Polyclonal lymphocyte and plasma cell disorders can be classified into two major groups (Table 49–1):
— Primary disorders that result from defects intrinsic to B lymphocytes (e.g., X-linked agammaglobulinemia), T lymphocytes (e.g., congenital thymic aplasia), and/or natural killer cells, the latter usually coupled with a B or T cell deficiency (e.g., interleukin (IL)-7 receptor α-chain deficiency) (see Chap. 51).
— Acquired disorders that result from physiologic or pathophysiologic responses to extrinsic factors, usually infectious agents (e.g., Epstein-Barr virus or human immunodeficiency virus infection). (See Chaps. 50, 52, 53.)
The monoclonal lymphoid disorders are classified in Chap. 54 and individual neoplastic lymphoid diseases are described in Chaps. 55–72.
— Disparate disorders can have similar clinical manifestations, such as recurrent infections as a result of either B or T cell deficiency.
Lymphocyte disorders can have clinical manifestations that are not restricted to cells of the immune system (e.g., leprosy or systemic lupus erythematosus).
In some cases, classification is influenced by disease manifestations:
— Diseases caused by production of pathologic autoantibodies; e.g., autoimmune hemolytic disease (see Chaps. 24–26), autoimmune thrombocytopenia (see Chap. 120), and systemic autoimmune diseases (e.g., myasthenia gravis).
— Diseases caused by excess production of lymphocyte cytokines; e.g., chronic inflammatory disorders.