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Although the correlation is not 100 percent, CD4-bearing T cells are associated with helper functions and CD8-bearing T cells are associated with cytotoxicity. These functional distinctions based on CD4 and CD8 markers are useful in defining the function of each type.

Helper t cells and their cytokines

Helper T cells (Th) , bearing the CD4 molecule, function by secreting cytokines that act to enhance other immune responses. There are two classes of Th cells, and they act on different components of the immune response. These cells are not distinguished by their surface molecules but by the characteristic set of cytokines they secrete ( [link] ).

Th1 cells    are a type of helper T cell that secretes cytokines that regulate the immunological activity and development of a variety of cells, including macrophages and other types of T cells.

Th2 cells    , on the other hand, are cytokine-secreting cells that act on B cells to drive their differentiation into plasma cells that make antibody. In fact, T cell help is required for antibody responses to most protein antigens, and these are called T cell-dependent antigens.

Cytotoxic t cells

Cytotoxic T cells (Tc) are T cells that kill target cells by inducing apoptosis using the same mechanism as NK cells. They either express Fas ligand, which binds to the fas molecule on the target cell, or act by using perforins and granzymes contained in their cytoplasmic granules. As was discussed earlier with NK cells, killing a virally infected cell before the virus can complete its replication cycle results in the production of no infectious particles. As more Tc cells are developed during an immune response, they overwhelm the ability of the virus to cause disease. In addition, each Tc cell can kill more than one target cell, making them especially effective. Tc cells are so important in the antiviral immune response that some speculate that this was the main reason the adaptive immune response evolved in the first place.

Regulatory t cells

Regulatory T cells (Treg) , or suppressor T cells, are the most recently discovered of the types listed here, so less is understood about them. In addition to CD4, they bear the molecules CD25 and FOXP3. Exactly how they function is still under investigation, but it is known that they suppress other T cell immune responses. This is an important feature of the immune response, because if clonal expansion during immune responses were allowed to continue uncontrolled, these responses could lead to autoimmune diseases and other medical issues.

Not only do T cells directly destroy pathogens, but they regulate nearly all other types of the adaptive immune response as well, as evidenced by the functions of the T cell types, their surface markers, the cells they work on, and the types of pathogens they work against (see [link] ).

Functions of T Cell Types and Their Cytokines
T cell Main target Function Pathogen Surface marker MHC Cytokines or mediators
Tc Infected cells Cytotoxicity Intracellular CD8 Class I Perforins, granzymes, and fas ligand
Th1 Macrophage Helper inducer Extracellular CD4 Class II Interferon-γ and TGF-β
Th2 B cell Helper inducer Extracellular CD4 Class II IL-4, IL-6, IL-10, and others
Treg Th cell Suppressor None CD4, CD25 ? TGF-β and IL-10

Chapter review

T cells recognize antigens with their antigen receptor, a complex of two protein chains on their surface. They do not recognize self-antigens, however, but only processed antigen presented on their surfaces in a binding groove of a major histocompatibility complex molecule. T cells develop in the thymus, where they learn to use self-MHC molecules to recognize only foreign antigens, thus making them tolerant to self-antigens. There are several functional types of T lymphocytes, the major ones being helper, regulatory, and cytotoxic T cells.

Questions & Answers

structure of the cell
BELLO Reply
what do u want to know about the structure of the cell?
Ebeneezer
Process of bone healing
Thelma Reply
The fractured bones are brought closer (reduction of fracture). the fibroblast cells at broken ends divide rapidly and secrete collagen that forms collar of callus. The callus holds the bones together which slowly clacifies (remodelling) and later replaced by bone tissue.
Biplav
what is the name of the two subunits of L chain of a antibody structure
Arshi Reply
The pituitary gland lies in the
Aamir Reply
bony cavity,sella tursica
Arshi
how does endochrondral ossification start in short bones?
Steven Reply
the chondroblast cells forms a cartilaginous bone model which becomes calcified in mid region and is innervated by perosteal capillaries. These capillaris replaces cartilages with bone tissue.
Biplav
define negative feedback
Oageng
mechanism that cause supression of another process. eg. the secretion of one hormone can supress the other hormone secretion.
Biplav
simply a self regulating mechanism which retun a deviated parameter to normal condition
Japhar
secretion of hormones get supressed by other hormone secretion
Kodeck
by like 😂😂😂😂
Zozo
what is RH blood group
kuukyile Reply
It is a type of system for classifying blood groups according to the presence or absence of the Rh antigen.
Rakshith
What is the most important organ in the human body?
Gbemi Reply
the heart
Phodiso
or brain
Phodiso
Why?
Gbemi
heart
Kelly
the brain specifically is referred to as the control centre ..all nerve impulses are send to the brain which stimulates other specific parts of the body
Phodiso
please if l am Blood group B+ can l marry a lady with O- blood group?
kuukyile
structure of a serous membrane
Ziyanda Reply
are you asking?
Isa
yes
MOHD
In anatomy, serous membrane (or serosa) is a smooth tissue membrane consisting of two layers of mesothelium, which secrete serous fluid. The inner layer that covers organs (viscera) in body cavities is called the visceral membrane. A second layer of epithelial cells of the serous membrane, called th
Isa
The two layers of serous membranes are named parietal and visceral. Between the two layers is a thin fluid filled space.[2] The fluid is produced by the serous membranes and stays between the two layers to reduce friction between the walls of the cavities and the internal organs when they move with
Isa
a continuation from the 1st one:: A second layer of epithelial cells of the serous membrane, called the parietal layer, lines the body wall. Between the two layers is a potential space, mostly empty except for a few milliliters of lubricating serous fluid that is secreted by the two serous membranes
Isa
Lubricated secretion of skin is called sebum
Jazil
haematopoietic
oyewale
what is the greater tronchanter?
Phodiso
the greater trochanter is  femur is a large, irregular, quadrilateral eminence and a is a part of the system of the skeleton
Jessie
Thanks Jessie...
Phodiso
what is the easiest way to learn labels of Anatomical structures?
Phodiso
what's the anatomical plan of the horse lung
musa
Name the two phases of metabolism
Grace Reply
reproduction and growth
Zozo
how about anabolism and catabolism?
Japhar
In Simply Anabolism means formation... Catabolism means breakdown
Jazil
two phases of reproductio?
Japhar
Anabolism indicates potential & catabolism potential converts to kinetic
Doctor
Name the most important life process in the human body in terms of anatomy and physiology
Grace
Nervous system
Nimco
Every system is important for body functions
Jazil
what is the difference between the functions of the adhesion belt and the desmosomes?
Mason Reply
what are the derivatives of the germ layer?
Miriam Reply
zygote
Zozo
Pls explain the atlas of the cervical vertebral column
Ifunanya Reply
why does the material not allow in mri
Simran Reply
what do you mean 'mri'
Nimco
short for magnetic resonance imaging. "the researchers used MRI to record the brain activity" a medical examination performed using magnetic resonance imaging. "he's having an MRI to determine the extent of the injury" an image obtained by magnetic resonance imaging. "after looking at the MRI, the d
Riyaz
what is the meaning of sutures
Ibrahim Reply
i do not know
Nimo
immovable joints btn two bones.eg the skull bones
Japhar
Really,it's true
Nimco
Sutures are immovable junction between two bones e.g those of the skull
Surphy
what should I do to get or to know what to do for me to be excellent in the course of anatomy and physiology
Sandra Reply
study harder
Japhar

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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