Resistance to experimental autoimmune encephalomyelitis development in Lewis rats from a conventional animal facility

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the brain and spinal cord that is mediated by CD4+ T lymphocytes specific to myelin components. In this study we compared development of EAE in Lewis rats from two colonies, one kept in pathogen-free conditions (CEMIB colony) and the other (Botucatu colony) kept in a conventional animal facility. Female Lewis rats were immunized with 100 μl of an emulsion containing 50 μg of myelin, associated with incomplete Freund's adjuvant plus Mycobacterium butyricum. Animals were daily evaluated for clinical score and weight. CEMIB colony presented high EAE incidence with clinical scores that varied from three to four along with significant weight losses. A variable disease incidence was observed in the Botucatu colony with clinical scores not higher than one and no weight loss. Immunological and histopathological characteristics were also compared after 20 days of immunization. Significant amounts of IFN-γ , TNF-α and IL-10 were induced by myelin in cultures from CEMIB animals but not from the Botucatu colony. Significantly higher levels of anti-myelin IgG1 were detected in the CEMIB colony. Clear histopathological differences were also found. Cervical spinal cord sections from CEMIB animals showed typical perivascular inflammatory foci whereas samples from the Botucatu colony showed a scanty inflammatory infiltration. Helminths were found in animals from Botucatu colony but not, as expected, in the CEMIB pathogen-free animals. As the animals maintained in a conventional animal facility developed a very discrete clinical, and histopathological EAE in comparison to the rats kept in pathogen-free conditions, we believe that environmental factors such as intestinal parasites could underlie this resistance to EAE development, supporting the applicability of the hygiene hypothesis to EAE.