L05 – Introduction to the Immune System Flashcards
List the primary lymphoid organs and their function?
Bone marrow, Thymus
Provide appropriate microenvironment for lymphocytes to develop from lymphoid stem cells and proliferation + mature
List the secondary lymphoid organs and their function?
Spleen
Lymph nodes
Mucosa- associated lymphoid tissues (MALT) i.e. Tonsils, Peyer’s patches in ileum
Provide appropriate microenvironment for lymphocytes to interact with antigens, accessory cells
Distribution of immune cells in body?
Circulating cells in blood, lymph
Anatomically defined collections in lymphoid organs
Scattered cells in virtually all tissues
Outline the general functions of lymphocytes? Sites of maturation?
Recognize and respond to foreign antigens and provide immune specificity
B lymphocyte:
- Bone marrow development
- diff. into memory B cells or Plasma cells to produce Ab, immunological memory
T lymphocytes:
a) CD4 Helper: secrete cytokines, interact with B cells, macrophages
b) CD8 Cytotoxic: direct cytotoxicity to target cells
- BM origin with Thymus maturation
NK cells: 15% of lymphocytes with neither B or T antigen, recognize and kill tumour cells
List types and functions of Accessory cells?
- Mononuclear phagocytes: Monocytes, Macrophages: phagocytose pathogens, senescent cells and chemotaxis response (i.e. cytokines)
- Antigen-presenting cells (APC): macrophages, B lymphocytes and dendritic cells: immunostimulatory capacity by presenting antigens to T and B cells
What is the most potent APC? Function (3)?
Dendritic cells
1) Activate B cell to diff. into plasma cells»_space; Ab secretion
2) APC to Cytotoxic T cell > lysis of infected cells
3) APC to T Helper > Secretion of cytokines to activate B and T cells
List the 2 immune mechanisms.
- Non-specific (innate / natural) immunity
- Specific/ adaptive/ acquired immunity
Bridged by dendritic cells (can activate B cells, T cells etc.)
Basic pathogenesis of SLE?
Systemic lupus erythematosus
Impaired clearance of apoptotic cells
> Cells become secondary necrotic and release danger signals
> Inflammation and release autoantigens
> Autoimmune reaction with loss of tolerance
List the components of Innate immunity?
Physical barriers
Phagocytic cells / phagocytes
Neutrophils
NK cells
Various molecules i.e complement system
What is the common connection between Anemia and SLE?
Impaired clearance of cells with oxidative damage/ cellular senescence
Compare the specificity, sensitivity and time span of Innate and adaptive immunity?
Adaptive:
- Specific Ag recognition
- Response enhanced after successive exposure to Ag
- Acquired during life, induced by exposure to Ag
Innate:
- Non-discriminatory against most Ag, rely on pattern recognition (Toll-like receptor, Scavenger receptor)
- Not enhanced by succesive exposure
- Present at birth
Distinguish Humoral immunity and cellular immunity?
2 divisions of Specific Immunity based on the components:
1) Humoral = Mediated by substances in the cell-free portion of the blood: e.g. Ab (secreted by B lymphocytes)
2) Cellular = Mediated by cells in immunized person:
e. g. T lymphocytes
Phases of specific immune response?
Recognition
Activation
Reaction
What confers the recognition phase in specific immunity?
Lymphocytes recognize and bind to Ag with specific receptors:
EPITOPE = antigenic determinant, immunologically active region on Ag recognized by both B and T cells
What confers the Activation phase in specific immunity?
all lymphocytes undergo 2 major changes:
1) Proliferation (clonal expansion)
2) Differentiation into 2 types of lymphocytes:
a) Effector cells (e.g. plasma cells for B cells)
b) Memory cells
What confers the Reaction phase in specific immunity?
Effector cells eliminate Ag
i.e. Plasma cells secrete Ab
List the 5 features of specific immune responses?
- Specificity
- Discriminate self/ non-self
- Immunological memory
- Self-regulation
- Diversity
How is specificity achieved in specific immunity?
B, T lymphocytes express membrane receptors that distinguish differences between distinct antigens
immune responses = specific for distinct antigens
How is diversity achieved in specific immunity?
Gene rearrangement = generate numerous clones of lymphocytes that can discriminate large number of Ag
How is memory achieved in specific immunity?
exposure of immune system to a foreign antigen enhances its ability to respond to that antigen
secondary immune responses are usually more rapid, stronger
Mediated by memory B cells
How is self-regulation achieved in specific immunity?
All immune responses return to normal after antigenic elimination
Name one disease caused by defective immune regulation?
Canale-Smith syndrome
Fas-gene mutation (fas+/-)
> > Elevated levels of Igs (hyper-gammaglobulinemia) and Failure of lymphocytic apoptosis
Increase in number of lymphocytes (5-20 fold)
Lymphadenopathy, splenomegaly
Define immune tolerance?
Discrimination of self from non-self:
Lymphocytes recognize and respond to foreign antigens but are normally unresponsive to the self antigens
Define the stages of Clonal selection theory.
- Immunocompetent T or B cell express surface receptor for single Ag epitope
- Exposed to Ag, epitope on Ag binds to specific cells with matching receptor > Clonal selection
- Specific binding of epitope to BCR/ TCR induces proliferation of these lymphocytes into clones with the same receptors > Clonal expansion
- B cells mature into plasma cells secreting antibodies with the same specificity as the surface receptors on the parent B cell
- Some clone cells generated become “memory cells” with same antigen specificity.
- Removal of antigen-specific clones will result in antigen-specific non-responsiveness i.e. tolerance.
