Signals from the IL-1 Receptor Homolog, Toll, Can Activate an Immune Response in a Drosophila Hemocyte Cell Line

The Toll gene encodes an interleukin 1 receptor-like protein that mediates dorsoventral polarity in the Drosophila embryo. The possible involvement of Toll or Toll-like proteins also in the Drosophila immune response was investigated by overexpressing Toll 10B, a constitutively active mutant protein, in the Drosophila blood cell line mbn-2. Induction of the Cecropin A1 ( CecA1) gene, coding for a bactericidal peptide, was used as an indicator for the immune response. Toll 10B was found to increase CecA1 transcription, as detected with a cotransfected CecA1-lacZ reporter gene construct. This effect depends on the presence of a κB-like site in the CecA1 promoter. The endogenous Toll gene is expressed in mbn-2 cells, indicating that this gene may normally play a role in Drosophila blood cells.