Immunology Flashcards
Name the cells part of the innate response
- Phagocytes
- Dendritic
- Eosinophil
- Basophil
- Mast cell
- Natural Killer Cell
- Complement protein
Name the adaptive response cells
- B cells
- T cells (CD4 and CD8)
Describe the main role of the innate immune system
First line of attack, it is not specific and has no memory cells so produces same response each time microbe invades
Phagocytoses and degrades foreign bodies
Describe the main role of the adaptive immune system
Highly specific immune response that has an immunological memory so releases specific antibodies if antigen returns
Initiated by innate response if attack too severe or prolonged - produces antibodies and T cells
What is self tolerance?
Immunological unresponsiveness to self-antigens
Able to do this by elimination of lymphocytes which react to self-antigens at early stages.
What are the 1st lines of defence?
- Skin
- Mucosal barrier - reproductive, respiratory and digestive tracts
- Complement in blood
What are the 2nd lines of defence?
- Lymphocytes
- Antibodies in blood
Function of Natural Killer Cells
To degrade antigens in innate immune response
Mechanism 1 of NKC
Bore holes in cell surface of target cell by secreting perforin onto them forming a membrane attack complex (MAC) and secrete enzymes that enter cell and initiate cell suicide
Mechanism 2 of NKC - activating
FasL receptors on NKC bind with Fas proteins on target cell surface and binding produces signal to induce target cell death
Mechanism 2 of NKC - inhibitory
MHC1 receptors bind MCH1 proteins target cell and do not initiate cell death as it recognises it
Inhibitory receptor dominant when present
Lack of MCH1 indicates infected cell
Process of phagocytosis
- Microbe engulfed by phagocyte - phagosome
- Phagolysosome fuses fuses and releases digestive enzyme
- Indigestible material
- Microbe broken down and excreted
Function of primary lymphoid organ
Where lymphocytes form and mature - stem cells differentiate into T/B cells (haemopoesis)
T-cell and B-cells are made in the bone marrow but B cells also mature there whereas T-cells migrate to the thymus to mature (train)
Describe POSITIVE selection in Thymus
T cells must be able to bind to MCH1 and MCH2
If cannot bind then taken to bone marrow for apoptosis
Describe NEGATIVE selection in Thymus
T cells NOT allowed to bind to MHC self-antigen and undergoes apoptosis if it does (in bone marrow)
What happens if T cells are NOT self-tolerant?
Causes autoimmunity i.e. in MS when cells attack myelin sheath around axons
Function of secondary lymphoid organs
Site of lymphocyte activation by antigens
Folicular dendritic cells (FDCs) display antigen to B cells and induce antibody production
Name secondary lymphoid organs
- Lymph node and lymphatic system
- Splee
- Toncil
What two proteins are in the antibody?
Light chain (Lc) and heavy chain (Hc)
What do you call the ‘top half’ and ‘bottom half’ of an antibody?
- Top: Antigen binding region (Fab)
- Bottom: Fc region - receptor allowing for Ig recognition
Describe T cell dependent B cell activation
Requires binding between B cell receptors (BCR) and pathogen.
Then binding of T helper cells.
Describe T cell independent B cell activation
When BCRs are clustered together by an antigen with many epitopes (Ab binding site)
Function of IgM
Fixing complement and opsonisation
Function of IgG
Opsoniser (crosses placenta)
Function of IgA
- Protects mucosal surfaces
- Resistant to stomach acid
Function of IgE
- Defends against parasites
- Cause anaphylactic shock and allergies
Function of MHC1
Presents peptide to CD8+ T cells which trigger cytotoxic response
-On all nucleated cell surfaces
Function of MCH2
Presents foreign Ag to CD4 T cells and activate macrophages and B cells
Only on antigen presenting cells (APCs)
Describe process of antigen presenting cells
- Endocytosis products bind to MHC2 on cell surface
- Ag binds to Ab: B cell engulfs MHC and Ag and can proliferate into more B cells
- When activated, B cells produce Ab to attack pathogen
Describe the role of T helper cells (Th) - CD4+
Activate and direct other immune cells to attack foreign bodies
Describe the role of cytotoxic T cells (Tc) - CD8+
- When exposed to infected cells, Tc cells release perforin - pore in target cell
- Releases Granzyme B that enters the pore and induces apoptosis
What are the three activation pathways for the complement system?
Classical, alternative and Lectin
Overall function of the complement system?
Group of 20 proteins in the blood and when activate they induce lysis of target cell and opsonisation of pathogens
Innate complement system pathways
Alternative and lectin
Adaptive complement system pathway
Classical
How is the classical complement pathway activated?
Antigen-antibody reaction
How is the alternative complement pathway activated?
Bacterial endotoxin
How is the lectin complement pathway activated?
Presence of mannose binding lectin protein (MBL)
Describe the Alternative pathway
- Spontaneous hydrolysis of C3 to C3b
- Factor B joins to C3b - opens b active site
- Formation of C3 convertase
- C3 convertase converts C3 to C3b and C3a
- Formation of C5 convertase
- C5 con. converts C5 to C5b and C5a
- C5b joins complement proteins on cell wall and form MAC
- C9 froms hole in target cell
Describe the Lectin pathway
- MASP protease bind MCL
- MASP activate C4 and C2 into subcomponents
- C4b and 2b join to form C3 convertase
- C3 convertase cleave C3 into C3b and C3a
- Formation on C5 protease which cleaves C5 into C5b and C5a
- C5b joins MAC
- C9 forms hole in target cell
Describe the Classical pathway
- Ag-Ab reaction activate C1
- C1 cleaves C4 into C4a and C4b
- C2 converted into C2a and C2b
- C4b and 2b form C3 convertase
- C3 con. cleaves C3 into C3a and C3b
- Formation of C5 converts
- C5 con. cleaves C5 into C5a and C5b
- C5b join complement proteins and form MAC on target cell
What happens to C3a, C4a and C5a?
Activates macrophages and neutrophils
Immune effects of complement products
- Opsonisation: C3b activates neutrophils and macrophages
- Cell lysis from MAC
- Chemotaxis: C5a attracts neutrophils and macrophages to antigen
Autocrine cytokines
Works on same cell that induced it
Paracrine cytokines
Works on nearby cells
Endocrine cytokine
Works on cells in different organs - travels by blood
Where are macrophages made and what are they derived from?
Made in bone marrow (stem cells and are derived from monocytes which are relies from the blood and differentiated and mature into macrophages in the tissue
What is the action of macrophages?
- Give off chemicals that restrict blood flow away from the site of injury (redness)
- Initiate contraction of endothelial cells in capillary wall - allows fluid to leak into the tissue and cause swelling
- Produce cytokines to alert other cells of the foreign body and alert them to travel to the site of injury
- Carry out phagocytosis
Function of neutrophils
- Most abundant WBC
- Carry out phagocytosis
- Short life span and so are recruited from BV during infection
Function of Eosinophils
- Help combat parasitic infections
- Involved in allergy and asthma
- Made in the bone marrow and are granulocytes; contain granules which contain many enzymes which are mediator that are toxic to parasite and HOST tissue
- Found in the thymus, GIT, ovary, uterus, spleen and lymph nodes
Mast cells
Protect against parasites an contain granules containing pharmacologically active chemical - histamine
How do mast cells cause anaphylactic shock?
Mast cells release granules onto the parasite to kill it - the granules can cause an allergic reaction in the host which if it is severe enough can cause anaphylactic shock
Mast cell and IgE
Exposure to allergen initiates IgE antibody production - Mast cells have receptors which can bind to the Fc region of the IgE antibodies which also bind the allergen and sends a signal to mast cell to release granules
Function of Basophils
- Least common granulcye
- Contain large cytoplasms granules which obscure nucleus under microscope
- Cells store histamine in the granules
- Found in parasitic infections
- Responsible for allergic reaction symptoms; runny nose, itching, water eyes etc
What are cytokines?
Chemicals used by cells to communicate with other cells
What occurs in the white pulp of the spleen?
Lymphatic tissue surrounding arteries - periaterioriorlar lymphocyte sheath (PALS) contains T cells and the the penifollicular zone which contains B cells (in follicles).
The last layer is the marginal zone which contains B cells and specialised macrophages
What occurs in the red pulp of the spleen?
It’s a vascular sinusoid (BV) that contain RBC, macrophages, dendritic cells, lymphocytes, plasma cells
Filters blood of microbes and damaged RBC
What is the high endothelial venules?
Secondary lymphoid organs (not spleen) have HEVs which allows B cells and T cells to enter the secondary lymphoid organ from the blood - this section of the blood vessel contain columnar cells loosely fitted together to allow lymphocytes to pass through
What does the inner cortex of the lymph node contain?
- CD4+ helper T cells and few CD8+ helper T cells
- HEVs
What does the outer cortex of the lymph node contain?
- B cells (in lymphoid follicle)
- Dendritic cells
- Lymphatic sinuses
What are Peyer’s Patches/MALT?
Germinal centres that contain B cells, few CD4+ T cells and M cells
Mc ells are specialised epithelial cells that transport Ag from the lumen of the intestine to the Lymphatic follicle (Peter’s patch)
What is cancer of the lymphatic system called?
Lymphoma and is a common site of metastasis
What are non-specific humoral factors and examples?
- Growth inhibitions
- Enzyme inhibitors
- Lysins
- Complement proteins
Functions of the lymphatic system
- Removes ISF from tissues
- Absorbs and transports FA and fats as chyle to the circulatory system
- Production of lymphocytes (bone marrow, thymus, spleen)
