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Topic 3 - Immune System
White Blood Cell Types
Neutrophils - Neutrophils are important in fighting off infections, particularly those caused by bacteria.
Monocytes - Monocytes are the largest type of leukocyte and can differentiate into macrophages and myeloid lineage dendritic cells. As a part of the innate immune system, Monocytes also influence the process of adaptive immunity.
Eosinophils - Eosinophils are involved in inflammation, parasitic infections, allergic reactions or cancer. They are found in high levels at the sites of infection or inflammation.
Basophils - Basophils appear in many specific kinds of inflammatory reactions, particularly those that cause allergic symptoms. Basophils contain Heparin, which prevents the blood from clotting too quickly, as well as the vasodilator Histamine, which promotes blood flow to the tissues.
B Lymphocytes - B Lymphocytes function in the humoral immunity component of the Adaptive Immune
System by secreting antibodies.
T Lymphocytes - T lymphocytes play a central role in cell-mediated immunity.
Natural Killer Cells (NK) - Natural Killer Cells are a type of lymphocyte, and a component of the Innate
Immune System, NK cells play a major role in the host-rejection of both tumours and virally infected cells.
The Responses of the Body to Pathogens of Varying Size
Eosinophils and Basophils [Very Big] - Worms are large organisms and cannot just be ingested, so the substances needed to kill it are released around the organism (damage to surrounding cells). So, Eosinophils and Basophils attempt to destroy them whilst minimising damage to the other cells.
Neutrophils and Monocytes [Big] - Bacteria must be eliminated very rapidly, as they can proliferate very quickly in the body, and they often enter via small areas of trauma. The smaller size of bacteria allows them to be engulfed within cells, allowing their destruction internally without damaging the tissues.
T Lymphocytes and Natural Killer Cells [Small] - Viruses infect normal cells and replicate within them, and they are therefore hidden from the immune system. So, the major role of T-lymphocytes and Natural Killer
Cells is to recognise these infected cells and destroy them, without affecting the normal cells.
B Lymphocytes [Very Small] - Toxins may circulate in the body, and B Lymphocytes recognise these using antibodies, which they secrete in large amounts to destroy or neutralise foreign proteins. The B Lymphocyte then retains a memory of the antigen, so it can be activated quickly if it invades again.
Innate Immune System
The Innate Immune System is the ancient evolutionary conserved system used to recognise self from nonself, which they will attack. These need to be mobile, interacting with other cells and recognising their features.
It includes cells such as Neutrophils, Eosinophils, Basophils and Monocytes that patrol the blood, recognising common proteins in the bacterial cell walls or their released bacterial components.
The Innate Immune system more specifically uses PAMPs and DAMPs to target invading pathogens.
Once the pathogen is recognised small molecules are released to help recruit sand activate the WBCs:
Cytokines - Cytokines cause an increased formation and early release of white blood cells from the marrow.
Chemokines - Chemokines are small peptide hormones that attract cells and cause the recruitment of neutrophils to the sites of infection.
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