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Flashcards in 11/6/12 Deck (27):

function of mhc molecules

present peptides for recognition by TCR


mhc I get peptides from where and how?

intracellular Ag that are digested by protease

peptide transported to ER and loaded onto MHC as it is synthesized/secreted to plasma membrane


mhc II gets peptides from where and how?

protein phagocytosed, degraded into peptides in phagolysosome.

mhc II syn in golgi buds off and fuses with phagolysosome where mhc II binds peptide

transported to plasma membrane


what expresses mhc I

almost all cells except RBC

less-so on neurons


what expresses mhc II


B cells, macrophages, DC, thymic epithelium


implications of mhc I?

problem in cells

i.e. APC infected. Get rid of cell.


implications of mhc II?

problem outside cells

i.e. APC has detected an infection. Don't necessarily get rid of cell


What do t cells do that recognize mhc I?

CD8 T cells are cytotoxic to mhc I presenters


what do t cells do that recognize mhc II?

CD4 t cells help activate APC via cytokines, cell-surface contact mediated stimulation

Also, recognize B cell MHC II (Ab that binds Ag) and help B cell activate


what are the two cells that are cytotoxic?

CD8 T cells
Natural Killer cells


mechanism of cytolysis?

specific recognition

release of lytic granules via cytoplasmic rearrangement and release


what kinds of cells are lysed?

virally infected cells

infected cells with cytoplasmic bacteria

neoplastic cells


what are the two main categories of helper T cells?




Th1 do what?

post-regulatory molecules and cytokine release that help cells do cell-mediated responses


Th2 do what?

help Ab-mediated responses (or humoral responses)


what are the two major cytokines that differentiate?

Th1 -- IFN-gamma --> cell-mediated responses

Th2 -- IL-4 --> Ab-mediated response (also release IL-10 for plasma cell differentiation effect)


what are the choices for B cell development

1. become a plasma cell
2. become a memory b cell


how does B cell become plasma cell

Th2 produces IL-10 and B cell becomes short-lived plasma cell that produces Ab


how does B cell become memory B cell

Th2 cell produces IL-4 and B cell becomes long-lived memory cell


discuss somatic hypermutation during B cell development

during b cell/t cell interaction, b cells modify their DNA for Ab.

in area that encodes the binding site

dependent on activation-induced cytidine deaminas (AID)


discuss affinity maturation in b cell development

select for B cells that express Ab's w/ high affinity for Ag and remove those that do not


discuss isotype switching in b cell maturation

Th2 produce cytokines that induce b cell to change the heavy chain of Ig (maintain same Ag binding site)

DNA recombination


isotype functions

IgM/IgG - trigger complement pathway

IgG - binds Fc receptors on NK cells and triggers antibody-dependent cell-mediated cytotoxicity (ADCC)
-from mother is able to cross placenta

IgA - transported across epithelial surfaces (important for immunity at mucosal surfaces)

IgE - triggers degranulation by Mast cells (allergic responses).


cytokines and their effect

IL-4 (Th2) = promotes IgE (anti-helminth responses and allergy)

IFN-gamma (Th1) = promote IgG sub-classes (cell-mediate responses)


how do T cells take on their specific cytokine production?

DC determine polarization of T cells via its own cytokine production

DC produces IL-12 --> Th1 cytokines by T cell

DC produces low IL-12 --> Th2 cytokines by T cell


how do you favor cytotoxic cell differentiation in adaptive

CD4 Th1 cells can produce IL-2 that help activation CD8 T cells favoring cell-mediated responses.

IL-12 from DC also trigger this


what determines DC IL-12 production?

The nature of the PRR stimulation

Thus, the initial, innate stimulation (type of pathogen) determines the characteristics of the adaptive immune response