Adaptive Immunity Flashcards
What tissue are APC pathogen sensors (PRRs) found in?
Skin (SALT), mucous membranes, lymphoid organs, blood circulation
How do APCs capture pathogens?
Phagocytosis, micropinocytosis
Where are APC pathogen sensors (PRRs) found on the cell?
Extracellular (bacteria), intracellular (viruses)
Dendritic and Langerhans (APCs) present Ag to?
Naïve T cells
Macrophages (APCs) present Ag to?
Effector T cells
B cells (APCs) present Ag to?
Effector T cells and naïve T cells
What are effector T cells?
includes helper, killer, regulatory, and potentially other T cell types
Briefly explain capture/processing/presentation of extracellular microbes
PAMPs on extracellular microbe bind PRRs, phagocytosis, processed and Ag presented on MHC II, which can bind CD4+ T cells
Briefly explain capture/processing/presentation of intracellular microbes
Intracellular microbe broken down, processed and Ag presented on MCH I, which can bind CD8+ T cells
What does MHC stand for?
Major histocompatibility complex
MHC that can bind CD8+ are class I, where are they found?
All nucleated cells
MHC that can bind CD4+ are class II, where are they found?
Dendritic cells, macrophages, B cells
MHC I are what genes?
HLA-A, HLA-B HLA-C
MHC II are what genes?
HLA-DR, HLA-DQ, HLA-DP
Outline the key features of MHC class I and II and the benefits that gives
Co-dominant expression = both parental genes expressed = increased number of diff MHC.
Polymorphic genes = diff alleles = increased presentation of diff Ag
Briefly outline the exogenous APCs pathway
Phagocytosis/micropinocytosis, matched to MCH II inside the cells, expressed on the surface of the cell, to a CD4+
Briefly outline the endogenous pathway of Ag presentation in all cells
Virus or tumour Ag is broken down by proteasome to antigenic peptide, matched to MHC I inside ER then presented on the surface of the cell, to a CD8+
What is the diff between slow and rapid processors in terms of HIV?
Slow = MHC present key peptides for survival of virus = effective T cell response. Rapid = MHC present mutated peptides = poor recognition and poor T cell response
What are the downsides of MHC molecules?
Major cause for organ transport rejection, autoimmune disease when process is faulty
When CD4+ T cells are activated what immune response takes place?
Humoral immunity = Ab, complement.
Cell-dependent immunity = Ab, complement, macrophages.
When CD8+ T cells are activated what immune response takes place?
Activation of cytotoxic T cells
Give examples of intracellular vs extracellular microbes
E = bacteria parasites, worms, fungi. I = viruses bacteria, protozoa.
What is a T helper cell and its role?
CD4+ cell = assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages
How are T helper cells defined?
secrete different cytokines to facilitate different types of immune responses = TH1, TH2, TH3, TH17, TH9, or TFH
How is the right T helper cell activated?
First signal = naïve TH0 CD4 binds APC MHC II.
Second signal = naïve TH0 CD28 bind APC CD80/86 = co-stimulatory molecules.
Activated T helper cell releases:
IL-2, autocrine, actives proliferation = TH1 for intracellular microbes,
OR
IL-4 switches to TH2 or TH17 for extracellular microbes
Outline the T cell response to intracellular microbes
Activated by binding APC:
TH1 CD4+ prod IFN-γ which causes B cells to switch to plasma cells and macrophages to become active both killing opsonised microbes.
TH1 CD4+ also activates CD8+ (which will bind MHC I)
How do CD8+ cells kill?
Bind MHC I = prod perforin (makes holes) and granzymes (starts apoptosis)
Outline the T cell response to extracellular microbes
TH17 CD4+ bind APC = IL-17 prod = neutrophils activated = phagocytosis.
TH2 CD4+ bind APC = Il-5 = activates eosinophils, IL-4 = activated B cells + mast cells
How does B cell Ab/Ig production differ in primary vs secondary responses?
P = high IgM. S = High IgG
Name each Ig and where it is found
IgG = secondary response, complement neonatal immunity. IgE = allergies, helminths. IgA = mucosal. IgM = primary response, complement
What happens if there are no CD4+ cells e.g. HIV?
there is no activation of CD8+ T cells
What is cross presentation?
feature of APC
can present intracellular microbes on MHC I and II to activate both CD4+ and CD8+
