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

    15
    ReputationRep:
    Hi,

    So I'm a bit confused about MHC 2 presentation. I'm not sure of where B cells fit into this in terms of clonal selection and expansion.

    To my understanding:

    Antibodies on B cells recognise antigens from invading pathogens and bind to them which activates B cells. (clonal selection)

    It is then taken up by the B cell (phagocytosis?) and part of it is presented on MHC 2.

    T cells bind to the MHC 2 - peptide complex,

    The B cells can then undergo clonal expansion.

    Is this a correct summary?

    Thanks!
    Offline

    11
    ReputationRep:
    (Original post by white_o)
    Hi,

    So I'm a bit confused about MHC 2 presentation. I'm not sure of where B cells fit into this in terms of clonal selection and expansion.

    To my understanding:

    Antibodies on B cells recognise antigens from invading pathogens and bind to them which activates B cells. (clonal selection)

    It is then taken up by the B cell (phagocytosis?) and part of it is presented on MHC 2.

    T cells bind to the MHC 2 - peptide complex,

    The B cells can then undergo clonal expansion.

    Is this a correct summary?

    Thanks!
    MHC II molecules are only expressed on the surface of professional antigen presenting cells (APCs) such as dendritic cells, macrophages and B-cells. This is in contrast to MHC I molecules, which present endogenous peptides (i.e. originating from within the cell), which are expressed on the surface of all nucleated cells.

    Let's use the B-cell as the APC, as that is what you mentioned. When antigen binds to the B-cell receptor, it is taken into the B-cell via endocytosis and lysosomes then fuse with the phagosome, which degrade the antigen into multiple peptides (phagocytosis). The peptides then associate with MHC II molecules and are transported to the cell surface, where the MHC II: peptide complex is presented to helper T-cells (CD4+ T cells). The T-cell receptor then binds to the MHC II: peptide complex, which activates the helper T cell. The helper T cell then release cytokines which activates the B-cell, causing it to proliferate differentiate into plasma cells (which secrete antibody) or memory B-cells.

    The APC doesn't have to be a B-cell though. As I said, it could be a dendritic cell or a macrophage. The process is the same. Macrophages/dendritic cells phagocytose the antigen and present peptides on MHC II molecules on their surface. Helper T cells then bind to the MHC II: peptide complex, which activates the helper T cell. The activated helper T cell proliferates and differentiates into effector helper T cells and memory T cells. The effector helper T cells secrete cytokines which can activate B-cells (amongst other things), causing B-cells to proliferate and differentiate, as I mentioned previously.
 
 
 
  • 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
    Will you be richer or poorer than your parents?
  • 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.