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Class notes Biomedical Sciences (BSc) Cellular and Molecular Immunology, ISBN: 9780323479783
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Lecture Notes BB3720 Medical Immunology at Brunel University
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BB3720 Medical ImmunologyInnate immunity
Levels of defence against pathogens
- There are three levels of defence
o Epithelial barriers → if the epithelial barriers do not work, the immune system kick
in
Mechanical: clean anything off that is trying to take hod and bind to cell
surface. Cilia will move the pathogens
Flow of air or fluid
Movement of cilia by fluid
Chemical
Enzymes (e.g. lysozymes in saliva, sweat and tears)
Antibacterial peptide (e.g. cryptidins in stomach)
Organ specific enzymes (low pH levels in stomach)
Microbiological
Normal flora – bacteria that lives in the body already.
o Innate immune response
o Adaptive immune response
Innate immune systems
- The innate response is the first line of defence. It is what every pathogen will encounter as
soon as it enters the body. It is immediate. It cannot recognise the pathogen in a specific
way.
- Innate and adaptive immune responses work together to eliminate pathogens and control
self-/non-self discrimination
- Innate immune response controls the adaptive immune system by regulating:
o Expression of co-stimulatory molecules on APC
o Effector mechanisms
Innate Adaptive
Present from birth Learnt from experience
Not antigen-specific Antigen-specific
Not enhanced by second Enhanced by second exposure
exposure
No memory Memory
Poorly effective without Poorly effective without innate
adaptive immunity immunity
Cellular and humeral components (cells, cytokines and soluble
molecules)
- The innate immune response is very immediate (0-4 hours). Upon infection, the innate
immune system will start immediately. Within 4 hours, there will be recognition of the
pathogen by the innate system and it will try to remove the infectious agent.
- Beyond 4 days, the adaptive immune response kick in. The pathogen will be transported
from the site of infection, broken down, the antigens will be taken to the lymphoid organs,
presented to adaptive immune cells and presented by dendritic cells. This will activate the T
and B cells which start to divide (clonal expansion), so that there will be enough to fight the
infection.
- The immune system mainly attacks a pathogen by an inflammatory response
o Cells move to the site of infection
, o Activation of complement (coats the pathogen for cells to take quicker)
o Cells that have taken up the pathogen will release cytokines and chemokines that
will attract cells from the adaptive immune response.
- Main mechanism for clearing the pathogens:
o Phagocytosis (eating up of the pathogen)
o Opsonisation (coating of pathogen)
- Components of innate immunity:
o Phagocytic cells
o Cell surface receptors
o Pathogen sensors
o Complement system
o Cytokines
o Soluble factors
Cells of the innate immune system
- Phagocytic cells – eat up microbe
o Monocytes/macrophages, neutrophils, dendritic cells (DC). Dendritic cell is the key
cell type to activate the adaptive immune system
- Cells that release soluble molecules to induce the inflammation response
o Basophils, mast cells and eosinophils
- Molecular components
o Cytokines, chemokines and complement
Cell population Function
Eosinophils/basophils - Polymorphonuclear – multiple lobular nucleus
- Granulocytes - granules with enzymes released
during infections, allergic reactions and asthma
- Short lived
- Rapidly recruited to sites of inflammation
- Key to combat allergies
- Eosinophils defend against parasites. The exact
function of basophils is unknown
Neutrophils - Polymorphonuclear
- Granulocytes
- Recruited to sites of inflammation – absent in
healthy tissue
- Phagocytic – contains phagosomes which can
swallow up bacteria by the use of cell surface
receptors
- Cell surface receptors are used for sensing and
detecting pathogens.
- Presence of glycogen in cell is what differentiates
them
- Very important component of innate immunity –
hereditary deficiencies result in bacterial
infection
- Most numerous innate cell
Mast cells - Single nucleus with granules (histamines)
- Reside near blood vessels. Mainly found in tissue
- When activated – increase in vascular
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