II MBBS

Professor Sudheer Kher

14-Apr-12

Dr. Sudheer Kher

Immunity 

Resistance exhibited by the host towards injury caused by micro- organisms & their products.

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Reaction of the body against any foreign antigen (Ag).

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2 types : Innate immunity Acquired immunity

14-Apr-12

Immunology Animations

Dr. Sudheer Kher

Innate Immunity

Non specific immunity

Species

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Racial

Dr. Sudheer Kher

Specific immunity

Individual

Acquired immunity

Active

Natural

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Passive

Artificial

Natural

Dr. Sudheer Kher

Artificial

Innate /Native Immunity 

Resistance of an individual because of his genetic & constitutional make up.

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Not affected by prior contact with microorganisms or by immunisations.

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Innate immunity can be – Non-specific : resistance to infection in general.

– Specific: resistance to a particular pathogen. 14-Apr-12

Dr. Sudheer Kher

Classification of Innate Immunity Considered at 3 different levels : 

Species - total or relative resistance to a pathogen shown by

all the members of a species. - due to physiological & biochemical differences

between the tissues of different host species. e.g. all human beings are unsusceptible to plant pathogens. 14-Apr-12

Dr. Sudheer Kher

Classification 

Racial : different races within a species may show differences in susceptibility to infections. e.g. resistance to falciparum malaria in parts of Africa.

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Individual : differences in innate immunity among different individuals in a race.

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Dr. Sudheer Kher

Factors affecting innate immunity in an individual 

AGE : low levels of immunity at the 2 extremes of life. Fetus/ Neonates - immatured immune system Old age - deteriorated immune system, physical abnormalities.

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HORMONAL INFLUENCES : Increased susceptibility in endocrine disorders like DM. Corticosteroids - depress host’s resistance (antiinflammatory & antiphagocytic effect) Pregnancy - increased steroid levels

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Dr. Sudheer Kher

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NUTRITION : Malnutrition Results in Reduced humoral & cell mediated immunity (immunodeficiency)

Paradoxically,  Some infections may not manifest in malnourished

individual e.g. malaria  Some viruses do not malnourished host. 14-Apr-12

Dr. Sudheer Kher

multiply

in

tissues

of

Mechanisms of Innate Immunity A.

B. C.

D. E. F. G.

Epithelial surfaces Antibacterial substances in blood & tissues Microbial antagonism Cellular factors Temperature Inflammatory process Acute phase proteins

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Dr. Sudheer Kher

A. Epithelial Surfaces 1. Skin & mucous membrane - protect against invasion by microbes. Healthy skin - high salt conc. in sweat - sebaceous secretions - long chain fatty acids & soaps

Respiratory tract - nose architecture - cough reflex - mucosal secretions - phagocytes in alveoli Intestinal mucosa - mucus , peristalsis 14-Apr-12

Dr. Sudheer Kher

A. Epithelial Surfaces 2. Saliva - inhibits many micro-organisms. 3. Gastric acidity - destroys many microbes. 4. Conjunctiva - flushing action of lachrymal secretions (tears - contains lysozymes) Lysozymes: 

antibacterial substance

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present in tissue fluid & all secretions except CSF, urine & sweat also present in phagocytes

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5. Flushing action of urine

6. Acidic pH of adult vagina 7. Spermine & zinc in semen is antibacterial 14-Apr-12

Dr. Sudheer Kher

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Dr. Sudheer Kher

B. Antibacterial substances in blood & tissues 1. 2.

3. 4. 5.

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Complement system Basic polypeptides – like leukins derived from leucocytes & platelets Lactic acid in muscle & inflammatory zone Lactoperoxidase in milk. Interferons - antiviral

Dr. Sudheer Kher

C. Microbial antagonism 1. resident flora on skin & mucosa prevent

colonisation by pathogens. 2. altered flora following oral antibiotics may lead to enterocolitis.

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Dr. Sudheer Kher

D. Cellular factors 1.

Phagocytic cells

2.

Natural killer cells

3.

Eosinophils

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Dr. Sudheer Kher

1. Phagocytic Cells Phagocytic cells : 2 types - polymorphonuclear leucocytes - mononuclear phagocytes: in blood & tissues monocytes

macrophages

Imp. link between innate & acquired immunity Chemotaxis - phagocytes are attracted to the site of infection by chemotactic factors. 14-Apr-12

Dr. Sudheer Kher

Phagocytosis 

Involve - recognition & binding - ingestion and - digestion

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Requires opsonins - molecules on the surface of certain bacteria which bind to the receptor on phagocytes - Opsonization.

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Dr. Sudheer Kher

release of lysosomal contents

phagolysosome

Invagination

fusion with lysosome

phagosome formation 14-Apr-12

Dr. Sudheer Kher

2. Natural killer cells 

Class of lymphocytes important in nonspecific defense against viral infections & tumor cells.

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Activated by interferons & selectively kills viral infected cells & tumor cells.

3.Eosinophils 

Number increases during parasitic infections & allergic conditions.

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Not efficient phagocytes but their granules contain molecules that are toxic to parasites.

. 14-Apr-12

Dr. Sudheer Kher

E. Temperature 1.

Many micro- organisms are temperature dependent e.g. tubercle bacilli, pathogenic to mammals, do not infect cold-blooded animals.

2.

destroys infecting pathogen e.g. fever induction used to destroy T. pallidum

before Pn became available for treatment.

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Dr. Sudheer Kher

F. Inflammation Non specific defense mechanism. 2. Follows tissue injury or irritation caused by the entry of pathogens or other irritants 3. Events that occur are 1.

– Vasodilatation - Increased vascular permeability & - Cellular infiltration 4. 5. 14-Apr-12

Changes are brought about by chemical mediators like histamine, PGs, LTs. Signs : redness, heat, swelling & pain. Dr. Sudheer Kher

G. Acute phase proteins 1.

Present in normal serum at very low levels but their concentration rises dramatically during an infection e.g. C-reactive protein (CRP)

2.

Enhance host resistance, prevent tissue injury & promote repair of inflammatory lesions.

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Dr. Sudheer Kher

Acquired Immunity 

Resistance that an individual acquires during life.

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2 types : 1. Active acquired immunity 2. Passive acquired immunity

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Dr. Sudheer Kher

1. Active Immunity 

Resistance developed by an individual as a result of an antigenic stimulus.

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Also called Adaptive immunity.

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Involves active functioning of the host’s immune system leading to the synthesis of antibodies and / or the production of immunologically active cells.

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Dr. Sudheer Kher

Types of Active Immunity A.

Natural active immunity – results from either a clinical or an inapparent infection by a parasite e.g. an attack of measles give lifelong immunity.

B.

Artificial active immunity – resistance induced by vaccines. Vaccines are preparations of live or killed micro- organisms or their products.

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Dr. Sudheer Kher

2. Passive Immunity 

Resistance transmitted to a recipient in a readymade form.

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Preformed antibodies are administered.

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No antigenic stimulus.

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Host’s immune system is not actively involved.

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Dr. Sudheer Kher

Types of Passive Immunity A.

Natural passive immunity – resistance passively transferred from mother to baby

B.

Artificial passive immunity – resistance passively transferred by the administration of readymade antibodies. e.g.tetanus immunoglobulin

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Indicated for immediate & temporary protection in a non immune host faced with the threat of infection. e.g.Rh immunoglobulin during delivery to Rh –ve mother with Rh+ve babies.

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Dr. Sudheer Kher

Comparison of Active & Passive Immunity Passive immunity

Active immunity   

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Produced actively by host’s immune system Induced by infection or by immunogen Durable effective protection Immunity effective only after lag period Immunological memory present Booster effective Negative phase may occur Not applicable in the immunodeficient

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Received passively,no active host participation Readymade antibody transferred Transient, less effective Immediate immunity

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No memory

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Not effective No negative phase Applicable in immunodeficient

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Dr. Sudheer Kher