Cell-associated ovalbumin is cross-presented much more efficiently than soluble ovalbumin in vivo

To better understand the antigenic requirements for cross-presentation, we compared the in vivo efficiency of presentation of cell-associated vs solub le OVA with the OT-I (CD8) and OT-II (CD4) TCR transgenic lines. Cross-pres entation of cell-associated OVA was very efficient, requiring as little as 21 ng of OVA to activate OT-II cells and 100-fold less to activate OT-I cel ls. In contrast, soluble OVA was presented inefficiently, requiring at leas t 10,000 ng OVA for activation of either T cell subset. Thus, cell-associat ed OVA was presented 500-fold more efficiently than soluble OVA to CD4 T ce lls and 50,000-fold more efficiently to CD8 T cells. These data, which repr esent the first quantitative in vivo analysis of cross-presentation, show t hat cell-associated OVA is very efficiently presented via the class 1 pathw ay.