Contribution of endosomal acidification to antigen processing

The role of endosomes in antigen processing was investigated with mutant cells, expressing a temperature-sensitive defect in endosomal acidification, as a source of antigen-presenting cells for CD4+ T cell responses. When the mutants were incubated at the nonpermissive temperature, their ability to process a variety of native antigens was greatly impaired. These cells could present peptide fragments normally, and the higher temperature did not affect antigen processing by the wild-type parental cells. The mutant cells do not have a defect in the internalization and overall degradation of native antigen. Upon return to the permissive temperature, the mutant cells rapidly recover their ability to process antigen. Therefore, acidified early endosomes have an important function in antigen processing, and other acidified organelles may also be involved.