Cells of the Immune System Flashcards
What are the 2 lineages of immune cell?
Lymphoid and myeloid
What are the 3 interacting barriers of the immune system?
- Epithelial & Mucosal surfaces
- Innate immune system (general inflammation response)
- Adaptive immune response to specific threat
What are the functions of epithelial cells?
- Block entry to microorganisms
- Produce antimicrobial proteins which kill most pathogens
- Produce regulatory proteins (cytokines & chemokines) and mucins
What are goblet/paneth cells?
Specialised cells found in endo and epithelial mucosal surfaces often exposed to infection
Contain crypts which secrete mucous and antimicrobial proteins
Describe the properties of neutrophils
- Small granulated cells with a lobate nucleus
- Have cytoplasm neutral staining
- 50-70% of blood leucocytes and have a short lifespan (5 days)
What is the function of neutrophils?
- Phagocytic, provide key role in inflammatory response
- Granules contain elastase and antimicrobial proteins (for intracellular killing of bacteria)
Describe the properties of eosinophils
- Slightly bigger than neutrophils with acidic staining
- 1-6% of blood leucocytes
- In blood for a few hours but in tissues for a few weeks
What is the function of eosinophils?
- Inflammatory response to parasites, allergic reactions and asthma
- Present antigen to T cells
- Granules release peroxidase, anti-parasite toxins, collagenase as extracellular effectors
Describe the properties of basophils
- Bilobate nucleus with granular basophilic cytoplasm
- Rarest of blood leucocyte types
- Life span of 70 hours
What are the functions of basophils?
- Granules release histamine, heparin, cytokines, serotonin & chondroitin
- Involved in inflammation & allergic reactions via IgE binding
Describe the properties of monocytes
- Large cells making up 3-8% of blood leucocytes
- Subsets distinguished by surface receptors
- Migrate to reservoirs in tissues (e.g spleen) where they mature to other leucocyte types
What are the functions of monocytes?
- Present antigens and produce signalling molecules
- Clear out debris via phagocytosis
What is the function of platelets/thrombocytes?
- Involved in clotting
- Express MHC I and possess receptors for IgG
- Release chemotactic factors
What are lymphocytes?
Small, round, non-phagocytic cells which are the made enactors of adaptive immunity
What are the 2 types of lymphocytes?
T-cells - mature in thymus and kill infected/cancer cells via antibodies (CD40)
B-cells - made in bone marrow and also secrete and synthesise antibodies (CD4 and CD8)
What are the 3 types of T cell? What are their markers?
T-helper - release cytokines, recognise antigens and activate T-killer cells and B-cells, CD4+ marker
T cytotoxic - Kill virus infected, cancerous, foreign and damaged cells. Has CD8+ marker
T regulatory - Modulates immunity and maintains self-tolerance, identified by CD4+ and CD25+ markers
What are natural killer (NK) cells?
- Small granules containing perforin and granzymes
- Kill cells without antibodies
- Produce cytokines
What is the role of macrophages?
- Found in tissues and derived from monocytes
- Large cells consume bacteria, debris and dead cells
- Also aid in adaptive response via antigen presentation
Describe dendritic cells?
- Small stellate cells derived from the bone marrow
- Sample blood for pathogens (common in tissues with external contact)
- When activated, interact with B and T cells in the lymph nodes in order to initiate an adaptive immune response
What is the function of mast cells?
- Highly granulated cells rich in histamine and heparin
- Present in connective tissue/mucosa
- Degranulation occurs upon injury or after binding to IgE or complement
Which lineage evolved first?
Myeloid (innate)
Where is the thymus found?
Between the lungs
Describe the maturation process of a T-cell
- T-cell precursors travel from the bone marrow to develop in the thymus, then are ‘selected’
- Mature T-cells leave the thymus and travel to the secondary lymphoid tissues (spleen, lymph node, GALT)
Describe the structure of the thymus
- Consists of lobules with outer cortex and inner medulla
- Cortex contains immature T-cells
- Medulla contains mature T-cells
Where are B cells found in the lymph nodes?
- In follicles where they undergo proliferation after activation
(note: T-cells found in areas around follicles)
What is the structure and function of the spleen?
- White pulp contains lymphocytes
- Red pulp contains blood sinuses & macrophages
- Role is to collect and destroy old red blood cells, filtering the blood and traping microorganisms
