Antibody responses to clostridial infection in humans.

Serum antibody responses to the major toxins produced by Clostridium difficile, Clostridium perfringens, Clostridium septicum, Clostridium tetani, and Clostridium botulinum have been documented following infection. Effective toxoid vaccines for tetanus and enteritis necroticans due to C. perfringens type C demonstrate the potential of antitoxin responses. Although individual serum and mucosal antibody responses to C. difficile enterotoxin (toxin A) vary, one-third of patients with C. difficile diarrhea develop neutralizing serum antibodies. IgA in the serum, not IgG, is typically responsible for this neutralization, suggesting a unique role for serum IgA in response to C. difficile infection, an infection that is usually limited to the intestinal mucosa. The relationship of naturally occurring antitoxin antibodies to the clinical course of C. difficile infection is controversial. However, patients with chronic relapsing C. difficile diarrhea and low levels of IgG to toxin A have shown clinical responses following intravenous therapy with immune globulin. Antibody responses to non-toxin C. difficile proteins also occur, but their significance is only partially known.