Determination of Serum Antibodies to C. difficile Toxin B and Their Neutralization Activity in IBD Patients

Abstract

Purpose:C. difficile affects patients with inflammatory bowel disease (IBD) at a higher frequency and severity, compared to the general population. Little is known about serum antibodies to toxin B (TcdB) from both the historical strain (10463) and hypervirulent strain (NAP1) associated with C. difficile disease. More importantly, it is not known whether such antibodies can effectively neutralize TcdB in the IBD population. The aim of this study is to investigate whether IBD patients have antibodies against TcdB and evaluate their neutralizing activity in vitro. Methods: IBD patients, both with relapsing disease (n=27) and in remission (n=30) as defined by the managing physician, were enrolled in addition to matched controls (n=29). Serum was obtained and antibody titers to both strains of TcdB were measured by ELISA. Neutralizing activity was determined by measuring viability of Chinese Hamster Ovarian cells incubated with serum and either 10463 or NAP1 TcdB in vitro. Results: Antibodies to 10463 TcdB were significantly (p<0.0001) elevated in the sera of IBD remission patients (average relative OD 0.442 ± 0.175) and IBD relapse patients (0.280 ± 0.182) compared to sera of control patients (0.167 ± 0.065). Similarly, antibodies to NAP1 TcdB were elevated in both IBD relapse (average relative OD 0.169 ± 0.158) and IBD remission (0.254 ± 0.166) compared to control (0.099 ± 0.049), although statistical significance was not seen with IBD relapse patients. Neutralization of 10463 TcdB was observed in approximately 14% (4/29) of control sera, 17% (5/30) of IBD remission sera, and 19% (5/27) of IBD relapse sera. A higher number of IBD patients - 52% of IBD relapse (14/27) and 43% of IBD remission (13/30) - had sera demonstrating neutralization of NAP1 TcdB in vitro, compared to 31% (9/29) of control patients. Conclusion: Antibodies to TcdB of both historical and hypervirulent strains of C. difficile were observed in control patients, consistent with previously known studies. IBD remission patients were observed to have higher antibody levels in their sera than IBD relapse patients. Interestingly, a higher proportion of IBD relapse patients had sera demonstrating neutralization of both strains of TcdB. This may reflect a higher rate of exposure to C. difficile disease among IBD relapse patients.