Immuno Question

[IllinoisStudent]

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There is T cell dependent and independent activation of B cells. In T-cell dependent activation of B cell, can any Th cell activate B cells, or only the activated Th cell (Th cell that has encountered the antigen) can activate the B cells?

If only activated Th cell can activate the B cells, then is it required that the Th cell encounter the same antigen, or can it be activated by any antigen?

 

[fancymylotus]

There is T cell dependent and independent activation of B cells. In T-cell dependent activation of B cell, can any Th cell activate B cells, or only the activated Th cell (Th cell that has encountered the antigen) can activate the B cells?

If only activated Th cell can activate the B cells, then is it required that the Th cell encounter the same antigen, or can it be activated by any antigen?

CD4-T cells (Th1), someone correct me if I am mistaken, must first be exposed to a specific antigen before these release particular cytokines to stimulate B-cells to become activated.

I don't understand your second question--"same antigen?"

 

[IllinoisStudent]

CD4-T cells (Th1), someone correct me if I am mistaken, must first be exposed to a specific antigen before these release particular cytokines to stimulate B-cells to become activated.

I don't understand your second question--"same antigen?"

What u said in the first part is true. However, cytokines are released to mainly attract/stimulate neutrophils and macrophages among others. Cytokines alone don't activate naive B cells in T cell dependent activation. Otherwise, NK cells also release cytokines.

I was refering to the CD40-CD40L interaction between naive/virgin B cell and T cell. I did some research and found out that only activated Th cells can activate naive B cells that have also encountered the antigen.

I will elaborate on my second question. Let's say the body is infected with antigen X. Can the B cell that recognizes antigen X be activated any activated Th cell (there are numerous Th cells in the body that can be activated by many different antigens other than X, say Y or Z ) or does it need to be activated by Th cell that also recognizes the antigen X? I know this is confusing.... In short, can the B cell that recognizes antigen X be activated by Th cell that recognizes antigen Y or Z?

 

[twinklz]

Are you talking about different epitopes of the same antigen or completely different antigens?

A T cell activated due to X (the flu) cannot activate a B cell specific for Y (leprosy). There's a specific name for this phenomenon but I don't remember it.

The only cell capable of activating a naive T cell is a dendritic cell (interdigitating not follicular). Once this cell has been activated it can help in activating a B cell, but only if it recognizes the peptide presented by the MHC. Please correct me if I'm wrong; its been a whopping 3 weeks since my final and I've forgotten a lot.

 

[microgin]

Are you talking about different epitopes of the same antigen or completely different antigens?

A T cell activated due to X (the flu) cannot activate a B cell specific for Y (leprosy). There's a specific name for this phenomenon but I don't remember it.

The only cell capable of activating a naive T cell is a dendritic cell (interdigitating not follicular). Once this cell has been activated it can help in activating a B cell, but only if it recognizes the peptide presented by the MHC. Please correct me if I'm wrong; its been a whopping 3 weeks since my final and I've forgotten a lot.

You were correct... don't underestimate that memory power 🙂

The phenomenon you are referring to is known as "linked recognition", i.e. the activation of B cells by helper T cells that respond to the SAME antigen. In a nutshell, before B cells can be induced to make Ab to a pathogen, a CD4 T cell specific for peptides from this pathogen must first be activated, usually through interaction with a dendritic cell. While the antigen recognized must be the same, the epitopes of that antigen recognized by the activated T helper cell and B cell DO NOT have to be the same.

As far as the CD40/CD40L interaction goes, it serves as the second signal, which in conjunction with the signal generated by mIg crosslinkage on the B cell, drives the B cell into the G1 phase of the cell cycle.

Hope this helps!!

 

[fancymylotus]

What u said in the first part is true. However, cytokines are released to mainly attract/stimulate neutrophils and macrophages among others. Cytokines alone don't activate naive B cells in T cell dependent activation. Otherwise, NK cells also release cytokines.

I was refering to the CD40-CD40L interaction between naive/virgin B cell and T cell. I did some research and found out that only activated Th cells can activate naive B cells that have also encountered the antigen.

I will elaborate on my second question. Let's say the body is infected with antigen X. Can the B cell that recognizes antigen X be activated any activated Th cell (there are numerous Th cells in the body that can be activated by many different antigens other than X, say Y or Z ) or does it need to be activated by Th cell that also recognizes the antigen X? I know this is confusing.... In short, can the B cell that recognizes antigen X be activated by Th cell that recognizes antigen Y or Z?

I am quite certain that CD4 T-cell Th2 cytokine activate B-cells to produce IgE. From this one can conclude that the B-cells must already have been exposed to the specific pathogen! 🙂

 

[Rendar5]

I am quite certain that CD4 T-cell Th2 cytokine activate B-cells to produce IgE. From this one can conclude that the B-cells must already have been exposed to the specific pathogen! 🙂

IgE and IgG3 are induced by IL-4 and IL-10 (I think it was 10?, 4 is definite), which are released by Th2 cells upon activation. They're also released by other cells, like eosinophils or macrophages, I forget which, which is why allergies (type 1) are self-sustaining, and htis is what allergy shots interfere with. B cells and other APC's always have to find Th cells that also recognize the antigen for activation. Anything I missed?

I need to go back over immuno before I forget it. It's been my favorite subject so far.

 

[IllinoisStudent]

You were correct... don't underestimate that memory power 🙂

The phenomenon you are referring to is known as "linked recognition", i.e. the activation of B cells by helper T cells that respond to the SAME antigen. In a nutshell, before B cells can be induced to make Ab to a pathogen, a CD4 T cell specific for peptides from this pathogen must first be activated, usually through interaction with a dendritic cell. While the antigen recognized must be the same, the epitopes of that antigen recognized by the activated T helper cell and B cell DO NOT have to be the same.

As far as the CD40/CD40L interaction goes, it serves as the second signal, which in conjunction with the signal generated by mIg crosslinkage on the B cell, drives the B cell into the G1 phase of the cell cycle.

Hope this helps!!

ditto. dats wat I was looking for. The answer just gives rise to one more question. How does the CD4+ T cell know which B cell to activate even though it recognizes different epitope than the corresponding B cell. I will try finding the answer to this one myself. Meanwhile, if anyone feels generous, they can help me enlighten myself.

Thanks to all those who tried to help.

 

[Rendar5]

ditto. dats wat I was looking for. The answer just gives rise to one more question. How does the CD4+ T cell know which B cell to activate even though it recognizes different epitope than the corresponding B cell. I will try finding the answer to this one myself. Meanwhile, if anyone feels generous, they can help me enlighten myself.

Thanks to all those who tried to help.

It activates whatever cell presents it with the activating antigen. The inactive B cell, like any good APC, seeks out the appropriate T cell as soon as it has something to present.

 

[Rendar5]

ditto. dats wat I was looking for. The answer just gives rise to one more question. How does the CD4+ T cell know which B cell to activate even though it recognizes different epitope than the corresponding B cell. I will try finding the answer to this one myself. Meanwhile, if anyone feels generous, they can help me enlighten myself.

Thanks to all those who tried to help.

It activates whatever cell presents it with the activating antigen. The inactive B cell, like any good APC, seeks out the appropriate T cell as soon as it has something to present.