Hey. I do AQA Biology and am currently in Year 12, today I have spent hours and hours trying to properly understand immunity, the cell-mediated response, and the humoral response and I'm STILL confused.
I will try and summarise what I'm most confused about.
So, B-lymphocytes are activated, and subsequently they produce memory-B cells, which circulate the bloodstream and become activated on a repeat infection; and plasma cells, which secrete antibodies.
I'm struggling to understand how exactly they are activated - I've had it from several different sources that:
a) Helper-T cells release cytokines, once they (t cells) have been activated by antigens presented by phagocytes. These cytokines stimulate the rapid division of B-lymphocytes into clones, which then differentiate into plasma and memory cells.
b) Activated Helper-T cells present the antigens of the pathogen to the antibody of the B-lymphocyte, stimulating it to divide and differentiate etc
c) B-lymphocyte engulfs free antigens from the blood and then presents them, enabling a T-helper cell to bind to it and thus activate the B-lymphocyte, leading to division/differentiation etc
Which of these is correct? Is more than one correct? Is there anything I have missed out?
I really hope someone can answer and help me to understand this because I've been struggling with it for ages. :/