Immunosuppressants are very commonly used for various diseases that are caused by overreactions or undesired reactions of your immune system. Glucocorticoids, for example, are very widespread for all sorts of stuff (rashes, asthma, allergies, inflammations, ...). Monoclonal antibodies are also getting popular as a way to treat allergic reactions by means such as "killing" your IgE antibodies (They're basically antibodies that, in this instance, are used against your own body's antibodies).