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De Serrano and Burkhart
J Nanobiotechnol (2017) 15:83
and as such are recognized by the
first line of defense in
the immune system, antigen presenting cells (APCs) such
as dendritic cells (DCs), macrophages and neutrophils.
The PAMPs are recognized by pattern recognition recep-
tors (PRRs) on the surface and in endosomes of APCs [
8
–
11
]. Vertebrates developed the adaptive immune system
as a second line of defense that could ‘remember’ patho-
gens and fight back upon re-challenge.
It is composed of
cells such as T and B cells that employ de novo synthe-
sized antigen-specific receptors (T- and B cell receptors,
TCRs and BCRs). TCR and BCRs are able to recognize
pathogen-specific antigens
when presented complexed
with major histocompatibility complexes (MHC) on the
surface of an APC. But polarization of the T or B cells
to ensure it acts appropriately against the pathogen,
relies on signals provided by the APC (such as co-stim-
ulatory molecules and precise cytokines)
in response
to the priming by PAMPs. These critical signals lead to
differentiation of effector and eventually memory cells
that are critical for driving the immune response against
future infections with the same pathogen.
While innate
immune responses are broadly applicable and adaptive
immune responses are antigen-specific, the two arms of
the immune system work in
close concert to mount an
effective response to clear the pathogen.
The development of PRRs by the immune system rep-
resent a significant advancement in the fight for survival
of the host. Therefore, an important
question arises to
that end: what type of PRRs have been discovered so far
and which ligands (or PAMPs) do they tend to recognize?
Some PRRs are secreted to the extracellular milieu and
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