Diffusion

The infectious cell releases molecules, which diffuse through all the other molecules in extracellular space. When  a molecule from the infectious cell gets close to a receptor on the Immune cell, the Immune cell moves in the direction of that receptor. Our goal is to get molecules into the receptors pointing closer to the infectious cell. Eventually, if time doesn't run out, the Immune cell reaches the infectious cell and destroys it.

To play, drag the infectious cell's molecules to the receptors on the Immune Cell.

I've been wanting to come back to this game for years, as I had to stop working on it when I ran out of money.