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Type I hypersensitivity
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Immune thrombocytopenic purpura
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Hemolytic disease of the newborn
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Blood transfusion reactions and transplant rejection: Pathology review
Immunodeficiencies: T-cell and B-cell disorders: Pathology review
Immunodeficiencies: Combined T-cell and B-cell disorders: Pathology review
Immunodeficiencies: Phagocyte and complement dysfunction: Pathology review
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chromosome affected p. 62
agammaglobulinemia p. 114
agammaglobulinemia p. 114
Tanner Marshall, MS
Samantha McBundy, MFA, CMI
With X-linked agammaglobulinemia, or XLA for short, gamma globulin is another name for immunoglobulin, which is another name for antibodies, a- means without, and -emia refers to the blood.
So this is a disease where there aren’t any antibodies in the blood, and X-linked means that it’s caused by a gene mutation on the X chromosome.
Now, normally, immunoglobulins are secreted into the blood by plasma cells, which are fully matured or differentiated B cells, a type of immune cell.
Way before that ever happens, though, those B cells start out in the bone marrow as pluripotent stem cells, pluripotent meaning that they can develop into a number of different types of cells.
But to become a B cell, first that pluripotent stem cell differentiates into a lymphoid precursor cell, then a pro-B cell, then a pre-B cell, then an immature B cell which migrates from the bone marrow to the spleen, where it becomes a mature or naive B cell, which after being exposed to the right antigen, moves into the blood or lymph and becomes an antibody-secreting plasma cell.
In XLA, this maturation process stops at the pre-B cell stage.
Why does it do that? Well, by the immature B cell stage, it has a B cell receptor, which is a membrane-bound antibody, specifically an immunoglobulin M or IgM.
But in the Pre- and Pro-B cell stages, this B cell receptor’s still being assembled, once it’s finished, it’s made up of heavy chain and light chain protein subunits, and the heavy chains are put together first.
Since it hasn’t been fully assembled yet, this IgM’s known as a pre-B cell receptor.
Now, an enzyme called bruton’s tyrosine kinase is super important for both the development and normal functioning of the B cell receptor.
X-linked agammaglobulinemia (XLA) is an x-linked genetic disorder of the immune system caused by mutations in the BTK (Bruton's tyrosine kinase) gene. XLA primarily affects males, as they only have one X chromosome, while females have two and are typically carriers of the mutated gene. Individuals with XLA have a deficiency in B cells. This results in an inability to mount an effective immune response against bacterial infections, leading to recurrent and often severe infections, especially of the respiratory tract and ears. The symptoms of XLA typically appear in early childhood, and affected individuals may experience recurrent bacterial infections, chronic diarrhea, and failure to thrive.
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