Phagocytosis:Phagocytosis: Phagocytes Phagocytes (eating cells)(eating cells) are body cells are body cells

specialized for specialized for capturecapture, ingestion and , ingestion and destruction of antigens (as bacteria and fungi), destruction of antigens (as bacteria and fungi), debris, and debris, and produce inflammatoryproduce inflammatory molecules molecules which regulate other components of the which regulate other components of the immune system. They express a wide range of immune system. They express a wide range of surface receptorssurface receptors that allow them to identify that allow them to identify microorganisms. Also, phagocytosis can be microorganisms. Also, phagocytosis can be enhanced by antibodies, complement and enhanced by antibodies, complement and acute phase proteins (all called acute phase proteins (all called opsoninsopsonins and and act as a bridge between the antigens and act as a bridge between the antigens and phagocytic cells). They are of TWO types:phagocytic cells). They are of TWO types:

1.1. 1.Polymorphnuclear leucocytes 1.Polymorphnuclear leucocytes (microphages); mainly neutrophils.(microphages); mainly neutrophils.

They are short-lived cells with a half They are short-lived cells with a half life of 6 hours.life of 6 hours.

2. Mononuclear cells (macrophages);2. Mononuclear cells (macrophages);

Monocytes after 7-10 hours in the blood Monocytes after 7-10 hours in the blood they migrate to tissues. In C.T. they migrate to tissues. In C.T. (histiocytes), or fixed in RES (e.g., liver, (histiocytes), or fixed in RES (e.g., liver, spleen, L.N., B.M… etc.). spleen, L.N., B.M… etc.).

The process of phagocytosis include the The process of phagocytosis include the following stages:following stages:

GranulocytesGranulocytes– Polymorphonuclear leukocytes Polymorphonuclear leukocytes

(PMN, neutrophils)(PMN, neutrophils)

– EosinophilsEosinophils– Basophils (blood)Basophils (blood)– Mast Cells (tissues)Mast Cells (tissues)

Mononuclear Phagocytes (RES)Mononuclear Phagocytes (RES)– Monocytes (blood)Monocytes (blood)– Macrophages (tissue)Macrophages (tissue)

allergic and hypersensitivity reactions

fight pathogens inflammation

fight pathogens inflammation cytotoxicity immune regulation

NeutrophilsNeutrophils(PMN)(PMN)

Present in blood (60-70% of WBC)Present in blood (60-70% of WBC) Not normally present in tissuesNot normally present in tissues Short lifespan - 12 hoursShort lifespan - 12 hours Functions:Functions:

– First cell at the site of infection/injuryFirst cell at the site of infection/injury

Ingest and kill microbes after bactericidal Ingest and kill microbes after bactericidal mechanisms activated (binding to pathogen)mechanisms activated (binding to pathogen)

MononuclearMononuclearPhagocytesPhagocytes

Blood - monocytesBlood - monocytes (1-6% WBC) (1-6% WBC) Tissues - macrophagesTissues - macrophages

– mature form of monocytesmature form of monocytes– found in tissues (ex., gastrointestinal tract, lung, liver, found in tissues (ex., gastrointestinal tract, lung, liver,

brain, skin, spleen); reticuloendothelial system (RES)brain, skin, spleen); reticuloendothelial system (RES) Functions:Functions:

– Phagocytize and kill after bactericidal mechanisms Phagocytize and kill after bactericidal mechanisms activated activated

– Produce cytokines/chemokines (initiate inflammation)Produce cytokines/chemokines (initiate inflammation)– Antigen presentation (activate adaptive immunity)Antigen presentation (activate adaptive immunity)– Tumor surveillance and cytotoxicityTumor surveillance and cytotoxicity

Reticuloendothelial SystemReticuloendothelial System

ConsistsConsists of fixed and wandering of fixed and wandering macrophagesmacrophages located throughout the body located throughout the body (tissues, sinusoids, lymph system)(tissues, sinusoids, lymph system)

Major locations: Major locations: Liver and LungLiver and Lung FunctionsFunctions: antibacterial resistance, tumor : antibacterial resistance, tumor

resistance, defense against shock, antigen resistance, defense against shock, antigen processing, lipid metabolism, protein processing, lipid metabolism, protein turnover, iron metabolismturnover, iron metabolism

A. Chemotaxis,Migration, & A. Chemotaxis,Migration, & Attachment:Attachment:

If epith. lining is breached by If epith. lining is breached by microbes, resident phagocytes microbes, resident phagocytes are attracted (influx) to the site are attracted (influx) to the site by chemotactic substances as by chemotactic substances as bacterial endotoxins (LPS), bacterial endotoxins (LPS), serun C5a, IL-8, and leukotriene serun C5a, IL-8, and leukotriene B4.B4.

The macrophages The macrophages produce cytokines as IL-1 & produce cytokines as IL-1 & TNF.These activate endothelial cells of nearby TNF.These activate endothelial cells of nearby venules to produce venules to produce adhesion molecules adhesion molecules (selectin, integrins, & ICAM)(selectin, integrins, & ICAM) and chemkines and chemkines (e.g.,IL-8) which mediate (e.g.,IL-8) which mediate MIGRATION MIGRATION of of leucocytes & monocytes from the blood to leucocytes & monocytes from the blood to tissues (diapedesis).tissues (diapedesis).

The phagocytes have receptors on their The phagocytes have receptors on their surface through which they ATTACH non-surface through which they ATTACH non-specifically to m.o. Examples:specifically to m.o. Examples: Receptors for Receptors for bacterial endotoxines, for mannose residues bacterial endotoxines, for mannose residues on glycoprotein of many bacteria, on glycoprotein of many bacteria, unmethylated bacterial DNA & double stranded unmethylated bacterial DNA & double stranded RNA of many viruses. The attachment and RNA of many viruses. The attachment and ingestion is enhanced if microbes are coated ingestion is enhanced if microbes are coated with IgG or C3b (opsonization).with IgG or C3b (opsonization).

Pattern Recognition Receptors (PRR)Pattern Recognition Receptors (PRR)Three broad classes based on expression profile, Three broad classes based on expression profile,

localization, functionlocalization, function

PRR that signal an infection:PRR that signal an infection: 1. Toll Receptor Family (Toll-like Receptor “TLR “ 1-1. Toll Receptor Family (Toll-like Receptor “TLR “ 1-

11)11)– Expressed externally or internallyExpressed externally or internally– Binding activates “pro-inflammatory” signaling pathwaysBinding activates “pro-inflammatory” signaling pathways

2. Phagocytic (endocytic) PRR2. Phagocytic (endocytic) PRR– Expressed on the surface of phagocytic cellsExpressed on the surface of phagocytic cells– Mediate uptake of microbe into phagocytesMediate uptake of microbe into phagocytes

3. Secreted PRR3. Secreted PRR– Secreted by MP, epithelial cells, hepatocytesSecreted by MP, epithelial cells, hepatocytes– Activate complement, opsonins, function as accessory Activate complement, opsonins, function as accessory

proteins for Pathogen-Associated Molecular Pattern (PAMP) proteins for Pathogen-Associated Molecular Pattern (PAMP) recognition on target cells such as microbes.recognition on target cells such as microbes.

Toll-Receptor Family:Toll-Receptor Family:

How do Macrophages Identify Microbes?How do Macrophages Identify Microbes?

Pattern Recognition Receptors (PPR )Pattern Recognition Receptors (PPR )– Recognize pathogen associated molecular Recognize pathogen associated molecular

patterns (PAMP); conserved molecular patterns (PAMP); conserved molecular patterns on microbes patterns on microbes

– Identify a class of microbes; ex., Identify a class of microbes; ex., LPS, LTA, LPS, LTA, peptidoglycan, lipoarabinomannan, dsRNA, mannose, peptidoglycan, lipoarabinomannan, dsRNA, mannose, b-glycans b-glycans

– PAMP are often essential for microbe survivalPAMP are often essential for microbe survival

Action TimeAction Time– Immediate activation of effectorsImmediate activation of effectors– Delays need for adaptive immunityDelays need for adaptive immunity

Leukocyte AdhesionLeukocyte Adhesion

selectins

B. Ingestion:B. Ingestion: The phogocytes engulf the antiges The phogocytes engulf the antiges

(e.g. organism) by extending (e.g. organism) by extending pseudopods around them. Then the pseudopods around them. Then the organism is included into vacuole organism is included into vacuole called PHAGOSOME. Lysosomal called PHAGOSOME. Lysosomal granules fuse with the phagosome granules fuse with the phagosome forming PHOGOLYSOSOME. Then is forming PHOGOLYSOSOME. Then is followed by DIGESTION of organismfollowed by DIGESTION of organism..

C. Intracellular killing or Digestion:C. Intracellular killing or Digestion: Anti-microbial and cytotoxic substances are Anti-microbial and cytotoxic substances are

produced that destroy phagocytosed m.o. by TWO produced that destroy phagocytosed m.o. by TWO mechanisms:mechanisms:

1. Oxygen-dependent (Respiratory Burst):1. Oxygen-dependent (Respiratory Burst): This killing system is mediated by NADPH oxidase This killing system is mediated by NADPH oxidase

enzymes complex, which converts oxygen into enzymes complex, which converts oxygen into reactive oxygen species such as hydrogen reactive oxygen species such as hydrogen peroxide and superoxide that are lethal to peroxide and superoxide that are lethal to micoorganisms. When combined with micoorganisms. When combined with myeloperoxidase, hypochlorous ions (HOCl -, myeloperoxidase, hypochlorous ions (HOCl -, analogous to bleach) are highly effective oxidants analogous to bleach) are highly effective oxidants and anti-microbial agentsand anti-microbial agents..

2. Oxygen-independent:2. Oxygen-independent: Killing in this system is the result of Killing in this system is the result of

lysozomal contents which include lysozomal contents which include lysozyme, lactoferrin, a group of cationic lysozyme, lactoferrin, a group of cationic proteins (defensins), and hydrolytic and proteins (defensins), and hydrolytic and proteolytic enzymes.proteolytic enzymes.

Some bacteria resist destruction for long Some bacteria resist destruction for long periods, others multiply within the periods, others multiply within the phagocytes (phagocytes (M. tuberculosis, M. lepraeM. tuberculosis, M. leprae). ). Wandering phagocytes transport these Wandering phagocytes transport these m.o. to new places (spread infection).m.o. to new places (spread infection).

Functions of macrophages:Functions of macrophages:

1.1. Initiation and amplification of the Initiation and amplification of the inflammatory response.inflammatory response.

2.2. Killing of microorganisms.Killing of microorganisms.

3.3. Resolution and repair of Resolution and repair of inflammation.inflammation.

4.4. Link between innate and adaptive Link between innate and adaptive immune system.immune system.

Cont…/Second line of innate immunity…Cont…/Second line of innate immunity… 3. 3. Natural Killer (NK) cells:Natural Killer (NK) cells: They comprise 10-15% of the peripheral They comprise 10-15% of the peripheral

lymphocytes. They are CD3 (-), CD11b lymphocytes. They are CD3 (-), CD11b (+), CD16 (+), and CD 56 (+). They have (+), CD16 (+), and CD 56 (+). They have non-specific non-specific CYTOTOXICCYTOTOXIC activity activity against tumour cells, graft cells, & virus against tumour cells, graft cells, & virus infected cells. Their function is NOT infected cells. Their function is NOT restricted by MHC. Their activity is restricted by MHC. Their activity is increased by INF, IL-2 & 12. They have increased by INF, IL-2 & 12. They have surface receptor to IgG - Fc (CD16).surface receptor to IgG - Fc (CD16).

4. Inflammatory barriers:4. Inflammatory barriers: Inflammatory response has 3 events:Inflammatory response has 3 events: 1.1. Vasodilatation of nearby capillaries Vasodilatation of nearby capillaries

leading to redness of tissues, increase leading to redness of tissues, increase tissue temperature, increase capillary tissue temperature, increase capillary permeability and influx of fluid and cells permeability and influx of fluid and cells (exudate) causing oedema. (exudate) causing oedema. 2.2. Influx of Influx of phagocytes which engulf m.o. & release phagocytes which engulf m.o. & release lytic enzymes that can result in tissue lytic enzymes that can result in tissue damage. damage. 3. 3. Chemical mediators are Chemical mediators are released from damaged tissues, m.o., released from damaged tissues, m.o., leucocytes & plasma enzyme systems leucocytes & plasma enzyme systems ( histamine,kinin,fibrine,cytokines &APP).( histamine,kinin,fibrine,cytokines &APP).

Functions of Phagocytes: Functions of Phagocytes: Inflammatory ResponsesInflammatory Responses

Injury or

Constitutional Factors affecting Constitutional Factors affecting Innate Immunity:Innate Immunity:

1.1. SpeciesSpecies : Some organisms are : Some organisms are pathogenic to certain species, e.g., pathogenic to certain species, e.g., M.leprae M.leprae affects man, but not monkey. affects man, but not monkey.

2. Race : 2. Race : Example; Negroes & red Indians Example; Negroes & red Indians are more susceptible than whites to are more susceptible than whites to M.M. tuberculosistuberculosis..

3. Individuals: GENETIC3. Individuals: GENETIC influences influences susceptibility (e.g., G6PD deficiency susceptibility (e.g., G6PD deficiency resistant to malaria). Extremes of resistant to malaria). Extremes of AGE ; AGE ; due to immaturity or aging of immune due to immaturity or aging of immune system in children & old respectively.system in children & old respectively.

4. Nutritional status: 4. Nutritional status: Under nutrition Under nutrition increases susceptibility to disease.increases susceptibility to disease.

5. Hormones:5. Hormones: Example: corticosteroid & Example: corticosteroid & other immunosuppressive drugs, other immunosuppressive drugs, diabetics (lack insulin) or pregnancy diabetics (lack insulin) or pregnancy increase susceptibility to infections. increase susceptibility to infections.

Cytokines of innate Immunity:Cytokines of innate Immunity: From activated macrophages: IL-1, IL-From activated macrophages: IL-1, IL-

2,TNF which increase extravasation of 2,TNF which increase extravasation of neutrophils, induce coagulation & neutrophils, induce coagulation & increase vascular permeability. Also IL-increase vascular permeability. Also IL-12 which activate NK cells. INF-gamma 12 which activate NK cells. INF-gamma (from NK) activate macrophages. INF-(from NK) activate macrophages. INF-alpha (from viral infected cell) inhibits V.alpha (from viral infected cell) inhibits V.

4. Nutritional status: 4. Nutritional status: Under nutrition Under nutrition increases susceptibility to disease.increases susceptibility to disease.

5. Hormones:5. Hormones: Example: corticosteroid & Example: corticosteroid & other immunosuppressive drugs, other immunosuppressive drugs, diabetics (lack insulin) or pregnancy diabetics (lack insulin) or pregnancy increase susceptibility to infections. increase susceptibility to infections.

Cytokines of innate Immunity:Cytokines of innate Immunity: From activated macrophages: IL-1, IL-From activated macrophages: IL-1, IL-

2,TNF which increase extravasation of 2,TNF which increase extravasation of neutrophils, induce coagulation & neutrophils, induce coagulation & increase vascular permeability. Also IL-12 increase vascular permeability. Also IL-12 which activate NK cells. INF-gamma (from which activate NK cells. INF-gamma (from NK) activate macrophages. INF-alpha NK) activate macrophages. INF-alpha (from viral infected cell) inhibits V.(from viral infected cell) inhibits V.

Summary:Summary: Aims of the immune system:Aims of the immune system:

– I. I. ProtectionProtection: by specific &non-specific : by specific &non-specific immunityimmunity

– 2.2.HypersensitivityHypersensitivity (I,II,III& IV). (I,II,III& IV).– 3.Tolerance and autoimmunity.3.Tolerance and autoimmunity.– 4. 4. Immunodeficiency diseasesImmunodeficiency diseases..

–IntroductionIntroduction to immunological words to immunological words as antigensas antigens, antibodies, complement ,T , antibodies, complement ,T cells, B-cells, HLA (MHC) system, CD cells, B-cells, HLA (MHC) system, CD markers, Monoclonal antibodies & markers, Monoclonal antibodies & cytokines.cytokines.

–BranchesBranches of recent and current of recent and current IMMUNOLOGY.IMMUNOLOGY.

–Innate immunity. Details.Innate immunity. Details.