Untitled - D Ank Unlimited

selective IgM deficiency 643 selective theory
and asymptomatic or may exhibit some form of an associated
disease. IgA is the principal immunoglobulin in secretions and
is an important part of the defense of mucosal surfaces; thus,
IgA-deficient individuals have increased incidence of respiratory,
gastrointestinal, and urogenital infections. They may
manifest sinopulmonary infections and diarrhea. Selective IgA
deficiency is diagnosed by the demonstration of less than 5 mg/
dL of IgA in serum. The etiology is unknown but is believed to
be arrested B cell development. B lymphocytes are normal with
surface IgA and IgM or surface IgA and IgD. Some patients
also have IgG 2 and IgG 4 subclass deficiencies and are likely to
develop infections. IgA-deficient patients show increased incidence
of respiratory allergies and autoimmune diseases such as
systemic lupus erythematosus (SLE) and rheumatoid arthritis.
The principal defect is in IgA B lymphocyte differentiation.
A 12-week-old fetus reveals the first IgA B lymphocytes that
bear IgM and IgD as well as IgA on their surfaces. At birth, the
formation of mature IgA B lymphocytes begins. Most IgA B
cells express IgA exclusively on their surfaces, with only 10%
expressing surface IgM and IgD in adults. Patients with selective
IgA deficiency usually express the immature phenotypes,
only a few of which can transform into IgA-synthesizing
plasma cells. Patients have increased incidence of HLA-A1,
-B8, and -Dw3. Their IgA cells form but do not secrete IgA.
The incidence of the disorder is increased in certain atopic
individuals. Some patients with selective IgA deficiency form
significant titers of antibody against IgA. They may develop
anaphylactic reactions upon receiving IgA-containing blood
transfusions. They exhibit increased incidence of celiac disease
and several autoimmune diseases as noted above. They synthesize
normal levels of IgG and IgM antibodies. Autosomalrecessive
and autosomal-dominant patterns of inheritance have
been described. The deficiency has been associated with several
cancers including thymoma, reticulum cell sarcoma, and
Direct template
T AG
T
AB
AB
Indirect template
T
T
AB
Natural selection
T-1
G1-1
T-2
G1-2
T-2
+
+
AG
AG
squamous cell carcinoma of the esophagus and lungs. Certain
cases may be linked to drugs such as phenytoin or other anticonvulsants.
Some individuals develop antibodies against IgG,
IgM, and IgA. γ globulin should not be administered to patients
with selective IgA deficiency.
selective IgM deficiency
Immunoglobulin M (IgM) is absent from the serum.
Although IgM may be demonstrable on plasma cell surfaces,
it is not secreted. This condition may be related to an
alteration in secretory peptide or arise from the actions of
suppressor T lymphocytes specifically on IgM-synthesizing
and -secreting cells. Gram-negative microorganisms may
induce septicemia in affected individuals, as the major role
of IgM in protection against infection is in the intravascular
compartment rather than in extravascular spaces where
other immunoglobulin classes may be active.
selective immunoglobulin deficiency
An insufficient quantity of one of the three major immunoglobulins
or a subclass of IgG or IgA. The most common is
selective IgA deficiency followed by IgG 3 and IgG 2 deficiencies.
Patients suffering from selective immunoglobulin
deficiency may appear normal or manifest increased risk for
bacterial infections.
selective theory
A hypothesis describing antibody synthesis as a process
in which antigen selects cells expressing receptors specific
for that antigen. The antigen–cell receptor interaction leads
to proliferation and differentiation of a clone of cells that
synthesizes significant quantities of antibodies of a single
specificity. Selective theories included the 1899 side chain
theory of Paul Ehrlich, the natural selection theory proposed
by Niels Jerne in 1955, and the cell selection theory Talmage
and Burnet proposed in 1957. Burnet named his version the
clonal selection theory of acquired immunity; its basic tenets
T AG T + AG
+ AG
G1-2 +
T-2
T-2
+
No reaction
Comparison of template with natural selection theories of antibody synthesis.
T
T
T
AG
AB
T-2
T-2
G1-2
T-2
G1-2
S