Abstract: Objective:To investigate the relative contributions of dendritic cell(DC)in the development of protective immunity to Listeria monocytogenes(LM).Methods:DC subpopulation and phenotype characteristics during early infection of LM were examined.The BALB/c mice were infected by intravenously injection of 2 105LM.Spleen cell suspension was prepared from the mice sacrificed on days 3,5,7 post infection(p.i.).Diluted homogenates in sterile PBS were plated on LB plates to quantify bacterial load in spleen.The percentages of DC subsets,as well as surface molecule CD80 or CD86 expressed on spleen DC were determined by flow cytometry. Results:The overall number of CD4 -CD8+ 、CD4+CD8- and CD4-CD8- DC in the spleen increased significantly after infection with LM.The increases were approximate 1.5-fold augment in the CD4+DC by day 7,and an approximate 3-fold augment in the CD4-CD8+ and CD4-CD8- DC by day 5.The expression of CD80 and CD86 were significantly increased on days 3-5 p.i.and reached its peak on day 3 p.i.for BALB/c mice.Conclusions:These data provide new insight into the relative abundance and function of distinct CD11c-expressing populations during the early stage of LM infection.