Practice question

Diphtheria and tetanus vaccines belong to toxoid class defined by formalin inactivated exotoxins maintaining immunogenicity while lacking toxicity. Diphtheria vaccine contains diphtheria toxoid derived from Corynebacterium diphtheriae Park-Williams 8 strain carrying corynebacteriophage tox gene encoding ADP-ribosyltransferase secreted into culture medium purified then detoxified. Tetanus vaccine uses tetanus toxoid from Clostridium tetani Harvard strain fermenter grown anaerobically producing tetanospasmin. Both toxoids formulated with aluminum phosphate or hydroxide adjuvant as DT, Td, DTP combos. Protection mediated not by antibacterial immunity but antitoxic antibodies binding toxin in extracellular fluid preventing entry into target cells: diphtheria antitoxin prevents binding heart muscle and nerves, tetanus antitoxin prevents attachment at neuromuscular junction. Antibody titer greater than 0.01 IU per mL provides minimal protection, 0.1 IU full. Vaccinated individuals may still colonize with Corynebacterium but do not develop systemic intoxication. Herd immunity reduces toxin circulation. Booster every ten years recommended for tetanus because environmental spores ubiquitous in soil. Discovery by Behring antitoxin serum therapy preceded toxoid use.