Posted 05 October 2009 - 12:23 AM
It is generally understood that MHC class I ligands occur virtually on all nucleated cells? CD4+ and CD8+ T-cells being classified as nucleated cells must therefore, constitutively express MHC-I ligands? Do they express MHC-I ligand and indeed present peptides to other naive specific CD8+ T-cells that sample these cells?
Posted 05 October 2009 - 05:58 AM
The APCs (antigen-presenting cells) present (display) foreign peptides via MHC (I or II) that leads to activation of naive T-cells. MHC I found on all nucleated cells provide these cells the ability to display foreign peptides (e.g., viral peptide) for recognition by experienced (previously activated) CD8+ T-cells (the killer/cytotoxic T-cells) in the event, for example, a virus has infected. This website www.roitt.com might give some additional insights.
Thank you for your time! But I was wondering if CD4+ and CD8+ T-cells possessed the ability to present peptide antigens (if they possessed MHC I ligands as they too are nucleated cells inasmuch as virtually any nucleated cells must have surface MHC I ligand 'happily' expressed!!!) to prime peptide specific naive CD8+ T-cells!
Hope now you are pretty clear with my question!
Posted 16 October 2009 - 09:29 AM
Thanks for this post sir..i am highly obliged for this post... APC pocesses both MHC class I and class II molecule... these are histone complexes in nature and i think total 4 classes are there.. am i right?
Got it. As a rule, at least two signals are required to activate naive T-cells. One signal is via MHC-I that interacts with T-cell receptors found on T-cells. Another is via the costimulatory molecule, one being "B7." B7 is found mainly on professional APCs (antigen-presenting cells) and interacts with CD28 found on T-cells. Thus, APCs possess both MHC-I and MHC-II along with co-stimulatory molecules such as B7 and have the capacity to activate naive CD8+ T-cells and CD4+ T-cells. Since T-cells do not have the qualities of APCs (in particular the aforementioned co-stimulatory molecules), they cannot activate naive T-cells.
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