Immunomodulation by Altered Gastrointestinal Tract Flora

We investigated the role of microbial products from the gastrointestinal tract in the pathogenesis of immunosuppression in critical illness. Rats were gavaged daily for three weeks with killed Staphylococcus epidermidis, Candida, and Pseudomonas--organisms frequently isolated from the upper gastrointestinal tract of the critically ill patient; nonspecific immunity was measured by the delayed-type hypersensitivity (DTH) response. Gavage with either Pseudomonas or Candida resulted in significant suppression of DTH responses, while gavage with S epidermidis produced modest enhancement of DTH. Animals given Pseudomonas demonstrated impaired ability to localize a subcutaneous Staphylococcus aureus challenge and decreased IgM but enhanced anti-Pseudomonas IgA and IgG responses after intraperitoneal immunization. Pulmonary bacterial clearance at seven days was normal. These findings suggest that gut colonization with Candida or Pseudomonas may contribute to impairment of cell-mediated immunity in the critically ill patient.