Cells of the Immune System

Meanings of Prefixes and Suffixes

  • Baso: foundation
  • Blasts: immature cells
  • Cyte: cell
  • Eosin: red coloured
  • Haemo: blood
  • Karyo: nucleus
  • Kine: motion
  • Lympho: lymphatic system
  • Lysis: broken down
  • Macro: large
  • Mega: large
  • Mono: single
  • Myelo: bone marrow
  • Neutro: neutral
  • Phage: eat
  • Phil: attraction
  • Pluri: multiple
  • Poietic: creative
  • Potent: potential
  • Pro: moving forward
  • Reticulo: net like

Pluripotent Haematopoietic Stem Cell

These are undifferentiated cells that have the potential to become a variety of blood cells. They initially become:

  • Myeloid Stem Cells
  • Lymphoid Stem Cells
  • Dendritic Cells (via various intermediate cells)

 

Myeloid Stem Cells

Myeloid stem cells become:

  • Megakaryocytes that produce platelets
  • Reticulocytes become:
    • Red Blood Cells (RBCs)
  • Promyelocytes become:
    • Monocytes – Macrophages
    • Neutrophils
    • Eosinophils
    • Mast Cells
    • Basophils

 

Lymphoid Stem Cells

Lymphoid Stem Cells travel to the thymus gland and differentiate into:

  • B lymphocytes (B cells) (mature in the bone marrow) that differentiate into:
    • Plasma Cells
    • Memory B Cells
  • T lymphocytes (T cells) (mature in the thymus) that differentiate into:
    • CD4 cells (T helper cells)
    • CD8 cells (Cytotoxic T Cells)
  • Natural Killer Cells

 

Megakaryocytes

  • Large cells
  • Big lobulated nucleus
  • Produce platelets
  • Platelets are essential for blood clotting

 

Reticulocytes

  • Immature red blood cells
  • Remnant RNA material called reticulum in cytoplasm
  • Released from bone marrow
  • Normally 1% of red blood cells are reticulocytes
  • Higher percentage indicates rapid turnover of blood, such as in:
    • Acute blood loss
    • Haemolysis
  • Loose their reticulum after a few days – becoming:

 

Red Blood Cells (RBCs)

  • RBCs contain large quantities of haemoglobin, and carry oxygen from the lungs to the tissues
  • They survive about 3 months

 

Macrophages

  • Monocytes circulate the blood stream
  • Enter tissues and differentiate into macrophages
  • Live in most tissues in the body
  • Have “Toll-Like Receptors
  • Recognise “Pathogen-associated molecular patterns” (PAMPs
  • Kill pathogens and abnormal cells by phagocytosis
  • Release cytokines that initiate the inflammatory response
  • Activate the other cells of the immune system

 

Neutrophils

  • Circulate through the blood and lymphatic system
  • Migrate to areas of inflammation
  • Kill pathogens and abnormal cells by phagocytosis

 

Eosinophils

  • Important in responding to parasites
  • They normally sit waiting in tissues
  • Contain granules with:
    • Proinflammatory cytokines
    • Chemicals toxic to pathogens, such as “major basic protein
  • They have two functions:
    • Exocytosis of their granules
    • Phagocytosis (but less than neutrophils and macrophages)

 

Mast Cells and Basophils

  • Mast cells are fixed in place in tissues
  • Basophils circulate through the blood
  • Contain cytoplasmic granules
  • Degranulation releases pro-inflammatory cytokines

 

B Lymphocytes

  • Also called B cells
  • Mature in the bone marrow
  • Cell surface lined with antibodies
  • Each B cell has a specific type of antibody for a specific antigen
  • There are millions of different possible antibodies and therefore millions of different specific B cells
  • B cells can only recognise antigens that match their antibodies
  • Once activated B cells become either:
    • Plasma cell – secrete antibodies (also called immunoglobulins)
    • Memory B cell – await a later infection with the same pathogen

 

T Lymphocytes

  • Also called T cells
  • Pro-thymocytes leave the bone marrow and travel to the thymus gland
  • Mature in the thymus gland into T cells
  • Cell surface lined with T-cell receptors
  • Each T cell has a specific type of T-cell Receptor (TcR) for a specific antigen
    • CD4 cells have CD4 TcRs that recognise MHC class 2 receptors
    • CD8 cells have CD8 TcRs that recognise MHC class 1 receptors
  • CD4 cells become T-helper cells when activated
  • T helper cells help other cells become activated, including CD8 cells
  • CD8 cells become cytotoxic T cells when activated
  • Cytotoxic T cells destroy infected cells via
    • Granule exocytosis causing destruction of the cell
    • Activating the Fas pathway causing cell apoptosis

 

Natural Killer Cells

  • Activated by cytokines from macrophages and interferons
  • Recognise infected or abnormal (e.g. cancerous) cells
  • Destroy these cells by cytokines
  • Release IFN-γ that activates macrophages

 

Dendritic Cells

  • Originate from several cell lines
  • Specialist dendritic cells found in the skin are called Langerhans cells
  • Take up antigens, process them and display them on their cell surface
  • Have both MHC class I and class II molecules
  • Act as messengers, taking antigens from infected tissues to lymph nodes to activate T cells
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