IRF1 and infection: Indeed, in a previous microarray analysis [19], while Irf1 transcript was induced by infection of wild-type MEFs with GRA15-expressing Pru(II) parasites, infection with this strain did not induce Irf1 transcript in p65−/− MEFs, strongly suggesting that induction of IRF1 expression by GRA15 is through the NF-κB p65 transcription factor.