What is the main characteristic of the adaptive immune response compared to the innate inflammatory response?
Slower, specific, and has memory
The adaptive immune response is longer lived and initiated by cells of the innate system.
What types of lymphocytes mediate the adaptive immune response?
- B lymphocytes
- T lymphocytes
B cells are responsible for humoral immunity, while T cells are responsible for cell-mediated immunity.
Adaptive immunity can be either active or passive depending on what?
Whether immune response components originated in the host or came from a donor
This distinction affects how immunity is acquired.
What are antigens?
Molecules that can react with components of the adaptive immune system
Immunogens are antigens that can initiate the adaptive immune response.
What is the antigen-binding molecule of the BCR?
Antibody
Antibodies are composed of four polypeptide chains and have variable and constant regions.
What are the classes of antibodies?
- IgG (most prevalent)
- IgA (mostly in secretions)
- IgE (most rare)
- IgD
- IgM (first and largest produced)
The class of antibody is determined by the constant regions of the heavy chains.
What must happen for most antigens to elicit an immune response?
They must be presented to lymphocytes by antigen-presenting cells
Endogenous antigens are presented by class I MHC, while exogenous antigens are presented by class II MHC.
Where is the MHC cluster of genes located?
On human chromosome 6
The products of these genes are also called HLA antigens and are highly polymorphic.
What is the role of cytokines in the adaptive immune response?
They communicate between cells and regulate B-cell and T-cell maturation
Cytokines can have both positive and negative regulatory effects.
Where does the generation of clonal diversity occur?
In the primary lymphoid organs (thymus for T cells, bone marrow for B cells)
This process allows the immune system to respond to virtually any antigen.
What happens to B cells and T cells that produce receptors against self-antigens?
They are eliminated by central tolerance
This process occurs during the generation of clonal diversity.
What characteristic surface markers are expressed by helper T cells?
CD4
Cytotoxic T cells express CD8, while B cells express CD21 and CD40.
Cells leaving the primary lymphoid organs are considered immunocompetent. What does this mean?
Capable of reacting to antigen
These cells enter circulation and secondary lymphoid organs.
What is clonal selection?
The process by which antigen selects lymphocytes with complementary TCRs or BCRs and induces an immune response
This leads to the production of specific antibody, cytotoxic T cells, or both.
For lymphocyte activation, most antigens must be processed and presented by an APC in the context of which molecules?
- MHC class I
- MHC class II
- CD1 molecules
These molecules are crucial for the activation of lymphocytes.
Most immune responses require which type of cells?
Helper T cells (Th cells)
Precursor Th cells interact with APCs and develop into Th1 or Th2 subsets.
What are the roles of Th1 and Th2 cells?
- Th1 cells: Help activate macrophages and cytotoxic T cells
- Th2 cells: Help activate B cells
Th cells interact with APCs through the TCR-CD4 complex and cytokines.
What is the function of Th17 cells?
Provide help in developing inflammation, particularly attracting neutrophils and macrophages
They also induce chemokine and antimicrobial protein production by epithelial cells.
B-cell activation results from recognition of soluble antigen by the BCR and presentation by which molecules?
MHC class II antigens to Th2 cells
Interactions with Th2 cells through adhesion molecules are also required.
What are the two phases of the humoral immune response?
- Primary phase
- Secondary phase
The secondary response has a higher proportion of IgG relative to IgM and occurs more rapidly due to memory cells.
What do B cells differentiate into upon activation?
- Plasma cells (synthesize antibodies)
- Memory B cells
Plasma cells function as factories for large amounts of specific antibodies.
T-cell activation results from recognition by the TCR and CD8 of antigen presented by which molecules?
MHC class I
Cytokines like IL-2 from Th1 cells are necessary for efficient differentiation.
What are superantigens?
Molecules produced by infectious agents that activate a large number of Th cells
They can cause excessive production of proinflammatory cytokines, leading to shock and death.
Give examples of superantigens.
- Bacterial toxins causing toxic shock syndrome
- Bacterial toxins causing food poisoning
These superantigens bind to TCRs and MHC class II on APCs.
