Immunological Memory Flashcards
What percentage of lymphocytes die after the first immune response?
> 95%
Which cells survive the detectable response?
plasma cells
Which cells survive the induced response?
- memory B lymphocytes
- memory Th lymphocytes
- memory Tc lymphocytes
Where are plasma cells present?
- spleen
- lymph nodes
- lamina propria
- bone marrow
Describe plasma cells
- secrete antibodies into bloodstream, lymph, mucosa - depending on location
- secretes specific antibodies even when no infections
What do plasma cells not do?
- class switch - already happened
- undergo somatic hypermutation - already happened
- function as an APC, move around
- proliferate
Describe common features of memory lymphocytes
- cells longer lasting
- less co-stimulation required than naive
- stronger responses after activation
- responses can occur faster
Describe memory B and T cells
- induced to respond when they see the antigen in a later infection
- features of cells can lead to immunity from infectious diseases
Describe passive immunity
- protection transferred from another person or animal
- temporary protection that wanes with time
- transfer of antibodies - not lymphocytes
- eventually ends due to catabolism of antibodies - natural destruction
Describe which diseases can be treated using passive immunity/anti-sera
- tetanus - used in horses and humans
- hepatitis A and B
- immunodeficient individuals
- snake bites
Describe passive immunity in early childhood
- most important here
- no/very few adult-like T or B cells in peripheral lymphoid tissues at birth so incomplete immune system
Describe passive immunity in humans
- placental transfer (3 layers)
- IgG transfers across to foetus
Describe passive immunity in farm animals
- placental transfer (6 layers)
- no antibodies
- colostrum and milk critical for IgG
- inadequate colostrum leads to increased mortality and illness in calves
Describe passive immunity in chickens
- serum immunoglobulins (IgY, IgM, IgA)
- IgY transported from hen sera (egg yolk)
- IgA/M transported from oviduct
- protection from 10-20 days
Describe active immunity
- protection produced by the person/animal’s own immune system
- long term
- infection & resolution leads to production of memory T and B cells plus plasma cells
- second infection can be same pathogen - stronger, faster, more specific response
Describe natural infection vs vaccination
natural - immunological memory but also symptoms/pathology
vaccination - still want strong immunological memory but no/very limited symptoms
Describe passive immunity in vaccination
- vaccination of mother with specific goal of creating passive immunity for the offspring
- example: Bovilis Rotavec Corona Emulsion
Describe passive immunity in vaccination in regards to Bovilis Rotavec Corona Emulsion
- contains inactivated rotavirus, inactivated coronavirus and attenuated E. coli
- vaccinate intra-muscular 3-12 weeks before calving
- calves will take up antibody from colostrum protected from enteric infection - 7 to 14 days
Describe B cell activation
- response characteristics of secondary memory response
- faster response
- most antibodies produced for longer
- isotype switching has occurred: IgM/D -> IgG/A/E
Describe serological memory and long lived plasma & B cells
- both plasma and memory B cells originate in active immune response
- specifically in germinal centres within secondary lymphoid organs
Describe affinity maturation
- as mature B cells proliferate they undergo somatic hypermutation - mutation of BCR - specifically V segments
- far higher than other genes
- generally single nucleotide changes
- competition is key to increased affinity
How is competition key to increased affinity?
- B cells compete for survival signals based on recognition of antigen
- present on follicular dendritic cells
How are most memory B cells identified?
presence of CD27 molecule - co-stimulatory receptor
What do memory T cells express higher levels of when activated?
- adhesion molecules - important in APC interaction
- IL-4 or IFN-ү - dependent on Th1 or Th2
- IL-2Rβ - receptor for IL-15 and IL-2
Describe IL-15
- cytokine
- lasts for a long time bound to IL-2Rβ
- allows for low level division when bound to IL-2Rβ
- antigen dependent
What are the different types of memory T cells?
- stem cell memory T cells - Tscm
- central memory T cells - Tcm
- effector memory T cells - Tem
- tissue resident memory T cells - Trm
Describe Tscm Cells
- CCR7 positive - binds CCL19 and CCL21
- CD62L high - L-selectin
- L-selectin and CCR7 homing receptors for secondary lymphoid tissues - recirculate through blood and lymph nodes
- increased proliferative potential upon re-stimulation
Describe Tcm cells
- CCR7 positive
- CD62L high
- highly similar to Tscm cells
- stem cell memory look more like naive T cells (CD45RA+)
Describe Tem cells
- CCR7 negative
- CD62L low
- circulate through blood, specialised for quickly entering inflamed tissue
- rapidly develop into effector cells following re-stimulation and quickly secrete large amounts of cytokines
Describe Trm cells
- CCR7 negative
- CD62L low
- resides in peripheral non-lymphoid tissues
- express high levels of local non-lymphoid tissue-homing molecules such as CD103 and CD69
What does it mean when T cell memory subsets are continuous?
some now discuss terminally differentiated effector memory cells vs others
