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.
HIV disrupts this process by directly infecting the helper T-cells. Your initial immune response does get rid of a great deal of HIV, but some of it manages to survive and infect these important cells. Once the infected helper T-cells are activated, they work to create new viruses instead of doing the job they are supposed to do in your immune system. In addition, many helper T-cells are destroyed in the HIV replication process. For more information, see NIAID's The Immune System.