Each antibody has a slightly different amino acid sequence that renders it specific to only one antigen. Antigens can be proteins, carbohydrates, nucleic acids, hormones, or other substances. Lupus, rheumatoid arthritis, and multiple sclerosis are examples of human autoimmune disease. B cells may be found in the bone marrow and in the blood circulation. Some CD antigens have a well-known function, but other CD antigens have no known function.
Cytokines can be both immunostimulatory and immunosuppressive.
Interleukins, interferons, and some growth factors are examples of cytokines. Proteins displayed on the cell surface serve as receptors for specific molecules. Each event is dependent upon the preceding event, and if one part of this chain is missing, signal transduction is interrupted. Like antibodies, T cell receptors are specific for only one antigen. T cells may be found in the thymus, lymph nodes and blood circulation.