Now let us move to studying the white cells in your
blood and we'll start with the lymphocytes,
the major cells of the adaptive immune system.
So these cells comprise the adaptive immune system
and as we discussed in the first lecture, two main
subtypes. (1)B cells, they make antibodies which are
very useful at binding to viruses and bacteria either
neutralizing those pathogens or signalling them
for destruction by neutrophils or monocytes whereas
(2)T cells play a role in regulating immunity.
They can help B cells to make high-quality antibodies
and they can directly kill virally infected cells.
In fact there's also an awful lot of interest now
in the importance of T cells in controlling cancer
and fighting off low-levels of transformed cells
perhaps in our body.
On the left you'll see a cartoon of a lymphocyte,again
showing a very large nuclear to cytoplasmic ratio
and some granules within the lymphocyte that is shown
again on the slide on the right where you'll see
the granules within the lymphocytes.
Although this course is about blood and haematology
we must remember that 95% of lymphocytes within your
body are not actually within the blood at any one time.
They are within the lymphoid tissue.
So lymphocytes are constantly entering lymph nodes
through lymph or through high endothelial venules and there
they are they're searching for any evidence of
infection brought to them by dendritic cells within
the lymph node, and then finally they leave the
lymph nodes via lymphatic vessels and come back
into the blood. On the right, we've got a
representation of this. You got the blood lymphocyte
pool at the top and as we move down that, those three
green arrows that lymphocytes may go out to the spleen,
some of them may go directly to tissues and the
majority can enter lymph nodes through these high
endothelial venules before being returned through
the lymph by the important thoracic duct into the
Most lymphocytes are actually found in what we call
mucosal-associated lymphoid tissue.
Your mucosa needs protection against external
pathogens and so here we've got a representation
in the cartoon of lymphoid tissue around the
oropharyngeal tract, the lung and indeed
the gastrointestinal system. That lymphoid tissue,
you know it as tonsils, adenoids and so forth
and this is where the majority of lymphocytes within
your body reside at any one time.
It's really very sophisticated system and the types
of lymphocytes in each of those different areas are
very different and if they are activated in one area
perhaps the lung, then they will return to the lung
and they home back to the region of activation.
Neutrophils are the classic cell of what we call the
innate immune system, the immediate immune response
to a pathogen.
As I explained in the first lecture they have this
very characteristic multilobed nucleus represented
on the left cartoon and on the right in the blood film.
They contain a lot of granules which have a range of
functions in killing bacteria.
As you can see on the left, tertiary granules,
azurophile granules and specific granules.
Also on that neutrophil, we've got complement
receptors, receptors for Fc portion of IgG
and really what those are doing is searching for any
pathogens or indeed cells which have been coated by
compliment or antibody and are deemed necessary to
be destroyed by the neutrophil system.
Let's have a look at this process, the phagocytosis.
Bacteria taken up by the biorecognition of molecules
directly by the neutrophil on the pathogen or
so-called pathogen associated molecules or by
attachment of antibody or complement-coated organisms.
As you can see there, the pathogen is taken in and
in this case we have attachment by complement and it
enters what we call a phagosome within the neutrophil
The neutrophil has now captured the pathogen within
the cell. And then you see those lysosomes,
they go and merge with these phagosomes and all of
the toxic molecules within the lysosome are unleashed
on to the bacteria and they form a phagosome and that
is usually enough to kill the bacteria or fungus.
Neutrophil production is of course highly regulated
as well by the body.
It is particularly increased during infection.
If you take a blood count from a patient with
inflammation or infection, almost the first thing
you'll see is an increase in the neutrophil count
and that's rather beautifully represented on this blood
film with this line of five neutrophils together.
Monocytes. We talked about this cell a little
in our introductory lecture. These cells also help
to ingest pathogens and kill bacteria and when
they migrate to tissues, we call them macrophages.
They also play an important role in linking this
innate immune response, this ingestion of pathogens
to the adaptive immune response where the T cells
and B cells are selected to generate a specific
memory immune response.
You'll see on the left where we have the cartoon
representation of the monocytes at the bottom,
the MHC class II there, which is a very important
molecule for triggering T-cell and B-cell activation.
On the right there is a classic blood film picture
of a monocyte, you can see that folded nucleus and
the slightly pale blue cytoplasm.
Now, As well as neutrophils, there are two other types
of closely related cells: eosinophils and basophils
When scientists were staining blood many decades ago,
they used stains with different pHs, basic or acidic.
Neutrophils stain with a neutral stain whereas the
eosinophils and basophils stain more with acid and
base stains- that's where these old names come from.
On the right there's a very beautiful blood film.
I think the person who generated that was very lucky
because we see these three cells all next to each other
In the middle you've got the neutrophil, above it,
a basophil - very darkly staining, very dark granules,
large granules so much that you can hardly see
through it, and at the bottom, the eosinophil,
characteristic two lobed nucleus and you can just see,
What's the function of these types of cells,
polymorphonuclear granular cells as we call them.
Well, eosinophils have a very important role in
immuneresponse to helminths, which is a posh word
for saying worms.
So when an eosinophil recognizes a worm,
it combine to it and as you'll see on the left,
it has these things called specific granules
which contain quite toxic substances such as major
basic protein and these will be released onto the
parasitic worm in an attempt to destroy it.
Actually in many societies of course, we have
eradicated helminth infections, we still see patients
who have increased eosinophils, why?s that?
The common reason now is allergy - patients with hay
fever, asthma, perhaps a drug reaction
and for some reason gas is also quite a
strong stimulus of eosinophil production.
The basophil, that's quite a rare cell and we don't
tend to see many in normal blood and to be honest,
we're not entirely sure what it does.
It may have relation to cells like histamine
from mast cells; it might be similar to mast
cell in some way.
This representation is just focusing on one area of
haemopoeisis and it just shows that myeloid cells
and monocytes can derive from a common precursor cell.
Scientists spent a long time in the last 20
or 30 years working out the different lineages of
heamopoeisis in our system.
In the top there, you'll see a cell which is called
a CFU-GM. What does that mean? well we've written it
down for you there, colony forming unit-granulocyte
monocyte and that's a common precursor cell.
A colony forming unit comes from the fact that when
people take the cells out of the blood or the
bone marrow and put them, and culture in the
laboratory they see colonies growing up
and that's where the name comes from.
All of these cells are myeloid cells and remember
that that will be very important when we talk
about the classification of leukaemia,
All of these are myeloid cells and can be involved
in myeloid leukaemia.
So In summary in this lecture, we've looked in more
detail the function of red cells
and the major white cells. We've learnt how red
cells have become perfectly evolved to
carry maximal amounts of oxygen into tissues.
We've seen how lymphocytes or the cells of
the immune system, they are primarily located
within lymphoid tissue constantly providing
surveillance against infection. Whereas granulocytes
such as neutrophils, eosinophils and basophils
are relatively short-lived and they are critical
in fighting infection and really constitute
very important cells within the innate immune