I used to have horrible allergies to cats. Throat close up, wheezing, itchy watery eyes. And now I have 3 cats and not a single reaction. What causes?

Cat allergieS. Two factors. 1- your age, with time, usually allergies tame down. 2- you may be less reactive to the cats you have, not all cats produce the same amount of allergens. You lucked out woth those three!
Cat allergens. You are allergic to the allergens associated with cats. Not all cats have the amount of allergens, so you may be more tolerant of certain breeds compared to others.