Q NBME F1 S4, plz explain

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Q NBME F1 S4, plz explain

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10 Posts

nadiabarati

03/14/06 - 07:31 AM

A 5-year-old boy with a history of recurrent ear infections receives his preschool booster immunization against diphtheria-tetanus-pertussis. He is participating in a community-sponsored study to determine the humoral immune response to tetanus toxoid (tt). His response is well below normal for age- and sex-matched children. Peripheral B lymphocyte count and T lymphocyte count and function are within the reference range. The antibody he makes is positive in both the passive hemagglutination and complement-mediated lysis of tt-coated erythrocytes. His antibodies do not opsonize tt-coated latex particles for phagocytosis and do not directly precipitate tt efficiently. This child most likely has a defect in which of the following processes? A-Affinity maturation of immunoglobulins
B-Immunoglobulin isotype switching
C-Recombination of heavy chain variable region genes
D-Recombination of light chain variable region genes
E Somatic mutation of immunoglobulin genes

skyhigh
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03/14/06 - 12:16 PM

maybe A due to lack of IgG confused

doc179
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03/14/06 - 12:18 PM

its B

doc179
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03/14/06 - 12:22 PM

Peripheral B lymphocyte count and T lymphocyte count and function are within the reference range. The antibody he makes is positive in both the passive hemagglutination and complement-mediated lysis of tt-coated erythrocytes.IgM is secreted normally and hence there is complement mediated lysis..
His antibodies do not opsonize tt-coated latex particles for phagocytosis ...IgG is necessary for opsonisation and thats deficient...

skyhigh
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03/14/06 - 12:23 PM

is it b/c of lack of class switch to IgA? can you explain, plz.

robin082006
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03/14/06 - 12:25 PM

How about B skyhigh?

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robin082006
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03/14/06 - 12:26 PM

I go with B

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skyhigh
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03/14/06 - 12:33 PM

from my understanding, IgM can isotype switch to IgE

and IgG can isotype switch to IgA.

so, if there is no IgG to begin with, how can there be a" defect in isotype switching?"

doc179
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03/14/06 - 12:47 PM

opsonization needs IgG and C3b...the primary response to any infection is by secreting IgM and then the plasma cell switches class to the relevant immunoglobulin..and that can be either A or E or G ....someone pls correct me if I am wrong

pawan.dr
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03/23/06 - 11:39 PM

#10

doc 179 is right, it is B

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