Far Eastern University – Nicanor Reyes Medical Foundation
Microbiology – Basic Immunology
Mary Joyce M. Saborrido-‐Teoxon, M.D.
IMMUNOLOGY
− Study of body’s protective and defensive mechanisms against foreign substances
− Discriminate self vs. non self − Antigen-‐antibody reaction
− Eliminate non-‐self (infectious agents)
Immune System
− Collection of organs, tissues, cells and soluble factors that allow individuals to defend against harmful agents such as viruses, bacteria, fungi, parasitic organisms, and tumor cells
Two (2) Important Roles of the Immune System:
1. Provides defense mechanism.
2. Identification and destruction of abnormal cells.
HISTORY
Louis Pasteur – father of immunology; actually the one who discovered
the rabies vaccine
Edward Jenner – discovered “small pox” vaccine from cowpox
Innate vs. Adaptive
First Line of Defense
a. Physiologic Barriers − Skin
• Hookworms can penetrate skin • Tinea corporis
• Dermatophytes b. Chemica Barriers
− Lysozymes: chemical barrier/enzyme that dissolves some bacterial cell wall
− Gastric pH of the stomach c. Biologic Barrier
− Nomal flora (Lactobacillus acidophilus)
Second Line of Defense
− Phagocytes: effective only for extracellular pathogens − Anti-‐microbial proteins and inflammatory response
ThirdLine of Defense
− Lymphocytes: can kill intracellular pathogens; memory cells
Acquired Immunity: Active vs. Passive
Active – actively producing antibody after an exposure to an antigen;
life-‐long protection
Passive – antibody from other source; immediate but short term
protection
Natural – naturally made; can’t be produce by humans Artificial – immunoglobulins; commercially availabe
Passive Immunity
Natural Artificial
→ Placental transfer of IgG → Colostral transfer of IgA
→ Antibodies or immunoglobulins → Immune cells Active Immunity Natural Artificial
→ exposure to sub-‐clinical
infections → Vaccination
Professional Phagocytic cells
− These cells have enzymatic constituents in their granules to oxidize, kill, digest, and destroy particulate material that they ingest. − Part of 2nd line of defense
1. Mononuclear phagocytes (formerly RES)
A. Monocytes (in the blood) B. Tissue Macrophages
a. Liver
à
Kupffer cellsb. Lungs
à
Alveolar macrophages/ Dust cells c. Kidneyà
Mesangial macrophages d. CNSà
Microglial cellse. Lymph nodes
à
Dendritic cells f. Skinà
Langerhan’s cells g. Spleenà
Spleenic macrophagesh. Connective tissue
à
Histiocytes i. Boneà
Osteoclast j. Peyer’s pathches k. Tonsils Functions of MØ a. Phagocytosis− Ingestion & killing of microbes − Mostly for extracellular pathogens − STEPS:
• Chemotaxis (C5a,LTB4,IL-‐8,N-‐formyl methionine) • Diapedesis
• Adherence
• Engulfment/ Opsonins (C3b, IgG) • Phagosome formation
• Fusion
• Digestion/Destruction
b. Antigen Presentation
− Presentation of antigen in association with class II MHC proteins to CD4 = helper T cells
− APCs: • MØ • B cells • Langerhans cells • Dendritic cells c. Cytokine Production
− Synthesis and release of cytokines such as IL-‐1 & TNF, and chemokines such as IL-‐8
2. Polymorphonuclear leukocytes (PMNs)
a. Neutrophils (most aggressive phagocyte) b. Eosinophils (antiparasitic phagocyte) c. Basophils (secretory cells)
NK cells
− LGL / Null cells
− Lack T cell receptor, CD3 proteins, and surface IgM & IgD − Thymus are not required for development
− Activity not enhance by prior exposure − Associated w/ ADCC
− CD56 & CD16
Functions of NK cells
− Kill virus-‐infected/ Cancer cells − Killing
• Non-‐specific
• Not dependent on foreign antigen presentation by class I or II MHC proteins
• Activated by the failure of a cell to present self antigen
• Produce perforins & granzymes, w/c cause apoptosis of target cell
Adaptive Immunity
− Antigen – Antibody reaction − Cells:
• B cells • T cells
Antigens & Immunogens Antigens
→ molecules that react w/ Abs
→ compound that does not necessarily elicit an immune response
Immunogens
→ molecules that induce an immune response (antibody) → at least 2 antigenic determinant
*All immunogens are antigens, but not all antigens are immunogens.
Two properties of Antigens:
− Immunogenecity: ability to induce specific immune response resulting to formation of antibodies or immune lymphocytes − Antigenecity/ Specificity: the ability to react specifically with the
antibody or cell that caused it to be produced
Parts of AG:
− Carrier portion
• The bigger part that is responsible for the MW of antigen • >10000 dalton more immunogenic
− Epitome/ Antigenic determinant
• Determines specificity of antigen, therefore, an antigen w/out epitope is said to be nonspecific.
• Reactive sites (Ab/ TCR)
HAPTENS
− Molecule that is not immunogenic by itself but can react w/ specific antibody
• Incomplete Ag
• Small molecules (<10,000D) • univalent
• HMW nucleic acids • Drugs (e.g. Penicillin) • Cathechol (plant oak)
CARRIER
− A molecule that when coupled to a hapten, renders hapten immunogenic. − E.g: • Albumin • Globulin • Synthetic polypeptides
Features of molecules that determine immunogenicity
− Foreignness − Molecular size
− Chemical-‐Structural Complexity − Antigenic Determinants (Epitopes)
Lymphoid System A. Primary/ Central
− are the sites for generation and early maturation of lymphocytes (B and T cells)
a. Bone Marrow (Bursa of Fabricus equivalent)
→ Hematopoeisis • RBC • Platelets • Monocytes • Granulocytes → Lymphopoeisis • B cells • T cell precursors • NK cells • Dendritic cells • Mast cells b. Thymus
→ Maturation & Differentiation of T cells
B. Secondary/ Peripheral
− T & B cells
à
Central L.T.à
Migrateà
Peripheral L.T.à
Respond to foreign antigensa. Lymph nodes
− Major antigen-‐trapping sites of the body
− Filters foreign substances from the tissue fluids and lymph − Central organ for lymphocyte traffic and circulation − PARTS:
CORTEX (Germinal center) à B cells PARACORTEX (Juxtamedullary) à T cells
Flow of lymph To thoracic
duct
b. Spleen
− Filters foreign substance from the blood − Critical line versus blood borne infections − Eliminates dead worn-‐out RBCs
− 2 pulps Red pulp and − White pulp
• Marginal zone • Germinal center • PALS (mostly T cells)
• Primary follicles (mostly B cells)
Mucosa-‐associated Lymphoid Tissue (MALT)
− GUT-‐associated lymphoid tissue (GALT) − Bronchus-‐associated lymphoid tissue (BALT)
BALT
− L.T. beneath the respiratory mucosa and the aggregates of nodular lymphatic tissues called Tonsils.
− Tonsils à nodular aggregates of B cells & diffuse areas that contain mostly of T cells
à for airborne and alimentary tract pathogens
T cells
− Responsible for foreign antigen recognition or cellular immune response, which include:
• rejection in organ transplantation • regulation of antibody production • secretion of soluble mediators
− It has the ability to bind with sheep’s RBC forming rosette.
Subsets of T cells
1. T helper cell (CD4 marker)
• Recognize Ag in association w/ MHC class II • Collaborate w/ B cells to produce Abs • Th1/Th2
2. T cytotoxic cell (CD8 marker)
• Has killer function
3. T effector cell
• Also called as TdTh cell
• Responsible for delayed type of HPS
4. T suppressor cell (CD8 marker)
• Involved in presenting autoimmunity activated by Ag
B cells
− Have shorter life span (5-‐7 days)
− Precursors, regulators, and effectors of immunity.
− May transform or differentiate into plasma cell to produce immune antibodies.
− CD19, CD20, CD21, CD22, CD35
Comparison of T & B cells
Complement
− Composed of several proteins found in human serum (other animal serum)
− Synthesize in the liver (main)
− Heat labile (inactivated by heating serum at 56 C for 30 mins) − 3 Pathways:
• Classic (activated by Ag-‐Ab(IgM & IgG only!); for IgM w/ 1pentameric structure and IgG w/ 2 monomeric structure) • Alternative • Lectin Classic
− Activator: Ag-‐Ab(IgM & IgG only!); for IgM w/ 1pentameric structure and IgG w/ 2 monomeric structure
→ 1st complement protein will be activated C1, usually attached to the FC portion of Ab is C1q.
• C1r surrounds C1q and C1s.
• C1s is the most active portion stimulating C4. → C4 will then be cleaved into two (C4a & C4b).
• C4a will serve as the anaphylatoxin (assoc. w/ hypersensitivity reaction resulting to increase vascular permeability stimulating swelling and inflammation). • C4b is the active part and will continue the process. → After C4 activation, C2 will be activated by C1s also. → C2 will be then cleaved into C2a and C2b.
• Either C2a or C2b will bind to C4b to become C3
convertase that will activate C3.
→ C3 will then be cleaved into C3a and C3b.
• C3a (anaphylatoxin) and C3b is the active portion that will have a separate action as the opsonin or can bind to C3 convertase forming C5 convertase that would then activate C5.
→ C5 will be cleaved into C5a that will act as the anaphylatoxin/chemotaxin and C5b will be the active portion and will stimulate C6C7C8C9 (Membrane attack complex).
Lectin
− Activator: MBP (found in the cell wall of gram + bacteria); doesn’t involve Ab, also called as “Antibody Independent Complement Pathway”
− No C1 activated, but MASP (Mannose Associated Serine Protease) will act as C1 that will activate C4 and so on…
Alternate
− Activator: Microbial surfaces
− Also “Antibody Independent”, alternate or shortcut, bypassing C1, C4, and C2. Automatically activates C3 that will split into C3a (anaphylatoxin) and C3b (active portion).
− Factor B, a unique component produced only in this pathway that will be cleaved into Ba (no biologic significance) and Bb will attach to C3b producing C3 convertase activating C3.
− C3 will be cleaved to C3a (anaphylatoxin) and C3b will bind to C3 convertase of alternative pathway producing C5 convertase that will then stimulate C5.
− C5 will be cleaved into C5a (anaphylatoxin) and C5b stimulate
C6C7C8C9 (MAC).
Functions of complement:
• Anaphylatoxins – C3a, 4a, 5a
• Chemoattractants-‐ C5a, LTB4, IL-‐8, bacterial products • Opsonins – C3b, IgG
• Bacterial cell lysis – C5b, 6, 7, 8, 9
CLASSIC Ag-‐Ab C1 q, r,s C4 C2 C4b2a/ C4b2b ( C3 Convertase) C3 C4b2a3b/ c4b2b3b (C5 Convertase) C5 C5bC6C7C8C9 (Membrane Attack Complex) MBP LECTIN
MASP ALTERNATIVE Microbial surface C3 B C3bBb (C3 Convertase)
C3bBb3b (C5 Convertase)
Complement Regulatory Proteins
Complement Deficiencies
¡ C1sINH à Hereditary Angioedema
¡ C2 à Increased incidence of Connective tissue d/o (SLE)
¡ C1/C4/C2 à Opsonization not efficient (LAD)
¡ C3 à Increased susceptibility to pyogenic infection