Membrane events after cross-linking of the chB6 alloantigen (111.42)

Abstract

Abstract Chickens are one of the classic models of vertebrate immunity. We have been interested in the role of the alloantigen chB6 (formerly called BU1) in the development of B cells within the bursa and have presented evidence that chB6 can trigger apoptosis. Furthermore, the pathway that triggers apoptosis is similar to that triggered by FAS, with caspase 8 as an initiator, caspases 9 and 3 as later caspases, and bcl-xl functioning as an inhibitor of apoptosis. We have been unable to demonstrate a steady state association of chB6 and caspase 8 in DT40, so the mechanism of caspase 8 activation remains unclear. Here we show that chB6 localizes in distinct clusters on the surface of DT40 cells, reminiscent of the SPOTS others have described in Fas signaling. These clusters co-localize with cholera toxin labeled lipid rafts and chB6 appears to be internalized by the B cells. Western blots indicate that chB6 is present in both detergent soluble and insoluble membrane fractions on resting DT 40 cells. However, cross-linking chB6 with a secondary antibody shows that chB6 is internalized selectively from detergent insoluble (lipid raft) fractions of the cell membrane. This suggests an active distribution of chB6 in the membrane and an internal trafficking that may be functionally important. This work offers a new insight into the signaling via chB6. This work supported by a grant from the DePaul University Research Council.