The term ZBA (Zero Balance Account) is sometimes used to describe a transit account. In reality, ZBAs are a completely different story and are usually used in an acquiring and merchant account context, where one party opens the account and another sweeps (clears) it daily.
Helper T cells are the major driving force and the main regulators of the immune defense. Their primary task is to activate B cells and killer T cells. However, the helper T cells themselves must be activated.
After a Killer T-cell finds and destroys an infected cell, this Helper T-cell message tells it to copy itself, making an army of Killer T-cells. Since only T-cells that can fight the invading virus are copied, your body saves energy and is still very good at killing the virus.