Dictionary #3

1. a) Exogenous pathway: Intracellular route taken by antigen that is processed for presentation by MHC class II, typically associate with proteins that are endocytosed.
b) Endogenous pathway: Intracellular route taken by antigen that is processed for presentation by MHC class I, typically associated with proteins generated in the cytosol.

2. Lipid Rafts: Parts of the membrane characterized by highly ordered, detergent-insoluble, sphingolipid- and cholesterol-rich regions. 

3. Periarteriolar lymphoid sheath (PALS): A collar of lymphocytes encasing small arterioles of the spleen.