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  • What are the two signals required for T cell-independent activation of B cells?
  • What is the function of a plasma cell?

T cell-dependent activation of b cells

T cell-dependent activation of B cells is more complex than T cell-independent activation, but the resulting immune response is stronger and develops memory. T cell-dependent activation can occur either in response to free protein antigens or to protein antigens associated with an intact pathogen. Interaction between the BCRs on a naïve mature B cell and a free protein antigen stimulate internalization of the antigen, whereas interaction with antigens associated with an intact pathogen initiates the extraction of the antigen from the pathogen before internalization. Once internalized inside the B cell, the protein antigen is processed and presented with MHC II . The presented antigen is then recognized by helper T cells specific to the same antigen. The TCR of the helper T cell recognizes the foreign antigen, and the T cell’s CD4 molecule interacts with MHC II on the B cell. The coordination between B cells and helper T cells that are specific to the same antigen is referred to as linked recognition .

Once activated by linked recognition, T H 2 cells produce and secrete cytokines that activate the B cell and cause proliferation into clonal daughter cells. After several rounds of proliferation, additional cytokines provided by the T H 2 cells stimulate the differentiation of activated B cell clones into memory B cells , which will quickly respond to subsequent exposures to the same protein epitope, and plasma cells that lose their membrane BCRs and initially secrete pentameric IgM ( [link] ).

After initial secretion of IgM, cytokines secreted by T H 2 cells stimulate the plasma cells to switch from IgM production to production of IgG , IgA , or IgE . This process, called class switching or isotype switching , allows plasma cells cloned from the same activated B cell to produce a variety of antibody classes with the same epitope specificity. Class switching is accomplished by genetic rearrangement of gene segments encoding the constant region , which determines an antibody’s class. The variable region is not changed, so the new class of antibody retains the original epitope specificity.

1: BCR interaction with antigen on intact pathogen. An antigen on the surface of a bacterium binds to the B cell receptor on the B cell. s: Antigen processing and presentation with MHC II. The antigen is on the MHC II. 3: Antigen presentation and activation of helper T cell. T cell receptor of helper T cell binds to antigen on MHCII. This is stabilized by CD4. Helper T releases cytokines. 4: Cytokines stimulate clonal proliferation and differentiation into memory B cells and antibody-secreting plasma cells.
In T cell-dependent activation of B cells, the B cell recognizes and internalizes an antigen and presents it to a helper T cell that is specific to the same antigen. The helper T cell interacts with the antigen presented by the B cell, which activates the T cell and stimulates the release of cytokines that then activate the B cell. Activation of the B cell triggers proliferation and differentiation into B cells and plasma cells.
  • What steps are required for T cell-dependent activation of B cells?
  • What is antibody class switching and why is it important?

Primary and secondary responses

T cell-dependent activation of B cells plays an important role in both the primary and secondary responses associated with adaptive immunity. With the first exposure to a protein antigen, a T cell-dependent primary antibody response occurs. The initial stage of the primary response is a lag period , or latent period , of approximately 10 days, during which no antibody can be detected in serum. This lag period is the time required for all of the steps of the primary response, including naïve mature B cell binding of antigen with BCRs, antigen processing and presentation, helper T cell activation, B cell activation, and clonal proliferation. The end of the lag period is characterized by a rise in IgM levels in the serum, as T H 2 cells stimulate B cell differentiation into plasma cells . IgM levels reach their peak around 14 days after primary antigen exposure; at about this same time, T H 2 stimulates antibody class switching, and IgM levels in serum begin to decline. Meanwhile, levels of IgG increase until they reach a peak about three weeks into the primary response ( [link] ).

During the primary response, some of the cloned B cells are differentiated into memory B cells programmed to respond to subsequent exposures. This secondary response occurs more quickly and forcefully than the primary response. The lag period is decreased to only a few days and the production of IgG is significantly higher than observed for the primary response ( [link] ). In addition, the antibodies produced during the secondary response are more effective and bind with higher affinity to the targeted epitopes. Plasma cells produced during secondary responses live longer than those produced during the primary response, so levels of specific antibody remain elevated for a longer period of time.

A graph with time on the X axis and antibody concentration in serum. At first there is very little antibody (near 0). The lag period does not see a significant increase. In the primary response, IgM peaks for about 5 days and drops. At the same time IgG increases and then drops. This creates an increase in antibody count with a plateau of about 5 days as both antibody types are present. The secondary response sees a peak of IgM for about 1 to 2 days and then a prolonged peak of IgG. The total antibody is also higher but isn’t at its plateau for as long as it is in the primary response.
Compared to the primary response, the secondary antibody response occurs more quickly and produces antibody levels that are higher and more sustained. The secondary response mostly involves IgG.
  • What events occur during the lag period of the primary antibody response?
  • Why do antibody levels remain elevated longer during the secondary antibody response?

Key concepts and summary

  • B lymphocytes or B cells produce antibodies involved in humoral immunity. B cells are produced in the bone marrow, where the initial stages of maturation occur, and travel to the spleen for final steps of maturation into naïve mature B cells.
  • B-cell receptors (BCRs) are membrane-bound monomeric forms of IgD and IgM that bind specific antigen epitopes with their Fab antigen-binding regions. Diversity of antigen binding specificity is created by genetic rearrangement of V, D, and J segments similar to the mechanism used for TCR diversity.
  • Protein antigens are called T-dependent antigens because they can only activate B cells with the cooperation of helper T cells. Other molecule classes do not require T cell cooperation and are called T-independent antigens .
  • T cell-independent activation of B cells involves cross-linkage of BCRs by repetitive nonprotein antigen epitopes. It is characterized by the production of IgM by plasma cells and does not produce memory B cells.
  • T cell-dependent activation of B cells involves processing and presentation of protein antigens to helper T cells, activation of the B cells by cytokines secreted from activated T H 2 cells, and plasma cells that produce different classes of antibodies as a result of class switching . Memory B cells are also produced.
  • Secondary exposures to T-dependent antigens result in a secondary antibody response initiated by memory B cells. The secondary response develops more quickly and produces higher and more sustained levels of antibody with higher affinity for the specific antigen.

Fill in the blank

________ antigens can stimulate B cells to become activated but require cytokine assistance delivered by helper T cells.

T-dependent

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T-independent antigens can stimulate B cells to become activated and secrete antibodies without assistance from helper T cells. These antigens possess ________ antigenic epitopes that cross-link BCRs.

repetitive

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Questions & Answers

it is the main memory of a person.
Kizza Reply
what is brain
Tope Reply
is the main memory of a person.
Kizza
it is the centre of the nervous system found in all vertebrates and most invertebrates.
Akhiomo
what are the two acids the skin produce
Caro Reply
alpha hydroxy and beta hydroxy there are water soluble compounds and often use as exfoliant
Enow
what must a positive strand of an RNA virus do first
Kelsi-Ann Reply
A positive-sense single-stranded RNA virus (or (+)ssRNA virus) is a virus that uses positive sense single stranded RNA as its genetic material. Single stranded RNA viruses are classified as positive or negative depending on the sense or polarity of the RNA.
Dejene
 The positive-sense viral RNA genome can serve as messenger RNA and can be translated into protein in the host cell. Positive-sense ssRNA viruses belong to Group IV in the Baltimore classification. Positive-sense RNA viruses account for a large fraction of known viruses, including many pathogens
Dejene
such as the hepaci virus C, West nail virus, dengue virus, SARS and MERS coronaviruses, and SARS-CoV-2 as well as less clinically serious pathogens such as the rhinoviruses that cause the common cold.
Dejene
Why strong acid and alkline are not harmful to mycobacterium bacili?
Brian
What are the types of bacteria
John Reply
Do you mean the shapes or the the two different types of bacteria? Bacteria are often described in terms of their general shape. Common shapes include spherical (coccus), rod-shaped (bacillus), or curved (spirillum, spirochete, or vibrio) The two different types are gram negative or gram positive.
Melanie
what other characteristics of prokaryotes a bacteria don't have?
Brian
Prokaryotes are single-celled organisms belonging to the domains Bacteria and Archaea. Prokaryotic cells are much smaller than eukaryotic cells, have no nucelus, and lack organelles. All prokaryotic cells are encased by a cell wall. Many also have a capsule or slime layer made of polysaccharide.
Dejene
gram positive bacteria and gram negative bacteria
mubeen
Most bacteria can be broadly classified as Gram positive or Gram negative. Gram positive bacteria have cell walls composed of thick layers of peptidoglycan.cells stain purple when subjected to a Gram stain procedure. Gram negative bacteria have cell walls with a thin layer of peptidoglycan.
Dejene
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demisew
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Dejene
guys what are the two acids the skin produce
Caro
what are the bacteria's involved in the decaying of food
Enow Reply
Some pathogenic bacteria, such as Clostridium perfringens and Bacillus cereus, are capable of causing spoilage.
Dejene
Corona has a gray and black cell structure ....if yes explain..if no explain
Joshua Reply
multiple questions and answers in microbiology and bio chemistry
Lakshmi Reply
is the study of a bacteria and other organisms
isir
yes..this book is about bacteria & others organisms
Hasan
biochemistry is the branch of science that dealing of chemical compounds reactions and other processes
isir
have you any question?
Hasan
yess, Why scientists not search coronavirus vaccines in short time.
demisew
they are on
Monyditchol
what are the symptoms for tuberculosis
Chiamaka
Most people infected with the bacteria that cause tuberculosis don't have symptoms. When symptoms do occur, they usually include a cough (sometimes blood-tinged), weight loss, night sweats and fever.
Dejene
symptoms tuberculosis. Fever Chills Night sweats Cough Loss of appetite Weight loss Blood in the sputum (phlegm) Loss of energy
lourdes
can corona virus transmitted from mother to her child through placenta ?
Abdul
probably
Mad
no
Oke
no,but it can through trait
Falere
mutation occur in the genome of corona virus. thats why the corona vaccines forming just difficult
Muzamil
intersted
Do
no
Esther
No
John
Yes
Suhaib
yes
Benjamin
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Rebecca
Yes
Ayan
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Abdul
because it damages the immune system by reduction the action of WBC
mike
reducing pls
mike
how is it possible for a woman to be pregnant and still See's her period
Prince Reply
we term it as discharge
Monyditchol
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evans Reply
What is a varuis
evans
A submicroscopic infectious organism, now understood to be a non-cellular structure consisting of a core of DNA or RNA surrounded by a protein coat. It requires a living cell to replicate, and often causes disease
Ebo
A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce thousands of identical copies of the original virus at an extraordinary rate
Dejene
A virus is a microorganism which invade our bodies causing diseases due to eliciting immune responses by the body against it, can replicate using our genome inducing production of proteins helping them to establish new life inside our bodies.
What are the important of capsules
Marriam Reply
what are the roles of male sex hormones
Marriam
Testosterone is the principal sex hormone inmales and is produced in the testes (testicles). Dihydrotestosterone is a hormonein which the double bond of testosterone has been reduced by enzyrne reactions in the body. ... The testes perform two functions: They produce sperm, and they producetestoster
Dejene
Capsules in bacteria protect them from phagocytosis of eukaryotic organisms. This is what makes them virulent and harmful without antibodies.
Lewis
any one told me definition of amoebic dysentery & amoebic liver dysentery?
Mira
Amoebiasis, also known amoebic dysentery, is an infection caused by any of the amobae of the Entamoeba group. Symptoms are most common during infection by Entamoeba histolytica. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include abdominal pain, diarrhea....
Dejene
tnx
Mira
u welcome mira
Dejene
people explain for me this words in public health.tb prevention 1:promotive 2:preventive 3:curative 4:rehabilitative
Obrian
Capsules function similarly to endospores they provide an extra layer of protection especially in acidic or basic environments. It is also a thicker membrane which can change the osmosis process and can provides resistance to antibotics depending if it is gram negative or positive.
Melanie
...As some antibotics focus on breaking down the cell wall and is not able to.
Melanie
what are the clinical classification of amoxicillin?
Rebecca
how does a autoimmune diso ders develop
Oliver Reply
simply autoimmune disease is not completely understood. There are many variations from genetically inherited to acquired by viruses like HIV. Genetically they may not be prominent until an unknown point in one's life. I am far from an expert, I am just reciting what I have learned. Take rheumatoid
Lewis
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Mohamed Reply
Anatomy is the study of parts of the human body
Matilda
the branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.
Dejene
Describe the halden effect
Suleiman
The Haldane effect is a property of haemoglobin first described by John ScottHaldane. Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide. This property is the Haldane effect.
Dejene
Difference between chief cells and parietal cells in the stomach
Suleiman
 Parietal cells are the epithelialcells that secrete HCl and intrinsic factor. They are located in the gastric glands found in lining of fundus and stomach. The gastric chief cells , are cells in the stomach that release pepsinogen and chymosin.
Dejene
is the study of structure and organs located in human life
isir
listen to Matilda
Lewis
essay on microbiology and how it contribute to the pharmacy assistant programme
Tagedevi Reply
I want to know how it contribute to the pharmacy assistant programme
chidiebube
Contribute how? If you want to contribute to pharmaceutical stuff you should look for websites with blogs that relate to your interests.
Lewis
hello i want to know how it contribute to microbiology programs
Dejene
Microbiology is the study of bacteria and and organisms such as viruses, fungi, and mold. How does this apply to medicine? It applies to medicine or pharmacology because when you get sick you are infected by a pathogen and understanding how these organisms interact with each other helps you to....
Melanie
develop medicine. A lot of bacteria infections can be cured with various medicines but not all medicines work equally. It depends if your sickness is based on gram positve or negative bacteria, if its s mold or fungus or a virius. Each medicine targets a certain one.
Melanie
If you need any ideas I recommend looking up Louis Pastar who used microbiology to invent a lot of medicines and contributed greatly to microbiology and pharmaceutical.
Melanie
what is a bacterial
Eric Reply
Bacteria is a microscopic organism belonging to the kingdom prokaryotic
John
what is prokaryotic
Oliver
if you are here, read this free book, it is mostly correct, there are a few pictures that should be corrected
Lewis
thanks
Eric
A prokaryotes does not have lipid- bilayer bound organelles, they can reproduce by binary fission, they have a DNA region, most have a cell well, contains a plasmid, 70s ribosomes, high mutation rate due lack of certain DNA replication enzymes.
Eric

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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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