Login with Facebook

What is the lymphocyte activation?

The activation of lymphocytes is the consequence of their interaction with an antigenic pathogen, directly for B lymphocytes and through the molecule of histocompatibility complex for T lymphocytes. Antigens are recognized by different characteristic structures present on their surfaces; 

This activation thus allows the lymphocytes to pass from a naive mature stage to an activated mature stage. They will correspond to the cytotoxic T lymphocytes, helper T lymphocytes, plasma cells, and memory cells. The activation signals will allow the activation of transcription factors and, thus, the expression of new molecules essential to activated mature cells, among other things, for their proliferation.

Activation of T lymphocytes

At the level of T lymphocytes, the antigenic fragment presented by the MHC molecule is recognized by the TCR. It is important to specify that the antigenic fragment recognized by the TCR is necessary for peptide nature.

1. Activation of T-CD4 lymphocytes

2. Recognition of the antigenic fragment

T-CD4 lymphocytes are activated by antigenic fragments presented by MHC-II molecules, themselves expressed by the antigen-presenting cells and more typically by the antigen-presenting cells.

Once present at the level of the secondary lymphoid organs, the antigen-presenting cells will be truly scanned by the naive T-CD4 lymphocytes. It will seek to specifically recognize the antigenic fragment of which they are specific. If the TCR recognizes an antigen, the T lymphocyte will stop, allowing the formation of a particular contact zone, which is called a "synapse."

Following the formation of the synapse, T-CD4 lymphocytes will be activated by two types of signals:

- Stimulation signals allowed by kinases, which Phosphorylation the ITAMs of intracytoplasmic regions of the CD3 chains associated with the TCR.

- Costimulation signals, essential for full activation of lymphocyte, which is induced by the interaction between the clusters of differentiation CD28 present on the surface of the T-CD4 lymphocyte receptor. Moreover, the interaction between the CD40 receptor-ligand (CD40-ligand) present on the surface of the lymphocyte and the CD40 differentiation cluster present on the surface of the antigen-presenting cell.

Differentiation of LT-CD4

Once these cells are activated, there will be a proliferation and differentiation phase. Indeed the destiny of the CD4 cell will be different depending on the cytokines produced by the antigen-presenting cell, which activates it. We thus distinguish:

- The auxiliary T lymphocytes 1 (or LT-H1) obtained due to the interleukins IL-12, IFN-γ, and TNF-β. LT-H1 is also responsible for the increase in expression of the B7 receptor essential for the formation of cytotoxic T lymphocytes.

- The helper T cells 2 (or LT-H2) obtained through the interleukin IL-4. They play a role in the activation of B lymphocytes.

- The helper T lymphocytes 17 (or LT-H17) obtained using interleukin IL-23.

1. Activation of T-CD8 lymphocytes

2. Recognition of the antigenic fragment

T-CD8 lymphocytes are activated by antigenic fragments presented by MHC-I molecules, themselves expressed by nucleated cells of the organism. In fact, the T-CD8 lymphocytes circulate in the pre-cytotoxic state and receive activation signals to become cytotoxic. These signals are given to them following their interaction, also in the form of a "synapse, "with the cell presenting the antigenic fragment associated with MHC-I. As for LT-CD4, there are two types of signals:

It is necessary to specify that most of the target nucleated cells express the MHC-I molecules, which is not the case for the B7 receptor expressed by the antigen-presenting cells. Activation is not direct and requires a second interaction with an antigen-presenting cell, which will mainly be the dendritic cell.

However, the dendritic cell sometimes expresses the B7 receptor too weakly. In this way, depending on the situation we are facing, the T-CD8 lymphocyte can be activated by:

- The infected dendritic cell: The infected dendritic cells present B7 directly and in sufficient quantity. They thus allow the activation of the cytotoxic LT, which will lyse the target cell presenting the antigen. The antigen must be presented by the MHC-I molecules and therefore correspond to antigens synthesized in the cell (viral antigen, etc.).

- The non-infected dendritic cell by cross-priming or cross-presentation: The non-infected dendritic cells require the internalization of the antigen. It will be degraded in the cytoplasm, in order to be presented by MHC-I molecules, although the antigen comes from outside.

- The cross-presentation is based on the fact that the phagosome wall contains constituents of the endoplasmic reticulum (MHC-I, transporters). After internalization, fragments of antigens are released into the cytoplasm through channels. These antigens are degraded by the proteasome and again internalized in the phagosome to associate with class 1 molecules of the MHC.

- The cross-priming is based on the fact that some infectious agents will induce apoptosis in phagocytic cells. Apoptotic micro-particles are thus formed, which will be internalized by dendritic cells.

- The concern of these cells is that it expresses B7 too weakly; this case requires the help of LT-CD4 (LT-H1 in particular). In fact, LT-H1 will recognize the antigens presented by MHC-II molecules expressed on the surface of dendritic cells. This is the interaction between the ligand of the CD40 receptor (CD40-ligand) present on the surface of LT -H1 and the CD40 differentiation cluster present on the surface of dendritic cells, which will induce the increase in expression of B7. This increase in expression of B7 will thus allow the formation of costimulation signals and, therefore, the activation of cytotoxic LT.

Mechanism of action of cytotoxic LT

Cytotoxic T lymphocytes are responsible for cellular immunity resulting in the death of the target cell. There is a release of cytotoxic granules (particular lysosomes) which contain two categories of molecules called cytotoxins:

- The perforin is a protein that by polymerizing forms pores in the membrane of the target cell.

- The purpose of serine-esterases is to destroy DNA by activating caspases, which will fragment the DNA in order to induce apoptosis.

Activation of B lymphocytes

Activation of B lymphocytes can be done in different ways depending on the involvement of T lymphocytes: thymo-dependent or thymo-independent.

1. Thymo-dependent activation

2. Activation signals

Thymo-dependent activation is the most commonly used, and just as for the activation of T lymphocytes. There are two types of signals which are induced by the antigen-BCR interaction:

- The stimulation signals are responsible for the one hand for the internalization. In other words, of the endocytosis, of the antigen-BCR complex, thus allowing the degradation of the antigen in the endosomal system. The peptide fragments obtained will be associated with MHC-II molecules, giving the B lymphocyte the status of an antigen-presenting cell. The stimulation signals are also responsible for the activation of tyrosine kinases. It will phosphorylate the ITAM motifs of the intra-cytoplasmic regions of the dimer Igα-Igβ associated with BCR. Thereby it causes the activation of the transcription factor, which will allow the expression of many molecules.

- The costimulatory signals are essential to total cell activation and are enabled by a number of co-receptors (CD19, CD21, and CD81) that amplify the signal.

Proliferation and increase of affinity

On the other hand, the activated LBs still receive proliferation signals, which this time is not induced by the antigen-BCR interaction but by the LT-H2. These signals will be induced by various means: the interaction between the CD40 receptor-ligand (CD40-ligand) present on the surface of LT-H2. And the CD40 differentiation cluster present on the surface of LB, the IL-4 interleukins produced by LT-H2.

Following this activation, the lymphocytes obtained will multiply intensely, and some of them will give plasma cells. It will then produce, as explained in the previous chapters, IgM of low affinity for the antigen.

The other cells will continue to multiply in the primary follicles in order to form germinal centers; these cells are then called centroblasts. The latter no longer express BCR because mutations take place at the level of the genes coding for the variable parts of the heavy chains and of the light chains.


The centroblasts will thus become centrocytes which no longer divide and which re-express on their surface a BCR, which always recognizes the same starting antigen but with a modified affinity. These centrocytes will be selected by antigen-BCR complexes present at the level of follicular dendritic cells, and in this way, only those expressing BCRs having a strong affinity for the antigen will receive the survival signal.

1. The fate of centrocytes

At this stage, the selected centrocytes will again interact with the LT-H2 allowing the formation of two types of cells:

- Plasma that will produce antibodies (IgM) of high affinity for the antigen. The secretion of interleukins will allow class switching, and in this way, there will no longer be secretion of IgM but of IgA, IgE or IgG. There will be a latency of 4 to 8 days between the production of low-affinity immunoglobulins and those of high affinity.

- Memory B cells that will leave the secondary follicles to go in traffic and in order to facilitate the encounter with antigen. These cells have the characteristic of being able to secrete directly, without latency time, high-affinity antibodies during a second infection with the same antigen. The response obtained occurs for much lower levels of antigen and is considerably greater in intensity.

2. Thymo-independent activations

Unlike thymo-dependent activation, thymo-independent activations do not require the help of LT-H2 to produce the antibodies. They are classified into two categories:

- The activation thymus-independent type 1 causes a polyclonal stimulation of B cells. This activation does not pass through the BCR but common to all LB receptors that recognize pathogens that are called mitogens.

- The thymo-independent type 2 activation results in monoclonal stimulation of the B lymphocytes. This activation this time passes through the BCR, which recognizes repetitive sugar determinants. HoweverT lymphocytes, essentially an IgM production will be observed.


Send Comment

Need a custom

We will write it for you.
Order now

Free Essay Examples

Free essays:

Analysis of Consumption and Investment
Analysis of Business Cycles
Analysis of Fiscal and Monetary Policies
An Overview Of Economic Studies
Biosensors for cancer diagnosis
Business Analysis: Pricing strategies and Demand Curve
Broadcasting: How to Be Good In Front of the Camera
Bioconjugates for the Drugs Delivery
Cells of Immune system
Challenges that IT Managers are facing
Cochlear implant: what it is and how it works
Current challenges to the health of women
Doppler ultrasound or simply eco Doppler
DNA extraction
Dynamic Systems Modeling with Machine Learning
Digital Imaging: What Is It?
Economy analysis: Business Cycle and Economic Trends
Exchange rate and foreign currency risk
Economic Factors Affecting Decision Making In A Business
Economy Analysis: Inflation, Unemployment And Policies
Factors Influencing Interest and Exchange Rates
Fiscal and Monetary Policies in Response to 2008/2009
Fermentation: how it works and what it is used for
Financial Markets and Functions
Genetic regulation networks: modeling in biology
How does the economics of war affect society?
How can immigrants blend in the American society?
How to make your business survive at economic crisis
Importance of corporate sustainability
Interaction of Consumer and Firm Choices in Markets
Introduction to Microeconomics
Introduction of Microfabrication techniques
Journalism: What is News?
Journalism: Broadcast media and Television Presenters
Journalism: Sources of News
Journalism and Law
Key Determinants of National Income
Key Factors That Affect Pricing Decisions
Kinetic models in biology and Related fields
Know about the different forms of traditional African dances
Latest technology trends
Latest dance trends
Methods of labeling of nucleic acid that enable their detection
Macroeconomics: International Economic Issues
Neuromuscular disorders
National Economies, Fluctuation, and Responses to Fluctuations
Neurotransmitters: what they are and different types
Nanomedicines to target tumors
Overcoming Hiring Challenges for Nonprofit Organization
Principles of Microeconomics - Producer Theory
Principles of Microeconomics - Consumer Theory
Principles of Economics
Role of media in wartime.
Role of technology in the modern business environment
Role of Homeostasis in Human Physiology
Role of a digital artist
Skills in Journalism: Effective Interview
Systems biology - An understanding the functioning of biological systems
Self-assembly for biological systems
School of American Ballet
Types of corporate responsibility
The Role of Government Policy in Improving Economic Outcomes
Types of bioreactors and their applications
Technological perspectives and reflections of neural engineering
Understanding Perfect and Imperfect Competition
Ultrasound: physical principles and image formation
Understanding social entrepreneurship
Understand the importance of investigative journalism
Various theoretical perspectives of sociology
Virtual reality, what it is and how it works
What is MBA with Concentrations
What are the Causes of financial instability?
4 Facts about Origin of Mathematics!
5 techniques to create an animation
10 strategies to maximize corporate profits
13 Best colleges for political science in the world
6 Medical Technologies that revolutionized the healthcare in 2020
All you need to know about the ACA Code of ethics
Architecture and Democracy: An Introduction
Architecture and Democracy: Democratic Values
Architecture and Democracy: Democratic Procedures
All You Need to Know About a Synthesis Essay
An essential guide to understanding Film Theory
Application of Artificial Intelligence in Cyber Security
Applications of electrical engineering
Augmented reality: what it is, how it works, examples
Advantages And Disadvantages Of Social Networking
All you need to know about Cryptography
Applications of astrophysical science
All you need to know about architecture engineering
Applications of geological engineering
Artificial intelligence and medicine: an increasingly close relationship
An insight into Computational Biology
ACA code of conduct
A Rose for Emily
Applications of Mathematics in daily life
Architecture mistakes to avoid
All you need to know about Toxicology
All you need to know about Holistic Medicine
All you need to know about linguistics
An introduction to Linguistics and its subfields
All you need to know about Anxiety disorder
All you need to know about Drones
A Brief Insight into Political Science
Assumptions related to feminism
All you need to know about Byzantine emperors
All you need to know about labour economics
An insight into xenobots -the first-ever robots
An ultimate guide about Biomaterials
A Comprehensive Introduction to the Mona Lisa
Analysis methods of Transport through biological membranes
An ultimate guide about biochemical reactions
Analysis of brain signals
Artificial Gene Synthesis
Application to synthetic biology of CAD methods
All you need to know about metabolic pathways
Applications of BIOMEMS
All you need to know about the epidemiology
Asian vs. western leadership styles
All you need to know about Smart prosthesis
Analysis of Economy: Output of Goods and Services (GNP), and GDP on Economic success
A Guide to Pricing Strategies
An Overview Of Economic Studies
Analysis of Fiscal and Monetary Policies
Analysis of Business Cycles
Analysis of Consumption and Investment
How to Write a Personal Essay
Housing Needs in America
How to Write a Description Essay
How to Create an Excellent Scholarship Essay?
How to write a cause and effect essay
How to Hire the Best Essay Writing Service Provider?
How to Write a College Application Essay?
How to get the most out of your English lectures
How to write Expository Essay
How to succeed in your psychology class?
How to Write an Academic Essay in the Shortest Time?
History of Journalism
How Different Sectors are Using Artificial intelligence (AI)
How to write an informative essay
How to deliver persuasive essays?
How to Give a Convincing Presentation
How to write an essay on leadership?
Historical Art Still Around Today
Humanoid robot: what it is, how it works and price
History of Chemistry
Healthcare Advanced Computer Power: Robotics, Medical Imaging, and More
Healthcare AI: Game Changers for Medical Decision-Making and Remote Patient Monitoring
How to understand different types of English
How to Cope with Chronic Pain
How African American choreographers and dancers have influenced American dance
How mobile robot can do in logistics or in production
How To Become a Successful Entrepreneur
History of the Philosophy of Feminism
How is the climate changing?
How to Track Your Content Marketing ROI
How to Gun control In the USA?
Historical and contemporary role of labour in the modern world
How breast cancers are classified?
How the cells of our body communicate?
How the Lymphatic System Works?
How Digestive System Works
How to complete your capstone projects effectively?
How to write a research project
Healthcare technologies that help patients with better self-management
How to choose the topic of the senior capstone project
How to make your business survive at economic crisis
How can immigrants blend in the American society?
How does the economics of war affect society?
The Looming Energy Crisis in America
Top benefits of performance-based engineering
The More Languages You Know, The More Times You Are a Man
Things to consider while writing an Argumentative Essay
Top Ways to Improve Your Academic Writing Skills
Tips to Excel in Creative Writing
The origins of films in the early 19th century
Top career options in Architecture
The Elevator Pitch
Top finance trends 2020
The basic Structure and functionality of robots
The Way to Success
The election system of the President in the United States of America
Two-party System in United States of America
Top trends in urban design
The history and theory of African American filmmaking
Top benefits of creative writing
Tinnitus Guide: Common Symptoms and Treatment Options
The language of dance
The digital image processing management
Top famous politicians of the World
Top methods of political science!
The history of the feminist movement
The blood flow in cardiovascular system - Biofluid Mechanics
The best of Leonardo Da Vinci
The Structure and Function of Macromolecules
The structure of cell: a research on the bricks of the human body!
Tissue and organ construction: Adhesion and recognition between cells
The kinetics of the transformation processes
The Modeling of Biological Systems
Tips for writing a great thesis statement
The Defense mechanisms against infections
The impact of the technological innovations in medicine
Top journalism trends to know about
The relation between mass media & politics
Theranostics: Diagnosis and Care through Nanoparticles
The practical Applications of X-rays
The applications of Ultrasound in medicine
Transfer mechanisms of genetic information in Bacteria
The regulation of cellular metabolism in the diagnosis
The Principles of MRI Contrast agents
The technical basis of optical coherence imaging
The New Media: Emerging Trends
The Structure of Interest Rates and the Yield Curve
Technological perspectives and reflections of neural engineering
Types of bioreactors and their applications
The Role of Government Policy in Improving Economic Outcomes
Types of corporate responsibility
What is a Definition Essay?
What are diagnostic essays?
What is the relation between art structural engineering?
What is a Narrative Essay
What are robotics and intelligence systems?
What are the benefits of studying health sciences?
What is artificial intelligence and why it matters?
What is comparative Literature?
Why study neuroscience
What is Wi-Fi and how does it works
What is French history famous for?
What are Humanistic Studies?
What is covered in Biophysics?
What is modern journalism?
What is Virtualization? Benefits & Applications
What are modern public relations?
What is plasma physics?
What is teacher preparation?
What is rapid prototyping for 3D printing?
What is contemporary European Politics?
Why should you learn American Ballet?
What is engineering physics?
What is the purpose of African American Literature?
Ways to learn the Rhythm
What is digital art used for?
What are Enzymes and how do they work
Who is the father of political science?
Why Study Political Science - Job?
What is the Philosophy of Feminism?
What is a quantum computer?
Ways B2B Startups Streamline Their Conversion Strategies
Why do biomedical signals need processing?
What are the long term effects of climate change?
Why study labour relations
What is Holoprosencephaly?
What is antisocial disorder?
What are the important principles of evolution?
What is the cytoplasm and its function?
What is biopolymers?
What Makes a Good Leader
Women empowerment in modern generation
What is the history of political thought?
What is Gene recombination
What is synthetic biology
What is business cost analysis?
What is Inflation
What are the consequences of unemployment?
What is lithotripsy and its types?
What is transition elastography?
What is the purpose of deep brain stimulation?
What is a Brain-Computer Interface (BCI)
What is neuroethics?
What is Market and Supply and Demand
What is optogenetics?
What are the techniques to record brain activity?
What happens if the interest rate increases?
What is immunotherapy?
What is the economic role of the financial market?
What are the factors behind illegal immigration?
What is the lymphocyte activation?
What is financial market and its types?
What is the structure of financial markets?
What are the methods of measuring business performance?
What is the Credit market?
What is business ethics and code of ethics
What are the Causes of financial instability?
What is MBA with Concentrations