some components in our immune system

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)



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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.


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.)


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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some components in our immune system