was significantly higher than that of Stx(-)O157 or the control. Three weeks after the second inoculation, all calves were challenged with Stx2(+)O157. Following the challenge, levels of fecal shedding of Stx2(+)O157 were similar in all three groups. Both groups inoculated with an O157 strain developed antibodies to O157 LPS. Calves initially inoculated with Stx(-)O157, but not those inoculated with Stx2(+)O157, developed statistically significant lymphoproliferative responses to heat-killed Stx2(+)O157. These results provide evidence that infections with STEC can suppress the development of specific cellular immune responses in cattle.