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Classes of Antigen-presenting Cells
MHC Cell type Phagocytic? Function
Class I Many No Stimulates cytotoxic T cell immune response
Class II Macrophage Yes Stimulates phagocytosis and presentation at primary infection site
Class II Dendritic Yes, in tissues Brings antigens to regional lymph nodes
Class II B cell Yes, internalizes surface Ig and antigen Stimulates antibody secretion by B cells

T cell development and differentiation

The process of eliminating T cells that might attack the cells of one’s own body is referred to as T cell tolerance    . While thymocytes are in the cortex of the thymus, they are referred to as “double negatives,” meaning that they do not bear the CD4 or CD8 molecules that you can use to follow their pathways of differentiation ( [link] ). In the cortex of the thymus, they are exposed to cortical epithelial cells. In a process known as positive selection    , double-negative thymocytes bind to the MHC molecules they observe on the thymic epithelia, and the MHC molecules of “self” are selected. This mechanism kills many thymocytes during T cell differentiation. In fact, only two percent of the thymocytes that enter the thymus leave it as mature, functional T cells.

Differentiation of t cells within the thymus

This multipart figure shows the different steps in the differentiation of a thymocyte into T cells. For each step of the process, accompanying text details the steps in the process. The right panel of this image shows the location of the different steps in the process.
Thymocytes enter the thymus and go through a series of developmental stages that ensures both function and tolerance before they leave and become functional components of the adaptive immune response.

Later, the cells become double positives that express both CD4 and CD8 markers and move from the cortex to the junction between the cortex and medulla. It is here that negative selection takes place. In negative selection    , self-antigens are brought into the thymus from other parts of the body by professional antigen-presenting cells. The T cells that bind to these self-antigens are selected for negatively and are killed by apoptosis. In summary, the only T cells left are those that can bind to MHC molecules of the body with foreign antigens presented on their binding clefts, preventing an attack on one’s own body tissues, at least under normal circumstances. Tolerance can be broken, however, by the development of an autoimmune response, to be discussed later in this chapter.

The cells that leave the thymus become single positives, expressing either CD4 or CD8, but not both (see [link] ). The CD4 + T cells will bind to class II MHC and the CD8 + cells will bind to class I MHC. The discussion that follows explains the functions of these molecules and how they can be used to differentiate between the different T cell functional types.

Mechanisms of t cell-mediated immune responses

Mature T cells become activated by recognizing processed foreign antigen in association with a self-MHC molecule and begin dividing rapidly by mitosis. This proliferation of T cells is called clonal expansion    and is necessary to make the immune response strong enough to effectively control a pathogen. How does the body select only those T cells that are needed against a specific pathogen? Again, the specificity of a T cell is based on the amino acid sequence and the three-dimensional shape of the antigen-binding site formed by the variable regions of the two chains of the T cell receptor ( [link] ). Clonal selection is the process of antigen binding only to those T cells that have receptors specific to that antigen. Each T cell that is activated has a specific receptor “hard-wired” into its DNA, and all of its progeny will have identical DNA and T cell receptors, forming clones of the original T cell.

Questions & Answers

Pls give me a brief description of vetebra
Deborah Reply
7 cervical (c1 atlas and c2 axis help the neck rotate) 12 thoracic 5 lumbar 1 sacral and 2 coccyx
Anna
breakfast at 7, lunch at 12, and dinner at 5. sacrum holds 5, coccyx holds 4
Patrick
really there's just one coccyx and sacrum
Patrick
atlas like the Greek God holds the weight of the world on top of him
Patrick
elasticity of the vagina
Mariam Reply
The vagina is an elastic muscular wall
antouman
*organ
antouman
It has I think squamous cuboidal or maybe columnar epithelium designed for secretion, expansion and friction.
Patrick
how can you remember the integumentary system
Naomi Reply
integumentary system is the skin the skin is protection all the body and contain deid cells
Drs
how can you remember the formation of bone?
Maame
the largest organ of the body
Toni
skin is largest organ
Zara
what is the best way to remember the cranial bones or any other bones ?
Savannah
skeletal system?
Savannah
look at the diagram structure and then remember it considering it your own body i memorise like that
Zara
hi guys! do you have to remember ALL the structures of the bones- I mean every single hole, depression or tuberosity?
Kristina
tuborisity
Zara
hey guz i hv to remember Immune antibodies and antigens how? i found it difficult
Zara
well, they are all grouped, aren't they? I mean they all come in series like H1, H2A, H2B and so on. In this case I learn the common part first and then that what's different
Kristina
nd what about IgG , IgE etc.
Zara
the majors
Toni
the thin skin does not have stratum lucidium I believe
Patrick
acronyms
Patrick
if u know the bones, the muscle has part of the name of the bone in it
Patrick
epidermis, I believe epi means on top. dermis in the middle and hypodermis, hypo meaning below. the hypodermis is actually considered not part of the skin or int system
Patrick
big sweet guys love candy = basale, spinosum, granulosum, lucidum ( only in thick skin), corneum
Anna
I love it ☝🏾
Savannah
thank you Zara !
Savannah
can anyone send diet plan for asthma patients
waseem
is
Drs
hey
Daud
jam how are you
Daud
Hey guys l am Matrin
Matrin
blood is a connective tissue which transport oxygen and other nutrients to body
Zara Reply
which type of protein is blood?
Zara
what is blood?
Masthan Reply
blood is a connective tissue which transport oxygen and nutrients to body
Zara
which type of protein is blood?
Zara
haemoglobin
Rashid
and what about its structure i think its Quartenary structure 🤔💭
Zara
yes it is
Rashid
it is globular
Rashid
a vascular structure compose of vessels.
Toni
what is the functions of lymph
moula Reply
what is plasma
Chukwu Reply
A plasma is a hot ionized gas consisting of approximately af a equal number of positive ly charged ionized and negative ly charged electron is called plasma.
Muhammad
what is an atomical position?
Madinatu
military position, body erect where by the body will be up straight..the cephalic and thoracic are straight
Mwita
functions of plasma membrane
Dinyando Reply
what is heparin
Lawrence Reply
why is it anatomy
Tenacious Reply
hello
ASIMENU
hi
asare
hws life
Tenacious
anatomy is the scientific study of the body's structure
Lawrence
great
Lawrence
good night
Kaaya
anatomy is the study of form, physiology is the study of function
Patrick
anatomy is the study of the structure of the body and the physical relationship between it constituent part
Florence
what is heparin
Lawrence
what is the trunk
Tenacious
trunk is define as a person's or animal's body apart from the limp and head
Lawrence
The trunk is part of the axial skeleton
Patrick
hellow friends
mickson
hi friends
mickson
Hi
REEMA
hii
sampath
hi
Inayat
am fine
Ematai
supine or dorsal position is used in clinical setting when patient is placed in position, to examine what?
Dinyando Reply
what do nurses/doctors detect when a patient is placed on dorsal position?
Dinyando
What is coroid process?
kelvin Reply
describe special situation with implications in medical ethics.
kelvin
what is the difference between anatomy and physiology
Dinyando Reply
anatomy is the study of human body . and physiology is the study of the brain
Maryiam
ok
Varun
hi friends
Varun
hi!
kelvin
hello
Maryiam
anatomy is the study of the human body,its form and it physical relations Whiles Physiology is the Study of the functions of the various part of the body
Madinatu
yes
Yeboah
hi friends
mickson
sorry I cant see the full question
Jessica Reply
what was the question?
evelyna
what is spine as a bone marking?
John
similar to a crest but raised more
evelyna
pointed process
evelyna
slender
evelyna
pointed projection i meant
evelyna
what fills the hallow space in the middle of bones? thanks
John
marrow
evelyna
bone marrow
evelyna
hey you gotta read a book
evelyna
i just happen to take this bone chapter in my book last week so i remember
evelyna
yeah i should. how about the correct match of the number of tarsal, metatarsal and phalanges?
John
10, fingers and toes, u know this
Patrick
what is the difference between basal laminal and basal membrane
Nartey Reply
I think they r the same
Patrick

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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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