Immunity and protection, the unfolding of a tale.

Immunological memory is at the core of protective mechanisms against microbial pathogens and possibly of defenses against tumors. Here, a new perspective is offered on the qualitative and quantitative aspects of the T cell response as it relates to protection. Two main points are proposed. First, the conditions of the initial immune response (priming) are critically important in the induction of T cell memory and protection. Second, at the present time, protection against microbial pathogens appears to correlate with the function of central memory T cells. A series of considerations and suggestions are being made for new ways to optimize the induction of protective T cell responses by vaccination both in the immunologically naive and experienced individual; emphasis is placed on: dose of antigen, the availability of T cell help, avoidance of overt inflammatory conditions and efforts to decelerate cellular senescence in responding T cells.