Case 7- innate immune response Flashcards
The immune system
A system of cells, molecules and organs that provide specific (adaptive) and non-specific (innate) protection against foreign bodies such as micro-organisms, toxins and malignant cells or anything that seems foreign to the body (allergen)
Roles of the immune system
- Recognition- recognising that a particle is foreign and not part of the self.
- Reaction- containment and elimination of infection/ foreign body/ toxin.
- Regulation- keep immune response under control.
- Retention- exposure to infective agent results in long lasting protective immunity.
Immunology
The study of the host defence (immune system) and what happens when the immune system goes wrong.
The immune response
The reaction of the cells and molecules of the immune system to the presence of a substance which is not recognised as part of the self
Immunity
The ability of an organism to resist infection
Innate immunity
The innate immune response is activated immediately after infection and injury. Non-specific immune response reacts the same way to lots of different pathogens. The cells of the innate response alert the acquired immune response.
Acquired (adaptive immunity)
Specific to the pathogen, it also boosts the secretion of the cells and mediators in the innate response. The innate response produces B lymphocytes (which produce antibodies) and T lymohocytes.
Immunogen
Any molecule that can cause an immune response
Antigen
An foreign molecule that generates antibodies, its a type of immunogen but not all immunogens are antigens. It is antibody generating. Usually proteins found on the surface of bacteria etc
Epitope
A small part of the antigen to which the antigen binding site of an antibody or the T cell receptor actually binds.
Characteristics of the innate immune response
Reacts the same to all invaders. Immediate, can cause fever. Has no immunological memory, so will respond to the same threat in the same way over and over again.
Main features of the innate immune response
Physical barriers (skin, gut, eyes and nose), sentinel cellular barriers (phagocytosis and inflammation), complement and cellular induced innate response
Physical barriers- epithelial cells
The epithelial cells are held together by tight junctions, the tight junctions stop bacteria from entering the body.
Where are physical barriers found
Physical barriers are in any location that face the external environment such as the eyes, mouth, nose, lungs, reproductive system and gut.
Physical barriers- skin
Air movement across the skin can flush out the bacteria so they don’t linger. The skin has a high concentration of antimicrobial fatty acids within its structure which works against a range of gram-positive bacteria. The skin structure also contains anti-bacterial peptides which protects the skin from pathogens. The commensal bacteria outcompete pathogenic bacteria for nutrients and supplies, so prevents them from taking over.
Physical barriers- gut
The flow of fluid through the gut flushes out any lingering bacteria so they can’t grow or multiple. The stomach has a low pH, the acid makes it hard for bacteria to grow and multiply. The gut structure contains anti-bacterial peptides which neutralises the effects of pathogens. You have normal gut flora which outcompete pathogenic bacteria for their niche. Enzymes catalyse the breakdown of the carbohydrates found in the wall of some bacteria so they die.
Physical barriers- eyes/nose
Tears allow for the free flow of fluid to wash away lingering pathogens. Nasal cilia allows the movement of mucus. Lysozyme catalyse the breakdown of the carbohydrates found in the wall of some bacteria so they die.
Physical barriers- lungs
- Cough reflux- removes microbes and mucus from the respiratory tract.
- Mucocillary escalator- made of ciliated cells on the pseudostratified columnar epithelia. The cilia push mucus (which contains the microorganisms) up the respiratory tract and into the throat. It can then be swallowed and destroyed in the stomach.
- Mucus- traps pathogens (chemical barrier).
- Antibacterial peptides (IgA)- binds to the surface of bacteria and neutralises them, so stops them from growing and dividing.
Innate response- cellular barrier
After the chemical and physical barriers are breached you rely on the cellular response to destroy the pathogens. This includes the resident alveolar Macrophages. Macrophages can be fixed or roaming.
What happens when a pathogen has gone through the physical barriers
- Most pathogens gain entry through compromised epithelial barriers
- They are usually and almost immediately recognised by resident tissue macrophages within the submucosal tissues, which is just beneath the epithelial lining. They act as look outs or ‘sentinels.’ The first cellular barrier is resident Macrophages
- Once the macrophages encounter pathogens they are normally phagocytosed
Phagocytosis
Internalisation of particulate matter (normally viruses or bacteria) resulting in the death of the invader
How do Macrophages recognise the pathogen
The sentinel Macrophages contain pattern recognition receptors (PRR) which can be either phagocytic or signalling. They recognised pathogen associated molecular patterns (PAMP) on the pathogen
Types of PAMP’s
PAMP’s include bacterial wall and pili components- Peptidoglycan, Lipopolysaccharide (LPS), Glucan and Mannose. They can also be flagella proteins which are found on some parasites and bacteria. You also have fungal wall components (Mannan, Glucan) and surface viral components (surface glycoproteins. Viruses have intracellular PAMPS which recognise viral RNA/DNA as they reproduce inside the cell.
