3. Types of Acquired Immunity
1. Naturally acquired immunity. It is the immunity which could
be acquired passively during live to human from:-mother or
actively through infections.
2. Artificially acquired immunity . It is the immunity which
could be acquired passively to human through:
immunoglobulin injection or actively through vaccination.
4. Aquired (specific) immunity
Two mechanisms:
1) Humoral immune response:
- Antibodies are produced by B-lymphocytes
- These have the ability to recognize and bind
specifically to antigen that induced their formation
2) The cell mediated immune response (CMI)
- It is mediated by certain types of T-lymphocytes
- T-lymphocytes recognize foreign material by
means of surface receptors
- T-lymphocytes attack and destroy foreign material
directly or through release of soluble mediators
i.e. cytokines
6. Antigenic specificity
• The antigenic specificity of the immune system permits it to
distinguish subtle differences among antigens. Antibodies can
distinguish between two protein molecules that differ in only
a single amino acid.
7. Diversity
• The immune system is capable of generating tremendous
diversity in its recognition molecules, allowing it to recognize
billions of unique structures on foreign antigens
8. Immunologic memory
• Once the immune system has recognized and responded to an
antigen, it exhibits immunologic memory; that is, a second
encounter with the same antigen induces a heightened state
of immune reactivity. Because of this attribute, the immune
system can confer life-long immunity to many infectious
agents after an initial encounter.
9. Self/non-self recognition
• The ability of the immune system to distinguish self from
nonself
• respond only to non-self molecules is essential, for, as
described below, the outcome of an inappropriate response
to self molecules can be fatal.
10. Anamnestic response
• Rapid production of an antibody on the
second (or subsequent) encounter with the
same antigen.
11.
12. B Lymphocyte
B cell development and maturation
B cell activation and differentiation
13. B Lymphocyte
• B cell development and maturation
• B lymphocytes mature within the bone marrow; when they leave it, each
expresses a unique antigen-binding receptor on its membrane . This
antigen-binding or B-cell receptor is a membrane-bound antibody
molecule.
• Antibodies are glycoproteins that consist of two identical heavy
polypeptide chains and two identical light polypeptide chains. Each heavy
chain is joined with a light chain by disulfide bonds, and additional
disulfide bonds hold the two pairs together. The amino-terminal ends of
the pairs of heavy and light chains form a cleft within which antigen
binds.
15. B Lymphocyte
• B cell activation and differentiation
• When a naive B cell (one that has not previously encountered antigen) first
encounters the antigen that matches its membrane bound antibody, the
binding of the antigen to the antibody causes the cell to divide rapidly; its
progeny differentiate into :
memory B cells
effector B cells ( plasma cells.)
• Memory B cells have a longer life span than naive cells, and they express the
same membrane-bound antibody as their parent B cell.
• Plasma cells produce the antibody in a form that can be secreted and have
little or no membrane-bound antibody. Although plasma cells live for only a
few days, they secrete enormous amounts of antibody during this time.
• It has been estimated that a single plasma cell can secrete more than 2000
molecules of antibody per second. Secreted antibodies are the major effector
molecules of humoral immunity.
17. Different types of B cells have
different receptor molecules.
When a pathogen (germ) “locks
on” to a receptor, that type of B cell
is selected.
The selected B cell divides
rapidly to make lots of copies of
itself. The copies make lots of
antibodies against the pathogen.
Selection of B cells by antigen (clonal
selection)
(The key of specificity of adaptive immunity)
18. Bellow is a diagram of Clonal selection in
B cells
19. T Lymphocyte
• T cell development and maturation
• T cell activation and differentiation
20. T Lymphocyte
• T cell development and maturation
• T lymphocytes also arise in the bone marrow. Unlike B cells, which
mature within the bone marrow, T cells migrate to the thymus
gland to mature.
• During its maturation within the thymus, the T cell comes to
express a unique antigen-binding molecule, called the T-cell
receptor, on its membrane. Unlike membrane-bound antibodies on
B cells, which can recognize antigen alone, T-cell receptors can
recognize only antigen that is bound to cell-membrane proteins
called major histocompatibility complex (MHC) molecules.
21. T Lymphocyte
• T cell activation and differentiation
When a naive T cell encounters antigen combined with a MHC molecule on a cell, the
T cell proliferates and differentiates into memory T cells and various effector T cells.
There are two well-defined subpopulations of T cells:
T helper (TH) :
• start the immune response
• helper T cells continue to differentiate into individual subsets of helper T cells.
T cytotoxic (TC) cells : kill the body’s abnormal cells, like virus-infected cells and
cancer cells
T suppressor (TS) cell : suppress the activities of other T cells, helping to end the
immune response
T helper and T cytotoxic cells can be distinguished from one another by the
presence of either CD4 or CD8 membrane glycoproteins on their surfaces . T cells
displaying CD4 generally function as TH cells, whereas those displaying CD8
generally function as TC cells
22. T Lymphocyte
T cell activation and differentiation
• Many different subsets of helper T cells perform various functions :
• Th1 - which mediates cyotoxic T cell activity through cytokine release,
• Th2 - which presents antigens to B cells.
• Th17 - which only differentiates from effector cells if certain cytokines
are present, is important in regulating and inhibiting T-reg cell activity.
• T-memory cells: The population of these cells increases only
after their initial exposure to an antigen.
If the same antigen presents itself again, they are triggered to
convert themselves into cytotoxic T cells and kill the
pathogen.
23. • T follicular helper cells (Tfh) are a specialized subset of CD4+ T
cells that were first identified in the human tonsil.
They play a critical role in protective immunity helping B cells
produce antibody against foreign pathogens.
Tfh are located in secondary lymphoid organs (SLOs), including
the tonsil, spleen and lymph nodes.
24. T cell training
Positive selection of the T-cell
Negative selection
25. T cell training
Positive selection of the T-cell
• Is a process in the thymus that selects immature T cells
with receptors that recognize peptide antigens
presented by self-MHC molecules.
• Only cells that are positively selected are allowed to
continue their maturation Then go to the spleen and
lymph nodes, and wait for antigens. If they recognize an
antigen, some will “go into battle” and others become
memory cells .
26. Step 1. Positive selection
occurs in the thymic cortex
MHC self-
recognition
molecules
27. T cell training
Negative selection
Process in the thymus whereby developing T
cells that recognize self antigens are induced to
die by apoptosis.
