Immune system 2 Flashcards
Primary lymphoid structures
thymus
bone marrow
site of formation, differentiation and maturation of lymphoid cells
no antigen contact
Secondary lymphoid structures
spleen
lymph nodes
tonsils & adenoids
Peyer’s patches
contains both T and B cells
Have contact with antigens
Allow initiation of adaptive immune response
Humoral immunity
through the blood/humors of the body
protection against extracellular microbes
B lymphocytes and antibodies secreted by B lymphocytes
Cell-mediated immunity
protection against intracellular microbes
T lymphocytes
Lymphocytes
very specific to antigens but are also very diverse
can migrate to sites of inflammation
lymphocyte classes do not interact with each other unless a stimulus is present (antigen, chemical messengers)
Naive cell
mature lymphocyte that has not encountered its specific antigen
Effector cell
differentiation of lymphocyte after antigen recognition, functions to eliminate microbes
Memory cell
differentiated lymphocyte after antigen recognition, in a state of heightened awareness to more effectively fight microbe if it returns
B lymphocytes
produced and mature in the bone marrow
provide humoral immunity
have membrane bound antibodies
once activated –> differentiate into memory B cells and effector cells
professional APC
effector B cell
come from plasma cells
produce circulating antibodies
If B cells are naive
must have T helper cells and chemical messengers to differentiate and multiply
Fab region on antibodies
antigen-binding fragment that contain recognition sites for antigen
contain variable regions that determine antigenc specificity
Fc region on antibody
crystalline fragment that is constant, responsible for activation of complement cascade and opsonization
Defines the class of the antibody (IgE, IgG, etc)
T lymphocytes
cell mediated immunity
mature in the thymus
once activated: differentiate
T cells cannot recognize antigens directly, T cells recognize antigen peptides presented on MHC
T helper cells (Th)
T helper effector cells: release cytokines and raise the alarm bells
have CD4 co-receptors –> bind to MHC 2
attracted to antigens presented that occurred from OUTSIDE of the cell (exogenous)
must be present to fully activate naive B cells (double check)
Cytotoxic T cells (Tc)
Tc effector cells: kill bad cells
have CD8 co-receptors –> bind to MHC 1
attracted to antigens presented that occurred from INSIDE the cell (endogenous)
regulatory T cells (Treg)
subpopulation of Th cells – controls or limits the immune response, releases immunosuppressive cytokines, suppress antigen recognition
Each B or T cells have only a
single receptor specificity and can only recognize one single antigen
Generation of clonal diversity primarily occurs in
the fetus
Clonal diversity is developed…
before any exposures to antigens occur
occurs primarily in lymphoid organs
Where are T cells developed
liver in fetus
bone marrow in adults
Central tolerance for T cells
the deletion of auto-reactive T cells within the thymus
TCR that respond to self antigens are considered
auto reactive T cells
Clonal deletion
a T cell undergoes apoptosis during maturation in the thymus
Positive selection
process by which T cells are screened so that only those capable of binding to MHC are kept alive
Negative selection
the process by which T cells are screened so that those with a high affinity for binding to self antigens (and potentially causing autoimmunity) are destroyed
AIRE
autoimmune regulation = transcription factor
produced by medullary thymus epithelial cells and controls synthesis of self proteins found in periphery
allows expression of tissue-specific self antigens (TSAs) within the thymus medulla
Peripheral tolerance in T cells
the deletion or anergy of lymphocytes that recognize self antigen in peripheral tissue
Types of peripheral tolerance
Ignorance
Suppression
Anergy
Activation induced cell death
Ignorance in T cells
T cell does not have opportunity to come in contact with antigen – held captive in lymph
Suppression of T cells
t-regulatory cells is important in dampening the immune response
Ex: secretes cytokines IL-10 and TGF-beta
Anergy of T cells
normal cell will not have co-stimulatory signal that an APC has
Ex: no B7 co-stimulation or Ag may not be presented within MHC
no cytokine activity from innate immune system
Activation induced cell death
cell is activated repeatedly and induce apoptosis
Ex: reactivated cells induce Fas/FasL binding –> self apoptosis
This occurs mainly to cytotoxic T cells
Central tolerance for B cells
in bone marrow
reactive B cells to self antigens undergo Ag receptor gene rearrangement
‘try again’ method
if this fails –> apoptosis
Peripheral tolerance in B cells
anergy: B cells usually require TH activation
lack of this –> anergy or apoptosis
Ignorance in B cells
B cells in lymph nodes will not see self ag
Will not meet appropriate Th cell with the same self ag binding
