our bodies are in constant contact with
environmental factors epithelial
barriers like the skin or gut mucosa
represent the first line of defense in
the gut mucosa specialized immune cells
actively reinforce the barrier and
induce tolerance against food or
commensal bacteria among these immune
cells a recently discovered type of
lymphocytes called innate lymphoid cells
or ILCs orchestrate immune responses and
maintain tissue homeostasis
unlike the T and B lymphocytes ILCs do
not express adaptive antigen recognition
receptors as such their activation and
expansion is not driven by antigen but
rather by cytokine signals from the
tissue ILCs come in three types by LC 1
LC 2 and IL c 3 IL c 3s interact with
dendritic cells to maintain the
epithelial barrier dendritic cells which
are specialized in the presentation of
antigen acquire antigen from the gut
microbiota and secrete interleukin 23
il-23 stimulates the ILC 3 s to make IL
22 which then activates the epithelium
to secrete antimicrobial peptides or a
mps
that kill bacteria directly il 22 also
enhances il-23 production in dendritic
cells
this dialogue between dendritic cells
and ILC 3's maintains the barrier
against pathogenic or commensal bacteria
ILC 3's also interact with macrophages
to establish tolerance towards the
commensal microbiota antigen from gut
bacteria induces the inflammatory
cytokine il-10 in macrophages which in
turn triggers the secretion of gm-csf in
IL c 3s gm-csf signals back to
macrophages to induce retinoic acid
which promotes the differentiation of
regulatory t-cells regulatory t-cells
are essential in maintaining tolerance
towards the commensal microbiota il c2s
contribute to responses against
helminths
these parasitic worms release enzymes
that digest the mucus barrier and cause
massive cell death epithelial cells
sense the danger signals released by the
dying cells and produce alarm ins in
response to the alarm in IL 25 IL c2 s
make mediators that induce mucus
production from goblet cells send
activated dendritic cells to the lymph
node where they can prime t-cell
effectors recruit eosinophils and mast
cells and induce muscle contraction
these actions results in the expulsion
of worms from the gut in response to IL
33 il c2 s also make alpha regulan which
induces tissue repair following worm
clearance
however ILCs also contribute to tissue
pathology ILC ones which make the
inflammatory mediator interferon gamma
and ILC threes which can acquire the
ability to make interferon gamma during
chronic inflammation are found in
inflammatory bowel diseases such as
colitis and Crohn's disease and
contribute to gut pathology as such ALCS
participates in various aspects of
immunity from maintenance of the
epithelial barrier and tolerance against
commensals to immune responses against
parasites and pathology associated with
chronic inflammation
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