Immune system Flashcards
What are the two primary functions of the immune system?
- Immune response against pathogens
2. Recognition and elimination of transformed cells
How can the immune system be classified (into two main areas)?
Innate and adaptive
Within both innate and adaptive there is also cellular and humeral
Describe the innate immune system
Cellular; NK cells, neutrophils, dendritic cells, mast cells, eosinophils and macrophages
Humoral; complement, mannose binding lectin, LPD binding protein, CRP
Describe the adaptive immune system
Cellular; T cells, B cells
Humoral; antibodies
What are mechanisms of the innate immune system?
Phagocytosis
Complement (cascade)
Inflammation
NK cells
What are the stages of the adaptive immune response?
- antigen recognition (APC)
- lymphocyte activation (clonal expansion)
- antigen elimination (humoral + cell mediated)
- contraction (apoptosis)
- memory (surviving memory cells)
Where are T cells produced?
Thymus
Describe MCH Class I
Part of T cell; recognised by CD8
Proteins made by our body degraded and presented
If cancer or virus this will change and they recognise these changes
T cells with MCH Class I are CYTOTOXIC
Describe MHC Class II
Part of T cell; recognised by CD4
Presentation of degraded bacterial antigens
These are the T Helper cells; present antigens and facilitate apoptosis
Where are B cells produced?
bone marrow
Describe B cell activation
Occurs in lymph nodes, requires T cells presenting an antigen
Which antibody is produced first in response to infection?
IgM
What antibody mediates the long-term response of the immune system to infection?
IgG
What does IgE mediate?
Allergies via mast cell activation
Also involved in fighting parasites
Where is IgA?
Mucosal surfaces
Which antibody is most prevalent?
Overall IgA, in blood IgG
What are the functions of antibodies?
- neutralisation of antigens
- opsonisation of antigens; facilitates phagocytosis
- activates complement system
What are innate immune cells?
Mast cell
NKC
Basophil, neutrophil, eosinophil, monocyte
Mast cell, macrophage, dendritic cell
What do dendritic cells do?
Present antigen via MHCII
Sentinel for immune system
Activates adaptive immune system
Internalises pathogen and processes it into peptides which it presents (antigens)
Naive T cells are activated
Where do lymphocytes mature?
T cells; bone marrow then thymus
B cells; bone marrow
B and T cells then migrate to secondary lymphoid organs
Describe cytokines and their functions
- large and heterogeneous soluble proteins
- communication system; locally or at distance
- regulate and co-ordinate cells of innate and adaptive immunity
- produced during normal haematopoeisis
- produced in response to microbes, tissue damage or other antigens
- produced by many cell types esp macrophages and T helper cells
How do cytotoxic t cells kill cells?
Induce apoptosis in target cell
They induce the actions of phagocytic clearance
Describe function of NK cells
Important against intracellular pathogens
May respond via their activating receptors to activating ligands on infected cells
Can kill infected cells
Produce IFN-g which will help stimulate macrophages, TH1 cells, CD8+ cytotoxic T cells
How do NK cells induce apoptosis?
Release perforin which creates pore in membrane
Granzyme from NKC then enters cell and triggers apoptosis
How are antibodies bi-functional?
Fab portion (fragment antibody binding) binds to a specific antigen
Fc portion interacts with different cells of immune system or complement
When are antibodies produced?
IgM produced as fetus
IgG not until birth
IgA not until 1-2months after birth
Breast milk contains IgA
Describe antibody mediated immunity
First encounter pathogen; no antibodies while B cells differentiate into plasma cells. Then low vol IgM produced and small amounts IgG. Memory B cells also
Encounter again; accelerated response, quick B cell proliferation to plasma cells - fast release specific IgG ABs and low vol IgM.
Describe immunologic tolerance
unresponsiveness to an antigen induced by previous exposure to that antigen
What are antigens that induce tolerance called?
tolerogens
What are some mechanisms of peripheral tolerance?
Anergy (functional unresponsiveness)
Antigen recognition without co-stimulation
T-reg suppression
Deletion (cell death)
Some self-antigens are sequestered from immune system by anatomic barriers
When does autoimmune disease occur?
When auto-reactive T cells or autoantibodies cause tissue damage through hypersensitivity reaction types II, III and IV
What is AIRE?
transcription factor expressed mainly by medullary epithelial cells in thymus
“autoimmune regulator”
