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.
The cells of the immune system can engulf bacteria, kill parasites or tumor cells, or kill viral-infected cells. Often, these cells depend on the T helper subset for activation signals in the form of secretions formally known as cytokines, lymphokines, or more specifically interleukins.