| Adaptive Immunity |
Adaptive Immunity
Adaptive
Immunity:
- Functions: (1) Destroy invading pathogen or toxin, (2)
Specific to pathogen, (3) Innate and Adaptive immune collaborate
to eliminate the pathogen, (4) Immune memory protects for a long
period of time and (5) Distinguishes self from non-self.
- Two types of adaptive immunity: active and passive.
- Active Immunity: resistance by an organism to a pathogen or
antigen as a result of antigenic stimulation. The antigen would
have evoked an immune response.
- Passive Immunity: is immune protection by exogenously
supplied antibodies. Examples of this include transplacental
transmission of antibodies from bother to fetus and immune
globulin injections.
- Cells involved: Lymphocytes which make B lymphocytes (B
cells) and T lymphocytes (T cells). Antigen presenting cells (APC�s)
which include macrophages, B cells and Dendritic cells.
Lymphocytes:
- Circulate through blood and lymphatic system. They produce
and display receptors for antigen binding. They are further
classes into B-cells, T-cells, or T-lymphocytes.
- B-Cells, B-lymphocytes come from the bone marrow and mature
there. B-cells have receptors that are membrane bound antibody
molecules. They are inactive (na�ve) before exposure to an
antigen. Once activated they proliferate into memory cells and
antibody secreting effector cells or plasma cells.
- T-Cells, T-lymphocytes migrate to a lymphoid organ such as
the thymus where they mature. The mature T cell express a novel
antigen binding receptor called the T cell receptor (TCR). TCRs
only recognize antigens that are associated with cell membrane
proteins known as MHC (Major Histocompatibility Complex)
molecules. Cytotoxic T-cells defend against infections by
viruses and bacteria, diseases, tumors cells and transplanted
tissues.
- Antigen Presenting Cells (APC) is a cell that holds a
foreign antigen complexed with MHC on it surface. T-cells may
recognize the complex with the TCR. Many cells can present
antigens to T cells via MHC I molecules but the term is usually
limited to cells that prime T cells.
- Dendritic cell is APC and can be found in the skin, mucosa
and lymphoid tissues. They are involved in initiation of immune
responses by activating lymphocytes and secreting cytokines.
They have long membrane processes.
- An effective immune response involves lymphocytes and
antigen presenting cells.
- Two types of lymphocytes are B-cells and T-cells.
- Three main antigen presenting cells are: macrophages, B
cells, and dendritic cells.
Humoral Responses
- Two classes of adaptive immune
responses: Humoral (antibody) and Cell
Mediated immune responses.
- Humoral immune responses are carried out
by B-lymphocytes. Primary focus on
exogenous antigens.
- B-cells are activated to secrete
antibodies.
Cell Mediated Immune Response (CMI)
- Cell mediated immune responses are
carried out by T-lymphocytes. Primary
function endogenous antigens.
- Activated T cells react directly with a
presented antigen.
- CMI responses are carried out by TH
cells and TC cells.
- A function of T cell would be to kill a
host cell that is infected by a virus and is
displaying viral antigens.
- T cells produce signal molecules that
activate macrophages to destroy the microbes
that they have phagocytoses.
Clonal Selection B-Cells
- B-cells that have been antigenically
committed mature in the bone marrow.
- Different antibodies are produced
against the same antigen via gene
rearrangement in the step cell.
- Antigen dependent proliferation and
differentiation into plasma and memory
cells.
- Clonal selection by antigen antibody
binding occurs.
- Clonal selection of an antigen activated
B cell leads to a clone of effector B-cells
and memory B-cells.
- Plasma cells secrete antibodies to
neutralize and eliminate the antigens.
Clonal Selection T-Cells
- Clonal selection is similar to that of B
cells.
- T-cell population results in the clone
of effector T-cells and memory T-cells.
- Effector T-cells include T helper cells
and cytotoxic T lymphocytes.
Processing and Presentation of Antigen
- An antigen must be degraded into small
units (peptides) and complexed with MHC I or
II molecules in order for a T-cell to
recognize it.
- Antigen processing and presentation is
the conversion of antigens into MHC
associated fragments.
- The route that an antigen enters a cell
determines if it will be processes and
presented with class I or class II MHC
molecules (extracellular or intracellular
entry).
- Exogenous antigens are degraded by APCs
(macrophages, B-cells, dendritic cells) and
complexed with class II MHC and displayed on
the cell surfaced.
- Endogenous antigens like tumor or viral
proteins which alters �self cells� are
degraded in the cytoplasm and displayed with
class I MHC molecules on the cell surface.
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