19 - specific immune response Flashcards
what is an antigen?
a molecule that induces a specific immune response
what are the 2 arms of specific immunity?
humoural
cell-mediated
humoural specific immunity
transferred with serum
directed against ‘free antigens’
mediated by antibodies secreted by B lymphocytes
cell-mediated specific immunity
transferred by cells
directed against cell-associated antigens - intracellular pathogens
• intracellular pathogens are not free-floating
• we need a cell-mediated response to deal with them
mediated by T lymphocytes
what is humoural specific immunity mediated by?
antibodies (Ig)
• bind to epitopes on Ag
• can act alone
• can act as adaptors
what does the immune response used depend on?
- organism
- environment
- status of individual
- delivery of organism
what is cell-mediated specific immunity mediated by?
T lymphocytes
• recognise epitopes presented on MHC molecules
• CD8+ - cytotoxic T cells
• CD4+ - T helper cells
T cell sub-sets
classified based on surface markers/function: • T helper cells • cytotoxic T cells • T regulatory cells • memory T cells • NKT cells
how do antibodies increase inflammation by innate responses?
IgE
• mast cell degranulation
• histamine
IgM and IgG
• complement activation
• C3a and C5a - inflammatory mediators
how do T cells increase inflammation by innate responses?
produce inflammatory cytokines
eg. TNF-alpha
what are the 2 states of lymphocytes?
normal small lymphocytes
• resting
large lymphocytes
• active
normal small lymphocytes (resting)
pale blue cytoplasm and dense, dark stained nucleus
size of nucleus is approximately the same as a normal RBC
16-46% in a normal adult blood smear
• increased in disease
large lymphocytes (active)
larger cell with more abundant and granular cytoplasm
a small lymphocyte, B cell or T cell, becomes a large lymphocyte as it is stimulated to proliferate
such a cell can be shown to be able to incorporate tritiated thymidine, a marker of active DNA synthesis
what are the 2 stages of differentiation by T and B lymphocytes undergo?
1) differentiate from pluripotent stem cells in bone marrow
2) undergo further differentiation in response to antigen
therefore a specific response is an adaptive response
what happens after differentiation?
proliferation - clonal selection
features of specific immunity
clonally distributed receptors
low frequency of cells specific for any Ag
response takes time to develop
Ag induces effector and memory lymphocyte formation
immunological memory
on subsequent encounters with the antigen a secondary response occurs
due to memory B and T cells - an expanded population specific for antigen
B lymphocyte antigen receptors
B cell receptor (BCR/sIg), surface anchored Ig binds free antigen
T lymphocyte antigen receptors
T cell receptor (TCR)
binds complex of antigenic peptide plus MHC - T cells can only recognise proteins
T cells express a TCR which always remains anchored to the cell surface
clonal selection
1) removal of potentially self-reactive immature lymphocytes by clonal deletion
2) pool of mature naive lymphocytes
3) proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells
principle of antibody production
each resting B cell is specific to 1 antigen
contact with antigen activates B cell which divides
differentiates into plasma cells secreting antibody with same specificity as sIg
what is bone marrow?
soft spongey, highly cellular tissue that fills the internal cavity of bones
what is the thymus?
vascular tissue
only 2-3% of T cells produced actually make it - inefficient but need to get rid of them so they don’t react
secondary (peripheral) lymphoid tissues
lymph nodes, spleen, mucosal associated lymph tissue (MALTs), blood, lymphatics
lymphocytes recirculate and if they meet antigen, undergo clonal expansion and differentiation
immune responses occur in the secondary lymphoid tissues
basic structure of a lymph node
inner = medulla middle = paracortex outer = cortex
they have a good blood supply - need to be able to bring the antigen in but also bring the cells in once they develop in bone marrow and thymus
structure of the spleen
a spongey soft organ about the size of a persons fist
located in the upper left part of the abdomen, just under the rib cage
consists of white pulp (mainly lymphocytes) that functions similar to the nodules of the lymph nodes
red pulp contains mainly RBCs and macrophages - main function is to phagocytose old RBCs
mucosa associated lymphoid tissue (MALT)
non-encapsulated submucosal lymphoid nodules and diffuse lymphocytic infiltrates in the submucosa of the intestinal and respiratory tracts
gut-associated lymphoid tissue (GALT)
bronchus-associated lymphoid tissue (BALT)
