The only way one can become immune to a poison is if he/she takes very small doses (amount depending upon the poisons toxicity) and increase this amount slowly until ones system becomes familiar with the poison. This can change depending on the poison, as there are some varieties that you can not build up any sort of immunity to.
No.
It is rare to be immune to poison ivy, as most people are sensitive to the plant's oil, causing an itchy rash. Only a small percentage of the population is naturally immune to poison ivy.
Some people are immune to poison ivy because their immune system does not react to the specific oil in the plant that causes the itchy rash.
Immune
So then it doesn't have full effect on your body however just enough for your body to be immune.
Yes the only animals to be allergic to poison ivy are humans.
Yes it will.
Yes, it is possible for some people to be immune to poison ivy. This immunity is usually due to a genetic variation that makes them less sensitive to the irritant in poison ivy called urushiol.
There is a species of snake that is immune to them.
Yes, some people may have a natural immunity to poison ivy, but it is not common.
Poison Ivy is not REAL Poison. Its a issue in the immune system that will make it react to you. If you have a serious case or allergic reactions you would need to seek medical attention.
Alligators aren't immune to snake poison, Rat poison is questionable. I imagine it'd have to be a hefty dose to take out an adult alligator though.