[khanar]

A pharmacologist discovered a new fungal metabolite with unusual antimicrobial properties. It naturally concentrates in the endosomes, lysosomes, and phagolysosomes of cells and directly kills microorganisms (e.g Mycobacterium tuberculosis) that are normally resistant to degradation in the phagolysosome. The metabolite has the undesirable effect of increasing the PH within phagolysosomes. Which of the following processes will be primarily affected?

A- Class I MHC molecule peptide loading
B- Class II MHC molecule peptide loading
C- Peptide binding to T lymphocyte receptor αβ
D- Peptide binding to T lymphocyte receptor γδ

 

[drmodi44]

B ??

B- Class II MHC molecule peptide loading???

 

[doctorF]

i l go with B....

 

[khanar]

Please explain

I have no clue at all
Would you please explain why did you choose option B :sorry:

 

[doctorF]

YES OFFCOURSE Y NOT...

APCs engulf bacteria and the phagolysosomes cut their antigens to present in them on their MHC II grooves... so that helper T cells act on them... if phagolysosome has no acidic enzymes in them they wouldnot be able to do it well... and thus antigen presentation in MHC2 will not take place...

 

[inder]

Here is a picture of what doctor F essentially described...

http://www.nature.com/nri/journal/v7/n7/images/nri2103-f2.jpg

Antigen presentation in MHC I requires proteosomes which are found in the cytoplasm... the fragmented antigens are then translocated to the ER where the MHC I molecule is mounted with the antigen.

Conversely, mounting of the antigen in MHC class II occurs in a phagolysosome. One phagosome containing the engulfed antigen fuses with a vacoule which contains MHC class II molecule... the antigen is then degraded and mounted on the MHC class II molecule.

 

[usmle100]

i think A....