USMLE Immunology question

[aspiringmdgirl]

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Hello,
I'm a fob M1 so please excuse me if this question is too basic...

In thymus-independent antigens, I understand that there is no class switching because there is no helper T cell involvement. But why isn't there a immunogenic memory for this process?
Why wouldn't memory B cells get generated in this process?

Also, when one says "memory" B cell, does that mean, in the subsequent exposure to the antigen, the memory B cell can skip the whole activation and class switching steps and immediately ready to produce the necessary Ig with high affinity for that antigen?

Lastly, When one says memory T cells, does that mean effector T cells are rapidly available to go activate cytotoxic T cells without going through the initial T-cell activation steps involving dendritic cells?

Thank you!!

 

[aprilfools]

Memory B cells are only generated in a germinal center reaction. For a germinal center reaction to take place, you need a CD4 to stimulate the naive B cell to say "hey go over into the follicle to mature and figure your **** out and recognize this thing i found".

Your specific question about what exactly a memory B cell does is more or less correct.

To be honest I have never heard of memory T cells in a classroom setting. FA doesn't talk about them at all except to say they exist on one small page so I probably wouldn't worry about a memory T cell specifically, beyond the fact that memory cells produce a quicker immunologic response upon subsequent exposure to an antigen.

 

[DerpStore]

Hello,
I'm a fob M1 so please excuse me if this question is too basic...

In thymus-independent antigens, I understand that there is no class switching because there is no helper T cell involvement. But why isn't there a immunogenic memory for this process?
Why wouldn't memory B cells get generated in this process?

Also, when one says "memory" B cell, does that mean, in the subsequent exposure to the antigen, the memory B cell can skip the whole activation and class switching steps and immediately ready to produce the necessary Ig with high affinity for that antigen?

Lastly, When one says memory T cells, does that mean effector T cells are rapidly available to go activate cytotoxic T cells without going through the initial T-cell activation steps involving dendritic cells?

Thank you!!

aprilfools is correct about memory b cells.

Memory t cell differentiation is complicated and how this happens is up for debate.

At least for CD8+ t cells, upon recognition of cognate antigen by TCR, there are two main hypotheses. One is that there is asymmetric cell division, where one daughter cell goes on to become long-lived memory, and the other short-lived effector. The other is that upon TCR activation, subsequent progeny cells become effector, and some of these stay alive and become memory. The latter is the leading hypothesis. "Effector" means terminal differentiation (although in the second hypothesis, some of these effectors are capable of de-differentiation, likely through epigenetic mechanisms) with short life span, destined for "contraction" (ie mass apoptosis) after antigen clearance, whereas "Memory" are capable of homeostatic proliferation without antigen.

The memory CD8s are split into Central Memory (CCR7+, which circulate in the lymphatics waiting for antigen to be delivered and proliferate rapidly in response to rechallenge), Effector Memory (CCR7-, which circulate in periphery, divide poorly in response to rechallenge), and Tissue Resident (hang out in gut, other barrier tissue and lie in wait for antigen).

Normal (alpha beta TCR) T cells can only kill things in the context of MHC. CD8 memory cells will rapidly proliferate upon seeing their cognate antigen displayed on MHCI, leading to death of all cells expressing MHCI+antigen. Same with CD4, although CD4s are even more complicated.

None of this **** is on step 1, although it is very interesting.