AbstractThe TLR4 co-receptor CD14 was identified as an IBD candidate gene. Here, its influence on the intestinal barrier was addressed utilizingE. coliNissle (EcN), which induces severe inflammation in germfree TLR4−/−mice. After monoassociation, EcN was detected in spleens and livers of TLR4−/−and CD14−/−but not wildtype mice. Barrier impairment was characterized by increased apoptosis and decreased epithelial junction (EJ) expression and was reversed by TLR2 stimulation in CD14−/−mice. Bone marrow (BM) transplantation revealed contribution of hematopoietic and non-hematopoietic cells towards intestinal homeostasis. EcN inoculated WT mice showed B cell activation, CD14−/−and TLR4−/−mice cytotoxic T cell and impaired B cell responses. The latter was characterized by absence of B cells in TLR4−/−mice, decreased levels of EcN induced immunoglobulins and downregulation of their transporter pIgR. EcN colonization of mice with genetically or antibody induced impaired B cell response resulted in dissemination of EcN and downregulation of EJ. BM chimeras indicated that CD14 originating from radiation resistant cells is sufficient to restore EJ-function. Overall, CD14/TLR4 signalling seems to be critical for intestinal barrier function and for the crosstalk between B cells and the epithelium, underlining that CD14 serves as a protective modulator of intestinal homeostasis.