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Learning objectives

  • Describe the process of T-cell maturation and thymic selection
  • Explain the genetic events that lead to diversity of T-cell receptors
  • Compare and contrast the various classes and subtypes of T cells in terms of activation and function
  • Explain the mechanism by which superantigens effect unregulated T-cell activation

As explained in Overview of Specific Adaptive Immunity , the antibodies involved in humoral immunity often bind pathogens and toxins before they can attach to and invade host cells. Thus, humoral immunity is primarily concerned with fighting pathogens in extracellular spaces. However, pathogens that have already gained entry to host cells are largely protected from the humoral antibody-mediated defenses. Cellular immunity, on the other hand, targets and eliminates intracellular pathogens through the actions of T lymphocytes, or T cells ( [link] ). T cells also play a more central role in orchestrating the overall adaptive immune response (humoral as well as cellular) along with the cellular defenses of innate immunity.

A micrograph of a round cell approximately 7 micrometer in diameter. The cell has a studded surface.
This scanning electron micrograph shows a T lymphocyte, which is responsible for the cell-mediated immune response. The spike-like membrane structures increase surface area, allowing for greater interaction with other cell types and their signals. (credit: modification of work by NCI)

T cell production and maturation

T cells, like all other white blood cells involved in innate and adaptive immunity, are formed from multipotent hematopoietic stem cells (HSCs) in the bone marrow (see [link] ). However, unlike the white blood cells of innate immunity, eventual T cells differentiate first into lymphoid stem cells that then become small, immature lymphocytes, sometimes called lymphoblasts . The first steps of differentiation occur in the red marrow of bones ( [link] ), after which immature T lymphocytes enter the bloodstream and travel to the thymus for the final steps of maturation ( [link] ). Once in the thymus, the immature T lymphocytes are referred to as thymocytes .

The maturation of thymocytes within the thymus can be divided into tree critical steps of positive and negative selection, collectively referred to as thymic selection . The first step of thymic selection occurs in the cortex of the thymus and involves the development of a functional T-cell receptor (TCR) that is required for activation by APCs. Thymocytes with defective TCRs are removed by negative selection through the induction of apoptosis (programmed controlled cell death). The second step of thymic selection also occurs in the cortex and involves the positive selection of thymocytes that will interact appropriately with MHC molecules. Thymocytes that can interact appropriately with MHC molecules receive a positive stimulation that moves them further through the process of maturation, whereas thymocytes that do not interact appropriately are not stimulated and are eliminated by apoptosis . The third and final step of thymic selection occurs in both the cortex and medulla and involves negative selection to remove self-reacting thymocytes , those that react to self-antigens, by apoptosis. This final step is sometimes referred to as central tolerance because it prevents self-reacting T cells from reaching the bloodstream and potentially causing autoimmune disease , which occurs when the immune system attacks healthy “self” cells.

Questions & Answers

write the life cycle of HIV
Firomsa Reply
describe the internal and external structure of prokaryotic cell in terms of there appearance and functions
Lenia Reply
compare and contrast similar structures found in prokaryotic and eukaryotic cells
Lenia
control of microorganisms
ISTEFAZUL Reply
how can a doctor treat a person affected by endospore forming bacteria in his/her wound?
Mambo Reply
a 28 years old woman come to your clinic with complain of fever painful genital blisters which express clear fluid when ruptured burning sensation around the bristers what is the diagnosis?
Ramadhani Reply
genital herpes caused by a virus called herpe simplex virus
Doris
what is the reference between selective medium and differential medium?
Tony Reply
the micro flora of air is transient why
Princess
Hello.... Am new here
essien Reply
welcome essien
Muhammad
welcome essien
Beka
classification of gram positive
lissa Reply
classify gram positive
lissa
catalase test is done to differentiate between staph and strep. as staph is catalase positive while strep is catalase negative then staph is differentiate further on coagulase positive and coagulase negative. staph aureus is coagulase positive while staph epidermidis is coagulase negative.
Muhammad
gram positive staph is further differentiated on sensitivity test and manitol salt fermentation test while gram positive strep is differentiated on hemolysis pattern
Muhammad
more about gramm positive
lissa
please
lissa
ok
Blessing
am back any gist
Blessing
taxonomy
Rahul
can i use the graph of bacterial growth for my master's thesis?
Christoph Reply
facultative anaerobic bavteria gives uniform turdibity in nutrient broth why?
Princess Reply
oils and waxes are not sterilized in autoclave
Princess
what is the function of paraffin
Muhammad
@ MAHI because they can grow all over the media from surface to the bottom as they can utilize oxygen or conduct fermentation in its absence.
Online
2.@MAHI Autoclave uses steam under pressure. The steam cannot penetrate through oil and wax. Thus, dry heat sterilization is preferred than autoclave .
Online
thnku
Nadiya
how nutirent agar can converted into blood agar
Princess
thank you
Princess
take a nutrient agar ........and add 5ml blood and put in it ...........!
Nadiya
nutrient agar +blood 5ml+ distilled water =blood agar .
Nadiya
mixed wellllll
Nadiya
hi
Rahul
why agar is not a neutrient source?
Shimul
because it's a general purpose agar only use for growing bacteria
Richa
way is antigen
opaleye
what is antigen
opaleye
antigen is a foreign body that cause activation of antibody?
ASNAKE
Antigen is a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
Shimul
thanks for that
opaleye
what is pharmacology
Luyenu
a science that studies about the drug
ASNAKE
hello ever one
Sayid
y
Abdul
Work hard
Anigor
y
Abdul
thanks alot
Luyenu
What is the major different between gram positive and gram negative bacteria.
Asikur
bacteria kya hai
Mala
content of their cell wall
Doris
koi mujhse basic microbiology ki study k Lea book suggest kro .
Richa
Harley prescott
Vikas
what are the five predisposing factors of opportunistic infections
Asher Reply
1. long term exposure to diseases, that the body immunity weakens.
prosper
2. Nature Of some diseases to weaken body immunity such as, AIDS.
prosper
3. Use of immuno-suppresive drugs.
prosper
anyone... need a hand here 🙋😞
prosper
Low immune is the major cause eg for kaposis sarcoma
Davismith
suitable conditions e.g temp,
Muhammad
what os gnormal flora
kifayat Reply
morphological and genetic classification of bacteria
Potter Reply
what is the morphogical
Bupe
h
Sudhir
morphologycal is defined as relating to the branch of biology that deals with the form of living organisms,and with relationship between their structures.
Nadiya
relating to the form or structure of things .
Nadiya
what is the meaning of lessions
oluwa
i am frim Afghanistan.
wahidullah Reply
iam from iraq
Haidar
and i'm from pakistan
Muhammad
Nice
Amina
what's about the qualification
Muhammad
Hlo
Asiya
Hmm
Number
Almustafa Muhammad from Nigeria
Mujtafa
am ustaz Abdulsalam from Ghana
ustaz
am Bupe Chifita from Zambia
Bupe
what is microbiology
Bupe
is the study of invisible micro organism
Mujtafa
microbiology is the study of very too small organisms which we can't see with naked eyes ......in other words ....study of microorganism is called microbiology.
Nadiya
Hello! How Can Microorganisms Be Isolated From The Skin?.. 5 ways if possible. (briefly)
prosper
from skin swabbing is the prefer method worldwide
Muhammad
thanks Muhammad Nauman very much!
prosper
hi
Meek
hi Meek
prosper
are there any other ways pals?
prosper
hi prosper
Meek
hello Meek Mild.
prosper
Any question or ideas, Meek?😊
prosper
and if a patient have any blister or abscess on the skin then first cut the blister or abscess. inside material is taking by syringe.
Muhammad
in case of fingernail or toenails simply cut a small piece of nail and culture on the appropriate media at a required temperature and time
Muhammad
Again, thanks Mr. Muhammad! I appreciate the help.
prosper
you welcom prosper 😊
Muhammad
what are the media use for skin swab?
Sieh-Mlanwin
blood and macckonkey mostly usededia for skin bacteria
Muhammad
used media*
Muhammad
@ SIEH mostly fungal infection occurs in skin so SDA ( Sabouraud Dextrose Agar) or MEA ( Malt extract agar) are common.
Online
thanks
Sieh-Mlanwin
Microbiologicam source of vitamins
Bachi Reply
what do you mean?
Md
that's example?
Md
hi everyone
Muhammad
such as. c/s media
Md
hmm hlw
Md
just tell me about that ?
Md
where are u from
Muhammad
Practice MCQ 5

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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