MFM II - Antigen Processing and Presentation

what describes endogenous antigens?

the body’s own cellular components or intracellular pathogens

what describes exogenous antigens?

antigens that enter the body or system and freely circulate in the body fluids and are trapped by APCs

uptake of exogenous antigens by APCs are mainly mediated by what?

phagocytosis

B and T cells rely upon what to recognize antigens in order to respond?

cell surface receptors

activation of T cells requires what?

antigen display by antigen presenting cells

what are the most potent APC?

dendritic cells

what describes dendritic cells?

specialized class of APC that functions specifically to capture and process antigens and display on the cell surface in order to activate both CD4+ and CD8+ T cells

what are the functions of dendritic cells?

• capture Ag and process into small peptides for binding to MHC

• present Ag to active T cells

• support the functions of other cells (NK cells)

what are examples of APCs?

• dendritic cells

• macrophages

• B cells

what are the principle inducers of T cell-independent immune response?

dendritic cells

what describes macrophages role as APC?

phagocytose microbes, process Ags, and display on MHC to T cells (usually T cell is already activated)

what describes B cells role as APC?

ingest Ags and display them on MHC to CD4+ T helper cells in lymphoid tissues to generate humoral immunity (antibody response)

what describes the role of CD4 T helper cells?

produce cytokines that direct the ongoing response by enhancing the actions of other cells and increase inflammation

what kind of antigen presenting pathway is associated with CD4 T helper cells?

exogenous pathway

what describes the role of CD8 cytotoxic T lymphocytes?

release cytotoxins that kill infected tissue cells

what kind of antigen presenting pathway is associated with CD8 cytotoxic T lymphocytes?

endogenous pathway

Class I MHC is found on what cells?

all nucleated cells

Class II MHC is found on what cells?

professional APCs (dendritic cells, macrophage, B lymphocytes)

CD8+ T cells recognize peptides only when bound to what?

MHC class I molecules

what cells can process proteins and load peptides onto MHC class I molecules?

all nucleated cells

CD4+ T cells recognize peptides only when bound to what?

MHC class II molecules

what cells can process proteins and load peptides onto MHC class II molecules?

only professional APC and some thymic cells

what takes antigens/peptides from the cytosol to the lumen of the ER to be mounted onto MHC class I molecules?

TAP

oversized peptides are trimmed by what?

ERAP (ER resident AminoPeptidase)

in the case of MHC Class II molecules, what acidifies and degrades antigens?

endosome/phagosome brings the antigen into cell via vesicle and vesicle fuses with lysosomes to acidify and degrade antigens

what helps direct MHC class II molecules to vesicles holding the antigens?

invariant chain

what happens once the MHC class II vesicle fuses with the vesicle holding the antigen?

the MHC class II molecule becomes loaded with the peptide and then transported to the surface of the cell

what describes the cytosolic pathway of cross-presentation?

• DC phagosomes have inserted membrane-spanning pumps that transport degraded proteins into the cytosol

• proteins are diverted to proteasome and resultant peptides into the ER for MHC class I loading

• peptide-loaded MHC class I molecules transported by transport vesicles to the cell surface

what describes the vacuole pathway of cross-presentation?

• MHC class I molecules delivered to the phagosolysosome by a transport vesicle

• peptides are loaded onto MHC class I molecules in the phagolysosome/vesicle and then transported to the cell surface

cross-dressing involves what?

transfer of preformed MHC-peptide from migrating DC to LN resident DC

what describes the inheritance of HLA genes?

maternal and paternal chromosomes each have a set of MHC genes (6 HLA I and 5 HLD II), and both sets of genes are expressed (co-dominant)

mutations that distinguish MHC allotypes are concentrated where?

sites that affect peptide binding and TCR interaction

MHC diversity is a result of what?

natural selection

likely source or driver for mutations involve in MHC/HLA genes is what?

infections caused by pathogens

new variants of HLA alleles arise through what?

point mutations and several types of recombination events

“non-classical” MHC class Ib molecules are what?

ligands for NK cell receptors

how can nonprotein antigens be recognized by T cells?

CD1 and MHC class 1-related protein MR1 family of nonclassical class I molecules can present lipids, lipid-linked molecules, and for MR1 metabolites of vitamin B2

what describes MHC restriction?

T cells can only respond to Ags presented on MHC from the same host

what determines the type of peptide that each MHC binds?

variation in the peptide-contact residues on the floor and sides of the peptide binding groove