Thirdly, sources of the cells involved in innate and adaptive immunity used to be
considered different between both types of immunity. Myeloid or myelogenous
meant monocyte/macrophages and neutrophils and these cells alone were assumed
to arise from bone marrow. Myeloid cells were considered to be in charge of innate
immunity and lymphoid cells in adaptive immunity. However, lymphoid T cells or
B cells also originate from bone marrow (myelogenous) but need to mature in the
thymus or in the gut-associated mucosal tissue (GALT), respectively. NK cells
belonging to innate lymphoid cells are lymphoid and involved in innate immunity
in that they do not need the co-presentation of MHC I molecules for killing infected
or damaged cells without self-signal (missing-self). As was stated above, cytotoxic
response by NK cells to the second challenge of foreign materials are higher than
the first, meaning trainability [3]. NK cells do not have antigen specificity or TCR
and also lack recombination activation gene (RAG) obviating the re-arrangement of
V(D)J TCR gene. They are myelogenous and lymphoid, associated with innate
immunity, and trainable. Source does not help discriminate innate and adaptive
immunity. Unlike NK cells, NKT cells have TCR, TCR recombination, and are
myelogenous and lymphoid, and should have been trained in the thymus and
belong to adaptive immunity.
Fourthly, memory capability resides in central memory T cells or effector
memory T cells (helper T or cytotoxic T cells) or memory B cells. The exact
molecular mechanism of memory is still under active investigation using genomics,
epigenomics and single cell immunology. Memory, if we call trained innate
immunity as memory, is via epigenetic modification in innate immune cells. NK
cells belonging to innate lymphoid cell subgroup 1 (ILC1) remember the previous
challenges with the help of innate lymphoid cell subgroup 2 (ILC2). ILC2 cells
mimic helper T cells to help ILC1 such as NK cells [13–15].
In summary, key difference between adaptive immunity and innate immunity
might reside in whether they use V(D)J recombination to produce specific immune
response in Ig or TCR family genes or whether they use preset limited selectivity of
using molecules such as pentraxins (humoral) or TLR isotypes (TLR4 for LPS). If
one assumes that myeloid cells alone are responsible for innate immunity, one can
immediately find innate lymphoid cells as an exception. If one assumes that
adaptive immunity is associated with MHC I (cytotoxic) or MHC II (helper)
restriction, there is an easy exception that NKT cells sometimes use CD1 restriction
instead to MHC I restriction [16]. Sources, trainability or memory are not appropriate to characterize or discern innate and adaptive immunity. Due to this ambiguity of discriminating innate and adaptive immunity, understanding of bodily
immune responses to exogenous nanomaterials should not be prejudiced owing to
the past or even current dogma of differential characteristics of innate and adaptive
immunity. The immune response to the exogenous nanomaterials will be explained
further below keeping this confusion and progress of understanding in mind.
21 Innate Immunity to Nanomaterials
393
considered different between both types of immunity. Myeloid or myelogenous
meant monocyte/macrophages and neutrophils and these cells alone were assumed
to arise from bone marrow. Myeloid cells were considered to be in charge of innate
immunity and lymphoid cells in adaptive immunity. However, lymphoid T cells or
B cells also originate from bone marrow (myelogenous) but need to mature in the
thymus or in the gut-associated mucosal tissue (GALT), respectively. NK cells
belonging to innate lymphoid cells are lymphoid and involved in innate immunity
in that they do not need the co-presentation of MHC I molecules for killing infected
or damaged cells without self-signal (missing-self). As was stated above, cytotoxic
response by NK cells to the second challenge of foreign materials are higher than
the first, meaning trainability [3]. NK cells do not have antigen specificity or TCR
and also lack recombination activation gene (RAG) obviating the re-arrangement of
V(D)J TCR gene. They are myelogenous and lymphoid, associated with innate
immunity, and trainable. Source does not help discriminate innate and adaptive
immunity. Unlike NK cells, NKT cells have TCR, TCR recombination, and are
myelogenous and lymphoid, and should have been trained in the thymus and
belong to adaptive immunity.
Fourthly, memory capability resides in central memory T cells or effector
memory T cells (helper T or cytotoxic T cells) or memory B cells. The exact
molecular mechanism of memory is still under active investigation using genomics,
epigenomics and single cell immunology. Memory, if we call trained innate
immunity as memory, is via epigenetic modification in innate immune cells. NK
cells belonging to innate lymphoid cell subgroup 1 (ILC1) remember the previous
challenges with the help of innate lymphoid cell subgroup 2 (ILC2). ILC2 cells
mimic helper T cells to help ILC1 such as NK cells [13–15].
In summary, key difference between adaptive immunity and innate immunity
might reside in whether they use V(D)J recombination to produce specific immune
response in Ig or TCR family genes or whether they use preset limited selectivity of
using molecules such as pentraxins (humoral) or TLR isotypes (TLR4 for LPS). If
one assumes that myeloid cells alone are responsible for innate immunity, one can
immediately find innate lymphoid cells as an exception. If one assumes that
adaptive immunity is associated with MHC I (cytotoxic) or MHC II (helper)
restriction, there is an easy exception that NKT cells sometimes use CD1 restriction
instead to MHC I restriction [16]. Sources, trainability or memory are not appropriate to characterize or discern innate and adaptive immunity. Due to this ambiguity of discriminating innate and adaptive immunity, understanding of bodily
immune responses to exogenous nanomaterials should not be prejudiced owing to
the past or even current dogma of differential characteristics of innate and adaptive
immunity. The immune response to the exogenous nanomaterials will be explained
further below keeping this confusion and progress of understanding in mind.
21 Innate Immunity to Nanomaterials
393