Haematology and immunology: Pathology - General features of the immune system Flashcards
Define innate vs adaptive immunity
Innate: defense mechanisms present before infection and which have evolved specifically to recognise microbes
Adaptive: mechanisms stimulated by microbes, capable to recognising microbial and non-microbial substances
Five components of innate immune system
- Epithelial barrier (skin, mucosa)
- Phagocytes (neutrophils, macrophages)
- NK cells
- Dendritic cells
- Plama proteins (including complement)
Two types of adaptive immunity and their functions
Cellular (T cell): intracellular microbes
Humoral (B cell): extracellular microbes and toxins
Where are T cells generated?
Thymus
How do T cells recognise specific Ag?
Via T cell receptors (TCRs)
Main type of TCR. What does this receptor recognise?
AB (on 95% of T-cells)
Recognises Ag displayed on MHC by APCs
On what cells is MHC I found?
All nucleated cells and platelets
Which HLA encodes MHC I?
HLA-A, -B and -C
On what cells is MHC II found?
Antigen-presenting cells (macrophages, dendritic cells, B cells)
Which HLA encodes MHC II?
HLA-D
Differentiate between the functions of CD4+ and CD8+ T-cells
CD4+: helper T cells, bind MHC I and secrete cytokines
CD8+: cytotoxic T cells, bind MHC II and induce cell death (also secrete cytokines)
Cytokines secreted by TH1 cells
IFN-y
Function of TH1 cells
Defends against intracellular microbes
Role of TH1 cells in disease
Chronic inflammatory (AI) disease
Cytokines secreted by TH2 cells
IL-4, IL-5, IL-13
Function of TH2 cells
Defends against helminths
Role of TH2 cells in disease
Allergy
Cytokines secreted by TH17 cells
TGF-B, IL-1, IL-6, IL-23
Function of TH17 cells
Defends against extracellular microbes and fungi
Role of TH17 cells in disease
Role in chronic inflammatory (AI) disease
Which cytokine induces proliferation of T cells into effector and memory T cells? What kind of signalling does this represent?
IL-2
Autocrine (also secreted by T cells)
What % of the circulating peripheral lymphocyte populate do B cells constitute?
10-20%
How do naive B cells recognise Ag?
Via B-cell Ag receptor complex with IgM and IgD
What is the significance of CD21?
Receptor expressed by B cells which is also the EBV receptor
Compare the contrast the roles of IgG, IgA and IgE
IgG: opsonising and complement-fixing, transported across placenta to provide newborn immunity
IgA: secreted from mucosal epithelia (respiratory, GI) to neutralise microbes
IgE: with eosinophils works to kill parasites (stimulated by TH2 cells)
Three roles of macrophages in immunity
- Antigen-presenting to T cells
- Role in cell-mediated immunity (delayed hypersensitivity reaction)
- Phagocytose microbes opsonised by IgG or C3b
Two types of dendritic cells. Where are each found?
Interdigitating: found under epithelia and in interstitial tissue
Follicular: found in germinal centres of lymphoid follicles in spleen and lymph nodes
What are Langerhans cells?
Dendritic cells found in the skin
Function of interdigitating dendritic cells
Express receptors (e.g. mannose, TLRs) which capture and respond to microbes
Then recruited to T cell zones of lymphoid organs where they present Ag to CD4+ T cells via MHC II
Function of follicular dendritic cells
Express Fc receptors for IgG and receptors for C3b
Trap antigen bound to antibody or complement
What % of the circulating peripheral lymphocyte populate do NK cells constitute?
10-15%
What is the role of NK cells?
First line defence against viruses and tumours
What receptors are expressed by NK cells?
CD16
CD56
How do NK cells preferentially kill virus-infected and tumour cells?
Cytotoxic action is inhibited by self class I MHC
Reduced expression of self class I MHC in virus-infected and tumour cells
