Immunoglobulin vs antigen receptor? Q14 NS#4 exam

[Smelt]

This question describes a macrophage that can be inhibited by anti-CR3 antibodies

Question is whether CR-3 is is an immunoglobulin or an antigen receptor.

I'm a bit confused because immunoglobulin=antibody which can be presented on a surface or free floating and it recognizes antigens. How is this different than an antigen receptor? They are two separate answer choices. Immunoglobulins aren't only free floating are they? Arent antibodies antigen receptors?

This was their explanation: with B=antigen receptor. A=immunoglobulin.

"B is correct. The passage states that CA macrophage phagocytosis can be inhibited by blocking CR-3. Since this inhibition involves antibodies, we know that CR-3 must “live” in the membrane and face the exterior, meaning that it is likely to be some kind of receptor. Phagocytosis in macrophages occurs after the macrophage has identified its target via antigen receptors. Without an antigen receptor, the macrophage is effectively blind to pathogens (or, in this case, myelin).



A: This is tempting, but the final paragraph states that the phagocytosis was inhibited by anti-CR3 antibodies (immunoglobulins), not that CR3 is an antibody itself. Note that macrophages do not produce antibodies."

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[Pono_0001]

CR5 is a complement receptor, but you don't need to know that to answer the question correctly.

even if you get confused about if they are talking about membrane bound or secretory immunoglobin, antigen receptor will always be the better choice due to the lack of confusion.

 

[Smelt]

CR5 is a complement receptor, but you don't need to know that to answer the question correctly.

even if you get confused about if they are talking about membrane bound or secretory immunoglobin, antigen receptor will always be the better choice due to the lack of confusion.

Okay got it. But antigen receptor = membrane bound immunoglobin/antibody always or not necessarily?

 

[Pono_0001]

Okay got it. But antigen receptor = membrane bound immunoglobin/antibody always or not necessarily?

not always. my understanding is that membrane bound immunoglobin is only for B cells, since it's the cells that produces antibodies, other cells have other receptor to binds to antigen