The Basics of Immunology

Abstract

Humans have defense mechanisms against micro-organisms exemplified by the immune system that consists of an unspecific (“innate immunity”) and specific (“adaptive immunity”) arm, leading to an effective response via humoral and cellular mechanisms. Innate immunity is activable at any time (skin, tears, ciliae, …). It includes recognition of various chemical patterns on microorganisms. Such chemical structures are detected by macrophages or dendritic cells, which travel to the draining lymph nodes and are presented to cells of the adaptive immune system. The adaptive immune system is highly specific against individual microorganisms and directed against non-self-structures. It needs days to weeks to be effective and it induces immune memory, allowing for an immediate defense response upon re-infection. As a result of presentation of non-self-structures to the adaptive immune system, highly specific antibodies and cells are generated which may kill/neutralize microbial invaders. Currently, antibody responses are the cornerstone to vaccine licensure. Functional antibody tests detecting killing/neutralizing ability are the cornerstone of vaccine-induced immunity. Tests for cell-mediated immunity are also considered. Antibody responses to vaccines can be evaluated as o Geometric Mean Titer (GMT) or Geometric Mean Concentration (GMC) o Fold-rise pre/post vaccination o Percentage of study subjects achieving a clinically relevant amount of antibody (“sero-responders”) o Reverse Cumulative Distributions (RCDs), ideally showing data pre- and post-vaccination.