Infection defense is a learning tool designed to cater to the next generation of students. Learning upgraded. Your one goal is to prevent bacteria reaching the blood stream. Bacteria can replicate in the blood stream and the infection can spread to multiple parts of the body, killing the host. You are tasked with coordinating the immune system by using different human immune cells. Different immune cells do different things, some are motile, some are large and are stationary. Using the chemical messengers that are released from all immune cells, cytokines are the in-game currency. The more cytokines you receive, the more immune cells you can recruit.