Adaptive Immunity 1 Flashcards
what does the adaptive immune response consist of?
cell-mediated responses and antibody (humoral) responses
what do T cells do in adaptive immunity?
drive cell-mediated immunity
what cells does cell mediated immunity involve?
macrophages, natural killer cells, antigen-specific cytotoxic T-lymphocytes
what do B cells do in adaptive immunity?
produce antibodies and drive humoral immunity
what is a key feature of the adaptive immune system?
immunological memory
what is immunological memory?
each pathogen is remembered by a signature T cell and/or B cell receptor
what are the stages of adaptive immunity after infection?
transport of antigen to lymphoid organs, recognition by naive B and T cells, clonal expansion and differentiation to effector cells, removal of infectious agent
what is the threshold level of antigen?
amount of a pathogen present to mediate an immune response
why is the threshold level of antigen important?
the immune system does not need to mediate adaptive immunity if only a small amount of antigen is present as the innate immune system can clear the threat without the help of adaptive
what are the three main receptors in adaptive immunity?
T cell receptor (TCR), B cell receptor (immunoglobulins), major histocompatibility complex (MHC proteins)
what do multiple genes encoding allow?
the development of a repertoire of receptors with wide specificity
what is the difference between innate and adaptive receptors?
innate receptors (TLRs) DON’T have potential to rearrange and change shape to recognise different antigens whereas adaptive receptors CAN rearrange structure depending on gene expression of each protein subunit
where are T cells derived from?
bone marrow
where do T cells mature?
thymus
what do T cells give rise to?
cellular immunity
how do T cells recognise peptides?
through the T cell receptors
what does T cell repertoire mean?
diversity in TCR (can respond to numerous antigens)
what is thymic education?
checkpoints that are in place to ensure T cells only respond to foreign pathogens and not self peptides
what do T helper cells (CD4+) do?
function to hep support other immune cells to fight threats
what do cytotoxic cells (CD8+) do?
destroy our own cells which have become infected (usually virus-related)
what do regulatory T cells (Tregs) do?
regulate or suppress other cells in the immune system
what do all T cells start as?
naive T cells
what are the 3 types of T cell that naive T cells differentiate into?
T helper cells, cytotoxic cells, regulatory T cells
what are Tregs essential in?
trying to balance the homeostasis between pro- and anti- inflammatory responses
what is CD8?
a co-receptor that binds to MHC I
what is CD4?
a co-receptor that binds to MHC II
what is CD3?
a co-receptor involved in activation of both CD4+ and CD8+ T cells
what is MHC I usually expressed by?
virally infected cells
what is MHC II found on?
just found on antigen presenting cells
what are the different chains found on T cell receptors?
alpha and beta chains but a small portion express gamma and delta chains instead
what are the two regions of the alpha and beta chains?
constant and variable
what are the three genes that encode the variable region of alpha and beta chains of T cell receptors?
V (variable), D (diversity) and J (joining)
what is the alpha chain of T cell receptors encoded by?
two gene segments - V and J
what is the beta chain of T cell receptors encoded by?
three segments - V, D and J
how are genes rearranged?
by somatic recombination
what is somatic recombination driven by?
RAG (recombinase) enzymes
what does recombination lead to?
different receptor structures that can recognise different antigens
what are pre-thymic T cells?
undifferentiated lymphocytes
what are the two different types of selection?
positive and negative selection
what type of cells do T cells interact with in the thymus?
cortical epithelial cells
what is positive selection?
no recognition
what is negative selection?
recognition of self antigen
where are receptors rearranged?
in the thymus
where do positively and negatively selected CD4/CD8+ T cells with rearranged T cell receptors go once they leave the thymus?
they circulate in blood/lymphatics and some reside in the lymph nodes waiting for interactions with dendritic cells
what happens if you fail positive and negative selection?
apoptosis
where do immature dendritic cells take up and process antigens?
in the epidermis
what happens once immature dendritic cells take up and process antigens?
they migrate to lymph nodes and mature en route
what do mature dendritic cells have and do?
they have co-stimulatory activity and can prime naive T cells, they can also transfer antigen to dendritic cells resident in the lymph node
what is required for activation and determining fate of T cells?
three signals
what are the three signals needed to prime T cells?
1 - activation of T cells (MHC-TCR interactions) 2 - survival and clonal expansion of T cells, 3 - differentiation into subsets of effector T cells (specifically for CD4+ helper T cells)
for CD8+ what does the third signal lead to?
effector function e.g. production of enzymes for degradation
what enzymes induce target-cell apoptosis cooperatively?
perforin and granzyme
what are the different subsets of the CD4+ T cell
TH1, TH2, TH17, TFH, Tregs
what is TH1 found in
macrophage
what is TH2 found in
allergic responses/plasma cell generation
what is TH17 found in
epithelium and underlying tissue cell types
where is TFH found?
in lymph nodes and is important for B cell antibody generation
what do Tregs do?
control/dampen the immune response
what is the main function of TH1 cells?
supporting macrophage function
what is the main role of TH2 cells?
supporting humoral responses and allergic reactions
what is TH2 the source of?
interleukin 4,5 and 6 which instruct B cells to produce antibodies
what is TH1 the source of?
interferon-y
what is the main role of TH17?
supporting innate immune responses and enhances clearance of extracellular bacteria and fungi
what does TH17 produce?
interleukin-17 and 22
what does IL17 stimulate?
epithelial cells to produce antimicrobial peptides
what do Treg cells release?
inhibitory cytokines
what do Treg cells inhibit?
T cell activation and dendritic cell activation
how are CD8+ T cells activated?
from interactions between MHC I and TCR
what do CD8+ T cells do?
induce host cells to undergo apoptosis and produce enzymes such as granzyme/perforin
what does perforin do?
penetrate infected cells and target apoptotic signalling pathways
what does T cell priming result in?
generation of memory T cells
what is signal 3 of T cell priming?
cytokines drives differentiation of CD4+ T helper subsets
what does granzyme do?
induce apoptosis
