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Primary Immunodeficiencies – VI
Sqadia video demonstrates about AIDS and other Immunodeficiencies. Anatomically, the thymus is located in the upper anterior part of your chest directly behind your sternum and between your lungs. Thymosin is the hormone of the thymus, and it stimulates the development of disease-fighting T cells. Thymic malfunction has a profound effect on T-cell function; all populations of T cells, including helper, cytolytic, and regulatory varieties, are affected. Two major conditions of immune disorders involving thymus are:
- DiGeorge Syndrome
- Nezelof Syndrome
DiGeorge Syndrome, also known as congenital thymic aplasia, in its most severe form is the complete absence of a thymus. It is a developmental defect in which deletion of a region of chromosome number 22 occurs in the embryo. The immune defect includes:
- Depression of T-cell numbers
- Absence of T-cell responses.
For correcting the T-cell defects, thymic transplantation is preffered, but there is very low survival rate in patients with severe heart disease. Nezelof syndrome, is an inherited disorder. There is thymic hypoplasia and T-cell deficiency but normal immunoglobulin levels in this syndrome. The mode of inheritance for this rare disease is not known. The defect is a type of purine nucleoside phosphorylase deficiency with inactive phosphorylase.
Primary Immunodeficiencies – VII
Immunodeficiencies of the myeloid cell lineage affect the innate immune functions. Most of these defects result in impaired phagocytic processes. There are several stages at which the phagocytic processes may be faulty; these include: cell motility, adherence, phagocytosis of organisms, killing by macrophages. Neutrophils are circulating granulocytes with phagocytic function. The quantitative deficiencies in neutrophils may result from congenital defects or may be acquired through extrinsic factors. Neutropenia develops in autoimmune diseases such as Sjogren’s syndrome and Systemic lupus erythematosus. Chronic Granulomatous Disease (CGD) is a genetic disease that has at least two distinct forms:
- an X-linked form that occurs in about 70% of patients
- an autosomal recessive form found in the rest.
This disease is rooted in a defect in the oxidative pathway by which phagocytes generate hydrogen peroxide and hypochlorous acid. Several related defects may lead to CGD; these include a missing or defective cytochrome (cyt b558).
Primary Immunodeficiencies – VIII
Chediak-Higashi Syndrome, an autosomal recessive disease, and is characterized by recurrent bacterial infections, partial oculo-cutaneous albinismnand aggressive but non-malignant infiltration of organs by lymphoid cells. The molecular basis of the defect is a mutation in a protein (LYST) involved in the regulation of intracellular trafficking. Leukocyte Adhesion Deficiency (LAD) is a defect in cell adhesion molecules. Three of these adhesion molecules are, LFA-1, Mac-1, and gp150/95 (CD11a, b, and c, respectively) and they have a common beta-chain (CD18) and are variably present on different monocytic cells; CD11a is also expressed on B cells. This defect is called leukocyte adhesion deficiency.
Primary Immunodeficiencies – IX
Immunodeficiency disorders are treated by replacement of the defective element. Although there are no cures for immunodeficiency disorders, there are several treatment possibilities. Treatment options for the Immunodeficiencies include: replacement of a missing protein, replacement of a missing cell type or lineage, replacement of a missing or defective gene. For disorders that impair antibody production, the classic course of treatment is administration of the missing protein immunoglobulin. Pooled human gamma globulin given either intravenously or subcutaneously protects against recurrent infection in many types of immunodeficiency. Maintenance of reasonably high levels of serum immunoglobulin (5 mg/ml serum) will prevent most common infections in the agammaglobulinemic patient. Recent advances in the preparation of human monoclonal antibodies is the ability to genetically engineer chimeric antibodies to prepare antibodies specific for important pathogens. Advances in molecular biology make it possible to clone the genes that encode other immunologically important proteins, such as cytokines, and to express these genes in vitro, using bacterial or eukaryotic expression systems. Cell replacement as therapy for immunodeficiencies has been made possible by recent progress in bone-marrow transplantation. A variation of bone-marrow transplantation is the injection of paternal CD34+ cells in utero when the birth of an infant with SCID is expected. If a single gene defect has been identified, replacement of the defective gene may be a treatment option.
Primary Immunodeficiencies – X
Two well-studied animal models have been used for experimental purposes. One of these is the athymic, or nude, mouse; the other is the severe combined immunodeficiency, or SCID, mouse. In nude mouse a genetic trait designated nu, which is controlled by a recessive gene on chromosome 11, was discovered in certain mice. The nu/nu mouse cannot easily survive; under normal conditions, the mortality is 100% within 25 weeks and 50% die within the first two weeks after birth. Therefore, when these animals are to be used for experimental purposes, they must be maintained under conditions that protect them from infection. The SCID mouse was shown to have early B- and T-lineage cells. The SCID mouse can neither make antibody nor carry out delayed-type hypersensitivity (DTH) or graft-rejection reactions. SCID mouse has proven extremely useful in studies of cellular immunology. Because its rejection mechanisms do not operate, the SCID mouse can be used for studies on cells or organs from various sources.