What does the immune system do?
provide defence against infectious agents
What are the primary lymphoid organs?
thymus and bone marrow
What are the secondary lymphoid organs?
- lymph nodes
- spleen
- MALT
What are the 7 components of the innate immune system?
- physical barriers e.g. skin
- phagocytes e.g. macrophages, neutrophils, eosinophils, monocytes
- immune surveillance
- interferons
- complement
- inflammation
- fever
What are the 2 fates of lymphoid stem cells produced in red bone marrow?
- some remain and mature into B and NK cells which enter the bloodstream and move to peripheral tissue
- some migrate to the thymus and mature into T cells which enter the bloodstream and move to lymphoid tissues
What are the functions of the 6 ILs?
- IL-1 – fever
- IL-2 – T cell stimulator
- IL-3 – marrow stimulator
- IL-4 – IgE stimulator
- IL-5 – class switching to IgA
- IL-6 – stimulates acute phase protein
How can histology be used to identify the type of infection?
- bacteria attracts neutrophils
- virus attracts lymphocytes
- tuberculosis attracts macrophages
- foreign body/fungi attracts giant cells
What does the innate immune system response provide?
a rapid reaction to infection and the same magnitude of response each time the same pathogen is encountered
What is the adaptive immune response characterised by?
the ability to learn, so that second and subsequent encounters with a pathogen elicit a greater, more specific and faster response (basis of lifelong immunity to certain infection after an initial infection of vaccination)
How do B and T cells recognise foreign antigens respectively?
- B cells use surface immunoglobulin to bind native antigens
- T cells use T cell receptors to bind processed antigen fragments presented by host cells
What do MHC molecules do?
present antigenic peptides to T cells
What are the 2 main classes of MHC?
- class I – found on all nucleated cells and presents antigens to CD8+ cytotoxic T cells
- class II – found on antigen-presenting cells and presents antigens to CD4+ helper T cells
How do CD4+ T cells work?
- when a CD4+ helper T cell binds MHC II-antigen complex on an APC, both the APC and T cell release cytokines
- T cell clones itself in response to cytokines
- cloned T cells produce different cytokines that activate B cells and CD8+ cells
How do CD8+ T cells work?
- when a cytotoxic T cell interacts with the MHC I-epitope complex on an infected cell it produces granzymes and perforins
- the perforins form pores in the plasma membrane and granzymes enter the cell and break down proteins, lysing the cell
Where is the thymus gland located?
in the chest, between the lungs and behind the sternum
What is the thymus?
a primary lymphoid organ that has no follicles and lacks B cells and functions as a maturation site for T lymphocytes
What happens to the thymus with age?
it undergoes involution (shrinks)
What do lymph nodes do?
filter lymph and help activate the immune system by providing a site for immune cells to detect and respond to pathogens
Where are lymph nodes found?
clustered along lymphatic vessels
What is the outer layer of a lymph node?
a fibrous capsule that provides structural support and encloses the entire node
What does the lymph node capsule contain?
trabeculae that extend into the interior, dividing the node into compartments
What does the lymph node cortex contain?
- lymphoid follicles – spherical clusters of immune cells, mainly B cells
- germinal centres – inactive follicles that form where B cells rapidly proliferate and mature in response to an infection
- paracortex – located beneath the cortex, contains mostly T cells and dendritic cells; is the response zone where T cells encounter antigens presented by dendritic cells which triggers the immune response
What does the medulla of lymph nodes contain?
- medullary cords – strands of lymphatic tissue that contain B cells, plasma cells and macrophages
- medullary sinuses – spaces filled with lymph lined with macrophages that help filter out foreign material
Describe the pathway of lymph fluid through lymph nodes
enters via afferent vessels through the convex side then exits via efferent vessels through the hilum
