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01. Specific vs. Non-specific immunity

April 11, 2010 Edit this post

IMMUNOLOGY - study of the immune response IMMUNE RESPONSE: capable of recognizing foreign material and eliminating it from the body. ...

  • IMMUNOLOGY- study of the immune response
  • IMMUNE RESPONSE: capable of recognizing foreign material and eliminating it from the body.
  • There are 2 types of immune responses

 

Non-specific immunity or Innate immunity

Specific immunity or Acquired immunity
  • Present @ birth
  • Not specific to the pathogen
  • Has no memory
  • Present in invertebrates and vertebrates
  • develops after contact with the pathogen
  • Specific to the pathogen
  • Has immunological memory
  • Present in vertebrates only

Immune components

  • Natural barriers (Physical, Mechanical, Chemical,Normal flora)
  • Cellular factors : (Neutrophils, Macrophages, Mast cells, Eosinophils)
  • Humoral factors :(complement ,interferons-α & β, cytokines, acute phase proteins )
  • Cellular factors : ( T lymphocytes,T helper cells, T cytotoxic cells,via cytokines)
  • Humoral factors :(Antibodies secreted by B lymphocytes)

 

Non-specific immunity

 

A.   NATURAL BARRIES TO INFECTION


1.    Physical barriers    Intact skin(keratinized) and intact mucous membranes (Mucus traps pathogen, secretory IgA)


2.    Mechanical defenses     The cilia of the respiratory ,Coughing and sneezing reflexes ,peristalsis clears the gut, flushing action of urine, tears and saliva clean eyes and mouth.


3.    Chemical defenses     Sebaceous secretions (fatty acids) ,sweat(salt), acid pH of the stomach & vagina, Lysosyme (in tears, Sweat, saliva and mucus), lactoferrin (↓iron for  bacteria)


4.    Normal flora    prevent pathogens establishing by ↓ space and nutrients, produce fatty acids and bactericidins

 

 

B.    CELLULAR FACTORS


1.    Neutrophils(T1/2=6h) and Macrophages (Derived from mast cells)

 

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  • CHEMOTAXIS -Phagocytes(neutrophils, macrophages) are attract  to site of infection by cytokines (IL-1, IL-8) ,C5a, bacterial products, histamine, etc.
  • OPSONISATION- pathogen is coated with complement products like C3b or with antibody, C-reactive protein
    PHAGOCYTOSING- (engulfing) the pathogens into a phagosome. This phagosome fuses with lysosomes and lysis the pathogens
  • Macrophages →ACTIVATED macrophages by gamma interferon from T helper cells.

2.    Eosinophils    Extracellular killing of parasites by releasing toxic substances such as (MBP).


3.    Mast cells (Found in skin, mucous membranes and around blood vessels)

Activated by cross-linking of surface IgE by antigen or directly by C3a and C5a.

ACUTE INFLAMMATORY RESPONSE

  • FIRST/ IMMEDIATE RESPONSE - release preformed mediators  Histamine, heparin, eosinophil chemotactic factor, interleukin 8 (neutrophil chemotactic factor) → lead to vasodilatation, increased vascular permeability, increased mucus secretion and bronchoconstriction.
  • LATER secrete newly synthesised mediators Leukotrienes →prolonged bronchoconstriction ,Prostaglandins and thromboxane, cytokines-Platelet activating factor


LATE PHASE REACTION

  • Due to chemotaxis of  neutrophils and eosinophils as well as basophils, lymphocytes and macrophages to the mucosa.


4.    Natural Killer cells (Large granular lymphocytes)

 

1.    Recognized and kill virally infected cells & tumour cells (extracellular killing)
2.    ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADC) -Killing is made more efficient if the cell is coated with antibody
3.    kill their targets by: pore-forming proteins (perforin) →direct cell lysis, proteolytic enzymes ( granzymes) →apoptosis, cytokines (TNF-α, IL-1, IFN-α and IFN-γ )

 

 

 

C. HUMORAL FACTORS: Soluble factors found in plasma


1. COMPLEMENT CASCADE  group of about 20 proteins found in the serum

 

 

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Actions of complement:

1. Produces Acute Inflammation-due to C3a and C5a

  • triggering mast cells,chemotaxis of neutrophils , increasing vascular permeability.

2. Opsonisation-due to C3b

 

3. Lysis of pathogen-due to formation of the Membrane Attack Complex (MAC)

 

 

2.    INTERFERONS - ALPHA AND BETA


1.    secreted by virally infected cells
2.    induce a state of antiviral resistance in nearby uninfected cells.
3.    Interferons are species(human) specific but they are not virus specific.


3.    CYTOKLNES IN INNATE INIMUNITY (protein hormones secreted by cells and acting on other cells that have a role in both specific and non-specific immunity)

 

1.    Cytokines produced in the non-specific immune


•    alpha and beta interferons- produced by virally infected cells
•   tumour necrosis (INF), interleukin (IL-1) and interleukin 6 (Mk) -produced by macrophages.


2.    Cytokines produced by macrophages act


•    Locally-promote acute inflammation
•    brain -to give fever   

•    liver -to produce acute phase proteins
•    bone marrow -to produce a leucocytosis

 

4.    ACUTE PHASE PROTEINS    

  • Have a role host defense, also useful as markers of infection. eg. C reactive protein (CRP).
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