4-1BB Functions As a Survival Factor in Dendritic Cells

Abstract

4-1BB (CD137) is expressed on dendritic cells (DCs) and its biological function has remained largely unresolved. By comparing 4-1BB-intact (4-1BB+/+) and 4-1BB-deficient (4-1BB−/−) DCs, we found that 4-1BB was strongly induced on DCs during the maturation and that DC maturation was normal in the absence of 4-1BB. However, DC survival rate was low in the absence of 4-1BB, which was due to the decreased Bcl-2 and Bcl-xL in 4-1BB−/− DCs compared with 4-1BB+/+ DCs after DC maturation. Consistent with these results, 4-1BB−/− DCs showed an increased turnover rate in steady state and more severely decreased in spleen by injecting LPS compared with 4-1BB+/+ DCs. When OVA-pulsed DCs were adoptively transferred to recipient mice along with OVA-specific CD4+ T cells, 4-1BB−/− DCs did not properly migrate to the T cell zone in lymph nodes and poorly induced proliferation of CD4+ T cells, although both DCs comparably expressed functional CCR7. Eventually, 4-1BB−/− DCs generated a reduced number of OVA-specific memory CD4+ T cells compared with 4-1BB+/+ DCs. To further assess the role of 4-1BB on DC longevity in vivo, 4-1BB+/+ and 4-1BB−/− C57BL/6 were administrated with Propionibacterium acnes that develop liver granuloma by recruiting DCs. Number and size of granuloma were reduced in the absence of 4-1BB, but the inflammatory cytokine level was comparable between the mice, which implied that the granuloma might be reduced due to the decreased longevity of DCs. These results demonstrate that 4-1BB on DCs controls the duration, DC-T interaction, and, therefore, immunogenicity.