Introduction to Immunology Flashcards
What are 3 types of cells involved in innate immunity?
- neutrophils
- macrophages
- Natural Killer (NK) cells
What are 3 types of soluble factors involved in innate immunity?
- Acute-phase proteins
- Cytokines
- Complement
What are 5 cell types involved in acquired immunity?
- T lymphocytes
- B lymphocytes
- dendritic cells
- eosinophils
- basophils/mast cells
What is 1 type of soluble factor involved in acquired immunity?
antibodies
What is the acute inflammatory response?
innate response to tissue damage
What are 5 features of the acute-phase inflammatory response?
- Rise in body temperature (fever)
- Production of proteins (acute phase proteins) mainly by liver (CRP, SAP, MBL)
- CRP + SAP bind to molecules on cell wall of bacteria + fungi - pattern recognition
- MBL binds to mannose sugar molecules not often found on mammalian cells
- molecules are non-specific but direct phagocytes to identify + ingest infectious agent
What are the 3 key types of acute phase proteins, mainly produced by the liver, during the acute phase response?
- CRP
- Serum amyloid protein
- Mannan-binding lectin
What are cytokines?
- small proteins, carry messages between cells e.g. stimulate activation, killing, secretion, proliferation.
- kick-start acquired immune response
What 3 things can the cells of the innate immune system be divided into (remember: comprise of neutrophils, macrophages, NK cells)?
- Granluar leukocytes:
1. NK cells
2. Macrophages
3. Granulocytes (neutrophils, eosinophils, basophils)
What is the structure of neutrophils?
Polymorphonuclear (PMN) neutrophils - multi-lobed nucleus
What proportion of the circulating WBCs is formed by neutrophils?
50-70%
What is the broad function of neutrophils?
phagocytic
What is the structure of eosinophils?
bi-lobed nucleus
What proportion of the circulating WBC are eosinophils?
1-3%
What is the role of eosinophils in innate immunity?
immune response to parasites, helminths and allergic responses
What proportino of WBC are basophils?
<1%
What are 2 functions of basophils in innate immunity?
- not phagocytic - release granules containing histamines, serotonin, prostaglandins
- important in Th2 responses - kickstarting acquired immune response
What is the function of NK cells?
identify + kill virus-infected + tumour cells, complex recognition system - recognise HLA molecule of virus infected cell or tumour + kill them
What is the structure of macrophages?
mononuclear phagocytes
What are the 2 main functions of macrophages?
- garbage disposal
- present foreign cells to immune system
What are antigens?
glycoprotein molecules which react with antibodies or T cells; not all can induce immune response - those that can are termed immunogens
What is the structure of the most basic antibody?
bivalent - 2 binding sites
What proportion of serum Ig is formed by each Ig type?
- IgG: 75%
- IgM: 10%
- IgA: 15%
- IgE: <1%
- IgD: <1%
What are 2 important characteristics of IgG?
- crosses the placenta - protection of newborns
- long serum half-life
What is the structure of IgG?
bivalent - 2 identical antigen binding sites
What is the structure of IgM?
complex of 5 linked bivalent monomeric antibodies - 10 identical binding sites (multivalent), star-like shape
Which immune responses are IgG and IgM involved in respectively?
IgG - secondary, IgM - primary immune response
What is the structure of IgA and where is it found?
2 basic monomers - dimer with secretory piece, found in body secretions e.g. mucus membranes in GI tract
Why is the secretory component of IgA important?
protects it from digestive enzymes
How does IgE works?
binds to basophils + mast cells, triggers release of histamines
What is an epitope?
particular antibody recognises an antigen because that antibody’s inding site is complementary to the EPITOPE, a region approx. 6 amino acids long, on the antigen (forms basis of specificty of antigen recognition)
What are 4 mechanisms via which an antibody can kill a virus?
- binding to virus + preventing attachment to the cell
- opsonisation: virus-antibody complex recognised + phagocytosed by macrophage
- comlement-mediated lysis of enveloped viruses: cascade of enzymes in the blood which leads to destruction of cell membranes + destruction of viral envelope
- antibody-dependent cell-mediated cytotoxicity (ADCC) mediated by NK-like cells
What are 4 mechanisms via which an antibody can kill a virus?
- binding to virus + preventing attachment to the cell
- opsonisation: virus-antibody complex recognised + phagocytosed by macrophage
- comlement-mediated lysis of enveloped viruses: cascade of enzymes in the blood which leads to destruction of cell membranes + destruction of viral envelope
- antibody-dependent cell-mediated cytotoxicity (ADCC) mediated by NK-like cells
What are 4 mechanisms via which an antibody can kill a virus?
- binding to virus + preventing attachment to the cell
- opsonisation: virus-antibody complex recognised + phagocytosed by macrophage
- comlement-mediated lysis of enveloped viruses: cascade of enzymes in the blood which leads to destruction of cell membranes + destruction of viral envelope
- antibody-dependent cell-mediated cytotoxicity (ADCC) mediated by NK-like cells
What are lymphocytes?
agranular leuckocytes, 20-40% of circulating WBC
What are lymphocytes?
agranular leuckocytes, 20-40% of circulating WBC
What are 2 types of lymphocytes?
- T (thymus-derived) cells
- B (bone marrow-derived) cells
- NK (natural killer) cells
What are T cells divided into (2 types)?
- Helper T cells: recognise antigen, help B cells make antibodies and T cells to kill
- Cytotoxic T cells: poisonous to cells, kill cells infected by viruses and intracellular bacteria
What is the overall role of B cells?
make antibodies, have insoluble antigen-binding receptor on its surface; have multiple clones of this receptor -> monoclonal antibodies
Where are lymphocyte precursors producted?
haematopoietic tissue in the bone marrow
What proportion of T cells are destroyed in the thymus during thymal education and why?
95-99% - have the potential to recognise host cells
What is the B cell antigen receptor?
membrane-bound antibody - surface Ig
What is the B cell antigen receptor?
membrane-bound antibody - surface Ig
What is the T cell antigen receptor?
2 protein chains (alpha and beta) - together form TCR, binds to digested antigen fragments
What is recognised by the T-cell antigen receptor (TCR)?
complex of antigen peptide and HLA (MHC) molecule - HLA binds to little fragments of the pathogen + transports them to the cell surface to be recognised
What generates clonal diversity in a) B cells and b) T cells?
random genetic recombinations within each cell among multiple copies of a) Ig genes and b) TCR genes, undergo random splicing and recombination leading to large repertoire of anigen receptors
What proportion of naive T cells is a typical antigen recognised by?
1 in 10^5
What does clonal selection involve?
- antigen binds to surface receptor on B cell (Ig) or the TCR, causes seletive expansion of that clone
- the receptors which bind with highest affinity to the antigen are selected for, outcompete the other receptors proliferate + survive to form effector lymphocytes
What does clonal selection involve?
- antigen binds to surface receptor on B cell (Ig) or the TCR, causes seletive expansion of that clone
- the receptors which bind with highest affinity to the antigen are selected for, outcompete the other receptors proliferate + survive to form effector lymphocytes
What are 2 possible outcomes for lymphocytes that have proliferated recently?
- most: die after fulfilling function
- some: survive as memory cells, epigenetically modified so frequency of receptors increase next time host infected
What are 2 possible outcomes for lymphocytes that have proliferated recently?
- most: die after fulfilling function
- some: survive as memory cells, epigenetically modified so frequency of receptors increase next time host infected
What type of infected cells are killed by cytotoxic T lymphocytes?
cells infected by viruses or intracellular bacteria
How do CTL kill virus/intracellular bacteria infected cells?
recognises antigen peptide + HLA complex, releases granules of enzymes including proteases which digest DNA - APOPTOSIS
How does a T cell meet its antigen?
antigens are taken up by specialised APCs, transported from the tissues into secondary lymphoid organs (lymph nodes, spleen + MALT), where they meet T cells + initiate the acquired immune response
What are the 3 types of APCs?
- B lymphocytes
- Macrographes
- Dendritic cells (most efficient)
What are primary lymphoid organs + the 2 types?
produce lymphocytes - bone marrow + thymus
What are 3 types of secondary lymphoid organs?
- lymph nodes
- spleen
- mucosa-associated lymphoid tissue (MALT)
What proportion of the day do T cells spend in the blood vs the lymph?
1-2 hours in the blood, rest of ay in lymph
Where are antigens present in the blood taken to?
spleen
Does the innate immune response generate memory?
no
Does the innate immune response generate memory?
no
What happens to adaptive immune responses on repeated exposure to the potential pathogen?
adaptive responses can increase in magnitude
What is primary vs secondary response?
primary= response made by naive lymphocytes when they first encounter their specific antigen. secondary= response made by memory lymphocytes when they re-encounter the specific antigen
What are the 3 types of surface markers on T cells?
CD3, CD4, CD8
What are the surface markers associated with B cells?
CD19, CD20, surface immunoglobulin class II MHC
