Receptors of the Innate Immune System
The ability to sense the presence of microorganisms that could cause potentially
dangerous infections is a widespread property of cells, tissues and body fluids of all
multicellular organisms. This process is called innate immune recognition. This
recognition process is the first crucial step triggering the complex sequence of events
by which the body protects itself against infection. However, it is only since the 1980s
that most of the molecules (receptors) responsible for this recognition process have
been identified, and new examples of such innate receptors are still being found. The
receptors usually recognize components of microorganisms that are not found on
cells of the host, e.g. components of bacterial cell wall, bacterial flagella or viral
nucleic acids.
These target molecules have been named pathogen-associated molecular patterns
(PAMPS), and the receptors that recognize them pattern recognition receptors (PRRs).
Engagement of PRRs by PAMPs results in activation of intracellular signaling
pathways, resulting in alteration in gene transcription in the nucleus (left part of
figure 1) and ultimately a whole variety of different cellular responses, broadly
termed inflammation. Some innate immune receptors are also triggered by damage
to cells that arises in the absence of any infection, giving rise to the term
damage-associated molecular patterns (DAMPs). The activation of innate immunity is
an essential prerequisite for activation for most adaptive immune responses.
