T-cell activation

[SaintJude]

---

Members don't see this ad.

Mini-Paragraph

X-linked hyper-IgM syndrome is a disease caused by the absence of CD40 ligand. This ligand is responsible for T-cells binding to naive B-cells and macrophages. When T-cells are activate by antigens, CD40L is expressed on their surface. Binding of CD40L to CD40 on B-cells stimulates isotope switching in the B-cells and stimulates macrophages to kill phagocytosed microbes.

Q: Blood group antigens (A & B) stimulate B-cells. Will a child with X-linked hyper IgM immunodefiencey produce antibodies to their antigens (assuming the child is blood type O?)

A. No b/c immunodeficenty people cannot produce antibodies
B. No b/c the defect is in the B-cell's response to antigens
C. Yes, b/c the defect is in the T-cell response to antigens
D. Yes b/c the defect is in the T-cell activation of B-cells

How do you choose b/w C & D ?

 

[NeverADoubt]

"absence of CD40 ligand" So this is the defect.

"When T-cells are activate by antigens, CD40L is expressed on their surface" - so this CD40L is not the same as CD40.

"Binding of CD40L to CD40 on B-cells stimulates...."

Putting these three lines together, the defect is not in CD40L, which means the T-cells do properly respond to antigens. But because they can not bind to the misexpressed/nonexpressed CD40 on B-cells, then the answer is D.

Is that clear?

 

[SaintJude]

Nevermind--Edit: Oops, hadn't seen your post until I posted myself. Thanks for the response though!

I see now. The passage actually suggests that CD40L is expressed as a result of antigens activating T-cells (through some unstated process).

Also should have known since passage set up answer by focusing on the fact that the ligand is "responsible for T-cells binding to naive B-cells and macrophages"