STUDY OF IMMUNITY. NON-SPECIFIC RESISTANCE

1. Immunity. Types of immunity2. Innate immunity. Mechanism of innate immunity

IMMUNITY

• The resistance offered by the host to the harmful effect of pathogenic microbial infection is called immunity. Immunity against infectious diseases is of different types.

IMMUNITY

INNATE ACQUIREDADAPTIVE

Non specific

Specific

Passive Active

Natural

Artificial

Natural

Artificial

INNATE IMMUNITY• This is basic immunity, which may be

genetically passed on from one generation to other generation

• It does not depend on prior contacts with microorganisms

• It may be non-specific when it indicates a degree of resistance to all infection

• It is specific when it shows resistance to particular pathogens

The differences between Non-specific Immunity and Specific Immunity

Non-specific Immunity Specific Immunity

Response is antigen-independent

Response is antigen-dependent

There is immediate maximal response

There is a lag time between exposure and maximal

response

Not antigen-specific Antigen-specific

Exposure results in no immunologic memory

Exposure results in immunologic memory

INNATE IMMUNITY• Species immunity: Individuals of same

species show uniform pattern of susceptibility to different bacterial infection.

• Racial immunity: Within a species different races show differences in susceptibility to infection.

• Individual immunity: Individual in population shows variation in their response to microbial infections. Factors influencing level of innate immunity in an individual are: age; hormonal influence; nutrition.

DEFENSE MECHANISMS

OF BODY

• Epithelial surfaces: the intact skin and mucous membrane covering the body confers on it considerable protection against bacteria. They provide mechanical barrier. They also provide bactericidal secretions.

• Tissue defenses: If barrier of body is overcome by the organisms, a number of factors in normal tissue and body fluid, play their role.

Tissue factor may be divided into:

• Humoral factors - the body fluids and organized tissues of human organism naturally contain a variety of antimicrobial agent that kill or inhibit the growth of microbes. The sources and activities of a variety of host antimicrobial substances are summarized in the next slide

• Cellular factors

Humoral factors Substance Common

SourcesChemical

Composition Activity

Lysozyme Serum, saliva, sweat, tears Protein Bacterial cell lysis

Complement SerumProtein-

carbohydrate lipoprotein complex

Cell death or lysis of bacteria; participates in

inflammation

Basic proteins and polypeptides

(histones,lysins and other cationic proteins,

tissue polypeptides) 

Serum or organized tissues

Proteins or basic peptides

Disruption of bacterial plasma membrane

Lactoferrin and transferrin

Body secretions, serum, organized

tissue spaces Glycoprotein Inhibit microbial growth

by binding iron

Peroxidase Saliva, tissues, cells (neutrophils) Protein

Act with peroxide to cause lethal oxidations

of cells

Fibronectin Serum and mucosal surfaces Glycoprotein Clearance of bacteria

(opsonization)

Interferons Virus-infected cells, lymphocytes Protein Resistance to virus

infections 

Interleukins Macrophages, lymphocytes Protein

Cause fever; promote activation of immune

system

MICROBIAL ANTAGONISM• This refers to the protection of the

surfaces afforded by an intact normal flora in a healthy organism

E.coli bacteria (yellow) in the gut are part of the normal intestinalflora of humans

• Phagocytosis: Natural defense against invasion of blood and tissue by bacteria or others foreign particles are mediated by phagocytic cell which ingest and destroy them

Phagocyte attacks bacteria

PHAGOCYTOSIS CELLS MAY BE:

• Microphages, e.g. polymorphonuclear leucocytes.

• Macrophages: histocytes, fixed reticuloendothelial cells; monocytes.

Phagocytosis, a phagocyte (blue) engulfing a yeastcell (yellow)

The process of phagocytosis consist of:

• The first phase involves the approach of the phagocyte to the microbe by means of positive hemotaxis

• In the second phase absorption of the microorganism on the surface of the phagocyte take place

• The third phase is characterized by submergence of the microbe into the phagocyte

• In the fourth phase intracellular digestion of the engulfed microbes by the phagocytosis take place

Phagocytosis by a Macrophage

The neutrophils can form Neutrophil Extracellular Traps (NETs). Once triggered, the cells undergo a novel program leading to their death. While they perish, the cells release the content of their nuclei. The nucleic acid, mingled with bactericidal enzymes, forms a lethal network outside the cell. Invading bacteria and pathogenic fungi get caught and killed in the NETs

Neutrophil granulocytes have trapped

Shigella bacteria in

NETs (Neutrophil

Extracellular Traps)

Cilia: The ciliary escalator propels trapped particles out of the respiratory

tract

Cilia in the trachea rhythmically beating

NON-SPECIFIC IMMUNITY

• Inflammation: Tissue injury or irritation initiated by entry of bacteria or of other irritant leads to inflammation

• Fever: It is natural defense mechanism. It may actually destroythe infecting organism.Fever stimulates the production of interferonand helps in recoveryfrom virus infections

COMPLEMENT SYSTEM• Complement can be considered as part of the

constitutive host defense mechanisms because of its role in inflammation and phagocytosis.

• Complement is well known for its ability to react with wide variety of antigen antibody combination to produce important physiological results.

• At present complement is known to have 9 distinct components (C1-C9), making a total of 20 proteins.

Important physiological effects of complement system

• The destruction of erythrocytes as well as other tissue cells.

• The initiation of inflammatory changes.

• The lysis of bacteria cells.

• Enhancement of phagocytosis involving some opsonized particles.

Two ways of Complement’s activation

Classical pathway

Alternative pathway

С1

С2С4 С3

С5-С9

Increasing of per-meability

of vessels

Virus neutrali-zation

Kinin activation

PhagocytosisVirus

neutrali-zation

Immune adherence

Producing of MAC

Cell membran

e

Damage of membrane

Complement Fixation

– Ag mixed with test serum to be assayed for Ab– Standard amount of complement is added– Erythrocytes coated with Abs is added– Amount of erythrocyte lysis is determined

Ag

Patient’sserum

Ag No Ag

Ag

• Methodology