http://path2resilience.com/) had mentioned to me a few years ago: nibbling a bit of the leaves to build up immunity. I started small, with a bit no bigger than my pinky nail. I waited a couple of days without reaction and nothing happened so I ate another one of the small leaves. That was two days ago and I'm still here. I'll try one more small leaf this year and see if I react to the plant again.
An old timey journal says that anything alkaline (or basic) will temporarily alleviate symptoms but does not grant long-term immunity to poison ivy (Dr WF Dieffenbach's "Treatment of Ivy Poisoning" in Southern California Practitioner v.29). The author describes his experience developing a strong adverse response to poison ivy, finding out about auto-lacto therapy (drinking milk of an animal that had grazed on the toxin), and testing the treatment with success. He fed a cow grass and poison ivy then consumed a pint a day for two days. That year he developed no further rashes. In following years he developed a rash again, indicating that immunity is not permanent and follow-up treatments are required. Admittedly the article is quaint in its anecdotalness (it was published in 1917), but warrants a closer look at treatments for ivy poisoning. **It is appropriate to note here that the plural of anecdote is not data. Also pertinent is that I'm not an apothecary, healer, or medical professional and I only recommend doing this after doing your own research/asking the plant itself.
Ecological notes: Centennial Woods is filled with poison ivy, as are most places that are wet, but well drained, and rich, but not excessively so. As is convenient with mugwort growing near poison oak out west (mugwort can be used as a poultice to treat the itchiness caused by urushiol in poison oak), here in New England jewelweed (Impatiens capensis and I. pallida) almost always grows near poison ivy (but the reverse is not true as poison ivy is much less common).
Where: The photos are from Centennial Woods. Below are a couple of look-alikes, at least in the early stages. On the left is sarsaparilla, which has 3-5 leaflets, doesn't have a woody stem, and splits into three branchlets. On the right Virginia creeper (Parthenocissus quinquefolia), which has suction like discs on the ends of their tendrils and five, not three leaflets.
Other notes: Poison ivy is in the same genus as other toxic plants like Poison sumac (T. vernix), poison oak (T. diversiloba out west and T. pubescens out east). The genus is in the Cashew family, Anacardiaceae, which also includes staghorn sumac (delicious) and, not surprisingly, cashews. Members of Toxicodendron are occasionally placed in Rhus, the same genus as staghorn sumac.