How HIV attaches to a cell

For a virus to make you sick it first has to get inside one of your cells. The shell around HIV has some parts (made of protein) that stick out like spikes. Cells have similar proteins on their surface called receptors. HIV in your blood can only attach itself to a cell if its protein spikes fit closely with the cell’s receptors.

Imagine the virus’s spike as a key and the cell’s receptor as a lock. Most keys won’t even fit into the wrong lock, and even if they fit, they won’t be able to open the lock. The match between the lock and the key has to be exact.

For HIV, the cell it fits best is a type of white blood cell called a T lymphocyte (pronounced limb-foe-site), or simply a T cell.

Actually, HIV is even pickier. There are many different kinds of T cells but HIV only infects those with a particular receptor called CD4. CD4 is the lock that matches HIV’s key, the spike-like protein in its shell. T cells that have the CD4 receptor are called CD4 cells.