Asked by: saipeeps
Antigen presenting cells (APCs) have MHC I & well as MHC II.
APCs have to make sure all the cells recognize the invader properly.
Say, I draw a cartoon of someone on a coloring paper.
Not everyone can recognize the real person by the cartoon drawing.
Some people may need an oil painting on a proper portrait to recognize.
I drew the same thing but on different paper with different coloring material.
Think of MHC class II as the coloring paper & MHC class I as the oil painting.
Now, if I have to make sure that all my cops recognize the invader.. I’ll show both the cartoon drawing & the oil painting (MHC class I as well as MHC class II).
Helper CD4+ T cells will easily recognize through the cartoon drawing (MHC class II) and get activated.
Cytotoxic CD8+ T cells won’t recognize the cartoon, they’ll look at the oil painting (MHC class I) to recognize the invader.
I guess what confuses some is that they think T cells are all the same, they fail to realize that every cell is unique & different. There are different types of T cells & different ways to present antigens.
Hope it clears things =)
Read more: Why do Antigen Presenting cells have MHC class I?