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8/9/2019 some components in our immune system
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Some components in our immune system
S. SaengamnatdejAugust 30, 2010
T cells
60-70% of all peripheral blood lymphocytes.
Maturation stages: prothymocyte (from bone marrow) -thymocyte (in thymus) - T cell (tocirculation)
Functions
initiate, regulate, and fine-tune humoral immune responses
effector cells in cell-mediated immune responses
Delayed-type hypersensitivity
Contact sensitivity responses (a form of DTH directed against chemicals)
Transplantation immunity
Cytotoxic T cell responses Cell surface molecules
T-cell receptor (TCR)
an - or a - polypeptide-chain pair
CD3 complex
six molecules (one CD3, one CD3 , two CD3 , and an intracytoplasmic homodimer of
or CD247)
CD4 or CD8 as coreceptors.
B cells
5-20% of all peripheral blood lymphocytes.
Maturation in bone marrow (Bursa of Fabricius in birds)
Functions in production of immunoglobulins and antibodies.
Cell surface molecules
Surface immunoglobulin
Fc receptor (FcR)
Complement receptors
CR1 binds C3b
CR2 binds C4b (CR2 is also a receptor for EBV)
MHC class II
Natural killer cells
Large granular non-T, non-B lymphocytes
Functions in innate immunity (virally infected cells and spontaneously arising tumours)
Cell surface molecules
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Fc receptor (used in ADCC)
Monocytes/Macrophages
Mononuclear phagocytes
monocytes in circulation
macrophages in tissues like connective tissue, lung, spleen, liver (Kupffer cells), peritonealcavity, and gastrointestinal tract
Functions
housekeeper (internalize cellular debris, foreign cells, and particles)
degrade them with enzymes.
Cell surface molecules
Fc receptors
FcR binds Fc of IgG1 and IgG3 FcR binds Fc of IgA
Complement receptors
CR1 binds fragments of C3 and C4
CR3 binds iC3b
CR4 binds iC3b
MHC class II
Dendritic cells
functions
in sampling extracellular fluid for foreign cells by macropinocytosis.
as an APC to induce the activation of resting T cells
Neutrophils (Polymorphonuclear (PMN) cells)
60% of blood leukocytes (3,000-6,000 PMN cells per microlitre of blood)
The number of nuclear lobes change from an elongated nucleus (a band form) in bone marrowto bilobed nucleus and to multilobed (up to five) nucleus as the cell becomes maturer.
Have two types of cytoplasmic granules
specific granules
smaller size, but numerous
little affinity for basic or acidic dyes (hence, show a neutral colour)
contain lysozyme, collagenase, and lactoferrin.
azurophilic granules
less numerous
contain anti-microbial enzymes such as myeloperoxidase, lysozyme and defensins, andacid hydrolases.
Function in the first line of defense in microbial infection.
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Basophils and mast cells
less than 0.5% of blood leukocytes
both derive from a common hematopoietic bone marrow precursor.
Basophils: 10-12 microns (diameter), bilobed nucleus, purple-staining or basophilic
cytoplasmic granules. Mast cells: 10-15 microns (diameter), generally round, oval, or spindle-shaped with numerous
surface projections.
Their granules contain vasoactive amines
functions in allergic reactions (free IgE binds to the receptor. Antigen crosslinks the thereceptor-bound IgE antibody causing receptor aggregation that leads to degranulation.)
Cell surface molecules
FcRI binds IgE
Eosinophils
12-17 microns in diameter (slightly larger than PMNs)
bilobed nucleus
cytoplasmic granules stained with acidic dyes (eosin)
contain major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil-derivedneurotoxin (EDN), and eosinophil peroxidase (EPO).
function in resistance to parasitic infections
To be continued.
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