Immunity to Infection: Innate Immunity Flashcards
Dr. Idowu
What is an immune response?
The process by which the immune system defends the host against pathogens by using different recognition systems to rid the body of invading pathogens or its products.
What is innate immunity?
Innate immunity is an immediate and non-specific response to a pathogen that does not confer long-lasting protective immunity.
It includes barriers (such as the epithelium and mucous membranes) and immune components important in adaptive immunity.
Briefly highlight the barrier functions of innate immunity.
Body surfaces have an epithelial cell layer as a barrier. The epithelial cell layer has tight junctions and produces antimicrobial peptides e.g. lysozymes
The epithelium of the respiratory tract also produces mucus.
What are the components of mucus?
i. Mucin
ii. Proteins
iii. Proteases
iv. Protease inhibitors
What are the mechanisms of innate immunity?
- Microbial sensors
- Cellular components and phagocytosis
- Complement system
Discuss microbial sensors as a mechanism of innate immunity.
When a pathogen enters the skin, it is confronted by macrophages and phagocytic cells possessing ‘microbial sensors’
Three major microbial sensors are:
i. TLRs
ii. NOD-like receptors (NLRs)
iii. RIG-1-like helicases and MDA-5.
What are TLRs?
Toll-like receptor are a family of evolutionary conserved pattern recognition receptors (PRRs) that recognise pathogen-associated molecular patterns (PAMP).
Discuss cellular components as a mechanism of innate immunity.
During infection, circulating phagocytic cells increase and chemotactically migrate to invading pathogens to ingest and kill them. Any antigen that enters the body is engulfed by phagocytic cells, which include:
i. Monocytes and Macrophages
ii. Granulocytes e.g. neutrophils, eosinophils, basophils
iii. Dendritic cells
Mention and discuss the cellular components of innate immunity.
- Monocytes and Macrophages: Monocytes are leukocytes that circulate in blood and eventually mature into macrophages which reside in tissues (e.g. kupffer cells in the liver). They both engulf and kill pathogens. Macrophages are also APCs.
- Granulocytes: Leukocytes that contain densely staining granules. They include:
i. Neutrophils: they destroy pathogens within intracellular vesicles
ii. Eosinophils and Basophils: they store granules containing enzymes and toxic proteins that are released upon activation of the cells. - Dendritic cells: phagocytotic cells, which act as APCs to T cells by producing cytokines e.g. interferons
The migration of phagocytes is dependent on the release of chemoattractant signals produced by either the cells of the host or the pathogen.
True or False
True.
IL-8 is a potent chemotactic cytokine that attracts neutrophils.
True or False
True.
Discuss complement system as a mechanism of innate immunity.
The complement system is a system of 30 proteins found in serum or on the membrane of some cells, activation of which initiates a series of biochemical reactions that ultimately result in destruction of pathogens.
The three main complement pathways are:
i. classic
ii. alternative
iii. lectin
Alternative and lectin pathways serve as first line defense and provide immediate protection.
The alternative pathway is activated by cell surfaces and can proceed without antibodies.
The lectin pathway also bypasses antibodies and relies on lectin.
The complement proteins can achieve their defense mission in several ways, including:
i. Opsonisation
ii. Lysis of bacteria
iii. Amplification of inflammatory responses through the anaphylatoxins, C5a and C3a
Some microbes have acquired mechanisms to sabotage the complement system and evade the immune response.
Give an example of such a case.
For example, poxviruses ( such as vaccinia virus and smallpox) encode a soluble protein with that inhibit the complement system.
