adaptive immunity Flashcards
When is adaptive immunity activated?
When the innate immune response is insufficient to control an infection
Is adaptive immunity immediate?
No, it takes several days
What are the 2 types of adaptive responses and what cells are they controlled by?
- cell-mediated: carried out by T cells
2. humoral immune response: controlled by activated B cells & antibodies
Adaptive immunity also involves a _____ to provide the host with __________ from reinfection with the same type of pathogen
memory;
long-term protection
Antigen recognition is mediated by specific ________ which bind to antigens or are derived from pathogens.
antigen receptors
The challenge for T lymphocytes
Very few lymphocytes in the body are specific for any 1 antigen:
- specificity & diversity of antigen receptors
- frequency of antigen responsive lymphocytes
T cells NEVER bind to _____ in their native configuration.
T cells that bind to antigens from bacteria and viruses NEVER come in direct contact with the bacteria or virus.
antigens
T- cell receptors bind to a) ______ derived from foreign proteins.
The a)______ must be presented to T cells by b) ______________ encoded molecules.
a) peptides
b) Major Histocompatibility Complex (MHC)
Dendritic cells travel via circulation to lymph nodes. Once they arrived there, they start to present their antigens to ________ within ____ complexes on their cell surfaces.
naive T helper cells within MHC II
Naive cells are mainly found in ______ and _____
lymph nodes and spleen
List the antigen presenting cells (APCs)
dendritic cells
B cells
macrophages
Langerhans cells
Functions of APCs
1. Capture _______ & take them to the “correct” place (to the ______________, through whr naive lymphocytes circulate)
- Display _______ in a form that can be recognised by ______________
- Provide _______ for ______________ (cytokines induced by microbes– ensure that T cells respond best to microbial antigens)
- Capture antigens & take them to the “correct” place (to the peripheral/secondary lymphoid organs, through whr naive lymphocytes circulate)
- Display antigens in a form that can be recognised by specific T lymphocytes (MHC)
- Provide “2nd signals” for T cell activation (cytokines induced by microbes– ensure that T cells respond best to microbial antigens)
MHC is also called _________
human leukocyte antigens (HLA)
Antigen receptors of T cells have dual specificities:
1.
2.
- For peptide antigen (responsible for specificity of immune response)
- For self MHC molecules (responsible for MHC restriction)
T- cells learn self MHC restriction during ___________
development in the thymus
Antigen processing: conversion of 1. _______ (globular protein) into 2. ______ capable of binding to MHC molecules by 3. ________
- native antigen
- peptides
- proteolytic cleavage
- _____ antigens are displayed by MHC I
2. _____ antigens are displayed by MHC II
- intracellular
2. extracellular
T-cell activation requires 2 signals.
Both signals are provided by activated APCs:
Signal 1:
Signal 2:
Signal 1: peptide-MHC
Signal 2: costimulatory molecules & cytokines
Effector CD4+ T cells activate __________
macrophages, B cells, cytotoxic T cells, etc
Mature naive B cells expressing 1. __________ exit bone marrow and migrate to 2. ________.
They recirculate and enter B cell follicles in lymph nodes & spleen responding to 3. ________ and _____.
- surface immunoglobulin (BCR)
- secondary lymphoid organs
- antigen encounter with T cell help & proliferating
Activated B cells differentiate into 1. ________ which produce 2. _____ or ______.
- plasma cells
2. antibodies or memory B cells
Fragment antigen binding (Fab) region binds to _______ & interferes with their _____________.
binds to microbes & toxins
interferes with their ability to interact with cells
Fragment crystallisable (Fc) region activates 1. ______ in the immune cells that express Fc receptors (eg. phagocytosis) and 2. ______.
- effector function
2. complement
List some effector functions
- Neutralisation
- Complement activation
- Opsonisation
- ADCC
- Inflammation
- Lysis of microbes
B-cell activation depends on T cell.
Requires 2 signals:
Signal 1:
Signal 2:
Signal 1: binding of native antigen to surface lgM/lgD on naive follicular B cell
- B cell internalises antigen & presents peptide-MHC II to antigen-specific effector T helper cell = antigen specific T cell- B cell interaction
Signal 2: T cell receptor triggering up-regulates on costimulatory molecule, CD40L, on T cell & CD40 signaling promotes B cell activation
Define isotypes:
immunoglobulins with the same antigen specificity (same variable region) but different constant regions
Upon isotype switching, antibodies retain the same ________, but have different ______.
the same antigen specificity;
but different effector functions
Isotype switching is dependent on _______ in the form of ____
dependent on T cells in the form of CD40L
Purpose of isotype switching
diversifies the functional properties of the antibody (Fc region)
Are memory B cells longer lived than naive b cells?
Why?
Yes
The persistence of memory B cells after an immune response ensures that we have increased no. of B cells specific for antigen and ready to respond on re-encounter
In humoral immunity, ___ lymphocytes secrete _____ that eliminate extracellular microbes.
B lymphocytes secrete antibodies
In cell-mediated immunity, __ lymphocytes either activate _________ to destroy phagocytosed microbes, or kill _________. ___ lymphocytes also provide a helper function for __ cells.
T lymphocytes either activate macrophages to destroy phagocytosed microbes, or kill infected cells. T lymphocytes also provide a helper function for B cells.
- CD4 T cells recognise MHC ___ + peptide
2. CD8 T cells recognise MHC ___ + peptide
- II
2. I
