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Goals
Enable biomedical scientists to understand the role of microbes in health and disease at a level sufficient to integrate new knowledge in the field as it applies to his/her discipline.
Enable students to understand the nature and use of research tools developed from the study of microbiology and immunology (such as genetic manipulation and antibodies)
Microbiology and Immunology
A study of infectious organisms to understand the mechanisms of pathogenesis
A study of the host’s immune system to understand the mechanisms involved in the clearance of infection
Microbes as Infectious Agents
Multicellular - parasites, fungi
Unicellular - bacteria, fungi, protozoan parasites
Subcellular - viruses, prions
Infectious Agents: -bind to the host, replicate, in some cases produce toxins, -cause damage to the hosts’ tissues, -elicit an immune response from the host.
Distinguish from ‘normal flora’ that contributes to health of the host.
Red Blood Cell
Bacteria
Viruses
Bacteria
bacilli
streptococcistaphylococci
spirochetes
Viruses
Ebola HIV
HSV-1 Hepatitis B
Fungi
unicellular
multi-cellular
Parasites (unicellular and multi-cellular)
unicellular
multi-cellular
Robert Koch (1843-1910)
‘Koch’s Postulates’
The same organism must be found in all cases of a given disease.
The organism must be isolated and grown in pure culture.
The organisms from pure culture must reproduce the disease when inoculated into a healthy, susceptible animal.
The organism must then be again isolated from the experimentally-infected animal.
First to demonstrate that microorganisms cause a human disease (anthrax)
The Immune System:
System to maintain the integrity of the hosts’internal environment during insult from pathogens and toxins in the external environment.
Immunity is Mediated by:
Innate Factors (non-specific)&
Adaptive Factors (specific)
Innate Immunity
Anatomic Barriers
Intact epithelium(keratinized and non-keratinized)
Mucous
Cilia
Smooth muscle contraction
Physiologic (Chemical) BarrierstemperaturepH
enzymes (i.e. lysozyme, & peroxidase)
complement and acute phase reactants
Innate Immunity
Anatomic Barriers
Endocytic/Phagocytic Barriers
Phagocytic cells - internalize particles
Granulocytes (neutrophils, eosinophils)
Macrophages (monocytes)
Endocytosis: internalization of macromolecules(phagocytosis: specialized internalization of particlesSuch as whole bacteria)
Pinocytosis: Non-specific membrane invagination
Receptor Mediated Endocytosis: Endocytosis following binding of macromoleculesto surface receptors
Primary Lysozomes fromGolgi complex
Extracellular
Intracellular
Macromolecules binding to receptors on cell surface
Extracellular
Intracellular
Macromolecules binding to receptors on cell surface
Primary Lysozomes fromGolgi complex
EndosomeLysosome Fusion
Primary Lysozomes fromGolgi complex
Extracellular
Intracellular
Macromolecules binding to receptors on cell surface
Primary Lysozomes fromGolgi complex
ExtracellularMacromolecules binding to receptors on cell surface
Degradation of Macromolecules
Antimicrobial and cytotoxic activities of phagocytes
(in lysozomes)Oxygen-dependent
Oxygen-independent
reactive oxygen intermediatese.g. superoxide anions (O2
-) and hydrogen peroxide (H202)reactive nitrogen intermediates
e.g. nitric oxide (NO)
antibacterial proteins lysozyme and defensins
proteolytic enzymes elastase and cathepsin B, cathepsin L, and cathepsin G
Inflammation:
Non-specific reaction that occurs as a result of local tissue damage and the presence of foreign substances.
Five Cardinal Signs of Inflammation
1. Pain
2. Heat
3. Redness
4. Swelling
5. Loss of Function
Neutrophils RollingAlong Endothelium
SITE OF INFLAMMATION
Release of Vasoactive andChemotactic Substances
Margination: Neutrophil stops rolling and sticks to endothelium
SITE OF INFLAMMATION
Diapedesis: Neutrophil squeezes out ofblood vessel between endothelial cells
Chemotaxis: Neutrophil migrates toward site of tissue damage alongthe concentration gradient of chemotactic substances.
Chemotaxis: Neutrophil migrates toward site of tissue damage alongthe concentration gradient of chemotactic substances.
Margination: Neutrophil stops rolling and sticks to endothelium.
Diapedesis: Neutrophil squeezes out ofblood vessel between endothelial cells.
Interactions between endothelial cells and neutrophilsare mediated by molecules expressed on the surface ofboth the endothelial cells and the neutrophils.
The Complement System
Involved in inflammation and resistance to bacterial (and to a lesser extent fungal and viral) infections.
Complement deficiencies put patients in grave danger.
The Complement System
A system of about 20 proteins that are produced by the liver and found in blood serum.
Produced in an inactive form and are sequentially activatedto produce biologically active complexes.
Function of these complexes is 2-fold:direct killing of pathogens through formation of
the ‘membrane attack complex’ (MAC)enhance the inflammatory response by
opsonizing bacteria and increasing phagocyte chemotaxis
Complement components are sequentially activated
in a process often referred to as the ‘complement cascade’
1) the classical pathway2) the alternative pathway
3) lectin activation pathway
The complement cascade can be activated through 3 distinct pathways:
Complement components polymerize to form a Membrane Attack Complex (MAC) that inserts into the membrane and forms holes in the pathogen
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C5bC5b
C6C688
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C5bC5b
C6C688
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C5bC5b
C6C688
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C5bC5b
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Intracellular
Extracellular
Complement enhances the activity of phagocytic cells byopsonizing bacteria
C3b
Chemotaxis: Neutrophil migrates toward site of tissue damage alongthe concentration gradient of chemotactic substances.
C5a
Alternative Pathway and Lectin Mediated Pathway of Complement Activation:
1) Collection of serum proteins that are sequentially activatedto enhance the inflammatory response.
2) Initiated by the spontaneous cleavage of C3 and recognition of bacterial mannose-containing surface molecules (mannans)
3) C5-C9 forms the MAC, C3b opsonizes the pathogen, thereby promoting phagocytosis, and C5a promotes chemotaxis of phagocytes to the site of inflammation.
Pathogen
Anatomic Barriers
Inflammatory Response (chemical and phagocytic barriers) -local release of vasoactive and chemotactic substances -neutrophil infiltration (margination, diapedesis, chemotaxis) -complement activation resulting in MAC, opsonization, and increased neutrophil migration
The Innate Arm of the Immune System Express Receptors for Components of Microbial Pathogens PAMPs - ‘pathogen-associated molecular patterns’
PRRs - ‘pattern recognition receptors’
ImmuneCell
PAMP
PRR
Soluble PRRs Mannan Binding Lectin (MBL)C-reactive Protein (CRP)Serum Amyloid Protein (SAP)LPS Binding Protein (LBP) Cell Bound PRRs Toll-Like Receptors (TLRs) TLR2, TLR3, TLR4, TLR5, TLR9CD14
PRRs are Soluble or Expressed on the Cell Surface
Bind to various bacterial cell wall components andenhance killing
PAMPs Bacterial lipopolysaccharide (LPS) – the outer coating of certain bacteria (Gram negative)
Bacterial cell wall peptidoglycan – the rigid outer layer of bacteria
Bacterial flagellin – the protein that makes flagella, which are used for motility
Mannan from yeast or bacteria
Unmethylated CpG DNA – nucleic acid bases
Double stranded RNA (dsRNA) from viruses
Binding of PAMPs by PRRs can stimulate cells of the innate arm of the immune system to become:
-more phagocytic,
-more effective and initiating adaptive immune responses.
ImmuneCellPAMP Danger, Danger !!!!
Innate Immunity
Anatomic/Physiologic barriers
Phagocytosis/Endocytosis by granulocytes and macrophages
When Innate Immunity Fails to Eliminate the Pathogen, Specific Immune Responses are Initiated
Properties of Specific Adaptive Immunity
1. Specificity (exquisite)
2. Memory
Imm
un
e R
esp
on
se
Time (Days)
0 14 = 0 6 14
Pathogen A
1o anti-A
Pathogen A
Specificity and Memory
1o anti-B
2o anti-A
+ Pathogen B
Cells of the Immune System
Specific Immunity: Directed against foreign substances (termed antigens)following the failure of innate immunity
B-lymphocytes (Bursa-derived)
T-lymphocytes (Thymus-derived)
Antigen Presenting Cells (APC)
B-cells
B-cells produce and secrete proteins that bind to, and neutralize antigens (antibodies) .
B-cells that have contacted antigens furtherdifferentiate into either memory cells or plasma cells.
B-cells do not require APCs to become activated.
T-Lymphocytes
T-helper cells provide signals for the growth (proliferation) and differentiation of other immunologic effector cells. (Th)
T-cytotoxic cells can kill abnormal cells in the body - for example infected cells or tumor cells. (Tc)
T-regulatory cells can inhibit inflammatory responses. (Treg or Ts)
B-cells and T-cells are Antigen-Specific (Clonal)
Each T-cell recognizes a unique antigen on the surface of an APC.
Each B-cell recognizes a unique antigen, but does not require an APC.
Clonal Selection: Antigen Stimulates SpecificClones to Generate Antigen-Specific Responses
Expression of Differentiation Markers is used to Distinguish T-cells and B-cells
sIg
B-cell
TCRCD4
T-helper
TCRCD8
T-cytotoxic
Antigen-Presenting Cells (APC)
-dendritic cells, macrophages, and in some cases, B-cells.
-process antigens by endocytosis (or phagocytosis), degrading them into simplemolecular fragments, and re-expressingthese fragments on their cell surface.
Dendritic cell
dendritic cell macrophage B-cellAPCs
Primary Lymphoid Organs
Organs (Tissues) wherelymphocyte precursors mature to become lymphocytes
Bone marrow
Thymus
Fetal liverBursa of Fabricius (birds)
Pluripotent Hematopoietic Stem Cell
Lymphoid Stem Cell
earlypre-B
large pre-B
small pre-B
Virgin
Hematopoiesis
Plasma cell
MemoryB-cell
immaturethymocyte
T-helperT cytotoxic/suppressor
NK Cell
(blood cell formation)
RBC
EosinophilBasophil
Megakaryocyte
NeutrophilMonocyte
Macrophage
Cortex
Medulla
T-cell Development in the Thymus
90% ofthymocytes diein cortex
10% ofthymocytes mature to T-cells
Thymic InvolutionFollowing onset of puberty, the thymus decreases in size. This reduction in size results in decreased immune function that is
associated with old age.
Normal rat thymus
Secondary Lymphoid Tissues
Organs or tissues wherelymphocytes contact antigensand mediate their immune functions.
Spleen
Lymph Nodes
Lymphatic vessels
Splenic Blood Supply
Red Pulp
LFLF
LF
Paracortex (T-cells)Medulla
Cortex (B-cells)
PALS (T-cells)
Marginal Zone(B-cells)Afferent Lymphatics
Efferent LymphaticLymphaticBlood Supply
Lymph Node Spleen
Lymphatics drain tissueand direct dendritic cells with foreign substances or pathogens to the lymph nodes where they stimulate T-cells and B-cells
cortex
paracortexmedulla
Diagrams of a Lymph Node
Diagrams of Spleen
Summary
Innate and Specific (Adaptive)
Properties of the Immune Response
Cells and Tissues of the Immune System
Cells Involved in Innate and Specific Responses
Primary and Secondary LymphoidOrgans and Tissues