drswapna
Forum Senior
Topics: 52
Posts: 129
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A small 9-month-old male with a history of recurrent pyogenic infections
is seen in a clinic. Immunoglobulin levels and a CBC are performed. The CBC
is normal except for slight neutropenia and thrombocytopenia.
Determination of immunoglobulin levels indicates elevated IgM,
but deficiencies of IgG and IgA. The underlying defect involves
which of the following molecules?
A. CD40 ligand (CD40L) on the T cell
B. CD40 molecule on the B cell
C. Gamma interferon
D. Interleukin-2 (IL-2)
E. Interleukin-3 (IL-3)
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| zerocool79
Forum Junior
Topics: 8
Posts: 75
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hmmm.. i'm confused...
A. and B. both seem correct to me...
correct me if i'm wrong, but isn't CD40L aka. CD 154 on the Th-cell is necessary to bind to the CD40 molecule on the B-cell for isotype switching to occur?
wouldn't that make both answers A and B correct?
I believe:
gamma-interferon activates macrophages
IL-2 is secreted by Th cells, and activates other Th cells.
IL-3 stimulates hematopoietic cells to proliferate
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| Doc2378
Forum Guru
Topics: 46
Posts: 688
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Good discussion there zerocool...
Since no isotype switching from IgM to IgG or IgA has occured here so it has to be A or B
I'd go with B assuming that any defect in T-cell would predispose the kid to other kinds of infections as well and not neccesarily 'pyogenic'...
May be its an oversimplification...anybody else?
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| reet
Forum Fanatic
Topics: 152
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i think its A... CUZ CD 40 lingand is required for class switching.. it could be defected here..
High levels of IgM.... -- CD40 molecules are intact
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| drk1980
Forum Guru
Topics: 147
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Agree wth REET. If this is Hyper IgM syndrome.....CD40L is mutated
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| drswapna
Forum Senior
Topics: 52
Posts: 129
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Reet & drk r right
Patient's with hyper-IgM syndrome (HIGM) experience very little, if any, isotype switching. The B cells in these patients cannot undergo the switch from IgM to IgG, IgA, or IgE that normally occurs during B-cell maturation. When B cells undergo isotype switching they require two factors: IL-4, which binds to a specific receptor on the B cell, and the CD40 molecule on the B-cell surface, which binds to the CD40 ligand (CD40L) on an activated T-cell surface. The deficiency is due to mutations in the CD40L. This immunodeficiency results in patients who are IgG- and IgA-deficient, but synthesize large amounts of polyclonal IgM. Affected individuals are susceptible to pyogenic infections, and often form IgM autoantibodies to neutrophils, platelets, or tissue antigens. The disease is inherited as an X-linked recessive in 70% of the cases.
The problem is due to mutations in the CD40L, not the CD40 molecule on the B cell (choice B).
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| sarika
Forum Guru
Topics: 195
Posts: 1,200
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If the problem is only in class switching, Why pyogenic infections in particular?
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| doc179
Forum Guru
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Posts: 1,217
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cos those organisms are processed by MHC 2 and cos the cell mediated immunity is intact there wont be any viral infection or infection by intracellular organisms
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