BACKGROUND:Class II transactivator (CIITA) is a dominanttranscriptional element, controlling numerous genes in theimmune system. CIITA is expressed in a constitutive pattern inantigen presenting cells although its expression can occur inother cell types. Since the revelation of CIITA, there have beenconsiderable advances toward understanding its role as anactivator of MHC II genes in humans and mice; nonetheless,there is a lack of published data for this gene in other animals suchas chickens. OBJECTIVES: The goals of this study were todetermine the expression of class II transactivator (CIITA) inchicken and analysis of the CIITA gene sequence between fourIranian indigenous chicken ecotypes. METHODS:After securingthe research accuracy and optimization of reaction conditions,cDNA and DNA samples of gene were obtained from fourIranian indigenous chicken ecotypes. The PCR and RT-PCRproducts were sequenced and the data were analyzed bybioinformatics software. RESULTS: Comparison of thesequencing results with the reference sequence of the red junglefowl revealed that these sequences belonged to the predictedCIITA gene. There was a high conservation rate in the sequenceof CIITA. CONCLUSIONS: Our results indicated that like otherspecies, CIITA is transcripted in chickens' immune system cells.Further studies on chickens must be done to reveal CIITAroles inimmune responses of chickens.