RA is an autoimmune disorder that causes joint inflammation. Atopy follows family. These people tend to have higher levels of IgE and require specific antigens to trigger the event. Foods include allergies to shellfish, nuts, eggs which may present as hay fever, asthma, eczema, urticaria. The mechanisms are not well understood in this, however, it is believed that lower levels of T8 cells and greatly elevated levels of IgE are of significance in this reaction.
Drug hypersensitivities are primarily due to anti-microbial agents.
This reaction is the most common cause of hypersensitivity reactions. Unlike type I reactions, this reaction may occur with first or second exposure to the offending drug. The other name of these reactions is cell mediated hypersensitivity or delayed hypersensitivity. They are, then, delayed in response. One type IV reaction of BIG significance is contact dermatitis.