Elucidation of MHC class II-restricted antigen processing pathways using influenza virus epitopes
The processing and presentation of antigen is the backbone of an optimal T cell response. This field is generally divided into MHC class I molecules, which are responsible for the presentation of antigenic peptides to CD8+ T cells, and MHC class II molecules that do the same for CD4+ T cells. While much is understood about the pathways comprising this field, there are mechanisms still left uncovered. Herein, we focus on the processing of proteins for loading onto MHCII molecules using influenza A virus as a model system. We concentrate on three epitopes, all restricted to the same murine MHCII molecule, I-Ed. The first is derived from hemagglutinin (HA aa107-119, S1), and is generated in a conventional manner as it requires the harsh environment of the late endosome. The second originates in neuraminidase (NA aa79-93, NA79), and is alternatively processed with proteasome- and TAP- dependence. The last is also from hemagglutinin (HA aa302-313, S3), and can be presented like NA79, or from an exogenous source on recycling MHCII molecules. Using these epitopes, we demonstrate that HA can be transferred on exosomes and act as a source of antigen for S1 presentation in uninfected cells. Most noteworthy was the enhancement of presentation by the receptor-attachment ability of HA on the surface of exosomes. Next, we explore the differential proteolytic requirements of S1 compared to NA79, and illustrate a destructive function for asparaginyl endopeptidase in the processing of NA79. Additional studies aim at dissecting the role of reductases in the degradation of S1. Also, an observed skewing of the influenza CD4+ T cell response towards the disulfide-linked glycoproteins (HA and NA) is discussed. Further, we explain a system developed to identify the subcellular compartments where the aforementioned epitopes are loaded onto MHCII molecules. Finally, a model is suggested whereby exosomes are a more advantageous antigen source compared to free virus particles, and the implications of this research for the advancement of vaccine design and immunotherapeutic treatments are discussed.
Testa, James S., "Elucidation of MHC class II-restricted antigen processing pathways using influenza virus epitopes" (2010). ETD Collection for Thomas Jefferson University. AAI3444354.