A mutation in the gene that encodes for a transport-associated protein (TAP) results in the lack of class-I MHC molecule expression, which is manifested by a deficiency of CD8+ T lymphocytes. In the bare leukocyte syndrome, there is a mutation in the gene that encodes for the MHC class II transactivator (CIITA), resulting in the absence of class-II MHC molecule on antigen-presenting cells including macrophages and dendritic cells. These infants have partial monosomy of 22q11-pter or 10p. The T-cell defect is variable depending on the severity of the thymic lesion. The DiGeorge anomaly arises from a defect in the third and fourth pharyngeal pouches that causes a developmental abnormality of the thymus. Mutation in the genes encoding RAG1 or RAG2 causes an autosomal recessive form of SCID. The deficiency of these enzymes causes ribonucleotide reductase inhibition leading to a defect in DNA synthesis and cell replication. On the other hand, few cases of SCID are caused by defective genes that encode for adenosine deaminase or nucleoside phosphorylase. This chain forms a molecular part of the receptors for IL-2, IL-4, IL-7, IL-11, IL-15, and IL-21. The defective gene encodes the gamma chain of the interleukin-2 (IL-2) receptor. It is caused by a gene defect on the X chromosome in more than 50% of cases. Severe combined immunodeficiency disorders (SCID) are incompatible with life, and affected children usually die within the first 2 years. On the other hand, recurrent fungal infections may be caused by a lack of T lymphocytes. Recurrent pneumonia caused by extracellular bacteria suggests antibody deficiency. Primary immunodeficiency diseases result from intrinsic defects in immune cells, including T cells, complement components, and phagocytes. This activity reviews the different immunological disorders, their evaluation, and management, and highlights the role of the interprofessional team in caring for affected individuals. Secondary causes of immunodeficiency include steroids, nutrient deficiency, obesity, acquired immune deficiency syndrome (AIDS), or other viral infections. Selective immunoglobulin A deficiency is also a primary immunodeficiency. Primary immunodeficiencies leading to phagocyte deficiency include chronic granulomatous disease and leukocyte adhesion deficiency syndrome. Primary immunodeficiencies leading to complement deficiency include hereditary angioedema, deficiency of C3, deficiency of membrane attack complex, and C2 or C4 deficiency secondary to autoimmunity. Primary immunodeficiencies leading to both T-cell and B-cell deficiency include severe combined immunodeficiency disease, Wiskott-Aldrich syndrome, immunodeficiency with ataxia-telangiectasia, and Major Histocompatibility Complex deficiency. Primary immunodeficiency leading to B-cell deficiency includes X-linked agammaglobulinemia, also called Bruton agammaglobulinemia. Primary immunodeficiencies leading to T-cell deficiency include DiGeorge syndrome, also known as congenital thymic aplasia, chronic mucocutaneous candidiasis, hyper-immunoglobulin M syndrome, and interleukin-12 receptor deficiency. Primary immunodeficiency is subdivided into types that cause T-cell deficiency, B-cell deficiency, both T-cell and B-cell deficiency, complement deficiency, phagocyte deficiency, and immunoglobulin A deficiency. Immunodeficiencies can be primary or secondary. Immunodeficiency results from a failure or absence of elements of the immune system, including lymphocytes, phagocytes, and the complement system.
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