We’re going to look at the
cells of the immune system.
Hematopoiesis occurs in the bone marrow, where there are
self-renewing, multipotent, hematopoietic stem cells.
This means that these cells produce more stem cells, in
other words they’re self-renewing and they’re multipotent.
They can become many
different cell types.
And in order to develop into these different cell types,
they can differentiate down one of two different pathways.
Those that develop down the myeloid pathway of
cell differentiation will ultimately become either
erythrocytes - red blood cells, or they’ll produce the
megakaryocytes that produce ultimately the platelets.
Or a variety of cells of the innate immune
response which we’ll be discussing very shortly.
Alternatively, hematopoietic stem cells can develop
down the lymphoid pathway of cell differentiation.
And cells that go down this pathway will develop into
the cells of the adaptive immune response or into natural
killer cells, which are mostly cells of the innate response
and other types of so called innate lymphoid cells.
So let’s have a look at the different cell types that are
produced that will contribute towards innate immune responses.
The major white blood cell in the
circulation, in fact account for
around about 70% of circulating white
blood cells is the neutrophil.
And these are involved
predominantly in phagocytosis.
Monocytes which are found in the blood
and macrophages which are derived
from monocytes but found in the
tissues are also phagocytic cells.
Dendritic cells, whilst being phagocytic, their
main function is the activation of T-cells.
There is another cell type called the
follicular dendritic cell, which is an
entirely separate cell type from dendritic
cells despite their similar name.
These cells have involved in
the activation of B-cells.
Eosinophils, basophils and mast cells are specialized
for the production of inflammatory mediators.
And then finally, regarding cells of
the innate immune response, natural
killer cells and other innate lymphoid
cells have a variety of functions.
But the natural killer cell’s main
function is to kill infected cells whereas
other types of innate lymphoid cells
have a diverse range of functions.
In fact this group of cells, these innate lymphoid cells are
a relatively recently understood population of lymphocytes
and they are very much a active area of immunological
investigation, trying to tease out their precise properties.