[spondylosaurus]

Xolair works by targeting IgE antibodies, which are the part of your immune system that responds to allergens. The shot essentially neuters those antibodies to prevent them from reacting as often/severely, which dampens your body's allergic response across the board.

(Crucially, IgE antibodies are not the part of your immune system that responds to infectious disease, so anti-IgE meds won't make you immunocompromised in any significant way.)

[whatshisface]

Hold on, why even have IgE antibodies then?

Edit: >Several lines of evidence suggest that IgE is important in host defense against parasites (see Section 9-23). Many parasites invade their hosts by secreting proteolytic enzymes that break down connective tissue and allow the parasite access to host tissues, and it has been proposed that these enzymes are particularly active at promoting TH2 responses. This idea receives some support from the many examples of allergens that are enzymes.

[kortex]

Yep, you got the gist in the ninja edit.

The IgE-parasite connection is actually a bit part of the hygiene hypothesis, and I have personal experience with helminth therapy. It put a serious permanent dent in my animal and pollen allergies, long after the session (I forget how long they were active but I re-inocculated N. americanus twice and it was roughly a 2-3 year period).

Once you get over the squick factor and the really terrible itching at the site that lasts 12-24h, it's great.