Adaptive immune response to Clostridium difficile infection: A perspective for prevention and therapy.

Clostridium difficile infection (CDI) is one of the most important nosocomial illnesses and a major cause of morbidity and mortality. While initial treatment of CDI is usually successful, unprovoked relapses remain an important and frustrating problem. This review examines the literature describing the natural immune response to CDI, and to what extent it can explain the propensity for relapses. In particular, we discuss studies on antibody and, to a lesser extent, B cell and T cell responses in CDI. Despite years of study, there remains incomplete understanding of the natural antibody response to the major pathogenic toxins, TcdA and TcdB, and other bacterial antigens, in CDI. Recent literature suggests that a specific subset of neutralizing antibodies that target the putative carbohydrate-binding domains of TcdB and possibly TcdA have the greatest protective ability. This is further supported by recent successful clinical trials of a humanized monoclonal antibody to the major toxin TcdB. A better understanding of how and why the most protective adaptive immune response develops may lead to improved vaccine and therapeutic targets for recurrent CDI.