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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