Invariant chain-independent antigen presentation depends primarily upon the pool of newly synthesized MHC class II molecules
Swier, K.; Miller, J.
Journal of Immunology 155(4): 1851-1861
1995
ISSN/ISBN: 0022-1767 PMID: 7636238 Document Number: 440576
During biosynthesis, MHC class II molecules are diverted to endocytic compartments in which they bind antigenic peptides to be displayed on the surfaces of APC. For many Ags, the efficiency of class II presentation is enhanced by the intracellular association of class II with invariant chain (Ii), consistent with a role for newly synthesized class II molecules in Ag presentation. For a subset of Ags, however, efficient presentation does not require Ii. These Ags may also be bound by class II molecules en route to the cell surface. Alternatively, Ii-independent Ag presentation may utilize a pool of preexisting class II molecules that may gain access to endosomes following internalization from the cell surface. To examine the role of newly synthesized class II in the presentation of the Ii-independent Ag, RNase, we placed class II biosynthesis under the translational control of an iron response element. Chelation of iron from the media resulted in efficient diminution of class II synthesis and a marked decrease in the efficiency of RNase presentation. When compared with other cells expressing varying amounts of class II, we found that the ability to present RNase correlates with the level of class II biosynthesis and not with the level of class II surface expression. Because these cells internalize class II at a significant rate, we conclude that even in the absence of Ii, class II molecules can reach endocytic compartments containing antigenic peptides and they do so on their biosynthetic pathway.