Key Elements of Immunity

Before examining the specifics of oral infections and the host response, several key elements involved in immunity will be summarized. In higher animals, resistance to a pathogen includes a non-adaptive, non-specific or innate response (natural immunity) and an adaptive or acquired response, which act in concert to protect the host. A simple way to remember this is to consider innate immunity as what you are born with. The innate response occurs in the same way and to the same extent regardless of how many times a pathogen is encountered. In contrast, an adaptive or acquired response occurs after a pathogen comes into contact with the host and a “specific response” to that pathogen is developed and stored in a memory bank for any future contact. On second contact with the pathogen, a more rapid and heightened immune response ensues to eliminate it.

Innate immunity includes the following component parts:

  • External barriers such as skin, oral mucosa, body secretions and even endogenous (normal) microbial inhabitants
  • Physiological factors as body pH and temperature
  • Blood and tissue leukocytes (neutrophils, monocytes, macrophages, mast cells, basophils, eosinophils and natural killer cells)
  • Dendritic cells for immune surveillance and antigen presentation
  • Primary and secondary lymphoid tissue
  • Soluble mediators of inflammation including acute phase proteins, complement and cytokines

The adaptive or acquired immune response system is mediated by T and B lymphocytes which are commonly referred to as T Cells and B Cells. There are three important characteristics to adaptive immunity:

  • Self-recognition (or recognition of non-self)
  • Specificity
  • Memory