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Function – Blood Cells

by Paul Moss, PhD
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    00:00 haemoglobin helps with removal of carbon dioxide from tissues.

    00:01 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.

    00:41 They can help B cells to make high-quality antibodies and they can directly kill virally infected cells.

    00:50 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.

    01:02 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.

    01:37 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 blood system.

    02:40 Most lymphocytes are actually found in what we call mucosal-associated lymphoid tissue.

    02:47 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.

    03:19 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.

    03:41 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.

    04:01 They contain a lot of granules which have a range of functions in killing bacteria.

    04:08 As you can see on the left, tertiary granules, azurophile granules and specific granules.

    04:15 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.

    04:41 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.

    05:38 Neutrophil production is of course highly regulated as well by the body.

    05:44 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.

    06:05 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.

    06:22 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.

    07:09 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.

    07:31 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.

    07:44 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, slightly pink.

    08:12 What's the function of these types of cells, polymorphonuclear granular cells as we call them.

    08:18 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.

    09:21 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.

    09:41 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.

    10:00 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.

    10:15 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.

    10:47 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 response.


    About the Lecture

    The lecture Function – Blood Cells by Paul Moss, PhD is from the course Hematology: Basics.


    Included Quiz Questions

    1. Monocyte
    2. T lymphocyte
    3. Eosinophil
    4. B lymphocyte
    5. Platelet

    Author of lecture Function – Blood Cells

     Paul Moss, PhD

    Paul Moss, PhD


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