Immunology Notes on Innate immunity or Non-specific defence mechanism

Innate immunity or Non-specific defence mechanism
Our body is equipped with bombs and machine guns to combat with intruders. But our body has also fortress wall with highly sensitive alarms and are heavily guarded.
Why innate immunity is called non-specific defence mechanism?
This defence strategy is same for most type of infections or pathogens, hence called as non-specific defence mechanism. It protects body from infection primarily by blocking pathogen entry or destroying pathogens that has entered, by different means other than antibodies.
Innate immunity is also known as inborn/familial/natural or genetic immunity.
Major features of innate immunity
  •  It is inherited from parents and present from birth itself
  •   It offers immunity throughout life time
  •  Prior contact or interaction with pathogen or its antigen is not essential
  • t protects the individual from getting diseases of other organisms
  • Innate immunity involves removal of pathogens at two levels either externally or internally
Innate immunity and Acquired immunity
External defence or First line of defence in the immune system
External defence involves physical and chemical barriers that prevent pathogen entry into the body.
What are the physical barriers?
First Line of Defense

This Figure depicts major physical and chemical barriers that blocks pathogen entry
Skin layers
Skin the largest organ in the body and is undoubtedly the major physical barrier that blocks pathogen entry. Apart from its role as an impenetrable barrier, it secretes various chemical weapons that avoid pathogen entry. The skin epidermis is approximately 10-30 cells thick, as thick as a page.
 The outer layer is the stratum corneum which are exposed and subjected to injury, and wear and tear. Such damaged cells of stratum corneum are continuously replaced by cells produced in the innermost layer of epidermis, stratum basale. The cells in the stratum basale pass through a middle layer,stratum spinosum where protein keratin is added which makes skin tough and water resistant. The new cells that reach stratum corneum remain for a month before they are shed and replaced by newer cells from stratum basale. In short,outer layer of skin, stratum corneum is a tough fully keratinised layer of dead cells capable of preventing pathogen entry efficiently.
Contextual point: Why psoriasis?
Psoriasis is a chronic skin disorder in which epidermal cells (cells at the stratum corneum) are replaced every 3 to 4 days that is about eight timed faster than normal.
Otherpotential routes of pathogen entry are the openings in the body to the outside that is digestive tract, respiratory tract and urogenital tract. Microbes are always at the door step of these tracts for getting an entry. But our body has different plans. Let us look in detail as points.

  •  Mucus secreted by mucous membrane that traps microbes and immobilise them
  •  Microbes inhaled are trapped by mucus secreted by cells lining the smaller bronchi and bronchioles. In addition to this,cilia in all these passages help in sweeping out entrapped microbes.
Chemical barriers:
Skin glands and receptors

· Skin secretes oil and sweat by sebaceous and sudoriferous glands that makes skin surface acidic, (pH of 3-5) capable of inhibiting growth of many microbes. Sweat also contains lysozyme that digests bacterial cell wall.
  • Saliva has lysozyme that destroys bacterial cell wall
  • Acidic environment of the stomach and digestive enzymes (gastric juice)
  •  Lysozyme are present in tears, tissue fluids and majority of secretions
  •  Cerumen (earwax) traps and kills microbes and repel insects
  •  Vaginal secretions are sticky and acidic ensuring protection from bacterial infection. Bacterial symbionts in vagina like lactobacilli produce lactic acid that maintains low pH and kills microbes.
  •   Acidic urine continuously washes pathogens from the urinary tract.
  • Somehow if a pathogen enters body systems, then body uses defencemechanisms such as vomiting, diarrhoea, coughing sneezing and mucous secretions to expel pathogen.
We have discussed only the physical barriers of first line of defence. Now you may thing, is it possible for a pathogen to enter human body?
Our defence system is more sophisticated and complex than a nations defence system. It is almost fool proof. But our enemies are also evolving side by side. The race is on and let us discusses the internal defence of first line of defence in the next post
Now the microbe has breached the physical barrier, what will our defence system do?
Letus check out….
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