I need help with an immunobiology question we are talking about in class: While

Question

I need help with an immunobiology question we are talking about in class:

While limiting the expression of MHC class II to so-called "professional" APCs partially ameliorates the problem of self non self recognition among CD4+ T cells, it remains difficult to understand how it is possible that even these cells' class II molecules are not deluged with processed "self" molecules (for example, albumin is present at extremely high quantities in the serum, so one might imagine that peptides from this alone would suffice to compete for any transiently present non-self proteins). Speculate on and/or research potential mechanisms that would afford enhanced processing or recognition of potentially dangerous molecules.

Explanation / Answer

5. Those self-reactive T cells that escape intrathymic negative selection in the thymus can inflict cell injury unless they are deleted or effectively muzzled in the peripheral tissue chiefly by nTreg cells (see central tolerance above).

6. Appropriate reactivity toward certain antigens can also be quieted by induction of tolerance after repeated exposure, or exposure in a certain context.

7.In these cases, there is a differentiation of naïve CD4+ helper T cells into induced Treg cells (iTreg cells) in the peripheral tissue or nearby lymphoid tissue (lymph nodes, mucosal-associated lymphoid tissue, etc.).

8.This differentiation is mediated by IL-2 produced upon T cell activation, and TGF- from any of a variety of sources, including tolerizing dendritic cells (DCs), other antigen presenting cells, or in certain conditions surrounding tissue.

9. Treg cells are not the only cells that mediate peripheral tolerance.

10. Other regulatory immune cells include T cell subsets similar to but phenotypically distinct from Treg cells, including TR1 cells that make IL-10 but do not express Foxp3, TGF--secreting TH3 cells, as well as other less well-characterized cells that help establish a local tolerogenic environment.

11.B cells also express CD22, a non-specific inhibitor receptor that dampens B cell receptor activation.

12.A subset of B regulatory cells that makes IL-10 and TGF- also exists.

13. Some DCs can make Indoleamine 2,3-dioxygenase (IDO) that depletes the amino acid tryptophan needed by T cells to proliferate and thus reduce responsiveness.

14.DCs also have the capacity to directly induce anergy in T cells that recognize antigen expressed at high levels and thus presented at steady-state by DCs.

15. In addition, FasL expression by immune privileged tissues can result in activation-induced cell death of T cells.

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