In an attempt to elucidate which cells in the lung were TUNEL-positive following infection with avian E. coli strains, we infected monolayer cultures of HD11 chicken macrophages with MT78, UEL17, IMT5155 and IMT5104 (Afecal) and analyzed the numbers of bacteria associated with the cells, and caspase-3/7 activation in cell extracts. This evidence concerns the gene CASP3 and infection.