Case 1: X-linked Agmmaglobulinemia 1. Bill was will for the first 10 months of t

Question

Case 1: X-linked Agmmaglobulinemia

1. Bill was will for the first 10 months of this life. how do explain this

2. Patients with immunodeficiency diseases should never be given live viral vaccines. Several male infants with X-linked agammaglobulineia have been given live oral polio vaccine and have developed paralytic poliomyelitis. What sequence of events led to the development of polio in these boys?

3. Bills recurrent infections were due almost exclusively to Streptococcus and Haemophilus species. Theses bacteria have a slimy capsule composed primarily of polysaccharide polymers, which protect them from all direct attack by phagocytes. Humans make IgG2 antibodies against theses polysaccharide polymers. The IgG2 antibodies opsonize the bacteria by fixing complement on their surface, thereby facilitating the rapid uptake of theses bacteria by phagocytic cells. What other genetic defect in the immune system might clinically mimic X-linked agammaglobulinemia?

Explanation / Answer

1. X-linked agammaglobulinemia is a genetic disorder caused by a defect in the gene encoding Brutons kinase (Btk), which is crucial for development of B-cells. This leads to no production of antibodies in children harbouring this mutation, and antibodies are important for eliminating and killing many microbes. In the abscence of these antibodies in patients suffering from X-linked agammaglobulinemia, they suffer from recurring infections with Streptococcus pneumonia, Haemophilus influenzae, and many viruses during their early age. Hence Bill was ill for the first 10 months of his life.

2. Live oral polio vaccines contains live attenuated polivirus. This vaccine activates both B and T cells thereby activating both arms of immunity: humoral and cell mediated, in the intestine. Antibodies effectively neutralize these attenuated virus particles, present in the gut. Whereas, boys with X-linked agammaglobulinemia lacks mature B cells, hence they cannot mount a humoral or antibody response against the attenuated virus, giving it a chance to recombine and become virulent and causing neurological infection.

3. Defect in the complement proteins can also mimic X-linked agammaglobulinemia. Bacteria coated with antibody molecules, leads to complement fixation and after sequential activation of a number of complement molecules, makes membrane attack complex on the bacteria leading to lysis of bacterium.It also aids in uptake of bacteria by phagocytic cells by opsonizing the bacteria.

Deficiency of any one of the complement proteins such as Properdin deficiency can lead to increased incidence of bacterial infections.

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