Adaptive Immune System Flashcards
What are the key differences between the adaptive and innate immune systems?
- innate based on receptors that do not change and recognise specific structures
- adaptive based on receptors that randomly recombine within lifetime of individual to target any structure
- adaptive vertebrates only, innate in all
Describe B Lymphocytes
- secrete antibodies/immunoglobulins
- develop in bone marrow
Describe T-Lymphocytes
- 2 cell types: CD4+ (helper), CD8+ (cytotoxic)
- T-cell progenitors arise in bone marrow and migrate to thymus
Describe CD4 and CD8 T cells
- CD4+ secretes kinase and other substances to assist immune cells
- CD8+ kills infected host cells
Which lymphoid organs to B and T cells migrate through in the bloodstream?
- lymph nodes
- spleen
- mucosal surfaces
What are the main 2 antigen receptors?
- T-Cell Receptor (TCR)
- B-Cell Receptor (BCR)
both surface transmembrane immunoglobulin
Describe antigens
- any substance that can bind to specific lymphocyte receptors and so induce an immune response
- can be lipids, carbohydrates, proteins
- a pathogen will contain multiple
What is T and B cell diversity and how is it created?
- each naïve cell has a different receptor on surface
- created by random rearrangements in DNA that encode the TCR/BCR
Describe B-Cell receptor function
- can be shed into the blood and tissue fluid as antibodies
- antibodies are soluble BCRs
Describe antibody structure
- monomers have 2 heavy and 2 light polypeptide chains
- disulphide bonds link chains
- antigen binding region is the variable region
- Fab fragment = light chains
- Fc fragment = heavy chains
Describe B cell activation
- cross-linked BCRs help activate
- activated cells release cytokines and antibodies
- produces more B cells with correct antibody
- endocytose, process and present antigens to T cells via MHC class II
Describe TCR function
- interact with antigenic peptides in MHC molecules
- will only recognise antigens if shown off by an MHC
- only peptides
What does MHC stand for?
Major Histocompatibility Complex
What are the 2 types of MHC?
- class I
- class II
Describe MHC class I
- mostly presents intracellular antigens
- helps detect and kill infected cells
- present on nearly all cells
- function is T-Cell mediated killing of intracellularly infected cells
- only CD8+ T cells interact with class I
Describe MHC class II
- mostly presents extracellular antigens
- helps respond to extracellular and intracellular infections
- present on dendritic cells, macrophages, B-Cells
- function is T-Cell mediated help cytokine release, activating B-Cells
- CD4+ T Cells only interact with class II
Describe Cytotoxic T-Lymphocyte (CTL)
- major effector of adaptive immune system
- requires activation in lymphoid tissues via MHC class I or TCR interaction
- then migrates to infection site and recognises infected cells via MHC class I
- continually scans and monitors every cell
Describe the 2 killing mechanisms of CTL
- perforin/granzyme killing - secretions that trigger an apoptotic process
- FAS mediated killing
Describe adaptive immune system memory
- during an infection, activated T and B cells divide
- cytokine IL-2 released and IL-2 receptor expressed
- IL-2 drives T-cell proliferation
- at resolution of infection, most specific T and B cells die
- some remain as memory T or B cells and plasma cells
- can survive in an individual for a lifetime
Describe the effects of memory T and B cells on a 2nd exposure immune response
allows it to be:
- faster - easier to activate memory cells
- larger - more antibodies
- more efficient - higher affinity BCR/TCR
- more effective - different antibody sub-classes
