What are two ways T cells contribute to immunity?

Answer 1

There are two types of T-Cells CD4+ and CD8+. CD4+ is known as helper T-cells and actually go around the body inspecting cells. They literally ask to see the cells details and the cell shows it (it presents MHC class II if you are interested). If the cell sees something that indicates the cell is foreign or has been invaded by bacteria... it releases cytokines to attract other white cells. These other cells take care of the problem.

CD8+ or cytotoxic T-cells inspect the cells in the same way (except they "ask" to see MHC class I which shows up viruses) and if they notice something is off... they kill the cell involved directly by sticking a tube into it and pumping in chemicals telling the cell to commit suicide.

I hope this helps! Immunology is realllllllllly interesting and I assure that there is more to the story than the basics above and that it is really fun!

Answer 2

T cells secrete molecules that destroy the cell to which they have hooked on to.
This is a very useful function if the target cell is infected with a virus because the cell is usually destroyed before it can release a fresh crop of viruses able to infect other cells.
T cells also bind to an antigen presented by B cells to reproduce good cells in your body to block out more bad cells.