Re a story on HIV vaccine trials: http://www.theage.com.au/articles/2003/06/04/1054700265445.html
I read the definition of a vaccine as something that “stimulates antibody production or cellular immunity against the pathogen.”
Does this mean a vaccine can only be used preventatively, or after infection as well?
Depends on the disease and the vaccine. If the disease is fairly slow to develop then a vaccine can be effective post infection. The idea is that before the bugs get a chance to develop a lethal population you fool the body into thinking they have. The resultant immune response kills the bugs before they have a chance to multiply. Basically you’re allowing the body to jump the gun and start preparing for the infection before it’s become an infection.
It’s common procedure to give tetanus vaccinations after serious wounds if it’s been a few years since the last booster.
Since AIDS is so slow to develop post HIV infection I suspect that the AIDS vaccine should work reasonably well post infection. But that’s a WAG. Of course since the tests all work on antibodies anyway by the time you know you’re infected it would probably be too late.
The tetanus vaccine is give after serious wounds because the infection is very, very fast. The immunity given by the vaccine, unlike those for many other illnesses is an ‘artificial passive immunity’, whereby the antibodies themselves are injected into the bloodstream. The B and T Lymphocytes see these, copy them and use them to fight the tetanus antigens.
This is why the tetanus vaccine works if it’s given after the infection may have started. Other vaccines can either be similar to the tetanus one, or be ‘artificial active immunity’, such as the BCG vaccine for TB. Less harmful versions of the antigens are injected into the bloodstream and the body has time to combat them without any signs of illness. Since the antigens fought are very similar to the disease vaccinated against, the body develops an immunulogical memory to that disease, and can fight it quickly. However, if they are injected after an infection, they cannot help. This is because the body does not have the time to make the antibodies. By the time that it’s worked out how to combat the antigens, you’re most likely very irrepairably ill.
I’m feeling rather more confident that my As Human Health and Disease modular exam on monday went OK now!
Cheers, Harry
I don’t want to shake your confidence Harry, but I think you’re confusing the distinction between the tetanus vaccine and tetanus antiserum.
Tetanus vaccine (as contained in the DTP vaccine) contains inactivated tetanus toxin (termed a toxoid), and it does stimulate an active immune response, resulting in antibody production. The antibodies are directed against the toxin and are protective because they bind to the toxin, preventing it from exerting its toxic effects. More importantly, though, is that stimulation by the toxoid results in the formation of “memory” lymphocytes that can quickly re-initiate antibody production should the need arise. The problem with this system is that the protection conferred by the vaccine does wear off with time, hence the need for “boosters.”
The tetanus antiserum is a blood product which contains antibodies directed against the tetanus toxin. Giving this confers passive immunity by introducing exogenously produced antibodies into the patient’s body. This protection is short lasting, though, as once the antibodies are cleared from the patient’s system, the body doesn’t “know” how to make more because it never learned how.
So why the two?
Patients who were never immunized or who haven’t gotten a recent booster are given the antiserum in addition to the vaccine. Since these patient’s immune systems haven’t been sensitized, the vaccine will produce a primary immune response, which is too slow to be protective. The passive immunization given by the antiserum works almost immediately, so it will protect the patient from the toxin’s effects. Giving them the vaccine is done as a preventative measure for future exposures.
Patients who are current with their immunizations are given a booster, which will cause their sensitized immune systems to create a secondary immune response (which is much faster than the primary response) and elevate the antibody levels before the toxin has caused any major damage.
On another note, the only disease that I’m aware of where the vaccine is routinely given after infection is rabies. That is made possible because the rabies infection progresses very slowly.
As for the OP, the approach here seems to be to stimulate the response of cytotoxic cells, which are immune cells that function by killing infected cells. It’s an interesting approach, as the AIDS virus can hide in human cells by integrating itself into our DNA. In theory, cytotoxic cells could kill off these infected cells. I would think for this to work, one would need to be vaccinated prior to exposure, as the idea would be to help the immune system prevent the infection from taking hold in the body (also, AIDS degrades your immune response so vaccines may not work properly), but the article is vague about the actual method, making most of this paragraph a semi-WAG.
Yeah, you’re right. After posting, I went to check in my biology textbook to see if I was correct. In there, it only talks of the one vaccine for tetanus, and how it is often given passively after a big wound. Fortunately, that means that I dont have to know that for the course specification, but it’s something intresting to learn! Thanks for picking up on that Mezantius, and making sure I didn’t misinform dopers.
Sorry to hi-jack the thread, but since I wouldn’t know where to start looking, are there any passive immunizations that are given prior to any possible infections, obviously aside from breastfeeding!
Thanks, Harry
Hmm, I dont think I made myself clear enough in my last post. My book didn’t really tell me whether I was right or wrong, but you obviously know what you’re talking about, and I clearly wasn’t totally right. I shall check up on t’internet soon as it seems something intresting to look up (yes, I’m that boring).
Check this link out for more tetanus info:
http://www.cdc.gov/nip/publications/surv-manual/chpt13_tetanus.pdf
The only vaccine that’s regularly given post-infection is the rabies vaccine. This is because the rabies virus stays confined to the nervous system and never gets out in the blood, so the immune system isn’t able to mount a response. However, giving the vaccine post-infection primes the immune system, which is then able to recognize infected nerve cells and fight the virus off.
Thankyou very much for the link Mezantius, and welcome to the boards! (should have said that sooner, but until recently, I’ve always seen myself as a bit of a newbie, but my post count is rising, I guess)
I’m gonna get down to reading this properly once it’s loaded.
I’ve also just realised that I burned my 100[sup]th[/sup] post without so much as a celebratory postscript!