Immunology and Immune Disorders: Innate Immunity

Anatomical barriers -Mechanical, chemical, biological

 Humoral components - Complement, coagulation system, cytokines

 Cellular components - Neutrophils, monocytes & macrophages, NK cells, eosinophils

The skin

• Thick outer epidermis – physical barrier

 Keratin - waterproof, Keratinocytes produce Antibacterial proteins e.g. psoriasin

• Sebaceous glands – chemical barrier. Sebum (contains lactic acid, fatty acids)

• Sweat glands – chemical barrier

Mucous membranes – physical/chemical barriers

• Line alimentary (gastro tract), respiratory, and urogenital tracts

• Secrete viscous fluid : Mucus contain antibacterial proteins- lysozyme (digests away bacterial cell wall) Contain antibodies

• Some covered in cilia E.g. lower respiratory tract–Physical barrier - Hair-like protrusions that beat synchronously.

Commensal organisms –Biological Barrier

• Normal flora: ‘friendly’ indigenous bacteria

• Examples: Lactic acid producing bacteria: Lactobacillus acidophilus

• Probiotics: Indigenous bacteria- Prevent adherence of pathogenic bacteria

• Bind receptors on epithelial cell wall and Create a ‘barrier effect’ against pathogenic  bacteria: “colonisation resistance”

• Inhibit growth of pathogenic organisms by producing: Lactic acid, bacteriocins

• Compete with pathogenic bacteria for nutrients

Complement

• Found in plasma and can be activated by : Bacteria, Antibodies

• Lysis of bacterial cells

• Stimulation of phagocytosis

• Promotion of the inflammatory response

Cytokines

• Hormone-like small protein molecules that are secreted by cells of the immune and other 

systems

• Induce their function by binding to cell-surface receptors

• Can play a regulatory function

• Cytokine families carry signals locally between cells ie. can have overlapping / synergistic effect 

Interleukins

• Produced by leukocytes, targeting other leukocytes

• Interferons - Mainly anti-viral function

• Chemokines - Chemotactic function

• Colony stimulating factors - Main function in haematopoiesis

• Tumour necrosis factors - Role in the inflammatory response

Phagocytic cells

• Most abundant white cell- >100 billion produced /day – can increase 10 fold during acute 

inflammation

• Cytoplasm contains primary (azurophilic) and secondary granules

• Granules contain: Defensins – antimicrobial, lysozyme, myeloperoxidase, Hydrogen peroxide

• Hypochlorous acid (HOCL)

These contents kill or inhibit growth of bacteria & fungi

monocytes

• Cells in transit from the bone marrow

• Leave the blood (8hr) and enter solid tissue

• Mature cell is the macrophage

Macrophages

• All tissues contain macrophages, for example:

 In Brain: Microglial cells

 In lungs: Alveolar macrophages

 In liver: Kupffer cells

• Some organs have large numbers of macrophages, eg. Spleen, tonsil, lymph nodes, liver, lungs.

• These organs form the : Reticuloendothelial system (RES)

macrophage

1. move out of vascular sytem via cell membrane of capillaries enter area between cells in pursuit of invading pathogens

2. bacteria binds to receptors. engulf and destroy

3.chemokines released stimulate more macrophages to the site

tumoricidal - destructive to tumours

initiate acute. can act as anitgen presenting (dendiritic)

receptors for complement FCyR

activated by interferon gamma(y)

Eosinophils

highly granular secret range of highly toxic proteins which cause tissue damage during allergic reactions

crystalloid granules- contain cationic proteins for multicellular parasites (MBP- major basic protein) nematodes/tapeworms = eosionophilia

activation and toxin release is tightly regulated…