1. Understand the role of the immune system
  2. Understand the factors that contribute to pathogenicity and host
    • Virulence
    • Attributes of the pathogen
    • Eg: Escherichia coli, there are harmless forms in the gut (normal) and
    • forms with virulence factors- enterotoxigenic, enteropathogenic,
    • enterohemorrhagic, uropathogenic, etc.
    • Susceptibility
    • Attributes of the host (age, sex, stress, genetic, nutrition status, behavior)
    • Eg: immune suppression secondary to chemotherapy
  3. Understand barrier protection and innate immunity
    • Non-specific, endogenous
    • Present at major portals into the organism
    • Respiratory tract, gastrointestinal tract, reproductive
    • tract, SKIN
    • Relies on the fact that invading organisms differ from the
    • host’s normal body components
    • Initial defense against pathogen invasion
    • Skin
    • Prevents desiccation, blocks entry of large pathogens
    • Mucous membranes & ciliated epithelium
    • Gastrointestinal microbiota, mucociliary elevator
    • Biological functions
    • Coughing, sneezing, vomiting, diarrhea
  4. Know the role of PAMPs and TLRs in inflammation
    • pamps
    • Present on the cell surface of bacteria, viruses, and fungi
    • Contain highly conserved molecules
    • Complex carbohydrates, nucleic acids, lipoproteins
    • Detected by sentinel cells (host)
    • Receptors on sentinel cells bind PAMPs and initiate
    • immune response
    • Molecules located on the surface of the host’s sentinel cells or
    • intracellularly
    • Single-chain membrane glycoproteins
    • Most important class of pattern-recognition receptors
    • Bind PAMPs on the surface of microbial invaders
    • Initiate intracellular signaling cascade that results in production of
    • cytokines
    • At least 14 TLRs are known
  5. .Understand the role of inflammation in the host
    • Normal, rapid, physiological vascular and cellular
    • response to injury
    • Non-specific (innate immune response)
    • Deliver leukocytes and plasma proteins to the site of
    • cellular injury
    • Dilute, contain, and neutralize pathogens
    • Acute inflammation
    • Alters vascular diameter locally (vasodilation) and
    • causes increase in blood flow
    • Alters endothelium to permit plasma proteins and
    • leukocytes to be extravasated
    • Emigration of leukocytes from the circulation to
    • the site of injury to neutralize pathogen
    • Inflammation = ↑ vascular permeability
    • & release of chemokines = recruitment
    • of leukocytes from the blood
    • (neutrophils, monocytes, etc.)
    • t is inflammation that causes many of the signs and
    • symptoms that we associated with “being sick”
    • NOT the actual pathogen
    • Fever, anorexia, lethargy, depression are the product of
    • cytokine interaction with the central nervous system (CNS)
    • Interleukin (IL)-1, IL-6, tumor necrosis factor alpha
    • (TNFα), and high mobility box protein 1 (HMGB1
  6. Understand the role of complement in the innate immune system
    • Part of the innate immune system
    • Can also be activated by the acquired immune system
    • (classical pathway)
    • First identified as the heat-labile component of serum that
    • “complemented” antibodies in destroying pathogens
    • Consists of serum proteins and membrane receptors
    • Inflammatory, protective, and immunoregulatory role
  7. . Know the consequences of complement activation.
    ACTIVATES TEMINAL PATHWAYThis complex is known as a membrane attack complex (MAC) MACs form transmembrane channels in pathogenic microbes Allows extracellular fluid to rush into the microbe= cell lysis= cell death
  8. Understand the effect of complement deficiency on individuals
    • Canine C3 deficiency- seminar soon to come…
    • MBL deficiency in children
    • Porcine factor H deficiency
    • C6 and C7 deficiency in humans and laboratory
    • animals… ??
    • Occurs in about 5-10% of humans worldwide
    • Disease-associated mutations in the MBL2 gene
    • Gene that codes for proteins that produce MBL
    • Inheritance is unclear
    • Not all individuals with the mutation have the disease
    • Predilection for developing recurrent infections, particularly of the respiratory tract
    • Children are most susceptible to infections, but adults may develop recurrent infections as
    • well
    • Implications for cystic fibrosis??
    • Deficiency in complement-inhibitor
    • protein (factor H)
    • C3b produced in an uncontrolled
    • fashion (bad)
    • Lead to membranoproliferative
    • glomerulonephritis type II (quite bad)
    • Autosomal recessive
    • Common cause of early losses in
    • Yorkshire pigs
    • But… can be bred out of lineages
    • Virtually eradicated in Norway
  9. Understand how host cells utilize cytokines to communicate
    • mmune responses are the product of
    • communication and biochemical interaction of
    • different cell populations (host and pathogen)
    • Immune system must be able to communicate
    • between different cell populations to coordinate
    • effective response
    • Several hundred different proteins== cytokines
    • Short-lived proteins
    • Highly diverse structures and receptors
    • Local or systemic action
    • Pleiotropic
    • Redundant
    • Carefully regulated
    • Toxic in high doses
    • CYT
  10. Understand the differences between cytokines and hormones
    • Hormones generally have one target cell, whereas cytokines may have
    • many target cells
    • Endocrine cells usually secrete one kind of hormone at a time, immune
    • cells secrete several different types of cytokines simultaneously
    • Ex: activated macrophages release at least five different cytokines at
    • once (IL-1, IL-6, Il-12, IL 18, and TNF-α)
    • Many different cytokines have the same effect
    • Redundancy
    • Produced in response to T- and B-cell antigen
    • receptor activation, PAMPs, Ab-Ag complexes
    • Keys step in inflammation!
  11. Understand the role and importance of the acquired immune
    • A second branch of the immune system that “learns”
    • from previous pathogenic encounters
    • Allows the organism to destroy pathogens quickly
    • and more efficiently than the innate immune system
    • alone
    • The more often an organism encounters a specific
    • pathogen, the more efficient its immune system
    • becomes at destroying the pathogen
    • Acquired immune system takes several days to become
    • effective
    • Vs. immediate efficacy of innate immune system
    • Highly effective
    • When an organism develops acquired immunity to a pathogen
    • the risk of successful infection by that pathogen are very low
    • The organism may become immune to the pathogen or may
    • experience a markedly attenuated form of the resultant
    • disease syndrome
    • Ex: Varicella zoster virus (“chicken pox”) in humans
  12. Understand the key differences between the innate immune
    system and the acquired immune system.
  13. Be familiar with the differences between humoral and cellmediated
    immunity (we will discuss these much more in-depth
    throughout the semester).
    • Directed against exogenous antigens
    • Involves extensive employment of antibody (Ab), B cells, and Thelper
    • cells to destroy pathogens
    • Ab is a protective molecule found in the serum of an organism
    • that has experienced an acquired immune response to a
    • pathogen in the past
    • Ab is found in body fluids (humours)
    • Basis for efficacy of vaccination
    • Directed against endogenous (intracellular) pathogens
    • Viruses, intracellular bacteria/protozoa (Mycobacterium
    • tuberculosis, Listeria monocytogenes, Rickettsial parasites)
    • Does not involve Ab, but rather the use of specialized cells (T
    • cells) to identify and destroy pathogens
    • Can detect minute changes in cell populations and direct immune
    • response against invaders
    • Ie: transplants and grafts
  14. Understand how “memory” is generated within the acquired immune system
    • Cells that can trap and process antigen (Ag) and then present it for
    • recognition to the cells in the immune response
    • 2. Cells that have receptors for the processed Ag; can bind and respond to Ag
    • 3. Cells that, once activated by Ag, will produce specific Ab or will participate
    • in the CMI response against Ag
    • 4. Cells that will maintain memory of the event and react rapidly to that
    • specific Ag if it is encountered at a later time
    • 5. Cells that regulate this response and ensure that it functions at an
    • appropriate level
  15. Know the key cells involved in Ag capture, processing, and presentation
    and understand their respective roles
    • The most efficient of the exogenous Ag-processing cells
    • (“professional APC”), also act as sentinel cells (innate immunity)
    • Produced by bone marrow (pluripotent) stem cells
    • Migrate throughout the body and form reticular networks in
    • virtually every type of tissue
    • Excepting the brain, parts of the eye, and testes
    • Most prominent where pathogens are likely to be encountered
    • (eg: skin, lymph nodes, mucosal surfaces)
    • Dendritic cells perform three key functions:
    • 1. Sentinel cells that can activate innate
    • immunity
    • 2. Ag-processing cells that can activate acquired
    • immunity
    • 3. Regulatory cells of both the innate and
    • acquired immune system
    • Small cell body surrounded by a halo of dendrites
    • Dendrites are cytoplasmic processes that allow the
    • dendritic cell to “grab” pathogens
    • Morphology varies based upon the stage of
    • maturation or stage of activation of the dendritic
    • cell
  16. Understand the key differences between Ag processing and presentation
    for exogenous and endogenous Ag
  17. Understand the different roles of the subpopulations of dendritic cells in
    • Myeloid DCs (MDCs)
    • Derived from blood monocytes (the myeloid line)
    • Langerhans cells
    • Long-lived (18 months), found in the epidermis
    • Plasmacytoid DCs (PDCs)
    • Derived from lymphoid precursors (the lymphoid line)
    • Reside in lymphoid tissue (lymph nodes) and blood
    • When exposed to viruses they will produce large amounts of IFN-α and IFN-β- early
    • warning system
    • IMMATURE VS. MATURE Immature DCs are highly specialized Ag-trapping cells When they mature DCs become more efficient Ag-processing cells Maturation begins in response to alarmins (IL-1 and TNF-α) and PAMPs Heparan sulfate binding to TLR4 High mobility group box protein-1 (HMGB1) DCs are called to areas of invasion by HMGB1, chemokines, and defensinsIMMATURE DENDRITIC CELLS Migrate from bone marrow to blood, lymph organs, and peripheral tissues where they act as sentinel cells Short-lived unless they encounter a pathogen Capture cell fragments by phagocytosis, pinocytosis, and by interaction with cell-surface receptors Able to distinguish foreign cells from self cells If material does not activate a TLR, it will not induce an immune responseMATURE DENDRITIC CELLS Capture and process Ag before they are called back to the lymphoid organs Attracted to lymphoid organs by CCL20 When they reach the lymphoid center they mature rapidly Mature DCs secrete CCL22 to attract T cells T cells only bind fragments that are presented by the DCs if their receptors match Mature DCs are the only cells that can trigger a T cell response
  18. Understand the regulatory points in Ag processing and presentation, and
    initiation of an acquired immune response
    DENDRITIC CELLS (DC) The most efficient of the exogenous Ag-processing cells (“professional APC”), also act as sentinel cells (innate immunity) Produced by bone marrow (pluripotent) stem cells Migrate throughout the body and form reticular networks in virtually every type of tissue Excepting the brain, parts of the eye, and testes Most prominent where pathogens are likely to be encountered (eg: skin, lymph nodes, mucosal surfaces)
  19. Understand how B cells and T cells are produced
    • Lymphoid stem cells originate in the fetal liver and yolk sac
    • Migrate to the bone marrow of the fetus
    • Those that are destined to become T cells migrate to the
    • thymus of the fetus
    • Those that are destined to become B cells remain in the bone
    • marrow or bursa (species dependent)
    • By the time an animal is born the secondary lymphoid organs are
    • seeded with both B and T cells
    • Three broad stages
    • 1. Generation of mature, immunocompetent B
    • cells (maturation)
    • 2. Activation of mature B cells when they interact
    • with Ag
    • 3. Differentiation of activated B cells into plasma
    • cells and memory cells
    • ORGANS
    • Sites where lymphocytes go to develop and mature as
    • either T cells or B cells
    • Bone marrow (B cells) and the thymus (T cells) in
    • most mammals
    • Bursa of Fabricius in avian species
    • Peyer’s patches in ruminants
    • Bone marrow provides a microenvironment for
    • maturation and differentiation of B cells
    • Maturation is an orderly sequence of surface Ig-gene rearrangements—
    • Ag-independent phase of
    • development
    • Need direct contact with stromal cells in bone marrow
    • Pro-B cells removed from bone marrow and cultured
    • in vitro will not progress to mature B cells
    • Stromal cells provide cytokines that support B cell
    • development
  20. Know which receptors are important for maturation
    and differentiation of lymphocytes
    • T cells begin as hematopoeitic stem cells in the bone
    • marrow
    • Migrate to the thymus to complete their Agindependent
    • maturation
    • Develop specific T cell markers in the thymus
    • TCR, CD3, CD4, CD8, CD2
  21. Know the primary organs of lymphocyte development
    and maturation
    • Sites where lymphocytes go to develop and mature as
    • either T cells or B cells
    • Bone marrow (B cells) and the thymus (T cells) in
    • most mammals
    • Bursa of Fabricius in avian species
    • Peyer’s patches in ruminants
    • Bone marrow provides a microenvironment for
    • maturation and differentiation of B cells
    • Maturation is an orderly sequence of surface Ig-gene rearrangements—
    • Ag-independent phase of
    • development
    • Need direct contact with stromal cells in bone marrow
    • Pro-B cells removed from bone marrow and cultured
    • in vitro will not progress to mature B cells
    • Stromal cells provide cytokines that support B cell
    • development
  22. Understand the difference in passive and active immunity
    • Passive immunity
    • Antibodies that are made by another individual are transferred to the host
    • for protection
    • Maternal Ab transfer (placental or via colostrum)
    • Antitoxin
    • Gamma globulin
    • Active immunity
    • When a host makes their own endogenous Ab against a pathogen
    • Pros
    • Provides immediate protection to the recipient
    • Effective in hosts that do not yet have a sufficient immune
    • system to mount their own response (ie: neonates)
    • Cons
    • Antibodies are gradually catabolized
    • Recipient’s protection wanes and becomes susceptible again
    • Antibodies must be produced in a donor animal by that animal’s active
    • immunization
    • Donor animals are treated with toxoid
    • Toxoid is a formaldehyde-treated bacterial toxin
    • The serum of the donor animal then contains antibodies
    • (immunoglobulins) targeted to the pathogen
    • Once antibodies are produced the animal may or may not be treated with
    • injections that contain purified toxin
    • Donor animals undergo phlebotomy procedures until their antibody levels
    • drop, then they are re-immunized and antigen levels are boosted
    • The globulin fraction is separated from the blood, then is concentrated,
    • purified, and dispensed
    • Pros
    • A second exposure to the pathogen will result in a secondary
    • immune response and greatly enhanced immunity
    • Long-lasting immunity that is capable of re-stimulation
    • Cons
    • Protection is not conferred immediately
    • “Lag phase” in primary exposure
  23. Understand the different types of vaccines and how they are developed
    • Toxoid
    • Inactivated toxin (diphtheria, toxoid)
    • MLV
    • Modified live virus, capable of growth but not disease causation (some rabies vaccines,
    • cholera vaccine, MMR)
    • Killed vaccine
    • Viral (some rabies vaccines
    • Bacterin (leptospirosis vaccine, haemophilus vaccine)
    • Genetically engineered vaccines…
  24. Know the attributes of an “ideal” vaccine
    • Confers strong immunity
    • Free from side effects
    • Stable in storage
    • Inexpensive to produce
    • Adaptable to mass vaccination
    • Able to stimulate an appropriate immune response that is
    • distinguishable from that induced by active infection (DIVA)
  25. Understand how DIVA capabilities are engineered into vaccines
    • Differentiate infected from vaccinated animals
    • Involves the removal of genes for one or more of the
    • unnecessary antigen(s) on a pathogen
    • Immune response to those antigens is indicative of
    • natural infection
    • Pseudorabies in swine (Aujeszky’s disease)
    • Genes that code for glycoproteins gX and gI are deleted
    • from the vaccine but still present in natural infection
    • Vaccinated swine do not develop antibodies to X
    • and/or I
    • ELISA for X and I can differentiate antibody titer from
    • vaccination vs. natural infection
    • Ie: ELISA will be negative on vaccinated animals and
    • positive in animals that have/have had a natural
    • infection
  26. Understand how to calculate the preventive fraction of a pool of
    • Subjects must first be vaccinated then challenged in
    • order to assess the efficacy of a vaccine
    • PF= preventable fraction
    • PF= (% of controls dying- % of vaccinates
    • dying)/(% of controls dying)
    • Good, effective vaccines should have a PF of at least
    • 80%
    • Vaccinations are NOT a fail-safe mechanism for protection
    • but they precipitously lower the host’s susceptibility to
    • disease when administered properly
    • A vaccine with a PF of 80-90% is a sound vaccine
    • There are still 10-20% of vaccinates who are not protected
    • Failure can be caused by storage and administration
    • problems as well as endogenous factors of the host’s
    • immune system
  27. Understand the factors that lead to vaccine failure
  28. Understand how the immune system ultimately deals
    with bacterial and viral infection
    • natural history
    • eg: Pneumococcus spp. has a heavy polysaccharide capsule; it’s almost
    • impossible for a macrophage to phagocytose it without antibody (Ab)
    • opsonization
    • eg: Clostridium tetani produces exotoxin, which must be neutralized
    • by anti-toxin Ab before it can reach cellular receptors and induce
    • disease
    • eg: Mycobacteria spp. is a facultative intracellular bacteria and
    • therefore requires Th1 cells to activate macrophages
    • Chemotaxis
    • Directed migration of leukocytes that is facilitated by cytokines,
    • leukotrienes, and peptide molecules like C5a
    • Adherence
    • Leukocytes must adhere to the bacterium before it can be ingested
    • Facilitated by opsonins (Ab and complement by-product), which
    • bind to receptors on both the bacterium and the phagocyte to
    • create a “bridge”
    • Ingestion
    • The bacterium is engulfed by the phagocyte
    • Digestion
    • The engulfed bacterium must be killed:
    • Oxidative mechanism (lecture 2)
    • Non-oxidative mechanism
    • Variety of enzymatic granules and other molecules exist in
    • the cytoplasm of phagocytes to kill pathogens
    • Lysosomes fuse with phagocytic vacuoles after the
    • phagocyte engulfs a bacterium
    • Lysosome releases lysozyme, cathepsin G, elastase, and
    • proteases to digest the wall of the bacterium
    • Lactoferrin competes with bacteria for iron, which is a
    • necessary nutrient for bacterial reproduction
  29. Know the temporal development of immune response in utero
    • The immune system begins to develop during gestation
    • Animals develop in a sterile environment (the uterus)
    • There is a wide species variation regarding how mature the immune system is
    • when an animal is born
    • Innate immune system is developed at birth
    • The acquired immune system is developed to some extent at birth
    • In mammals the thymus is the first immune organ to develop
    • Secondary lymphoid organs develop after the thymus
    • Development of the immune system is driven by a
    • gradual increase in gene conversion and somatic
    • mutation to increase Ab diversity
    • In general, antigen (Ag) exposure while in utero
    • when the B cells are able to respond will result in the
    • production of IgM
    • Presence of antibody (Ab) in newborns who have not
    • suckled suggests intrauterine infection
    • Bovine viral diarrhea (BVD)
  30. Understand how the neonate is protected by passive transfer,
    including the process of Ig absorption from the neonatal gut.
    • In primates there is considerable transfer of IgG across the
    • placenta in utero (hemochorial placenta)
    • Neonates do not have an absolute colostrum requirement
    • Fetuses are exposed to IgG of the mother
    • In ruminants, swine, and equines there is no transfer of
    • immunoglobulin across the placenta
    • Neonates of these species have an absolute requirement for
    • colostrum
  31. Understand how immune exclusion and elimination function
    in mucosal immunity (ie: understand the cooperative roles of
    IgA and IgE)
    • IgA and IgE predominates in surface secretions
    • IgA is synthesized by plasma cells in the intestinal submucosa
    • IgA is not bactericidal and does not induce a complement
    • cascade
    • Prevents bacteria from adhering to epithelial surfaces
    • IgA can prevent viral growth before the surface of the
    • epithelium is damaged
    • IgE is a second line of defense after IgA
    • Destroys Ag that penetrates the mucosal barrier
    • IgE attaches to mast cells and causes rapid
    • degranulation, which releases vasoactive molecules
    • Inflammation!
    • IgA and IgE work in concert
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