Cells and Organs of the Immune System I and II

Question 1

describe antigen factors in immunogenicity

Answer 1

• molecular size: generally > 100,000 Da
• chemical composition:
  
  • greater complexity (heterogeneity) = greater immunogenicity
  • generally proteins > carbohydrates > lipids
  • susceptibility to processing and presentation
  • D-amino acids cannot be processed
• adjuvant:
  
  • BSA in mice; alum in humans
  • generally increase persistence of antigen and innate response (inflammation, stimulation of APC and/or lymphocytes)

Question 2

describe host factors in immunogenicity

Answer 2

• genotype of host:
  
  • MHC gene products
  • B cell receptors
  • TCR
• dosage and administration:
  
  • low doses may induce tolerance or fail to stimulate enough lymphocytes
  • boosters increase clonal selection
  • route: slow reelase is important for immune response:
    
    • subcutaneous > intraperitoneal > intravenous > intragastrical
    • oral route induce local mucosal immunity but not systemic immunity

Question 3

summarize the factors that influence the immunogenicity of proteins

Answer 3

Question 4

describe the innate arm of the immune system

Answer 4

• molecular and cellular mechanisms preformed and fully active (immediate reaction)
• non-specific
  
  • distinguishes between self and pathogens but not specialized to distinguish small differences in the foreign particles
• components:
  
  • barriers that protect host
    
    • skin, including its usual skin flora
    • mucous membrane
    • acidity of stomach
    • lysozymes in fluids
  • phagocytic cells
  • antimicrobial peptides (interferons, complement)
  • temperature

Question 5

describe the acquired (adaptive) arm of the immune system

Answer 5

• develops in response to infection
• adapts to recognize, eliminate, and remember pathogens
• highly specific
• takes several day for this arm to become fully functional
• components: cell-mediated immunity and antibody-mediated (humoral) immunity

Question 6

name the cellular and humoral components of the innate vs adaptive system

Answer 6

Question 7

summarize the lineage of immune cells from a stem cell

Answer 7

Question 8

summarize the CD markers on leukocytes

Answer 8

Question 9

describe the APCs

Answer 9

Question 10

describe the general activites of macrophages

Answer 10

• to survey tissue compartments and discover microbes, particulate matter and dead or injured cells
• to inget and eliminate these materials
• to extract immunogenic information from foreign matter

Question 11

describe neutrophils (granulocyte)

Answer 11

• multi-lobed nucleus: 2-5 lobes
• different granules
• 1st to arrive at site of inflammation
  
  • high #’s is 1st indication of infection
• destroy organisms by:
  
  • phagocytosis
  • release of hydrolytic enzymes
• neutrophiles are very short lived (10 hrs in blood, 1-3 days in tissue)
  
  • come out of blood vessels ready to kill, would cause too much damage to tissues if long lived

Question 12

describe eosinophils (granulocyte)

Answer 12

• bilobed nucleus
• located mainly in tissue
• small central Golgi apparatus, and limited ER and mt
• phagocytize
  
  • specific granules and azurophilic granules
  • specific granules (crystalloid):
    
    • inside: basic proteins, cationic protein, neurotoxin
    • outside: histaminase, peroxidase, cathepsin
• functions:
  
  • play a role in elimination of parasitic helminths and allergic reactions
  • phagocytize antigen-antibody complexes

Question 13

describe basophils (granulocyte)

Answer 13

• bilobed, S-shaped nucleus
• granules:
  
  • basophilic specific granules:
    
    • heparin, histamine, chemotactic factors, peroxidase
• survive long periods of time (2 years in mice)
• non-phagocytic
• functions:
  
  • play a role in allergic reactions

Question 14

describe mast cells (and 2 ways to activate them)

Answer 14

• similar to basophils
• play important role in development of allergies
• two pathways for activation:
  
  • innate TLRs
  • antibody-dependent (IgE)

Question 15

describe the function of the 3 classes of lymphocytes (T cells, B cells and NK cells)

Answer 15

• T cells are involved in cell-mediated immunity (cellular immunity)
• B cells are antibody-mediated immunity (humoral immunity) because antibodies circulate widely in body fluids
• NK cells perform immune surveillance, attacking foreign cells, body cells infected with viruses and cancer cells

Question 16

describe B-lymphocytes (B-cells)

Answer 16

• site of maturation
  
  • bone marrow in mammals
• display membrane-bound immunoglobulin (antibody)
• once antigen is encountered:
  
  • differentiation
  • plasma cells - antibody secreting cells, die within 1-2 weeks
  • memory B cells - same membrane-bound antibody as parent B cell, longer life span

Question 17

describe T lymphocytes

Answer 17

• site of maturation: thymus
• T cell receptor
  
  • only recognize antigen (peptides) that is bound to cell membrane proteins called major histocompatability complex (MHC)
  • once antigen is encountered with MHC:
    
    • differentiation
      
      • effector T cells
        
        • T helper, T cytotoxic, T regulatory or T suppresor
      • memory T cells

Question 18

describe T helper cells

Answer 18

• mature T_h cells express the surface glycoprotein CD4 and are referred to as CD4+ T cells
• recognizes antigen presented in MHC class II (extracellular/phagocytized)
• “help” activation of B cells, T_c cells, macrophages in immune response

Question 19

describe T cytotoxic cells

Answer 19

• mature Tc cells express the surface protein CD8 and are referred to as CD8+ T cells
• recognizes antigen presented in MHC class I
  
  • eliminates virus/intracellular microbes infected cells or cancerous cells

Question 20

describe T regulatory cells

Answer 20

• mature T regulatory (suppressor) cells express the surface glycoprotein CD4, CD25 and FOXP3
• help suppress the immune system after it’s been upregulated after the infelction is cleared
• maintain tolerance to self-antigens and prevent autoimmune diseases

Question 21

describe memory T cells

Answer 21

• T cells that have previously encountered and responded to their cognate antigen
• at a second encounter with the invader, memory T cells can reproduce to mount a faster and stronger immune response
• memory T cells may be either CD4+ or CD8+

Question 22

name the 2 major cytokines of T regulatory cells (CD25)

Answer 22

IL-10 and TGF-B

Question 23

summarize the functions of T cell types and their cytokines

Answer 23

Question 24

describe natural killer cells

Answer 24

• innate immune response
• large, mononuclear, granular
• surface markers CD16 (FcyRIII) and CD56

Question 25

contrast humoral immunity and cell-mediated immunity

Answer 25

Question 26

describe dendritic cells

Answer 26

• long membranous extensions (stellar)
• CD14+
• 4 major groups:
  
  • lymphoid or plasmacytoid-derived DC
  • monocyte-derived or myeloid DC
  • Langerhans DC
  • follicular DC
    
    • no MHCII
    • different from above 3 types in fxn
• functions:
  
  • surveillance
  • initiation of inflammatory response
  • stimulation of adaptive immune system
    
    • antigen processing and presentation
    • take a “snapshot” of what is happening in the tissues and carry this image to the lymph node

Question 27

describe the bone marrow (primary lymphoid organ)

Answer 27

• lymphocytes arise in the bone marrow
  
  • T cells go to thymus to mature
  • B cells mature in the bone marrow
    
    • 90% of plasma IgG and IgA comes from B cells in the bone marrow

Question 28

describe the thymus (primary lymphoid organ)

Answer 28

• T cell development and maturation
• thymus will induce death of those T cells that can’t:
  
  • recognize self-MHC molecules
  • those that interact with MHC molecules too strongly
• function decreases with age (from puberty)

Question 29

describe the cells located in the cortex vs medulla of the thymus

Answer 29

• cortex = immature thymocytes
• medulla = immunocompetent T cell (mature)

Question 30

describe the 3 regions of the lymph nodes (secondary lymphoid organs)

Answer 30

1. cortex
   
   • B cells mainly
   • primary follicle: un-activated lymphoid folicle
   • secondary follicle: activated
     
     • germinal centers = production of plasma and memory cells
2. paracortex
   
   • T cells, dendritic cells (APCs)
   • activation of T cells
   • interaction of T and B cells
3. Medulla
   
   • plasma cells secreting antibody and macrophages

Question 31

describe the spleen (secondary lymphoid organ)

Answer 31

• functions:
  
  • filter blood
  • activation of lymphocytes from blood borne pathogen
    
    • important in systemic infxns
• structure: surrounded by a capsule
  
  • compartments: separated by a marginal zone
    
    • red pulp: remove old or defective erythrocytes and platelets
    • white pulp: the periarteriolar lymphoid sheet (PALS) with T-cells
    • follicles with B lymphocytes
• marginal zone:
  
  • antigens meet APCs
  • phagocytosis of antigen by innate system
  • APCs meet lymphocytes that lead to initiation of immune response