The document summarizes key aspects of adaptive immunity, including B cells and T cells as the main cells involved. B cells produce antibodies and recognize pathogens through B cell receptors, while T cells help activate B cells and cytotoxic T cells kill infected cells. Adaptive immunity responses are specific and involve memory cells that allow for faster secondary responses. The humoral response produces antibodies, with primary responses having a longer lag period than secondary responses against the same antigen.

1. Content
 Introduction
 Adaptive immunity
 Cell of adaptive immunity
 B cell
 T cell
 Adaptive immune system response

2. Introduction
Immune system
What is Immune system?
 Immune system is a complex network of
cells
 tissues
Organs and the substances they make that helps the body fight infections and
other diseases.
Cellular Components of immune systems
The cells of the immune system originate in the bone marrow, where many of them
also mature.
Then migrate to guard the peripheral tissues, circulating in the blood and in a
specialized system of vessels called the lymphatic system.

4. Adaptive immunity
 Occurs after exposure to an antigen either from a pathogen or a vaccination.
Takes days or even weeks to become established much longer than the innate
response
however, adaptive immunity is more specific to an invading pathogen.
Depends on the function of two types of lymphocytes, called B cells and T cells

5. Cell of adaptive immunity
Lymphocytes (B cell and T cell)
Lymphocytes are B and T cells, white blood cells (leukocyte) that are produced from
the stem cells in the bone marrow.
They provide immunity for future invasions of
bacteria
viruses
 and parasites by producing antibodies, which have memory and will protect
against such antigens.
B cell
• involved in humoral immunity
• They make up around 20% of white blood cells.

6. Cont...
B cells originate and mature in the red bone marrow
Then after release they concentrate in the lymph nodes, respiratory tract,
gastrointestinal tract, and spleen, ready for pathogenic invaders
 There are 4 categories: Transitional B cells, Naïve B cells, Memory B cell, Plasma B
cells
Transitional B cells can be found in the bone marrow, peripheral blood as well as spleen
but only a small fraction of the immature B cells can survive the transitional phase
before maturing into matured cells
Can be found in two transitional stages; T1 and T2.

7. Cont...
T1 stage is the period between the migration of the cells from the bone marrow to
the point of entry into the spleen, whereas the
T2 stage occurs within the spleen, where the cells develop into mature B cells
Naïve B cells are the mature B cells that haven’t yet been exposed to antigens.
are the B cells at a stage of differentiation where the cells either develop into plasma
cells or memory cells after exposure to a specific antigen.
occur in the secondary lymphoid organs and have passed the transitional stage of B
cell development.

8. Cont...
 Plasma Cells
Plasma cells or plasma B cells, or effector B cells are the white blood cells that are
differentiated from naïve B cells that secrete large quantities of antibodies in response
to activation by antigens
The production of plasma cells requires that the naïve B cells present an antigen to a
helper T cell. This activates the T cell, which in turn activates the B cell
Some plasma cells can be also be activated by a second process called T-cell
independent antigen stimulation. The plasma cells produced by this method can only
secrete IgM antibodies

9. Cont...
The antibodies produced by plasma cells are specific to the antigen initially processed
by the naïve T cell during activation.
 A plasma cell, thus, cannot secrete more than one type of antibody.
Plasma cells have a shorter lifespan as compared to the memory B cells, and these
move through the body according to the distribution of cytokines to produce
antibodies closer to the site of infection.
Plasma cells are usually large in size with abundant cytoplasm

10. Cont.…
Memory B
cells are differentiated from naïve B cells during maturation and circulate through the
bloodstream
The primary function of memory cells is that these cells memorize the characteristics of
the antigen that activated the parent B cell
so that if the memory cell encounters the antigen again, it can trigger a
stronger secondary immune response.
Application of B cell
Antigen Presentation even though the primary function of B cells is an antibody-
mediated immune response, these cells also function as professional antigen-presenting
cells

11. Cont.…
have antigen-MHC complexes as well as T cell receptors involved in T-cell activation.
Cytokine Secretion produce cytokines which are essential for cell-cell
communication, especially during an immune response.
The cytokine production invites white blood cells to induce phagocytosis on antigens
attached to the B cell antibodies.
Antibody production Antibody production is the most important function of B cells
as these are involved in the antibody-mediated humoral immune response.
The antibodies fight against multiple antigens of different origins to protect the body
against possible harm.

12. Cont...
T cell
originate in the red bone marrow, mature in the tonsils or thymus gland
have a T cell receptor called αβ T cell receptor on the cell surface
There are three categories of T cells
Helper T cells (CD4+)
Helper T cells (Th cells) have a different co-receptor called CD4 on their cell surface.
CD4 also partners with the T cell receptor but interacts with MHC class II
molecules instead of MHC class I molecules.
This allows helper T cells to recognize pathogen peptides that have been displayed by
antigen presenting cells

13. Cont...

14. Cytotoxic T cells (CD8+)
Cytotoxic T cells (Tc cells) have a co-receptor called CD8 on their cell surface.
CD8 partners with the T cell receptor and with MHC class I molecules, acting as a
sort of bridge.
This bridge allows cytotoxic T cells to recognize normal cells that are infected by
a pathogen.
When the cytotoxic T cell recognizes the infected cell, it becomes activated and
produces molecules that kill the infected cell, destroying the pathogen in the process

15. Cont...
 When helper T cells recognize a peptide on an antigen presenting cell, they become
activated and begin to produce molecules called cytokines that signal to other
immune cells.
There are many subtypes of helper T cells (i.e., Th1, Th2, Th17).
Each subtype produces a specialized combination of cytokines that depends on type
of pathogen that the helper T cell has recognized some cytokines are more effective
than others in the process of eliminating certain invaders

16. Regulatory T cells
 (T reg cells) also have CD4 on their surface, but they do not activate the immune
system like helper T cells do.
Instead, play a protective role by shutting off the immune response when it is no longer
needed
This prevents excessive damage to the normal cells and tissues in the body.
Regulatory T cells suppress the immune response in several ways, including
Producing anti-inflammatory cytokines that suppress the immune response

17. cont.….
Releasing molecules that kill activated immune cells
Changing the way dendritic cells behave so they can't activate T cells
Lymphocyte( B cell and T cell ) Antigen Receptors
Lymphocyte antigen receptors, in the form of immunoglobulins on B cells and T-cell are
the means by which lymphocytes sense the presence of antigens in their environment
antigen specificities in the antigen receptor repertoire is due to variation in the amino
acid sequence at the antigen-binding site,
which is made up from the variable (V) regions of the receptor protein chains.

18. Cont...
In each chain the V region is linked to an invariant constant (C) region, which provides
effector or signalling functions
B cell receptor (BCR)
is a transmembrane protein on the surface of a B cell.
composed of a membrane-bound immunoglobulin molecule
Through biochemical signalling and by physically acquiring antigens from the immune
synapses, the BCR controls the activation of the B cell.
The B cell receptor is composed of two parts A membrane-bound immunoglobulin
and Signal transduction moiety

19. Cont...
A membrane-bound immunoglobulin molecule of one isotype (IgD, IgM, IgA, IgG, or
IgE).
With the exception of the presence of an integral membrane domain, these are identical
to a monomeric version of their secreted forms
Signal transduction moiety a heterodimer called Ig-α/Ig-β (CD79), bound together
by disulphide bridges
Each member of the dimer spans the plasma membrane and has a cytoplasmic tail
bearing an immunoreceptor tyrosine-based activation motif (ITAM).

20. Cont...

21. Cont...
BCR complex consists of an antigen-binding subunit known as the membrane
immunoglobulin (mIg),
which is composed of two immunoglobulin light chains (IgLs) and two
immunoglobulin heavy chains (IgHs)
as well as two heterodimer subunits of Ig-α and Ig-β.
 In order for mIgM molecules to transport to the surface of the cell, there must be a
combination of Ig-α and Ig-β with the mIgM molecules.
 Pre-B cells that do not generate any Ig molecule normally carry both Ig-α and Ig-β to
the cell surface.

22. Cont..
Within the BCR, the part that recognizes antigens is composed of three distinct genetic
regions, referred to as V, D, and J.
BCRs have distinctive binding sites that rely on the complementarity of the surface of
the epitope and the surface of the receptor, which often occurs by non-covalent forces.
In structure, the BCR for antigens are almost identical to secreted antibodies.
However, there is a distinctive structural dissimilarity in the C-terminal area of the
heavy chains, as it consists of a hydrophobic stretch that is short, which spreads across
the lipid bilayer of the membrane.

23. T cell receptor (TCR)
T cell receptor complex is composed of at least 7 different polypeptides
is one of the most sophisticated receptor.
There are two types of T cell receptor (TCR);
alpha beta and gamma delta
both of which are composed of a heterodimer and associated with invariant CD3
complexes on the cell surface.

24. Typical TCR

25. Cont.…..

26. Bcell activation
There are two ways by with B - cell get activated Based on the type of antigen
encountered
T cell independent and T cell dependent
T cell independent B cell activation multiple
Clustering BCR activate multiple Ig alpha a and Ig beta molecules and initiate
signalling process
The antigen , that trigger B cell activation without T cell help are called T independen
antigen Example polysaccharides , glycolipid , Nucleic acids
B - cell activation without I cell helps is known as T - independent B - cell Activation .

27. Cont
• Attributes of Adaptive Immunity:
• This immunity displays several characteristic attributes like:
• (1) Specificity,
• (2) Diversity,
• (3) Immunologic memory,
• (4) Specialisation,
• (5) Self/non-self recognition, and
• (6) Self- limitation

28. • Components of Adaptive Immunity:
• An effective adaptive immune response involves three major
groups of cells of vertebrate body:
• (i) Lymphocytes,
• (ii) Antigen- presenting cells and
• (iii) Effector cells

30. • Naïve CD4+ T cells engage MHC II molecules on antigen-presenting cells (APCs)
and become activated. Clones of the activated helper T cell, in turn, activate B cells
and CD8+ T cells, which become cytotoxic T cells. Cytotoxic T cells kill infected cells

31. Types of adaptive immunity response
• HUMORAL adaptive immunity response
• Primary response
• First encounter with the antigen
• Antibody response to that antigen (depends on nature, dose and
route of administration of the antigen) is detectable in the serum after
a longer lag period (7-10 days and more) than that occurs in the
secondary response
• The serum antibody concentration continues to rise for several weeks
and then declines; it may drop to very low levels
• A small clone of B cells (Memory Cells) and plasma cells specific for
the antigen are formed
• IgM is the first antibody to be formed, followed by IgG, IgA, or both
• IgM levels tend to decline sooner as compared to IgG levels

32. Cont…
• Secondary response
• Second encounter with the same antigen or a closely related “crossreacting” antigen &
antibody response is typically more rapid; months or
years after the primary response
• The lag period is typically very short (only 3–5 days) & has high antibody
levels
• Due to persistence of antigen-specific “memory cells” following primary
response which proliferate in large numbers to produce large clones of
specific B cells and plasma cells that mediate the secondary response
• Amount of IgM produced is qualitatively similar to that produced in
primary response; but more IgG is produced whose levels persist much
longer
• Covalent bonding between antigen & antibody (higher affinity) due to
Somatic hypermutation: improved antibody binding is due to mutations
occuring in the DNA that encodes the antigen-binding site

33. Cont…