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Gamma Globulins: One of the major fractions of proteins that are dissolved in the plasma. When plasma proteins are separated in the laboratory, they are given the designation of albumin or globulin. The globulins can be separated into three major groups called alpha, beta, or gamma fractions. The gamma globulins contain the antibodies in the plasma. These antibodies, or gamma globulins, are now sometimes referred to as immune globulins or immunoglobulins because they are globulins made by immune cells, specifically B-lymphocytes and their derivative plasma cells. Gamma globulins, or immunoglobulins, are key products of the immune system because they contain the antibodies that protect us from infection. Patients with immune deficiencies such as those with Chronic Lymphocytic Leukemia and some patients with lymphoma, whose B-lymphocytes cannot make gamma globulin, may be given pooled human gamma globulin periodically as a treatment in an effort to correct the deficiency and decrease the risk of infection. This process is imperfect because the gamma globulin pooled from several normal human plasma donors may not always carry enough of the specific antibodies needed by the patient.

Gammopathy: Normally the gamma globulins, which are the antibodies, are a mixture of a huge number of different types made by a large and diverse number of B-lymphocytes. In diseases that affect the behavior of B-lymphocytes, the amount of gamma globulin they produce may be increased above normal. These diseases are collectively called gammopathies. In a monoclonal gammopathy, which is a neoplasm, a transformation of B-Lymphocyte results in a large population of malignant T-cells derived from the original malignant lymphocyte. Those cells compose a clone; they are virtually identical copies of the transformed lymphocyte. They produce exactly the same gamma globulin. So instead of diverse gamma globulins being made by diverse lymphocytes (polyclonal), a single or monoclonal gammaglobulin is secreted and can be identified in the plasma. When nearly all gamma globulin being produced is one particular form this is called a monoclonal gammopathy. Myeloma, some lymphomas, and some cases of Chronic Lymphocytic Leukemia are monoclonal gammopathies.

Genes: The genes are composed of DNA and are carried on the chromosomes. Genes direct the production of all the molecules that form the structures that of a cell. Genes determine the inherited characteristics that distinguish one individual from another. Each human has an estimated 90,000 genes.

Glucocorticoids (Corticosteroids or Steroids): A group of hormones including a series of synthetic products; prednisone, prednisolone, methylprednisolone, and dexamethasone, used in the treatment of some lymphocytic leukemias, lymphomas, and myeloma. These hormones are used to suppress graft rejection and graft versus host disease following allogeneic stem cell transplantation. Side effects after long-term use of high doses include an increased risk of infection, osteoporosis, and diabetes.

Graft Rejection: Rarely, when a patient has an allogeneic stem cell transplant, the donor stem cells will fail to sustain blood cells production because the recipient's lymphocytes attack the donor stem cells. The conditioning of patients with cytotoxic therapy before transplantation is intended to suppress the recipient immune system sufficiently to avoid rejection of the graft. In occasional recipients, a graft may not be successful because too few donor cells are infused.

Graft Verses Host Disease: The immune attack by lymphocytes in the donor's marrow or blood cell suspension (the graft) against the tissues of the recipient (the host T). The immune cells most engaged in this reaction are donor T-lymphocytes, which are present in the donor's blood or marrow, the source of stem cells. The principal organs injured are the skin, the liver, and the gastrointestinal tract. The reaction does not occur in identical twin transplants. The reaction may be minimal in closely matched individuals or severe in less well-matched individuals. These reactions are mediated in part by antigens that are not in the HLA system and cannot be matched at this time prior to transplant. These are referred to as minor histocompatibilty antigens. For example, in the case of a female stem cell donor and a male recipient, the female donor's cells that do not share the genes on the Y chromosome may see factors that are produced by genes on the Y chromosome as foreign. This fact does not prohibit female donors and male recipients, but it makes the risk of immune reaction higher.

Graft Versus Leukemia Effect: Transplanted T-lymphocytes not only may attack the recipient's normal tissues (graft versus host T) but may recognize and attack the malignant T-cells in the recipient. This effect was noted when 1) leukemia recurrence after transplant was seen to be more likely if the donor and recipient were identical twins than if they were non-identical siblings, 2) the more prominent the graft versus host disease the less likely was leukemia recurrence, and 3) the removal of donor T-lymphocytes decreased graft versus host disease but also resulted in a higher frequency of leukemia relapse. Each of these observations could best be explained by an immune attack by donor lymphocytes against recipient leukemia cells. This effect seems to be most active in chronic myelogenous leukemia although it may occur in patients with myeloma and other hematologic malignancies as well.

Granulocytes: A type of white blood cell that has a large number of granules in the cell body. Neutrophils, eosinophils and basophils are types of granulocytes.

Granulocytic Sarcoma: This designation applies to a local tumor composed of leukemic myeloblasts and sometimes related myeloid cells. These tumors occur outside the marrow and have been observed beneath the skin and in many other sites. They may be the first evidence of leukemia, or may occur after the disease has been diagnosed.

Growth Factors: see Cytokines

Growth Hormone: A chemical secreted by the pituitary gland that controls linear growth in children and adolescents. Radiotherapy given to the head and neck of children with leukemia may lead to a deficiency in growth hormone. This deficiency may be replaced by administration of recombinant hormone.

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