HLA‐B27 modulates intracellular survival of Salmonella enteritidis in human monocytic cells

Abstract

Human major histocompatibility complex class I allele HLA-B27 is associated with a group of diseases called spondyloarthropathies. In reactive arthritis (ReA), the disease is triggered by certain infections, e.g. gastroenteritis caused by Salmonella. The host/microbe interaction is abnormal in susceptible individuals leading to inefficient elimination of arthritis-triggering bacteria, fragments of them, or both, after the initial infection. Using transfected human monocytic U937 cell lines, we demonstrate that the expression of the HLA-B27 antigen does not influence the uptake of S. enteritidis into U937 cells in vitro. Interestingly, HLA-B27 remarkably impairs the elimination of S. enteritidis within the HLA-B27 transfected U937 cells. The impaired elimination of ReA-triggering microbes by HLA-B27+ monocytes may offer an explanation for the persistence of ReA-triggering microbes in susceptible HLA-B27+ individuals. This modulation of the host/microbe interaction by HLA-B27 may have an important role in the pathogenesis of ReA.

Enhanced intracellular replication of Salmonella enteritidis in HLA–B27–expressing human monocytic cells: Dependency on glutamic acid at position 45 in the B pocket of HLA–B27

“…The U937 cell line expresses the HLA class I alleles A3, A26, B18, B51, Cw1, and Cw3 (22). U937 cells were cotransfected with HLA-B*2705 genomic DNA (B27g) (23), mutated HLA-B*2705 genomic DNA (see below), or HLA-A2 genomic DNA (24) and pSV2neo (to confer resistance to Geneticin [G-418]) by electroporation as described previously (4). For mock transfection, cells were transfected with pSV2neo alone.…”

“…Complementary DNA (cDNA) of HLA-B*2705 (B27cDNA) cloned into the Bam HI site of RSV5neo vector was introduced by using liposomal transfection (4). Mutant forms of HLA-B*2705 were constructed by site-directed mutagenesis (Altered Sites; Promega, Madison, WI) as described previously (7,10,11).…”

“…Cells were diluted to a concentration of 1.0 ϫ 10 6 /ml and seeded in tissue culture flasks (25 cm 2 or 75 cm 2 ; Greiner, Frickenhausen, Germany). The cells were first incubated with 10 ng/ml of phorbol myristate acetate (PMA; Sigma, St. Louis, MO) for 22-24 hours to differentiate them toward more mature macrophagelike cells (4,25). Two hours before infection, the medium was changed to prewarmed RPMI 1640 supplemented with 10% human AB serum (Finnish Red Cross, Helsinki, Finland).…”

“…The cells were then cocultured with S enteritidis at a multiplicity of infection between 6:1 and 15:1. Prior to the infection, S enteritidis was grown for 18 hours at 37°C in a 10-ml LB tube, and then 500 l of the bacterial culture was transferred into a 10-ml LB tube for a further 2 hours to obtain the logarithmic phase of growth (4).…”

“…To elucidate whether the expression of HLA-B27 would alter the function of host cells encountering ReA-triggering bacteria in vitro, we have generated cell line models. Our previous studies demonstrated impaired elimination of Salmonella enteritidis in B27-transfected human monocytic cells and in B27-transfected murine fibroblasts as compared with appropriate controls expressing other HLA class I molecules (4,5).…”