Lecture 5 Antigen presenting cells Flashcards
Where are macrophages made and the structure of macrophage
Most macrophages are made in the bone marrow
Macrophages have golgi, mitochondria, rounded nucleus, free ribosomes and rough endoplasmic reticulum
Where are macrophages distributed and what are they called in these places? (5)
Microglia in brain Kupffer cells in liver Histiocytes in connective tissue Monocytes in blood Alveolar macrophages in lungs
What are the 5 macrophage receptors
Transport receptors Cytokine receptors Complement receptors Antibody receptors Other receptors
What are the 5 main functions of macrophages
Phagocytosis (slower than neutrophils but can kill bigger)
Apoptosis - removal of dead cells
Produce different cytokines - facilitate further development of innate and adaptive immunity
Trigger tissue repair and wound healing
Antigen presentation
Describe the two types of Macrophages
M1 cells aggressively phagocytic
M2 cells trigger wound repair and healing
Can interchange
How do macrophages know when to kill dead cells (apoptosis)
Macrophages send chemical signals out to neutrophils and if they dont respond back to macrophages with same signal the macrophages kill them
Describe macrophage granuloma formation
If foreign material cant be removed/killed, M2 macrophages gather around it in large numbers and fibroplasts make a wall to prevent spread
Describe dendritic cells and the what are the 4 subpopulations of dendritic cells (DCs)
Most important APC. Have long dendrites that enable them to trap antigens Plasmacytoid DCs Myeloid/classical DCs Follicular DCs Langerhans DCs
Describe Classical DCs
Derived from macrophages
Classical DC 1s trigger type 1 responses
Classical DC 2s trigger type 2 responses and Th17 responses
Describe follicular dendritic cells
In lymph nodes and spleen
present antigen to antibody producing B cells
Trigger somatic mutation (b cells mutate to generate improved antibodies)
Describe Langerhan cells
In the skin
Traps antigens through epidermis
Describe difference between immature and mature DCs
Immature DCs capture antigens and process them
Mature DCs present antigens to T and B cells
Where do all APCS (Dendritic cells, B cells and macrophages) present their antigens to?
T helper cells
Describe the Uptake of antigen by macrophages and presentation to T helper cells (extracellular)
The immunogen (antigen) enters the macrophages endosome and the endosome and lysosome fuse in the macrophage. Its here where the antigen is fragmented and the fragment binds to MHC II molecule and the MHC epitope molecule is transported to the surface of the macrophage were it can interact with the specific TCR on T helper cell.
How is the T helper cell activated
The T helper cell requires 2 signals to become activated.
One signal is the binding of TCR to class II MHC molecule on APC
Other signal is provided by cytokines (chemotaxis) secreted by APC.
Describe endogenous antigen processing
Virus enters the cell and forms a viral protein from its viral nucleic acid. The viral protein is ubiquninated is then fragmented by proteosome. The fragments then bind to MHC I molecules in cell and then transport on surface of cell. Recognised by and trigger responses in cytotoxic T cells
Describe the role of T cells (Th and Tc)
APCs present Ag on MHC class II molecules to TCR on T helper cells
Presentation to a TH2 cell results in cytokine production that promotes Ab production
Presentation to a TH1 cell results in cytokine production that promotes CMI responses
Almost all nucleated cells can present Ag on MHC class I molecules to TCR of cytotoxic cells
Describe the activation of B cells
B cells BCR binds to the specific MHC II antigen complex on a T H cell (already activated) The B cell can then proliferate into a memory B cell for future reference or differentiate into a plasma cell which will make antibodies for the antigen.
Describe difference between T helper 1 cells and T helper 2 cells
T helper 2 cells after being bound to APC activate and secrete cytokines to initiate antibody production from B cells (humoral)
T helper 1 cells after being bound to APC activate and initiate CMI response (CMI)
What is IL-2 and BCGF/BCDF
IL-2 released by Th cells to activate Tc cells
BCGF - B cell growth factor
BCDF - B cell differentiation factor
Th cells secrete BCGF and BCDF depending on if B cells want to proliferate (memory cells) or differentiate (plasma cells then antibodies)
