Cells of Immune System

Question 1

What are the principles of the immune system

Answer 1

• Cell communication
• Control of cell migration
• Compartmentalisation of tissues
• Regulation of gene expression in leukocytes (cytokines, Ag receptors, adhesion molecules)
• Homeostatic mechanisms that keep cells alive or that direct cell death
• Tailored to the particular organism involved

Question 2

How has our perspective of immunity changed from the 1900’s to 2020

Answer 2

• 1900s: Immunologists didn’t study plants or insects, focused on rodents or humans, innate immunity, microbiology and adaptive immunity all separate
• 1960-1990: Lymphocyte subsets, innate cell subsets, cytokines and signalling, PRRs intracellular vs extracellular, PRR ligands in humans, plants, animals and insects
• 1996-2020: Interconnection of innate immunity, adaptive immunity and microbiology through PAMPs, DAMPs and PRRs

Question 3

Who was Edward Jenner

Answer 3

• Edward Jenner: 18th, Introduced immunology, cow pox prevents against small pox
• Elie Metchnikoff: Discovered macrophages / phagocytic cells
• Robert Koch: Infection caused by microorganisms / pathogens (bacteria, fungi, parasites, viruses)
• Emil Von Behring / Shibasaburo Kitasato: Discovered antibodies, bind toxins and neutralise activity
• Louis Pasteur: Extended Jenners concepts to develop vaccines

Question 4

Briefly describe the innate vs adaptive immune response and their cooperation

Answer 4

• Innate: Response time of minutes to hours, limited and fixed specificity, response to repeat infection is the same each time, involves physical / chemical barriers, phagocytes (pattern recognition molecules)
• Adaptive: Response time of days, highly diverse specificity (adapts to improve), more rapid and effective response with subsequent exposure, T / B cells, antigen specific receptors and antibodies
• Cooperation: Activation of innate responses produce cytokines which stimulate and direct adaptive immune responses

Question 5

What is innate immunity

Answer 5

• Immediate activation of body’s innate and relatively nonspecific defence mechanisms
• Available to combat a wide range of pathogens
• Does not lead to lasting immunity
• First line of defence (fast but nonspecific)
• Uses germ line encoded recognition molecules / pattern recognition receptors (PRRs)
• Expressed by phagocytic cells, epithelial and endothelial cells

Question 6

What is adaptive immunity

Answer 6

• Takes time to develop
• Highly specific to antigen molecules
• Humoral and cell mediated
• Randomly generated antigen receptors (BCR / TCR)
• Response occurs over lifetime as an adaptation to infection with a pathogen
• Immunity to reinfection
• Mediated by clonal selection of antigen specific lymphocytes

Question 7

What are antigens and antibodies

Answer 7

• Antigens: Stimulate production of an antibody generation, any substance that can be recognised and responded to by the adaptive immune system
• Antibodies: Immunoglobulins produced by plasma cells to neutralise pathogens, can be induced against a vast range of substances

Question 8

What is the humoral vs cell mediated response

Answer 8

• Humoral: Combats pathogens via antibodies, antibodies are produced by B cells, antibodies can be transferred between individuals to provide passive immunity
• Cell Mediated: Involves primarily T lymphocytes, these can eradicate pathogens, clear infected self-cells, or aid other cells in inducing immunity

Question 9

What are the common myeloid progenitor cells

Answer 9

• Erythrocyte: RBC
• Myeloid / Conventional DCs: Presentation of Ag to naive T cells for initial activation
• Monocyte: Mononuclear phagocytic WBC, immature macrophage
• Granulocyte: WBC that contain cytoplasmic granules (basophil, eosinophil, neutrophil)
• Megakaryocyte: Hematopoietic cells in myeloid system that give rise to platelets

Question 10

What are subcategories of granulocytes

Answer 10

• Neutrophils: Phagocytic, involved in tissue remodelling, vasodilation, inflammation and regulation fo proteases, granules contain proteases, antimicrobial proteins, protease inhibitors and histamine)
• Basophils: A non-phagocytic granulocyte, granules contain cytokines, lipid mediators and histamine,
• Mast Cells: A bone-marrow-derived cell present in a variety of tissues, granules contain cytokines, lipid mediators and histamine, regulation of inflammation, vasodilation, adaptive immunity
• Eosinophils: Motile, phagocytic granulocytes, granules contain cationic proteins, ribonuclease’s, cytokines and chemokine’s antiviral activity, attract leucocytes

Question 11

What are the common lymphoid progenitor cells

Answer 11

• Plasmacytoid DCs: Specific role in antiviral immunity
• Lymphocytes: A mononuclear leukocyte that mediates humoral or cell-mediated immunity, produced in bone marrow or thymus, small cytoplasm, varying cell surface molecules
• Natural Killer Cells: Defensive cell (a type of lymphocyte) that can kill cancer cells and virus-infected body cells before the adaptive immune system is activated

Question 12

What are haematopoietic stem cells and what are the lineages resulting from differentiation

Answer 12

• Cell type from which all lineages of blood cells arise
• Undergo haematopoiesis (formation / differentiation of BC), progenitors (CMP / CLP)
  CMP
• Megakaryocyte
• Erythrocyte
• Mast cell
• Myeloblast (granulocyte)
• Myeloid / common DCs
  CLP
• Natural killer cell
• T lymphocyte
• B lymphocyte
• Plasmacytoid DCs

Question 13

What are the subcategories of lymphocytes

Answer 13

• B: Lymphocytes that mature in the bone marrow and express membrane-bound antibodies. After interacting with antigen, they differentiate into antibody-secreting plasma cells and memory cells.
  T: Lymphocytes that mediate cellular immunity; include helper, cytotoxic, regulatory, and memory cells

Question 14

What are the CD markers present on CLPs

Answer 14

• B: CD5, CD19, CD21, CD32, CD35, CD40, CD45
• Th: CD2, CD3, CD4, CD5, CD28, CD45
• Tc: CD2, CD3, CD5, CD8, CD28, CD45
• NK: CD2, CD5, CD16, CD45, CD56