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Interleukin 6 (IL-6)/B cell stimulatory factor 2 is a multifunctional cytokine produced by both lymphoid and nonlymphoid cells. IL-6 regulates immune response, acute phase reaction, and hematopoiesis. It was found that IL-6 production by T cells is dependent on macrophages, and IL-6 is one of essential factors for pokeweed mitogen induced immunoglobulin production. Both high- and low-affinity IL-6 receptors were identified. The molecular cloning of IL-6 receptors demonstrated that this receptor is a member of the immunoglobulin superfamily. The deregulated production of IL-6 is suggested to be involved in the pathogenesis of autoimmune diseases and in the development of multiple myeloma.

The myeloperoxidase (MPO) activity of patients treated with cytotoxic drugs and/or corticosteroids was lower than that of healthy controls. Cyclophosphamide decreases the number of leukocytes without affecting the MPO activity per cell. At the same dose of anti-inflammatory potency, dexamethasone caused more decrease than other corticosteroids in the MPO level, nitro-blue tetrazolium (NET) and number of polymorphonuclear leukocytes (PMN). However, on successive daily treatment with dexamethasone for 7 days, the MPO level and NET returned to normal, although phagocytosis of Candida by PMN diminished to about 60 % of the normal level. Pretreatment of rats with heat-killed Candida albicans protected the functions of PMN against dexamethasone.

Antibody molecules play an essential role not only in protection against viral or bacterial infections, but also in the induction of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, and immediate-type hypersensitivity. Therefore, the study of the mechanism regulating the activation, proliferation and immunoglobulin secretion of B lymphocytes is essential for the normal and abnormal regulations in the antibody response.