Epstein Barr Virus infects endothelial cells and B cells. About half of us are infected by the virus while very young, and do not suffer disease. Around half of individuals who avoid the virus while young are infected in the teenage years and develop a disease called mononucleosis. In this disease, lymph nodes swell painfully as our immune system produces large numbers of lymphocytes to eliminate virus-producing cells. These lymphocytes are probably:

A.	B cells which produce antibody eliminating virus-infected cells
B.	Cytotoxic T cells to destroy virus-containing cells
C.	Helper T cells which stimulate B cell clonal selection
D.	Granulocytes which invade areas of virus production

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Cellular system

Pathogens that escape antibody detection can enter and infect cells. The cellular system is composed of Cytotoxic T cells and Helper T cells. Cytotoxic T cells kill infected cells, preventing these cells from producing more pathogen. Receptors on the surface of cytotoxic T cells detect fragments of the virus on the surfaces of infected cells. A successful immune response against a virus means that we will make large numbers of virus specific cytotoxic T cells. In an EBV infection, cytotoxic T cells can make up the vast majority of our white blood cells.
Microscopic movie of cytotoxic T cells killing a tumor cell (1257 kb)
T cells contain a T cell receptor that is like the antibody of B cells. Each T cell has only one kind of receptor. Analogous to the genetic events of antibody production, T cells rearrange a set of genes coding for the T cell receptor. Each T cell ends up with a unique receptor, but the population of T cells contains billions of different receptors.