Immuno Q

[Aconitase]

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Hi All,

I know this may seem like an easy concept to some, but I am having a hard time understanding the difference in the role between signalling in the CD40L and CD40 pathway and the B7 and CD28 pathway. Both seem to do the same thing, in that they help make new isotypes. Is there a difference between when they are used? Thanks.

 

[Phloston]

Hi All,

I know this may seem like an easy concept to some, but I am having a hard time understanding the difference in the role between signalling in the CD40L and CD40 pathway and the B7 and CD28 pathway. Both seem to do the same thing, in that they help make new isotypes. Is there a difference between when they are used? Thanks.

B7 is found on your APCs (i.e. B-cell, macrophage, dendritic cell [e.g. Langerhan cell]). CD28 is found on your Th0-,1- and 2-cells. That interaction is secondary to MHC-II interacting with TCR, and is necessary for activating the Th0-, 1- or 2-cells, period. No class-switching has occurred at this point. If the APC is a B-cell, it will activate a Th2-cell, and the Th2-cell will in turn activate the B-cell so that it can begin producing IgM (macrophages, for instance, interact with Th1-cells, instead of Th2s). However once again, the B-cell hasn't received any signal to class-switch yet (i.e. to make different isotypes).

When different Ig classes are needed, a Th2-cell displays its CD40-L (CD154) to the B-cell's CD40. That's the first signal. The second one is an IL-4 for IgE class-switching; IL-5 is for IgA class-switching. The Th2-cell also secretes IL-6 and -13, but those aren't directly involved in class-switching as far as I'm aware.

 

[thehundredthone]

CD40L-40 is your main class switching signal. It's the one that is defective in Hyper IgM syndrome.

B7-CD28 is a costimulatory signal required for the transcription of cytokine genes.

Also, these two together are usually not enough to hold cells together, and that's where LFA3-CD2 comes into play, and causes the actual IL release. At least that's what I've written down.

 

[Phloston]

Basically the OP just needs to know that there's a two-signal interaction needed for the B-cell and Th2-cell to activate one another. However this has nothing to do with class-switching.

When class-switching occurs, there's another (and different) two-signal interaction that's needed.

 

[thehundredthone]

When class-switching occurs, there's another (and different) two-signal interaction that's needed.

B7-CD28 is a part of class switching too, so says FA anyway.

 

[Phloston]

B7-CD28 is a part of class switching too, so says FA anyway.

B7-CD28 is the standard Th2-B-cell secondary signal. You'll see it whenever those two cells interact.

I'm fairly sure we've covered the bases here though regardless.

 

[Aconitase]

thanks guys, i really appreciate the help! 🙂

 

[Zzmed]

I know this thread is kind of old but i want to clarify...

B7-CD28 interaction occurs only in Helper T cell activation.
CD40-CD40L interaction occurs only in B cell activation and class switching.
Am i right?

FA errata crosses out B7-CD28 from B cell activation and class switching process so we will not see it whenever those two cells interact. They are completely two different stories.. (Right Phloston?)

 

[Phloston]

I know this thread is kind of old but i want to clarify...

B7-CD28 interaction occurs only in Helper T cell activation.
CD40-CD40L interaction occurs only in B cell activation and class switching.
Am i right?

FA errata crosses out B7-CD28 from B cell activation and class switching process so we will not see it whenever those two cells interact. They are completely two different stories.. (Right Phloston?)

F***ing FA errata. Wow.

Quite frankly, I had thought that the B7-CD28 signal was omnipresent for B- and Th-cell interactions specifically based off of FA saying it also occurs during class-switching. Because if it occurs during class-switching, then it makes sense that it would be a "standard" signal. But if you say the FA errata crossed it out for class-switching, then I guess we'd only see it with B-cell activation.

I had gone through the errata once back in May. But I'm pretty annoyed that the updates they've made since then have been pretty significant.

 

[Zzmed]

When FA errata says that something is wrong doesn't mean that it is actually wrong.. Under certain circumstances it may be valid...
But do not risk it.. Be on the safe side.

Hey Phloston will you be visiting the step I forum after you're done with the exam?
We all need some backup from you man.

 

[Phloston]

When FA errata says that something is wrong doesn't mean that it is actually wrong.. Under certain circumstances it may be valid...
But do not risk it.. Be on the safe side.

Hey Phloston will you be visiting the step I forum after you're done with the exam?
We all need some backup from you man.

Hah, I appreciate you saying that. It's like when they talk about economic policy: supposedly the best predictor of the subsequent year is the results of the previous year. Meaning: I've noticed the trend over the course of this year that the vast vast majority of people who sit this exam pretty much disappear forever from this forum, even if they were hardcore posters beforehand. Occasionally ijn, kaputt or mrbeauregard will randomly make an appearance, so I too will probably pop my head in every once in a while, but I think it's just that there's so much time involved with this exam, that once it's over with, everyone's pretty much stoked to have it behind them forever. And you too will move on to bigger and better things eventually, even if Step1 is the most important thing in your life right now. Can't wait till this thing is over with haha.

 

[Old Style Nanny]

Hah, I appreciate you saying that. It's like when they talk about economic policy: supposedly the best predictor of the subsequent year is the results of the previous year. Meaning: I've noticed the trend over the course of this year that the vast vast majority of people who sit this exam pretty much disappear forever from this forum, even if they were hardcore posters beforehand. Occasionally ijn, kaputt or mrbeauregard will randomly make an appearance, so I too will probably pop my head in every once in a while, but I think it's just that there's so much time involved with this exam, that once it's over with, everyone's pretty much stoked to have it behind them forever. And you too will move on to bigger and better things eventually, even if Step1 is the most important thing in your life right now. Can't wait till this thing is over with haha.

I'm sure this part of the forum will miss your constant presence. Think about sticking around here until the coming summer or so at least when the majority of the current batch preparing for the step 1 would take their exams. Surely they'll appreciate you giving back to the forum even after you are done with your exam.

And, speaking of the exam, all the best for it!

 

[Phloston]

I'm sure this part of the forum will miss your constant presence. Think about sticking around here until the coming summer or so at least when the majority of the current batch preparing for the step 1 would take their exams. Surely they'll appreciate you giving back to the forum even after you are done with your exam.

And, speaking of the exam, all the best for it!

OldStyleNanny, you seem to have really great contributions yourself, and you're still early in your prep. Don't be surprised to find that you're the big poster on here by the time you take the real deal. Slow transitions.

 

[Zzmed]

You know, it does not have to do with big posters, but with true contributors. You guys just happen to be both.

I understand what you're saying, not wanting to hear anything related to the exam after you're done with it. But, as old style nanny said, this forum will miss your constant presence.

But you're right. Eventually we will move on to better and bigger things.

Good luck with your exam Phloston! Give us some feedback afterwards.