1. The word macrophage comes from the word macros "large" and phagein "eat". Macrophages are big cells that eat. The function of these cells is to phagocytose (engulf and then digest) cellular debris and also pathogens such as bacteria.

2. Dendritic cells are named after their branched projections called dendrites. These cells are the sentinels of the immune system and are always testing their surroundings in case they see any danger.

3. T cells are named after the organ they develop in, the Thymus
T cells are named after the organ they develop in, the Thymus. T helper cells organize and "help" to alert other cells to coordinate the immune system to clear pathogens (the bad guys).

4. Cytotoxic T cells (CTLs) are a special type of T cells with the ability to kill other cells. Usually they kill cells that have been infected with a virus. This way the virus can no longer use these cells for replicating inside of them.
CTLs secrete cytotoxins to kill the other cells and are therefore called "cytotoxic" T cells.

5. B cells develop in the bone marrow and are therefore called B cells.
Memory B Cells
B cells develop in the bone marrow and are therefore called B cells.
These cells are responsible for producing antibodies.
The Antibodies produced by B cells circulate around our body and bind to specific viruses or bacteria to neutralize them and help get them killed by other cells of the immune system.