Cells of Immune System Flashcards
How are immune cells classified?
According to:
• Origins: Lymphoid or Myeloid line
• System of immunity: Innate or Adaptive
• Cell structure: Granulocytes or Agranulocytes
• Function: phagocytosis, antigen presentation, cell cytotoxicity, antibody dependent cell mediated cytotoxicity (ADCC)
Where do all blood cells originate from?
Haematopoietic Stem Cells which are found in bone marrow
Different types of blood cell?
RBC,
Leukocytes - all white blood cells
Platelets
Which cells come under lymphoid progenitor?
T cells - T helper cells and Cytotoxic killer cells
B cells- plasma and memory cells
NK cells
Which are myeloid cells?
(7)
Neutrophil , Eosinophils, Basophils, Mast cells,
Monocytes —— dendritic cells and macrophages
Cells of innate system vs cells of adaptive system?
Adaptive- B and T
Innate - NK, Eosinophils, basophils, neutrophils, mast cells, monocytes—— dendritic cells and macrophages
Which of the lymphocytes are agranulocytes vs granulocytes?
Agra - Dendritic, monocytes, macrophages, lymphocytes (T, B and NK) and mast cells
Gran- eosinophils, neutrophils and basophils
3 APC?
B cells, macrophages and dendritic cells
Present antigens through MHC 2 class molecules
Which cells cause cell mediated cytotoxicity?
NK cells (innate)
Cytotoxic lymphocytes (adaptive)
Both kill the cell via apoptosis
Which cells cause antigen dependent cell mediated cytotoxicity?
Macrophages, neutrophils, eosinophils and NK cells
What is the mechanism of ADCC?
1- Specific antibodies bind to antigens expressed on the surface of cells which are infected with viruses or bacteria or cancer cells.
2- FcγR on NK cells, macrophages and neutrophils or FcεR on eosinophils recognise the bound antibody.
3-This leads to the activation of immune cells, resulting in the apoptosis (programmed cell death) of the target cell
What is the structure and function of neutrophils?
They make up 50-70% of circulating leukocytes and are first cells to arrive at the site of infection.
Neutrophils are granulocytes
Primary granules include: peroxydase, lysozyme
Secondary granules include: collagenase, lactoferrin
Functions include:
Phagocytosis, neutrophil extracellular traps, ADCC
What are monocytes
They circulate in blood for 8 hours after leaving the bone marrow.
They migrate into the tissues and differentiate into macrophages and dendritic cells
What is the structure and function of macrophage? How many types of macrophages are there?
Macrophages develop from monocytes
They undergo several changes:
Increased cell size (5–10 times larger than monocytes).
More intracellular organelles, proteolytic enzymes, secretion of soluble factors
There are 2 types of macrophages:
1- Resident macrophages have different functions in different tissues
Kupffer cells: Location: Line the sinusoids (small blood vessels) of the liver.
Function:
Phagocytose pathogens, dead cells, and toxins from the blood (especially those from the gut via the portal vein).
Play a key role in detoxification and immune surveillance.
Secrete growth factors and anti-inflammatory cytokines to assist in tissue repair and regeneration.
2- Wandering macrophages- these travel within and between tissues are involved in immune response
Functions of macrophages include: antigen presentation and phagocytosis, ADCC
What are dendritic cells and their function?
Express MHC1, MHC2, CD4 and CD8 molecules
Function : 1-Phagocytosis, DC undergoes maturation, and migrates from tissue to lymph nodes
2-professional antigen presenting cells (APC)
What are eosinophils and their function?
These are phagocytic granulocytes and make up 1-3% of circulating leukocytes.
They are mostly found in connective tissue under gut epithelium
They contain cell-surface receptors for cytokines, complement and Fc receptors for IgE.
Upon activation, eosinophils release:
1- free radicals and toxic proteins from granules. This kills microorganisms and parasites (can also induce allergic reactions)
2- prostaglandins and cytokines → amplification of inflammatory
response → activation of epithelial cells and recruitment of leukocytes
What are basophils and their functions?
They are nonphagocytic granulocytes which make less than 1% of circulating leukocytes
They are recruited from blood into tissues to the site of the infection.
They contain cell-surface receptors for cytokines and Fc receptors for IgE for antibody-dependent cell cytoxicity
Effector function:
* release histamine → ↑ vascular permeability
* with eosinophils – defence against parasites
* can induce allergic reactions
What are mast cells and their function?
They differentiate only upon entering tissues.
They are found in connective tissue, around blood and lymph vessels and nerves
They contain granules with histamines
Secrete cytokines
They contain receptors for Fc for IgE.
Their functions include:
Can induce allergic reactions via histamine.
Role in inflammation
Define phagocytosis?
Process of engulfing and destroying pathogens.
Phagocytosis involves 4 steps:
Adherence- Phagocytes have receptors which are highly specific and bind to pathogens.
Opsonins (antibodies and complement) enhance adherence by tagging pathogens and making them visible.
Ingestion- Phagocytes extend pseudopodia around the pathogen
Pathogen is enclosed in a vesicle called phagosome.
Digestion- Phagosome fuses with lysosomes, forming phagolysosome.
Lysosome contain hydrolytic enzymes such as lysozyme which breaks down the pathogens.
Excretion- Indigestible material is released outside the cell via exocytosis.
Some antigen-presenting cells (like dendritic cells) process pathogen fragments (digestible material) for antigen presentation.
What are NK cells?
▪ Kill only infected or cancerous host cells by detecting the “missing
self
▪ Cytotoxic granules containing perforin and granzymes (proteolytic enzymes)
What are 2 types of receptors expressed on the cell surface of NK cells
?
2 types of receptors include:
Activating receptors: (act like sensors)
These receptors detect stress signals on other cells, such as cells infected by a virus or cancerous cells.
When these stress signals are detected, NK cells are activated and they kill the target cells.
Inhibiting receptors: serve to protect normal healthy cells. These receptors are sensitive to MHC 1 molecules. If the cell has normal levels of MHC molecules, NK cells will not attack it
The NK cytotoxicity is mediated via apoptosis induced by which mechanisms?
1- Fas-dependent mechnasim
2- Fas-independent mechanism
3- Antibody-dependent cell cytotoxicity
Explain Fas-dependent mechanism?
The Fas-dependent mechanism allows NK cells to directly kill the target cell through receptor signaling without needing other immune components like antibodies.
Fas receptors (death receptors) are expressed on the surface of target cells.
NK cells have fas-ligand on their surface.
When FasL binds to Fas, it leads to apoptosis
Explain the Fas-independent mechanims.
Recognition and attachment: The NK cell identifies and binds to the target cell (infected or cancerous cells)
Membrane attack: The NK cell releases perforin and granzymes in the interstitial space
Perforin: This is a protein that forms pores (holes) in the membrane of the target cell.
Granezymes: These are enzymes that enter the target cell through the pores made by perforin. Granzymes then trigger the target cell to start the process of apoptosis
Dissociation: The NK cell detaches after releasing the toxic substances.
Target cell destruction: The target cell undergoes apoptosis, leading to its death
