Maternal vaccination with dPNAG protects foals against the intracellular pathogen Rhodococcus equi

Rhodococcus equi is a facultative intracellular pathogenic bacterium that causes a form of pneumonia similar to tuberculosis in foals and immunocompromised humans. A vaccine against R. equi is lacking. We studied the efficacy of maternal vaccination with deacetylated poly-N-acetyl glucosamine (dPNAG) oligosaccharide conjugated to tetanus toxoid to protect foals against R. equi . Pregnant mares (n=9) were randomly assigned to intramuscular injection 6 and 3 weeks prior to foaling with either vaccine (n=5) or saline (n=4). Foals were infected intrabronchially at age 28 days with 1 × 10 6 of a single strain of live, virulent R. equi . Foals were examined twice daily for clinical signs of R. equi pneumonia ( viz ., coughing, tachypnea, dyspnea, temperature u003e103°F), and weekly by thoracic ultrasonography. Blood samples were collected at age 2, 14, 28, 42, 56, and 84 days from all foals to detect antibodies by ELISA against dPNAG and native PNAG in serum and IFNγ production from peripheral blood mononuclear cells (PBMCs). The proportion of foals with pneumonia was significantly (P R. equi antigen was significantly greater (P R. equi and efficacy against R. equi was likely mediated by maternally-transferred antibodies and enhanced CMI responses, and contribute to a growing body of evidence for a key role of antibodies in protecting against intracellular pathogens.