Background: Leukocyte-specific protein 1 (LSP1), is a52-kDa cytoplasmic F-actin binding phosphoprotein expressed in all human andmurine leukocytes as well as in endothelial cells. LSP1 is an importantregulator of actin cytoskeleton remodeling, modulating leukocytes motility. Wepreviously showed that Lsp1-/- micehave an impaired CTL response after antigen exposure. We have also reportedthat Lsp1-/- dendritic cells (DCs)fail to induce a strong CTL response in vivo, with minimal alterations in Tcell compart- ment. In order to study the role of LSP1 in the ability of DCs toinduce immunity, we phenotypically and functionally characterized Lsp1-/- DCs. Methods: Murine bone marrowDCs (BMDCs) from Lsp1-/- and wild-type mice (B6background) were differentiated with Flt3L during 10 days and then stimulatedfor 18h with CpG-ODN. After stimulus, phenotypic maturation was determined byflow cytometry, and MHC I-restricted antigen presentation, was ana- lyzed byincubating DCs with latex beads conjugated to OVA and further incubation withthe H2-Kb-restricted OVAspecific CD8+ T cell hybridoma(B3Z). Results: BMDCs differentiate at similar rates from Lsp1-/- and wt mice, reaching in bothcases 85-90% of CD11c+ cells. After CpG-ODNstimulus, the frequency of CD8+ DCsand pDCs equally raise up to 20% in Lsp1-/- and wt BMDCs. Lsp1-/- BMDCs show similar expression of CD40, CD86 and PDL2but lower of I-Ab than wt BMDCs(p<0,01). Additionally, Lsp1-/- BMDCsproduce less IL-6 and IL-12 after CpG stimulus than wt BMDCs (p<0,05),Finally, although Lsp1-/- andwt BMDCs capture a similar amount of beads, Lsp1-/- BMDCs have difficulty to activate the B3Z hybridomaafter OVA-bead uptake. Conclusions: Lsp1-/- BMDCs have an impaired IL-12 production and a reducedantigen cross- presentation which could be involved in the diminished capacityof Lsp1 CTL response.