Toxoplasmosis is an infection caused by Toxoplasma gondii.Infection of pigs with T.gondii is a common source of human toxoplasmosis and causes serious economic losses.In vivo:indueed antigen technology (IVIAT) is an effective immunological technique to identify the antigens that a pathogen slpecifically expressed during infection.To discover the genes that are important in Toxoplasma gondii infection of pigs,we employed IVIAT using sera from infected pigs.Fourteen antigens were identified,including microneme protein 11 (MIC11),dense granule protein 5 (GRAS),18 kDa cyclophilin (C: 18),serine proteinase inhibitor (PI),calmodulin (CaM),leucine rich repeat protein (LRRP),D:3:phosphoglycerate dehydrogenase (D3PD),elongation factor 1:gamma (EF 1) and six hypothetical proteins.The increased transcription levels of five (MIC 11,GRA5,C: 18,PI and CaM) of the fourteen molecules identified by IVIAT were confirmed by real:time PCR.The full length or partial proteins encoded by these five genes were expressed in E.coli,and their immunogenicity was confirmed by Western blot analysis with positive porcine sera.Further functional studies were conducted with CaM.Suppression of CaM expression by RNA interference decreased T.gondii taehyzoite cell attachment,invasion and egress but did not influence their replication.The proteins identified in this study are predicted to be involved in cell invasion,ion/protein binding,protein folding,biosynthesis and metabolism.The results of the functional analysis support the hypothesis that CaM contributes to parasite pathogenesis during infection.These results may have significant implications for the discovery of candidate molecules for the development of potential therapies and preventive m easures against toxoplasmosis in pigs.