15 Lymphocytes Flashcards
Lymphocytes are derived from
Common lymphoid progenitors
Common lymphoid progenitors are found in the
Bone marrow
Key characteristics of adaptive immunity
- Fight against recurring infections
- Specificity to clear infection
- Has memory
- Focuses response on the site of infection (+ specific organism responsible)
Immunological memory occurs when
The immune system has recognised and responded toan antigen
What is the basis of immunological memory?
Antigen specific lymphocytes (B+T)
Memory responses are…
- More rapid and heightened immune responses
- Eliminate pathogens fast and prevent disease
Two families of lymphocytes
- B cells (humoral) –> antibodies
- T cells (cell-mediated) –> cytokines, killing
What is an antigen?
Molecules that induce an adaptive immune response (mostly protein)
What is an epitope?
The region of an antigen which the receptor binds to
‘small molecular fingerprint’
T cells can recognise
Linear epitopes (primary structure) in the context of MHC
B cells / antibodies can recognise
Structural epitopes (tertiary structure, folding)
Why do vaccines have to be kept cold?
To prevent the proteins from changing shape –> immune response would not match
To respond to many, different antigens
A very large pool of cells with specific receptors is needed
How is antigen receptor diversity generated?
Through recombination
- Different V + J regions can combine in different ways
What is immunoglobulin gene rearrangement?
- each BCR receptor chain is encoded by separate multigene families on different chromosomes
- During B cell maturation, these gene segments are rearranged and brought together
Immunoglobulin gene rearrangement generates
Diversity of the lymphocyte repertoire
How are T helper cells and cytotoxic cells activated?
Binding to an APC presenting an antigen to which that T cell is a perfect match
What does T helper cell activation due?
The activated T helper cell divides forming a clone army which:
- Signals to help other cells
- Attacks, defends, repairs
- Causes allergies
- Immune memory
What does cytotoxic cell activation due?
The activated T killer cell divides forming a clone army which:
- Signals to other cells
- Becomes powerful killers (killing pathogens, harmful/infected cells)
- Immune memory
What is the T cell receptor?
Part of a complex of proteins on the cell surface
- Variable region made by gene reassortment
- Recognises antigen fragments presented by other cells
What is the MHC?
-Encoded by HLA genes
- Presents antigen to T cells
- Defines self and non self
(crucial in surgery + donor matching)
MHC gene expression
- Polygenic, several class I and II loci
- Expression is co-dominant (both maternal and paternal expressed)
MHC class I
- All nucleated cells
- Various levels, altered during infection/by cytokines
MHC class II
- Only on professional APCs
- May be regulated by cytokines
MHC I
Process in?
Type?
Presented to?
Proteins being produced inside the cell
- Cytosol
- intracellular pathogen/antigen
- CD8 T cells (killer)
MHC II
Process in?
Type?
Presented to?
Resident in tissues/in circulation
- Endosomes
- Extracellular pathogen/antigen
- CD4 cells
Two families of T cells
- CD4 (helper)
- CD8 (killer)
Defined by cell surface molecules CD4 and CD8
How do CD8 cell kill targets?
Programmed cell death (apoptosis)
- Fragmentation of nuclear DNA
- Perforin (polymerise forming pores)
- Granzymes (poisons inserted into cell)
Viruses: Apoptosis or necrosis?
Apoptosis, as necrosis would release viral particles
Function of CD4 T helper cells
- Produce cytokines (inflammatory mediators)
influence outcome of immune response
Tfh
- Pro-antibody
- IL-21
Th1
- Pro-inflammatory
- Boost cellular immune response
- Interferon gamme, timour necrosis factor, IL-12
Th2
- Pro allergic
- Boost multicellular response
- Il-4, IL-5, IL-13
Th17
- Pro inflammtory
- Control bacterial and fungal infection
- IL-17, IL-23, IL-6
Treg (Th0)
- Anti-inflammtory
- Limit the immune response
- IL-10, TGFB
SLIDE 28
B cells and onwards
