In-vitro interactions of Lawsonia intracellularis with cultured enterocytes

Strains of the obligately intracellular bacterium Lawsonia intracellularis, the etiologic agent of porcine proliferative enteropathy, were co-cultured in rat enterocyte cell cultures (IEC-18) and examined ultrastructurally. No regular surface arrays typical of surface or S-layers were visible on any bacterial strain, with or without Triton-X-100 detergent treatment. In separate experiments, there was no difference in the ability of L. intracellularis to attach and enter enterocytes with or without the presence of added bovine plasma fibronectin, or the peptide Arg-Gly-Ser. Interestingly, there was an increase in the invasiveness of L. intracellularis in the presence of the peptide Arg-Gly-Asp (RGD), in a dose-related manner. A reduction was observed in the ability of L. intracellularis to invade enterocytes in the presence of monovalent fragments of IgG monoclonal antibodies to an outer surface component of L. intracellularis. This neutralization showed an antibody concentration-dependent titration effect and was not apparent with co-cultures incorporating control antibodies. The exact nature of ligand and cell receptor interactions for L. intracellularis remain to be determined.