Immuno antibody response concept

[aspiringmd1015]

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as we all know, b cells are antigen presenting cells as well, but if you wanted to elecit a humoral response (usually to extracellular antigens) will the antigen presenting cell always be a B cell? or can it also be dendritic/macrophages which present cells to b cells?

 

[EazyE1907]

as we all know, b cells are antigen presenting cells as well, but if you wanted to elecit a humoral response (usually to extracellular antigens) will the antigen presenting cell always be a B cell? or can it also be dendritic/macrophages which present cells to b cells?

or can it also be dendritic/macrophages which present cells to b cells?

No I'm pretty sure dendrites/macs don't present to b cells. only because these are part of the cell mediated/ innate response , whereas B-cells since they secrete AB's and such are humoral and adaptive.

will the antigen presenting cell always be a B cell?

And yeah pretty much. If that b-cell wants to be able to class switch then yes.

The other thing is that you can have a b-cell engulf antigen on it's own and in response switch into a ab secreting plasma cell. But in this case the ONLY Ig it would be able to express would be IgM on it's surface. this is because it's lacking the c0-stimulatory 2ndary signal from presenting it's antigen to the T-cell.

hope this helps and makes sense!

 

[aspiringmd1015]

thanks! but if i wanted to elicit a humoral response, one of my books shows that a macrophage is prsenting to a t cell, adn then the b cell becomes involved via cytokines secreted by the th2 t cell itself, so the b cell in this case isnt the antigen presenting cell. this confused me because i didnt understand how the idiotype of that b cell could correspond to that initial antigen that was initially engulfed and processed by the macrophage, but i looked at a diff diagram and it showed that the macrophage had engulfed the antigen and presented it with mhc2 to the t cell, the B cell also had the same antigen attatched to it via igM. so i guess a B cell humoral response can be stimulated both ways, as it it being the primary antigen presenting cell, and also not being the APC. If im incorrect let me know, it was bugging the **** out of me lmao

 

[EazyE1907]

thanks! but if i wanted to elicit a humoral response, one of my books shows that a macrophage is prsenting to a t cell, adn then the b cell becomes involved via cytokines secreted by the th2 t cell itself, so the b cell in this case isnt the antigen presenting cell. this confused me because i didnt understand how the idiotype of that b cell could correspond to that initial antigen/QUOTE]

yeah, I'm not sure maybe the diagram was wrong or you interpreted it wrong. Either way, the only way a b-cell can become involved is if it presents an antigen to an activated t-cell. which later lead to a 2ndary signal allowing for class switching.

 

[aspiringmd1015]

only posting this to clear the concept

 

[SBR249]

You do want to be careful. During the germinal center reaction, B cells undergoing somatic hypermutation will require follicular dendritic cells because FDCs present antigens on their surface that the B cells use to test antigen binding affinity. Those B cells that fail to generate high affinity antibodies would then die because they cannot adequately compete for survival signals.

This might be too much detail for Step 1 but it is still important.

But to answer your original question, the humoral response may actually involve multiple steps with multiple antigen-presentation stages

1. B cell encounters and recognizes an extracellular antigen via the B cell receptor. Antigen binding then causes activation of B cell as well as internalization and antigen processing for MHC presentation

2. Macrophages/dendritic cells independently ingest the same extracellular antigen and presents it to T cells causing T cell activation and differentiation into T helper cells. This step happens concurrently with #1

3. The activated T cell then encounters the activated B cell which is presenting processed antigen on its surface. The activated T cell then recognizes antigen on B cell surface and secretes cytokines.

Step 2 is optional because the T cell in step #3 could be naive as well. But it just shows that macrophages/DCs could be involved.

 

[aspiringmd1015]

so without B cells presenting them, they cant be involved in the humoral response? as in if a macrophage/dendritic cells presents an antigen to a helper t cell, which then becomes th2, which then secretes il 4 and 5 ultimately forming activated B cells which undero class switching and somatic hypermutation, and while this happened the B cell also had independently bound the antigen via IgM, so it has the corresponding idiotype to respond to the antigen in the first place?

 

[aspiringmd1015]

one of the big diff is igM on the surface of B cells when coming in contact with antigens, the antigens can be of a variety of structures, proteins, sugars, nucleic acids, etc. Other apc's can only present peptides bc loading them onto MHC requires them to be protein in nature. Hope this helped

 

[SBR249]

Not sure what you mean, even when B cells act as APCs they still present antigens on MHCs. The surface BCR is solely for purposes of activating the B cell itself and internalizing the antigen.

 

[dyspareunia]

as we all know, b cells are antigen presenting cells as well, but if you wanted to elecit a humoral response (usually to extracellular antigens) will the antigen presenting cell always be a B cell? or can it also be dendritic/macrophages which present cells to b cells?

Any of the APCs can be involved. What determines humoral vs cell mediated is cytokines.