Steve and Joe were dismantling an old shed on Steve's farm when part of the shed collapsed onto Joe's leg, causing a gash and pinning Joe under the debris. In the process of trying to free Joe, Steve received numerous punctures to his hands and arms from nails embedded in the collapsed lumber. Both went to the hospital emergency room and were treated for their injuries. The emergency room nurse asked each for a medical history, including how long it had been since his last tetanus booster. Joe had had a booster at his annual physical just six months previously. His gash had bled quite a bit, which had helped to clean out the wound. He was stitched up and told to watch for redness and pus around the stitches. Steve couldn't remember how long ago he had had a tetanus shot, but it was probably more than ten years. His deeper punctures were cleaned as well as possible and he was given a tetanus booster (inactivated tetanus toxin, Td) and also tetanus immune globulin (human antibody to tetanus toxin). Both Steve and Joe made full recoveries with no symptoms of tetanus.
Clostridium tetani is a Gram positive rod-shaped bacterium which lives in soil. Under conditions which are not favorable for growth, it forms spores which can survive for long periods, then become vegetative cells when conditions are more favorable. C. tetani grows only in the absence of oxygen, thriving in deep wounds. It is an extracellular pathogen, using enzymes to invade host tissues. C. tetani secretes a neurotoxin which causes the muscle spasms that give tetanus its other name, "lockjaw".
Infants are injected with tetanus toxoid (Td), an inactivated C. tetani exotoxin, three times during their first two years after birth and again at ages 5 and 15 as part of the DPT (Diphtheria, Pertussis, and Tetanus) vaccine. The recommendation is for a tetanus booster (tetanus toxoid) to be given at least every ten years to maintain immunity. More information about tetanus can be found at http://www.cdc.gov/; click on Health Topics A-Z in the left hand column and then Tetanus.
1. The molecules "seen" by the immune system are called antigens. What are the antigens that the immune system will see if Clostridium tetani spores have entered Steve and Joe's wounds and germinated to form vegetative cells that produce toxin? [In general, what molecules on bacteria will be antigens?] What other molecules (in general) can be antigens?
2. What factors led to different treatments being used for Steve and Joe? Did either of them have immunity to tetanus? How can you tell is someone is immune? Is immunity a general or antigen-specific property? What would you expect to find in the blood of someone who was immune to tetanus?
3. Tetanus toxoid (Td) is an antigen; injecting it into Steve will cause his immune system to make antibodies and memory B cells. This process is called active immunization. Tetanus immune globulin is antibody to Td that has been purified from the blood of immune humans; it provides passive immunization. How can antibody protect someone from the effects of a toxin? Why do you think Steve was given both treatments? Would you give both injections at the same site? Why or why not?
4. Where will the immune system first come in contact with C. tetani? Where are antibodies produced? Where and how will the bacteria be eliminated from the body?
5. Based on the information in Chapter 1, how will the immune system respond to this infection? List each immune effector and its function as bullets. (For example, will macrophages be involved? If so, what will they do and where? Will there be inflammation? Where will antibodies be produced? What will T cells do?)
Supplementary Materials: Infectious Disease Immunity Rules Antigen ToolBox