Immunology Flashcards
What are some physical barriers to pathogens
- Skin (Cillia in respiratory tract)
- Body temperature (Fever)
- pH
- Competition (non-pathogenic bacteria in the gut)
- Host-specificity
What is the complement system
A part of the humoral, innate immune system which enhances the ability of antibodies and phagocytic cells to clear microbes. Also promotes inflammation.
* Classical pathway
* Lectin pathway
* Alternative pathway
What do all pathways in the complement system do
Produce C3 convertase
Describe the lectin pathway
- MBL recognises and binds to manose on bacteria cell surface
- MASP-2 cleaves C4 -> C4a + C4b
- C4b binds to bacteria
- C2 binds to c4b
- MASP-2 cleaves C2 ->C2a + C2b
- C2b remains attached to C4b forming C3 convertase
MBL - Manose-binding lectin
Describe the classical pathway
Antibodies come and bind to antigens on microbe surface forming a complex.
1. C1q activates by binding to antigen-antibody complex on microbe
2. C1q cleaves C4 -> C4a +C4b
3. C4b binds to the microbe + C2 comes and binds to C4b
4. C1q cleaves C2 -> C2b remains attached to C4b
- Forms C3 convertase
Describe the alternative pathway
C3b binds to microbial surfaces
1. Protein B binds to C3b
2. Protein D cleaves B into Bb and Ba
3. Protein Bb remains bound to C3b
4. Forms C3 convertase
What is the function of C3b
C3b binds to microbes and opsonizes marking them for phagocytes.
C3b binds to C5: C3 convertase cleaves C5 into C5a and C5b.
* C5a is an inflammatory peptide
* C5b recruits C6, C7, C8 and A LOT of C9 to bind to the microbes cell surface forming pores and ultimately destroying the microbe
How are the complement systems activated
- Classical is activated via the binding of C1 on antibody-antigen complexes.
- Lectin is activated via MBL binding to manose on microbe cell surfaces.
- Alternative is activated via C3b binding to C5 on microbes
What are the three outcomes of the complement system
- Opsonization
- Phagocytosis
- Lysis
What is the membrane attack complex and what does it do
- C2b+C4b+C3b = C5 convertase
- C5 convertase cleaves into C5a and C5b
- C5b recruits C6,7,8,9 to attach to the microbe cell surface and form pores leading to cell lysis
What are the symptoms of inflammation
- Rubor - Redness
- Dolour - Pain
- Calor - Heat, fever
- Tumor - Swelling
- Loss of function
What is stage 1 of inflammation
Neutrophils and monocytes that are attacking the pathogen release Kinin, Prostaglandins, Leukotrienes and Histamine
* Histamines - cause vasodilation
* ∴ More blood
* ∴ More immune cells migrate to the site of inflammation
* Migration, Margination and diapedesis occurs
What is margination and diapedesis
Migration is the same as diapedesis
Margination is the binding of leukocytes to the blood stream which is then followed by diapedesis.
Diapedesis is the movement of leukocytes out of the blood circulation and force themselves through small gaps in the endothelium layer to rach the tissue of inflammation.
What is stage 2 of inflammation
- Phagocytes are attracted to microorganisms via chemokines
- Phagocytes destroy microorganisms
- Tissue repair - Dead/damaged cells are rebuilt
What is the difference between monocytes and macrophages
Monocytes are young macrophages in the blood circulation.
Monocytes differentiate to mature macrophages once migrating out of the circulation.
Describe the process of phagocytosis
- Microbe is engulfed by macrophages cell membrane
- Stored in a phagosome (phacytic vesicle)
- Lysosome fuses with phagosome forming a Phagolysosome
- Microbe is digested by enzymes
- Indigestible material leaves the cell via exocytosis
What are NK cells and how do they work
Neutral killer cells are part of the immune system. They consist of an activating receptor and an inhibitory receptor. NK cell activates and kills when the activating receptor is activated.
How are NK cells regulated
MHC class 1 is found in all human cell (except for red blood cells). If present, it naturally binds to the inhibitory receptor thereby activating phosphotase to deactivate the ‘killing signal’.
What do NK cells do?
They are part of the cell-mediated response.
* When NK cells receive interleukin 12 cytokines from macrophages they release interferon-γ.
* IFN-γ enables macrophages to digest and kill microbes
* NK cells can also binds to virus-infected cells and kill them.
What is the role of MHC class I
- Bind to CD8 positive T-cells (Cytolytic T lymphocytes)
- Present antigen to them
- Activate them
What is the role of MHC class II
- Bind to CD4 positive T-cells (T-helper cells)
- Presents antigen to receptor
- Activate them
What cell types are good at presenting antigens?
Matured dendritic cells