That's a type II hypersensitivity (IgM or IgG antibodies starting the complement cascade) and it's different from type I allergies (IgE causing mast cell degran

That's a type II hypersensitivity (IgM or IgG antibodies starting the complement cascade) and it's different from type I allergies (IgE causing mast cell degranulation). Type IV (cell-meditated, lymphocyte reaction) hypersensitivity, like poison ivy, is also different. And then there's a whole bunch of other hypersensitivities that are poorly understood, like atopy.