2. Characteristics of Adaptive Immunity
• Discrimination between self and non-self – usually responds
selectively to non-self, producing specific responses against the stimulus
• Diversity – generates enormous diversity of molecules
• Specificity – can be directed against one specific pathogen or foreign
substance among trillions
• Memory – response to a second exposure to a pathogen is so fast that
there is no noticeable pathogenesis
3. Types of Adaptive Immunity
• Naturally acquired active immunity – type of specific immunity a
host develops after exposure to foreign substance (you sick & recover)
• Naturally acquired passive immunity – transfer of antibodies, e.g.,
mother to fetus across placenta, mother to infant in breast milk
• Artificially acquired active immunity (vaccination) – intentional
exposure to a foreign material
• Artificially acquired passive immunity – preformed antibodies or
lymphocytes produced by one host are introduced into another host
5. • Two components to adaptive immunity
Humoral immunity –immunity mediated by antibodies (via B cells)
• Humoral immunity has extracellular targets
• which remove viruses, bacteria, and toxins from body tissue fluids and
blood by recognizing antigens and making antibodies against them.
Cellular immunity –immunity mediated by cells (via T cells)
• Cellular immunity center on attacking antigens (bacteria, toxins viruses
etc) that make their way inside cells
• T cells (like B cells) respond to antigens by means of receptors on their
surface—T cell receptors (TCRs).
6. Cell Mediated Immunity
• immunity describes any immune response where T cells have the main role.
• B cells required helper T cells to activate against antigen. The activation of T
cells is an essential first stage in virtually all adaptive immune responses. This is
called the “T cell-dependent immune response”.
• T cell receptors bind to fragments of antigens (epitopes) that are presented on
the surface of antigen presenting cells (APC).
There are three main types of APC: • Macrophages • Dendritic cells • B cells
• When T cells recognize an antigen presented by the APC, they can differentiate
into several different types of T cells:
• Cytotoxic T cells: Kill cells infected with intracellular pathogens such as viruses
• Helper T cells:
o Activate antigen and stimulate B cells to differentiate and produce antibodies
o Activate macrophages to become more efficient at killing the pathogen
• Regulatory T cells: Suppress lymphocytes and control the immune response
7.
8. • Humoral immunity
• antibodies either kill the extracellular organism and the intracellular organism as it is moving from cell to cell or
bind the pathogen and present it to T cells.
• B cells display immunoglobulin molecules (antibodies) on their surface membranes, which act as receptors for the
antigens. B cell antibody receptors can either bind to helper T cells that have interacted with an APC or bind to
extracellular microorganisms such as bacteria.
• Once an antigen binds to an antibody with the best “fit”, the B cell differentiates into plasma cells or B memory
cells.
Plasma cells: These cells operate as factories to manufacture the chosen antibody and then secrete those antibodies.
B memory cells: These cells mediate immunological memory. They respond rapidly on re-exposure to the antigen
that originally induced them.
T cell-dependent antigens
• Most antigens require the interaction of T cells (TH) and B cells to generate the production of antibodies. These
antigens are referred to as T cell-dependent antigens.
• The antibodies produced in response to T cell-dependent antigens are primarily IgG and the response produces
immunologic memory.
T cell-independent antigens
• In some situations, B cells can create antibodies without the help of T cells.
• Many common extracellular bacteria (e.g., Haemophilus influenzae type b) are surrounded by a polysaccharide
capsule that enables them to resist ingestion by phagocytes and therefore avoid stimulating the T cell response.
• Antibodies produced are of the IgM class and immunologic memory is not created.
9. Antigen
• Antibody generators
• Antigens –proteins or polysaccharides
that stimulate the immune system
• Often external structures of pathogens
(capsules, cell walls, flagella, fimbriae,
and toxins of bacteria; the coats of
viruses)
• Or pollen, egg whites, cells & tissues
• Generally, antibodies recognize and
interact with specific regions on
antigens called epitopes or antigenic
determinants
• Most antigens have a molecular weight
of 10,000 or higher.
10. • A foreign substance that has a low molecular weight is often not antigenic
unless it is attached to a carrier molecule.
• These low molecular-weight compounds are called haptens.
• Once an antibody against the hapten has been formed, the antibody will
react with the hapten independent of the carrier molecule
11. Antibody
• Antibodies are also known as “immunoglobulins” (Ig)
• Antibodies are made in response to an antigen
• Recognize and bind to an antigen
• Antibodies are “Y-shaped” globulin proteins
12. Antibody Structure
Each antibody has at least two identical antigen-binding sites that bind to epitopes.
The number of antigen-binding sites on an antibody is called the valence of that antibody.
Human are bivalent.
• Because a bivalent antibody has the simplest molecular structure, it is called a monomer.
• A typical antibody monomer has four protein chains: two identical light chains and two
identical heavy chains.
• The chains are joined by disulfide links and other bonds to form a Y-shaped molecule.
• The two sections located at the ends of the Y arms are called variable (V) regions.
• The stem of the antibody monomer and the lower parts of the arms of the Y are called the
constant (C) regions.
• They are the same for a particular class of immunoglobulin.
• There are five major types of C regions, which account for the five major classes of
immunoglobulins.
• The stem of the Y-shaped antibody monomer is called the Fc region, so named because
when antibody structure was first being identified, it was a fragment (F) that crystallized (c)
in cold storage.
