What activates the B and T cells?

Answer 1

Naive T cells are activated by antigen presenting cells (dendritic cells). This begins when an antigen (eg. bacterial protein) is taken up/detected by a dendritic cell. In order for the T cell to become activated, it requires 3 different signals:

1. MHC (Major Histocompatibilty Complex) presenting foreign antigen to a T cell receptor -> creates specificity so that the T cell relates to this antigen

2. B7 (on dendritic cell) binds to CD28 (on T cell) - this is known as the co-stimulatory signal. This is basically how the T cell knows that it is interacting with a "professional" antigen presenting cell. Without this signal, the T cell will not be activated by the MHC/antigen signal.

3. Cytokines - these are signalling molecules released by the dendritic cells and stimulate T cell differentiation (tells the T cells what functions to undergo).

Answer 2

The immune system is one of nature's more fascinating inventions. With ease, it protects us against billions of bacteria, viruses, and other parasites. Most of us never reflect upon the fact that while we hang out with our friends, watch TV, or go to school, inside our bodies, our immune system is constantly on the alert, attacking at the first sign of an invasion by harmful organisms.