How many sensitivities to a particular antigen be determined?

After working in a mushroom farm for several months, a worker develops these hives, edema, and swelling lymph node

a) What do these symptoms indicate?

b) What mediators cause these symptoms?

c) How many sensitivities to a particular antigen be determined?

d) Other employees do not appear to have any immunological reactions. What could explain this?

(Hint: The allergen is conidiophores from molds growing in the mushroom farm)