2.2 Principles of adaptive immunity to infection Flashcards
Differentiate in bone marrow
Lymphocytes:
- T cells
- B cells
Differentiate in thymus?
T cells:
CD4 T cells
CD8 T cells
Differentiate in secondary-lymphoid tissues ?
CD4 T cells:
- helper T cells
- regulatory T cells
CD8 T cells:
- Killer T cells
B cells:
- antibodies
How do B cells detect antigen?
B cell receptor detects whole antigen (protein) on the surface of pathogens in the ECF
How T cells detect antigen?
detects digested antigen fragments (peptides) ‘displayed’ on the surface of other cells in association with MHC molecules
B cells secrete ?
Antibodies
T cells secrete?
Cytokines
T Cell mediated immunity: antigen is brought to lymphoid tissues by?
Dendritic cell -here it is processed and presented
Dendritic cells originate from ?
Monocytes
- express PRR
How do T cells enter lymphoid tissues?
Via HEVs ( High epithelial valves)
- once here they examine dendritic cells present in paracortex
T cells expess:
TCRs that recognize foreign peptides displayed by carrier molecules known as Major Histocompatibility Complex (MHC)
Immunological synapse:
Gets info about innate immune system to adaptive immune system about what pathogen is present
MHC Class I molecules present peptide fragments of antigen from the
Cytoplasm
Ex: ICF/ cytoplasmic antigens
MHC Class II molecules present peptide fragments of
antigen from the
Tissue fluid
Ex ECF antigen
CD8+ T cells are only allowed to interact with
MHC Class I : peptides
– Detect intracellular infection
CD4+ T cells are only allowed to interact with
MHC Class II : peptides
– Detect extracellular infection
When naïve T cells are first activated they
proliferate: CLONAL EXPANSION
CD8+ T cells differentiate into
Killer T cells
– aka cytotoxic T lymphocytes (CTL) (marines)
CD4+ T cells have a choice for differentiation:
– HELPER T cells (infantry)
– REGULATORY T cells (military police)
Naive T cells:
- in ‘SURVEILLANCE MODE’
- They move around the body in search of antigen which is trapped in the secondary lymphoid organs
TH1 help
Macrophages
TH2 help
B cells make antibody
CD4+ T lymphocytes jobs (2):
- Some T helper cells make cytokines to activate macrophages
- Other T helper cells make cytokines to activate B cells
Important in vesicular infections where pathogens deliberately infect macrophages
– e.g. mycobacteria such as TB
– Interferon gamma is required to ‘hulkify’ your macrophages
CD4 TH1 cells
CD4+ TH2 cells are important for production of
Antibodies:
- produce cytokines (such as IL-4) to tell the B cells which type of antibody to secrete
– IgG vs IgA vs IgE
Regulatory T cell produce
immunosuppressive cytokines such as IL-10
Plasma cells
antibody secreting factories
Where to plasma cells develop and migrate?
- Develop in germinal centers in lymph node secondary follicles
- They migrate to medullary cords of LNs where they secrete antibody into efferent lymph> blood
** some migrate to the bone marrow and produce antibody directly into bloodstream
Where do plasma cells remain?
In the lymph nodes - they fire antibody out into circulation that act at the site of infection
Basic structure of antibody:
- 2 light chains
- 2 heavy chains
What happens once the antibody finds its target?
- neutralization: antibody prevents adherence
- opsonization: antibody promotes phagocytosis
- complement activation: antibody activates complement, which lyses bacteria
IgG
IgD
IgE
IgA
IgM
Which immunoglobulins are be cell receptors?
- IgD
- IgM
Which immunoglobulins are associated with antibody?
- IgM
- IgG
- IgA
- IgE
What is the first antibody produced in the immune system?
IgM
IgM:
- Pentamer – binds 10 antigens at once
- Agglutinin
- Good at triggering the complement cascade
When is IgG produced?
Produced after receiving TH2-cell help – CLASS-SWITCHING
IgG:
- Neutralising antibody in viral infection
- Enhances phagocytosis of bacteria
- Triggers complement activation
Where is IgA produced?
Produced by B cells in the MALT and secretes onto mucosal surface as a dimer
IgA:
- Important neutralising antibody for protection of GIT and respiratory tract
- Important component of colostrum and milk for neonatal health
Where is IgE produced?
Produced by B cells in response to parasite infections
IgE:
- Binds to receptors on the surface of mast cells
- Enhances parasite killing response
- most specialized
Mast cells have receptors for
IgE a recognition triggers degranulation of cells
is produced to neutralise viruses and aid in response to bacteria (enhanced phagocytosis and complement activation)
Igg
is produced for mucosal defence (neutralising antibody)
IgA
is produced for anti-parasite defence to aid mast cell response (assist degranulation)
IgE
Lag phase:
Antibody negative during LAG phase (first 5-7 days)
Log phase:
IgM > IgG = recent exposure (7-14 days previously)
Plateau phase of IgG:
Can last months / years
