UW Immuno Q - chilandru81

[ArchivalUser]

A 6 year old boy with a history of recurrent lower respiratory tract infections presents with persistent diarrhea. He is found to have low serum levels of a specific immunoglobulin type, and Giardia Lamblia is isolated from duodenal aspirated. This patient is most likely deficient in cells bearing which of the following markers?
A) CD 15
B) CD 19
C) CD 4
D) CD 8
E) CD 16

[ArchivalUser]

bb

[ArchivalUser]

? CD19 - Common variable hypogammaglobulinemia

[ArchivalUser]

B) CD 19

[ArchivalUser]

Answer mentioned in U World is B) CD 19 simply because it is the only B cell marker out of the above choices.

Here is the explanation from UW: This patients history and lab suggests IgA deficiency. B cell synthesize all;type of Ab including IgA. All the choice mentioned in the question are T-cell surface markers except CD 19 which is a B cell surface marker. CD 20 and CD 21 are other B cell surface markers. X-linked agammaglobulinemia (XLA) is B cell immunodeficiency diorder with low levels of immunoglobulins including IgA.

When i was doing this question, i selected CD 4 even though i knew CD 19 is the B cell marker: my reasoning- sinus and pulmonary infection + Diarrhea (giardiasis) is clearly IgA deficiency. Now, in order to have low IgA levels there should be a problem in the class switching in the B cells. B cell class switching requires : signal 1 (IL-4, IL-5, IL-6 from Th2 cell) and signal 2 (CD40 receptor activation by binding CD 40 ligand on Th cell). Therefore Th cell (CD 4) plays a major role is this. CD 19 on B cell don't do anything, so why is CD 19 the correct answer????????

My knowledge is strictly limited to FA,so anyone who has read Immunology in detail, please clear my concept.

Thank you!!

[ArchivalUser]

i think this is Selectve immunogl deficiency which is dysfunction of b cell..so CD19
i am not sure how to pick between Cd19 n CD20(if it were in choice?) I remeber it as b-cell deficeincy=cd19 or cd20
Can some 1 explain?

[ArchivalUser]

This patient has a mucosal surface pathogen : Giarda Lamblia. It also mentions he is low in a specific immunoglobulin. Therefore you are right docmp. He has "Selective IgA Deficiency". There is a dysfunction in B Cells and the only B Cell marker listed above is CD 19.

[ArchivalUser]

@docmp & ddl: Selective IgA Deficiency is possibly due to a defect in isotype switching not due to defect in B cells per se. T helper cells (CD4) release IL 4,5 which stimulate the production of IgE & IgG (IL-4) and IgA (IL-5) from IgM. If cells bearing CD4 marker (T helper cells) are deficient, IgA production will be halted. so wjy is the answer CD19??