5 replies to this topic

[Shankar]

Hi there,

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?

Regards,
Shankar

[CellSpecific.com]

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. The cell displaying the foreign viral peptide will be destroyed to stop viral spread. This website www.roitt.com might give some additional insights.

Edited by CellSpecific.com, 05 October 2009 - 05:53 AM.

[Shankar]

CellSpecific.com, on Oct 5 2009, 06:48 AM, said:

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!
Thanks
Shankar

[CellSpecific.com]

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.

Edited by CellSpecific.com, 05 October 2009 - 06:47 AM.

[rozer henry]

CellSpecific.com, on Oct 5 2009, 06:46 AM, said:

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.

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?
Rozer Online Pharmacy

[CellSpecific.com]

Indeed, APCs posses both MHC-I and MHC-II (MHC= Major Histocompatibility Complex). Here is a simple diagram from roitt.com: http://www.roitt.com/scripts/roitt/figure....fig=f04-13a.jpg

The cleft is where a short peptide sits. The T-cell receptor found on T-cells interacts with the peptide within the context of the MHC.

Here's another link that summarizes this interaction: http://people.rit.edu/~gtfsbi/imm/parhamim...ure%2003-30.jpg