any abnormal immune response. Includes:
1. deficient or absent response. See combined immune deficiency syndrome (disease).
2. excess production of gamma globulins (hypergammaglobulinemia), e.g. in the excessive proliferation of plasma cells in a multiple myeloma.
3. over-reaction to extrinsic antigens as in immediate and delayed type hypersensitivity.
4. over-reaction to intrinsic antigens, abnormal response of the body to its own tissues, e.g. the autoimmune diseases such as lupus erythematosus and thyroiditis.