Lesson 3.1 - Immune Defenses Flashcards
Immune Defenses
Why is immunology important?
- Health - Illness - Homeostasis
- Immune system disorders
- Opportunistic infections & cytokine storm
- Understand vaccination & antibody therapy
- Study bacteria and viruses
- Educate patients and discredit pseudoscience
What is a cytokine storm?
Life-threatening systemic inflammatory syndrome caused by high cyotkine levels
Define antigens
- Substances that bind to immunoglobulin receptors / T-cell receptor
- Induce immune response
Define epitopes
- Immunologically active regions of antigens
- Part of antigen by which antibody attaches
Define Pathogen-associated molecular patterns (PAMPs)
- Molecules unique to microorganisms (not human cells)
- Recognized by innate immune cells & toll-like receptors (TLRs) on leukocytes
- Have epitopes
Examples of PAMPs
Carbohydrates, lipoproteins, Lipid A-endotoxin, peptidoglycan, flagellar proteins, nucleic acids
Define cytokines
- Low weight, soluble, chemical messengers
- Regulate innate & adaptive immune systems
- Stimulate hematopoiesis
*Cells that produce cytokines:
Macrophages, dendritic cells, T-lymphocytes, Natural killer cells, endothelial cells, & mucosal epithelial cells
Define chemokine
Cytokines produced during inflammation, that organize leukocytes
[3] Classifications of Cytokines
- Pleiotropic
- Cytokine acts on a # of different types of cells
- Redundant
- Different cytokines carry out same function
- Multifunctional
- Same cytokine regulates diff. functions
Variable region of antibody
Fab = fragment antigen binding; highly specific for epitope
Constant region of antibody
Fc = fragment crytallizable
[6] Parts of Antibody
- Fab region
- Fc region
- Heavy chain
- w/ 1 variable, followed by 1 constant domain, 1 hinge, and 2 constant domains
- Light chain
- w/ 1 variable & 1 constant domain
- Antigen binding site = paratope
- Hinge regions
[3] Lines of Defenses
- 1st: External Barriers
- 2nd: Innate - Non-specific
- 3rd: Adaptive - Specific
External Barriers
1st line of defense
Skin, sebaceous gland, ear wax, cilia, nasal hair, mucous, saliva, tears (lysozome), stomach acid, urine flow, microflora in digestive/upper respiratory
Innate Defenses
- Non-specific & lacks immunological memory
- Acts immediately after foreign substance exposure
- Contains cellular & non-cellular components
[2] Types of Innate Defenses
- Cellular defenses
- Non-cellular defenses
Cellular defenses
- All cells originated from bone marrow stem cells
- Several types involved in innate response
Non-cellular defenses
- Heparin: anticoagulant
- Histamines: inflammatory response
- Lysozyme: hydrolyzes ß-1,4 peptidoglycan
- Complement pathway: antimicrobial proteins
Examples of leukocytes (of innate immunity)
Basophils, neutrophils, eosinophils, monocyte (macrophages & dendritic cells), mast cells
Basophils
Inflammatory histamine & anti-coagulant heparin
Mast cells
Histamines & heparin; confined to tissues
Eosinophils
Phagocytic & secrete protein toxins (kills parasitic worms)
Neutrophils
- Phagocytic; release O2- and H2O2
- Extracellular traps (NETs); DNA entangles cells
- Perform diapedesis
Diapedesis
Movement of leukocytes, through intact capillary walls, into surrounding body tissue
Monocytes
- Mature into macrophages & dendritic cells
-
Wandering macrophages
- Move throughout body
- Scavenge bacteria, fungi, spores, dust, and dead body cells
-
Fixed macrophages
- Stay within defined area/organ
- Alveolar (lung), microglia (CNS), Kupffer cells (liver)
-
Wandering macrophages
Dendritic Cells
- Long, thin cytoplasmic extensions; phagocytic
- Found under skin surface & mucous membranes
- Migrate to lymph nodes
Phagocytosis
phagosome + lysosome = phagolysosome
Leukocyte chemotaxis
- Movement of organism/cell along chemical concreation gradient either toward/away from chemical stimulus
- Leukocytes attracted to injury because lots of attractants
Complement Pathway - antimicrobial peptides (& Functions)
- Can be brought in action by adaptive immune system
- 20 antimicrobial proteins in C1 pathway
- Functions:
- Attach to bacteria via antibodies
- Lyse bacterial cells
- Signal phagocytes (chemotaxis)
- Activate inflammation
- Vasodilation
___ binds to the Fc region of antibodies, a microbe or C-reactive protein
C1q
_________ increases when there is a condition causing inflammation
C-reactive protein
Activation of C1 during Classical Complement Pathway
- Fab of 2 IgG molecules OR 1 IgM molecule bind to epitopes
- C1 binds, becomes active enzyme
- C1 cleaves C2 & C4
- C2 & C4 combine, cleaves C3 = C3a + C3b
- C3b joins C2, cleaves C5 = C5a + C5b
- C3b & C4b = opsonins (facilitate binding)
- C5b: used for membrane attack complex (MAC)
3rd Line of Defense Overview
- Antigen-specific
- Immunological memory
Define antigens
- Pieces of foreign molecules
- Adaptive immune system recognizes as part of microorganism
Antigen-MHC complex
Macrophages & dendritic cells digest pathogens and present antigens
Antigen Presenting Cells (APC)
- Migrate to lymphatic system
- Lymph nodes, spleen, & other lymphatic tissue
- Release cytokines that attracted helper T cells (TH)
- Interact with lymphocytes (B & T cells)
Define Lymphocytes (and types)
- Main cells of Adaptive Immune Sys.
- Arise and mature in lymphatic system organs: bone marrow & thymus
- Types:
- B cells
- T cells
- Natural Killer cells
B cells
Produce antibodies (Abs) that flag pathogens in blood, lymph, & tissue fluids
T cells
Destroy virally infected & some neoplastic cells; regulate immune response
Natural Killer cells
Secrete teoxins that kill virally infected cells & some neoplasms; don’t need to be activated
Helper T cells (TH)
- Have receptors that may bind to antigen by APC
- Randomly generated during development
- May have 100k identical receptors
- Replicate furiously upon recognition
- Some become effectors; others memory cells
- Effector TH cells release cytokines to activate cytotoxic T cells (TC)
Cytotoxic T cells (TC)
- Kill infected cells; activated by interleukin-2 (IL-2)
- Leave lymphatic system in search of infected host cells
- Effector TC stimulates proliferation of TC cell
- Bind and release perforin = infected cell dies
Humoral immunity
- Antibodies (Abs)
- TH cells release IL-4 and IL-5 to activate B cells
- B cells have antibodies on surface
How are B cells activated?
- Binds to both an antigen and is stimulated by a TH cell
- Divides rapidly when activated (long-lived memory & short-lived plasma cells)
Neutralization
- Abs coat surface of viral particles preventing them from attaching to cell receptors
Agglutination
Clumping of cells (i.e. bacteria, erythrocytes) in presence of antibody
Define opsonins.
Any molecule that forms connections b/t phagocyte & antigen; increases efficiency (not required)
What can affect the success of the adaptive response?
- Number of pathogens
- Virulence of pathogens
- Status of host immune system
- Immunocompromised
Cellular vs Humoral Immunity
