Human Tumor Antigens and Cancer Immunotherapy

Figure 4

Proteasome subtypes. Mammalian 20S proteasomes are composed four stacked rings of seven subunits each. The two outer rings are made of α-subunits and delimit the entrance of the catalytic chamber. The two inner rings are made of β subunits, three of which (β1, β2, and β5) are catalytically active. In immune cells or upon induction with IFNγ, catalytic subunits β1, β2, and β5 are replaced with their inducible counterparts β1i, β2i, and β5i to form immunoproteasomes. Besides standard and immunoproteasomes, two additional forms of proteasome exist, which contain a mixture of standard and immune catalytic subunits, as indicated. The processing ability of these four types of proteasomes was studied for the indicated peptides (lower part of the figure). ++: efficiently produced, : slightly produced, and −: not produced.