Adaptive Immune System

Question 1

What are the key differences between the adaptive and innate immune systems?

Answer 1

• 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

Question 2

Describe B Lymphocytes

Answer 2

• secrete antibodies/immunoglobulins
• develop in bone marrow

Question 3

Describe T-Lymphocytes

Answer 3

• 2 cell types: CD4+ (helper), CD8+ (cytotoxic)
• T-cell progenitors arise in bone marrow and migrate to thymus

Question 4

Describe CD4 and CD8 T cells

Answer 4

• CD4+ secretes kinase and other substances to assist immune cells
• CD8+ kills infected host cells

Question 5

Which lymphoid organs to B and T cells migrate through in the bloodstream?

Answer 5

• lymph nodes
• spleen
• mucosal surfaces

Question 6

What are the main 2 antigen receptors?

Answer 6

• T-Cell Receptor (TCR)
• B-Cell Receptor (BCR)
  both surface transmembrane immunoglobulin

Question 7

Describe antigens

Answer 7

• 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

Question 8

What is T and B cell diversity and how is it created?

Answer 8

• each naïve cell has a different receptor on surface
• created by random rearrangements in DNA that encode the TCR/BCR

Question 9

Describe B-Cell receptor function

Answer 9

• can be shed into the blood and tissue fluid as antibodies
• antibodies are soluble BCRs

Question 10

Describe antibody structure

Answer 10

• 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

Question 11

Describe B cell activation

Answer 11

• 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

Question 12

Describe TCR function

Answer 12

• interact with antigenic peptides in MHC molecules
• will only recognise antigens if shown off by an MHC
• only peptides

Question 13

What does MHC stand for?

Answer 13

Major Histocompatibility Complex

Question 14

What are the 2 types of MHC?

Answer 14

• class I
• class II

Question 15

Describe MHC class I

Answer 15

• 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

Question 16

Describe MHC class II

Answer 16

• 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

Question 17

Describe Cytotoxic T-Lymphocyte (CTL)

Answer 17

• 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

Question 18

Describe the 2 killing mechanisms of CTL

Answer 18

• perforin/granzyme killing - secretions that trigger an apoptotic process
• FAS mediated killing

Question 19

Describe adaptive immune system memory

Answer 19

• 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

Question 20

Describe the effects of memory T and B cells on a 2nd exposure immune response

Answer 20

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