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[RC] poison oak and horses - Amy MajorKat wrote: In humans, generally, a reaction to poison oak gets worse with more exposure rather than better. It is an allergic response, and, as with most allergies, the more you are exposed to the allergen, the more sensitive you become to it. It is unlikely that continued exposure has conferred immunity. More likely that horses generally don't have a problem with it at all. This is true to some extent but is also the basis of allergy shots. What happens sometimes is that as you become exposed you become "sensitized" and then if you run into a large amount of the allergen it can cause a real problem. Same example is someone who is not "allergic" to bee stings but every time they get stung, they are being sensitized and the immune system is going on notice, then they get into
a situation where enough antigen pushes the response from "on the alert" to "hyper-activation" a very dangerous situation indeed. But everyone is an individual so it is difficult to generalize in these situations. However, controlled continued exposure is the basis of allergy shots. Starting out with a small amount of the offending antigen and then increasing the dose until the immune system becomes "desensitized". (HMM sounds like natural horsemanship). Sort of realizes that the allergen is not something that it needs to go crazy over. An interesting fact is that there is an immune phenomenon called "oral tolerance" this means that antigens introduced to the immune system via the gut become "non-reactive" or the immune system "tolerates" them. But this is a complicated thing and dose and timing of exposure are important for this to work so I doubt that the horses are
"immune" because they eat the stuff (but maybe...I am not on my equine immunology and how similar it is to humans). It is probably just that most are NOT sensitive to it. But I would not say that they don't EVER get it.
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