Immune System Question

Question

I had a quick question about some confusions. ​ My understand is that helper T-cells bind to the MHC class II molecules on B-Lymphocytes which help those cells proliferate into plasma cells, which then secrete antibodies and carry out a humeral response. ​ Where MHC class I molecules bind to macrophages specifically, not B-lymphocytes. And these then release cytotoxins which initiate apoptosis, as well as stimulation of more cytoxic T cell creation. ​ With that said, TBR states that neutrophils and macrophages similarly to peroxisomes, have hydrogen peroxide within them which can break down pathogens. If that is the case, why are cytotoxins needed to initiate apoptosis of the pathogen.

Answer 1

Hello!

This question might be waaaay beyond the scope of the MCAT but if you are curious, cytotoxins are essentially co-stimulatory signals that give the cell the "GO" signal to kill itself.

As you may already know, apoptosis is a highly highly regulated pathway with several checkpoints because proteases are heavily involved in this process. If the cell does not receive some sort of external or internal signal, then gene expression of pro-apoptotic proteins remain suppressed. BUT, if you have granzymes or other secretory proteins that can alert the cell of an injury or an infection, pro-apoptotic proteins are allowed to be expressed within the cell so that apoptosis is activated.

Hope this helps!