Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    12
    ReputationRep:
    Hey. I do AQA Biology and am currently in Year 12, today I have spent hours and hours trying to properly understand immunity, the cell-mediated response, and the humoral response and I'm STILL confused.

    I will try and summarise what I'm most confused about.
    So, B-lymphocytes are activated, and subsequently they produce memory-B cells, which circulate the bloodstream and become activated on a repeat infection; and plasma cells, which secrete antibodies.
    I'm struggling to understand how exactly they are activated - I've had it from several different sources that:

    a) Helper-T cells release cytokines, once they (t cells) have been activated by antigens presented by phagocytes. These cytokines stimulate the rapid division of B-lymphocytes into clones, which then differentiate into plasma and memory cells.

    b) Activated Helper-T cells present the antigens of the pathogen to the antibody of the B-lymphocyte, stimulating it to divide and differentiate etc

    c) B-lymphocyte engulfs free antigens from the blood and then presents them, enabling a T-helper cell to bind to it and thus activate the B-lymphocyte, leading to division/differentiation etc

    Which of these is correct? Is more than one correct? Is there anything I have missed out?
    I really hope someone can answer and help me to understand this because I've been struggling with it for ages. :/
    Offline

    11
    ReputationRep:
    (Original post by ConfusedSnowball)
    Hey. I do AQA Biology and am currently in Year 12, today I have spent hours and hours trying to properly understand immunity, the cell-mediated response, and the humoral response and I'm STILL confused.

    I will try and summarise what I'm most confused about.
    So, B-lymphocytes are activated, and subsequently they produce memory-B cells, which circulate the bloodstream and become activated on a repeat infection; and plasma cells, which secrete antibodies.
    I'm struggling to understand how exactly they are activated - I've had it from several different sources that:

    a) Helper-T cells release cytokines, once they (t cells) have been activated by antigens presented by phagocytes. These cytokines stimulate the rapid division of B-lymphocytes into clones, which then differentiate into plasma and memory cells.

    b) Activated Helper-T cells present the antigens of the pathogen to the antibody of the B-lymphocyte, stimulating it to divide and differentiate etc
    All right except this:
    c) B-lymphocyte engulfs free antigens from the blood and then presents them, enabling a T-helper cell to bind to it and thus activate the B-lymphocyte, leading to division/differentiation etc/
    A specific B-lympocyte will recognise a free floating, non processed specific antigen with its receptor(s), but the binding itself will cause clonal expansion and activation. Helper T cells can stimulate B-cells though, making them "more" activated.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by h3rmit)
    All right except this:


    A specific B-lympocyte will recognise a free floating, non processed specific antigen with its receptor(s), but the binding itself will cause clonal expansion and activation. Helper T cells can stimulate B-cells though, making them "more" activated.
    Thank you for your reply! So would I be correct in saying that b-lymphocytes are stimulated by contact with either a processed (from a t-helper cell) or non-processed (free floating) specific antigen which binds to their antibody, but they can additionally be stimulated by cytokines released from helper-t cells?


    Posted from TSR Mobile
    Offline

    10
    ReputationRep:
    (Original post by ConfusedSnowball)
    Hey. I do AQA Biology and am currently in Year 12, today I have spent hours and hours trying to properly understand immunity, the cell-mediated response, and the humoral response and I'm STILL confused.

    I will try and summarise what I'm most confused about.
    So, B-lymphocytes are activated, and subsequently they produce memory-B cells, which circulate the bloodstream and become activated on a repeat infection; and plasma cells, which secrete antibodies.
    I'm struggling to understand how exactly they are activated - I've had it from several different sources that:

    a) Helper-T cells release cytokines, once they (t cells) have been activated by antigens presented by phagocytes. These cytokines stimulate the rapid division of B-lymphocytes into clones, which then differentiate into plasma and memory cells.

    b) Activated Helper-T cells present the antigens of the pathogen to the antibody of the B-lymphocyte, stimulating it to divide and differentiate etc

    c) B-lymphocyte engulfs free antigens from the blood and then presents them, enabling a T-helper cell to bind to it and thus activate the B-lymphocyte, leading to division/differentiation etc

    Which of these is correct? Is more than one correct? Is there anything I have missed out?
    I really hope someone can answer and help me to understand this because I've been struggling with it for ages. :/
    Let me explain using a summary I made last year (1st year of med school). B cells are activated in 2 ways:

    - T-cell independent activation = A B-cell is activated directly by an antigen and proceeds to release IgM antibodies
    - T-cell dependent activation = This is where cells called dendritic cells phagocytose the antigen and present it on its cell surface using MHC II molecules, which are recognised by Th2 CD4 cells (T-helper cells). These T-helper cells become activated and when they meet a B cell presenting the same antigen then they activate that B cell. There is always co-stimulation in these processes.

    Hopefully that answers your question a little, if it doesn't at all then let me know and I can make a better attempt at explaining it simply haha

    Note: I edited it because I got something a little wrong, I hope everything above is correct now!
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by AortaStudyMore)
    Let me explain using a summary I made last year (1st year of med school). B cells are activated in 2 ways:

    - T-cell independent activation = A B-cell is activated directly by an antigen and proceeds to release IgM antibodies
    - T-cell dependent activation = This is where cells called dendritic cells phagocytose the antigen and present it on its cell surface using MHC II molecules, which are recognised by Th2 CD4 cells (T-helper cells). These T-helper cells become activated and when they meet a B cell presenting the same antigen then they activate that B cell. There is always co-stimulation in these processes.

    Hopefully that answers your question a little, if it doesn't at all then let me know and I can make a better attempt at explaining it simply haha

    Note: I edited it because I got something a little wrong, I hope everything above is correct now!
    Ah okay, and where would the cytokines come in?
    For a T-helper cell to activate a B cell, must the B cell be presenting an antigen they acquired through T-cell independent activation?
    Can a B cell be activated by contact with a pathogen presenting its own antigens?
    And what do you mean by 'co-stimulation'?

    Sorry for all the questions haha. And btw, I love your username!
    Offline

    10
    ReputationRep:
    (Original post by ConfusedSnowball)
    Ah okay, and where would the cytokines come in?
    For a T-helper cell to activate a B cell, must the B cell be presenting an antigen they acquired through T-cell independent activation?
    Can a B cell be activated by contact with a pathogen presenting its own antigens?
    And what do you mean by 'co-stimulation'?

    Sorry for all the questions haha. And btw, I love your username!
    No don't worry about the questions! Let me explain a bit better:

    B cells and dendritic cells are known as antigen presenting cells (APCs), this means that they phagocytose antigens and present a bit of it on their surface (known as the "epitope" I think). These dendritic cells and B cells then migrate to the lymph nodes. The dendritic cells present the antigen on its surface which is then bound to by a T-helper cell. The T-helper cell is now active and begins searching for a B cell that is also presenting the same antigen on its surface (because remember that B cells are also APCs), if the T cell finds a B cell presenting the antigen, then it will bind and activate the B cell to begin forming plasma cells (and memory cells).

    The co-stimulation I referred to will be the release of cytokines when a receptor binds to an antigen being presented on a cell, you need the receptor binding AND the stimulation by cytokines for activation to occur. Cytokines are released all over the place in immune responses, in particular interleukins and interferons. So in answer to your original question, B cells are activated by T cell dependent activation when they present an antigen on their surface from phagocytosis and are then bound to by a T helper cell.

    As for your second question, as I said before, B cells CAN be activated directly by the antigen (T cell independent activation), but as far as I know this only occurs with specfic antigens.

    Anyway I hope that helps, my immunology is a bit shaky as it's been just under a year since I revised it all, and it's a complicated topic, I tried summarising the whole immune resonse on an A4 page last year, it's really good but very confusing!
    Offline

    10
    ReputationRep:
    (Original post by ConfusedSnowball)
    Ah okay, and where would the cytokines come in?
    For a T-helper cell to activate a B cell, must the B cell be presenting an antigen they acquired through T-cell independent activation?
    Can a B cell be activated by contact with a pathogen presenting its own antigens?
    And what do you mean by 'co-stimulation'?

    Sorry for all the questions haha. And btw, I love your username!
    Name:  16491424_1564530726909221_1881026463_o.jpg
Views: 23
Size:  108.6 KB

    Here you go, here's my summary if you're interested (you obviously won't need to know this much detail for AS level, but if you're into medicine/immunity then it might be a little interesting). But don't worry if you can't understand most of it, because I don't either and I made it..
    Offline

    11
    ReputationRep:
    (Original post by AortaStudyMore)
    The T-helper cell is now active and begins searching for a B cell that is also presenting the same antigen on its surface (because remember that B cells are also APCs), if the T cell finds a B cell presenting the antigen, then it will bind and activate the B cell to begin forming plasma cells (and memory cells).
    Shouldn't this be if the B cell has a receptor that's complementary to the epitope, as wouldn't the B-cell already have been activated if it was bound to its complementary antigen?
    Offline

    10
    ReputationRep:
    (Original post by h3rmit)
    Shouldn't this be if the B cell has a receptor that's complementary to the epitope, as wouldn't the B-cell already have been activated if it was bound to its complementary antigen?
    The BCR binds to the antigen and takes up the antigen before processing it and presenting it on MHCII molecules. The T-helper cells have CD4 molecules and so bind to cells presenting MHCII, ie the B cells. Once bound, the T cell releases cytokines to stimulate the production of transcription factors in the B cell that allows it to differentiate into a plasma cell. The B cell is activated by the T cell, which was originally activated by the dendritic cell. As my diagram shows, I think follicular dendritic cells can directly activate B cells, but I never really got around the mechanism of that when revising for my exam last year.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.