High prevalence of subclass-specific binding and neutralizing antibodies against Clostridium difficile toxins in adult cystic fibrosis sera: possible mode of immunoprotection against symptomatic C. difficile infection

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Objectives: Despite multiple risk factors and a high rate of colonization for Clostridium difficile , the occurrence of C . difficile infection in patients with cystic fibrosis is rare. The aim of this study was to compare the prevalence of binding C . difficile toxin-specific immunoglobulin (Ig)A, IgG and anti-toxin neutralizing antibodies in the sera of adults with cystic fibrosis, symptomatic C . difficile infection (without cystic fibrosis) and healthy controls. Methods: Subclass-specific IgA and IgG responses to highly purified whole C . difficile toxins A and B (toxinotype 0, strain VPI 10463, ribotype 087), toxin B from a C . difficile toxin-B-only expressing strain (CCUG 20309) and precursor form of B fragment of binary toxin, pCDTb, were determined by protein microarray. Neutralizing antibodies to C . difficile toxins A and B were evaluated using a Caco-2 cell-based neutralization assay. Results: Serum IgA anti-toxin A and B levels and neutralizing antibodies against toxin A were significantly higher in adult cystic fibrosis patients (n=16) compared with healthy controls (n=17) and patients with symptomatic C . difficile infection (n=16); p ≤0.05. The same pattern of response prevailed for IgG, except that there was no difference in anti-toxin A IgG levels between the groups. Compared with healthy controls (toxins A and B) and patients with C . difficile infection (toxin A), sera from cystic fibrosis patients exhibited significantly stronger protective anti-toxin neutralizing antibody responses. Conclusion: A superior ability to generate robust humoral immunity to C . difficile toxins in the cystic fibrosis population is likely to confer protection against symptomatic C . difficile infection. This protection may be lost in the post-transplantation setting, where sera monitoring of anti- C . difficile toxin antibody titers may be of clinical value. Keywords: Clostridium difficile , cystic fibrosis, antibodies

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