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Primary Immunodeficiencies - I
This Sqadia video illustrates about AIDS and other immunodeficiencies. Immune system is subject to failure of some or all of its parts. This failure can have dire consequences. When the system loses its sense of self and begins to attack host cells and tissues, the result is autoimmunity. By far the most common secondary immunodeficiency is acquired immunodeficiency syndrome, or AIDS, which results from infection with the human immunodeficiency virus 1 (HIV-1). A primary immunodeficiency may affect either adaptive or innate immune functions. Deficiencies involving components of adaptive immunity, such as T or B cells, are thus differentiated from immunodeficiencies in which the nonspecific mediators of innate immunity, such as phagocytes or complement, are impaired. Immunodeficiencies are conveniently categorized by the type or the developmental stage of the cells involved. Defects in more highly differentiated compartments of the immune system have consequences that are more specific and usually less severe. For example, an individual with selective IgA deficiency may enjoy a full life span, troubled only by a greater than normal susceptibility to infections of the respiratory and genitourinary tracts.
Primary Immunodeficiencies - II
The combined forms of lymphoid immunodeficiency affect both lineages and are generally lethal within the first few years of life; these arise from defects early in developmental pathways. Patients with these disorders usually are subject to recurrent bacterial infections but display normal immunity to most viral and fungal infections, because the T-cell branch of the immune system is largely unaffected. The family of disorders termed SCID stems from defects in lymphoid development that affect either T cells or both T and B cells. All forms of SCID have common features despite differences in the underlying genetic defects.
Primary Immunodeficiencies - III
SCID results in severe recurrent infections and is usually fatal in the early years of life. Although both the T and B lineages may be affected, the initial manifestation of SCID in infants is almost always infection by agents, such as fungi or viruses, that are normally dealt with by T-cell immunity. The B-cell defect is not evident in the first few months of the affected infant’s life because antibodies are passively obtained from transplacental circulation or from mother’s milk. The search for defects that underlie SCID has revealed several different causes for this general failure of immunity. A survey of 141 patients by Rebecca Buckley indicated that the most common cause (64 cases) was deficiency of the common gamma chain of the IL-2 receptor. There are other known defects that give rise to SCID. There is a defect characterized by depletion of CD8+ T cells that involves the tyrosine kinase ZAP-70, an important element in T-cell signal transduction.
Primary Immunodeficiencies - IV
The severity of this X-linked disorder increases with age and usually results in fatal infection or lymphoid malignancy. Initially, T and B lymphocytes are present in normal numbers. Wiskott-aldrich syndrome (WAS) first manifests itself by defective responses to bacterial polysaccharides and by lower-than-average IgM levels. A recently described immunodeficiency that falls into the mixed-cell category involves a defect in the receptor for interferon gamma. A B-cell defect called X-linked agammaglobulinemia (XLA) or Bruton’s hypogammaglobulinemia is characterized by extremely low IgG levels and by the absence of other immunoglobulin classes. Individuals with XLA have no peripheral B cells and suffer from recurrent bacterial infections, beginning at about nine months of age. A peculiar immunoglobulin deficiency first thought to result from a B-cell defect has recently been shown to result instead from a defect in a T-cell surface molecule. X-linked hyper IgM (XHM) syndrome is characterized by a deficiency of IgG, IgA, and IgE, and elevated levels of IgM.
Primary Immunodeficiencies - V
Common variable immunodeficiency (CVI) is characterized by a profound decrease in numbers of antibody-producing plasma cells, low levels of most immunoglobulin isotypes (hypogammaglobulinemia), and recurrent infections. A number of immunodeficiency states are characterized by significantly lowered amounts of specific immunoglobulin isotypes. Although not classified primarily as an immunodeficiency, ataxia telangiectasia is a disease syndrome that includes deficiency of IgA and sometimes of IgE. Other immunoglobulin deficiencies have been reported, but these are rarer. An IgM deficiency has been identified as an autosomal recessive trait. The syndrome is characterized by difficulty in maintaining balance (ataxia) and by the appearance of broken capillaries (telangiectasia) in the eyes.