3: Adaptive Immunity Flashcards
what does the adaptive immune system do?
responds to pathogens by specifically recognising antigens
innate vs. adaptive immune system
both provide self/non-self differentiation
adaptive recognises the type of bacteria and specific antigens
- more exquisite recognition since it recognises antigens
- high specificity and memory
innate only knows that it is present
antigens
molecules from pathogens recognised through the immune system
non-pathogens can also be antigens
pitfalls of innate and adaptive immune systems
both can have incorrect responses to pathogens and you end up with auto-immunity or other diseases
what does the adaptive immune system recognise?
smaller pieces of antigens called epitopes or antigenic determinants
relationship between pathogens, antigens and epitopes
pathogens made up of different antigens
each antigen can have many epitopes
characteristics of adaptive immunity
distinguish between small differences in antigens
- greater specificity than innate
takes 5-7 days to initiate antigen specific adaptive immune responses when exposed to pathogens
- takes longer than innate
creates immune memory cells that provides a faster immune response when infected again with the same pathogen
- memory unlike innate
immunological memory
second exposure to an antigen results in a more potent immune response
differentiate between vaccine antigens and antigens in the virus
- some viruses have envelope proteins that you’ve never seen before infection so vaccines don’t help
what should the adaptive immune system do when correct?
should only respond to foreign and harmful, not to foreign and not harmful
adaptive immunity responses initiation
primary infection/first exposure
- takes a few days to initiate
- T and B cells have to be activated and expanded, then spread around the body
secondary infection/subsequent exposure
- quicker adaptive immune response because of memory cells that can be activated quicker when they recognise the pathogen
cells of the adaptive immune system
all lymphocytes
T cells or B cells
- cytokines come and bind to the surface of cells to activate them
- DCs as important in this process
macs and DCs play important roles in activating adaptive immunity but do not form memory cells
B cell mediated immunity
antibodies produced by B cells interact with pathogens and their toxic products in the blood or other spaces
- B cells recognise antigens whereas T cells recognise proteins
B cells activated from the virus just being there
T cell mediated immunity
T cells only recognise antigens as small peptide fragments bound to MHC molecules and displayed at the cell surface
controlling the immune system and killing infected cells
3 tools of the adaptive immune response
antibodies made by B cells
cytokines made by T helper cells
killing of infected cells by cytotoxic T cells (CTLs)
- only cells that are memory cells and lymphocytes
- harness all other immune cells (neutrophils and macs)
main function of B cells
antibody mediated immune response
main function to produce antibodies
antigen binding sites / variable regions (Fab)
one part binds specifically to antigens
highly variable
each antibody has 2 identical Fabs which are specific to an antigen
constant region (Fc)
binds to other immune cells
4 main antibody isotypes
- IgM, IgG, IgA and IgE
- IgA important because it’s the mucosal antibody
memory antibody during immunisations leads to mostly IgG
- if you get infected and make many antibodies, it will be both IgG and IgA
functions of antibodies
neutralisation
- antibodies bind to antigens to block toxin function and neutralise them
- mostly IgG and IgA
opsonisation
- antibodies enhance phagocytosis
- bind to surface of the pathogen to enhance phagocytosis
- mostly IgG and IgM
phagocytosis and lysis
- mostly IgG and IgM
- binds to pathogens or infected cells to kill them
neutralisation
blocks active site for adherence
neutralising antibodies usually high affinity so better at binding
mainly IgG and IgA
- spike neutralising IgG from vaccines but IgA also helps neutralise when you get infected
opsonisation
Fc of antibody binds to Fc receptors on phagocytic cells to provide enhanced uptake
complement activation
- complement protein binds to Fc receptors
- whole bunch of enzymes to lyse pathogens
2 main types of T cells
cytotoxic T cells (CD8 T cells)
- specifically kills virally-infected cells
T helper cells (CD4 T cells)
- produce cytokines
T helper cells (Th)
master regulators of adaptive immune responses
key immune cells need cytokines produced by Th to be activated
- Th cytokines mostly different than innate immunity cytokines
cytokines needed for
- B cells to produce antibodies
- cytotoxic T cells to become maximally effective killers
- macs to kill pathogens inside
T cell receptors (TCR)
specific to one antigen and one epitope for each pathogen
activates T cells
each T cell has only one unique TCR but will have many copies of that same TCR
similar to antibodies with a variable and constant region
only recognises antigen when the antigen is presented by specialised molecules (MHC)
major histocompatibility (MHC)
MHC molecules display fragments of pathogens on the host cell surface on the DC to present to T cells
antigen taken up by phagocytosis by DC, DC presents antigen with MHC molecules, looks for T cell with TCR specific to that
MHC called HLA (human leukocyte antigen) in humans
how do DCs initiate adaptive immune response?
DCs pick up pathogens at sites of infection, then bring it to lymph nodes or spleen
a DC can bind to 50-100 T cells to present antigens and activate them
how are cytotoxic T cells activated?
when activated, known as CTLs (cytotoxic T lymphocytes)
when TCR of a specific CTL recognises antigen presented on MHC by infected cell, CTL kills infected cell
CTL killing is very specific
- targets infected cells unlike other immune cells
