MHC & Ag presentation Encounter:

In class we have been studying the major histocompatibility complex along with antigen presentation. There are two pathways in which antigen is processed and presented to T cells depending on whether the peptide is associated with MHC class- I or MHC class-II. The Endogenous pathway is the pathway taken by peptides generated within the cell (MHC I). The Exogenous pathway is the pathway taken by peptides taken up from the extracellular environment by endocytosis (MHC II).

This past weekend our acrobatic team was away at Andrews University in Michigan for our annual Acrofest. During our nine hour bus ride there one of my teammates threw up in the bus on his way to the trashcan. Our coach made a stop to attempt to clean the area since we still had a couple hours till arriving at our destination. However, germs are hard to kill especially in an enclosed environment filled with people such as our bus. When we arrived at acrofest three other teammates progressively got sick and started to throw up as well. In the midst of this happening I couldn’t help but think about immunology and what was happening on the inside of my teammates as they were trying to fight off this virus or stomach flu. To this day we aren’t sure what exactly plagued our team.

What I am sure about is that these antigen peptides from the throw up were spreading and as they started to inhabit my teammates their immune systems were at work. These peptides were coming from the outside, therefore their system was fighting through the exogenous pathway. In the exogenous pathway the antigen is engulfed into endocytic compartments where they are degraded by acidic pH-dependent endosomal and lysosomal enzymes. These throw up peptides were then able to associate with MHC class –II and the MHC-peptide complexes were then transported to the cell membrane in preparation for antigen presentation to CD4+ T helper cells. Thankfully these teammates were able to recuperate before our performance Saturday night, meaning that their antigen presentation was successful and their immune system was actively at work in fighting off this stomach illness.