Disorders of the immune system may also be due to deficiencies of the system. These deficiencies may be congenital or iatrogenic (induced by immunosuppressive drugs), or they may result from malignancies occurring in the lymphatic system.
Abnormalities of the B-lymphocytes result in an immunodeficiency accompanied by abnormal production of antibodies. These abnormalities may result from infections such as diseases of the liver, from immune complex disorders such as systemic lupus erythematosus, or from malignancies. Multiple myeloma is a malignant disease of plasma cells in which certain clones of B-lymphocytes produce an overabundance of antibodies. The antibodies are excreted into the urine, where they are known as Bence Jones proteins.
Decreased ability of the B-lymphocytes to produce antibodies is calledhypogammaglobulinemia. Such a condition may result from a genetic defect or the failure of the body to produce B-lymphocytes. Bone marrow disorders may also be a cause.
Abnormalities of the T-lymphocytes result in reduced capacity for cell-mediated immunity. This condition, called DiGeorge's syndrome, often develops from malformation or absence of the thymus gland. An individual with this syndrome is highly susceptible to infection by fungi, protozoa, and viruses.
When both B-lymphocytes and T-lymphocytes are deficient, the condition is calledsevere combined immunodeficiency. Recent procedures employing transplantation of bone marrow tissue have attempted to relieve this condition.