B and T cells

B and T cells

1. Humoral responce

   • Is activated when the infection is no in any cell
   • Activation phase
     • 1. Antigen-presenting cells engulf and breakdown antigens that are invading the host organism via the usage of Lysozyme
     • 2. Broken down antigens combine with MHC 2 proteins and are presented to the surface of the APC
     • 3. Helper T cells recognise the MHC-2 and antigen complex and bind to the APC
     • 4. The binding activates the APC to release cytokines that activate the Helper T cell
     • 5. The activated helper T cell then releases cytokines that help it proliferate causes more T cells to be made with the specific MHC-2 complex receptor
   • Effector phase
     • 6. A B-cell with an igm-receptor that corresponds to the antigen attaches to the pathogen
     • 7. The antigen is then engulfed with the receptor and they are both degraded via lysozyme
     • 8. The MHC-2 and antigen bind to form the MHC-2 complex and are presented onto the surface of the B-cell
     • 9. The helper T-cell and B-cell bind causing the helper T-cell to release cytokines that cause the B-cell to proliferate into many identical B-cells
     • 10. The new B-cells either form plasma cells or memory cells
       • 10.1. Plasma cells release antibodies that are specific to the antigen present and bind to the antigen via lock and key for killer cells to attach, engulf and breakdown
       • 10.2. Memory cells remain after the infection is treated incase the antigen attacks again

2. Cellular Responce

   • Activation Phase
     • 1. Antigen-presenting cells engulf and breakdown antigens that are invading the host organism via the usage of Lysozyme
     • 2. Broken down antigens combine with MHC 2 proteins and are presented to the surface of the APC
     • 3. Whilst this occurs the virus infects epithelial cells, these cells also use lysozyme to breakdown the antigen and present it with MHC 1 to the surface
     • 4. A helper T cell recognises the MHC-2 and antigen complex on the APC
     • 5. The helper T cell release singling proteins bringing more and more helper T cells, Cytotoxic T cells (CD8+)
   • Effector Phase
     • 6. Cytotoxic T cells recognise the MHC1 and antigen complex presented on the endothelial cells and bind to the complex
     • 7. The binding causes the release of Perforin, which punches holes into the infected cells causing lysis
     • 8. As the infection comes under control regulatory T cells inactivate the Cytotoxic T cells
     • 9. Memory T cells remain behind incase the infection begins to attack again
   • Is activated when a cell is already infected

3. B cells

   • General Facts
     • 15% of lymphocytes
     • Matures in bone marrow
     • Generally need T cells for activation
     • Effective antigen presenting cells
   • Antigen recognition
     • MHC 2 is unregulated
     • Anti CD40 induce B cells response to Ab-Ag + IL-4= mimics T cell
     • No further signal from IL-4 or BCR = cell death
   • B cell after differentiation into plasma cells helped by T cells, become Antibody factories

4. T cells

   • General facts
     • Two types
       • CD4+ 65%
       • CD8+ 35%
     • Originates in bone marrow but matures in the thymus
     • After negative and positive selection at the thymus they acquire the capacity to distinguish self from non self.
   • Antigen recognition
     • The combination of TCR binding peptide with either the MHC 1 or MHC 2 allows the T cell to recognise antigens
     • For recognition TCR must bind with other accessory proteins to make a TCR complex
     • The signal is not transduced by the TCR but by the accessory proteins, which causes a cascade of events causing cell action
   • T cell receptors recognize peptides only when they are presented by the MHC