Cell-mediated immunity to myelin basic protein in Lewis rats made unresponsive to experimental allergic encephalomyelitis

Spontaneous recovery of rats from experimental allergic encephalomyelitis is dependent on regulation of the immune system by endogenous adrenal corticosteroids

Lewis rats with experimental allergic encephalomyelitis (EAE), induced either by the subcutaneous injection of guinea pig myelin basic protein (MBP) or by the adoptive transfer of MBP-primed spleen cells, suffer from a single episode of paralysis from which they recover spontaneously. Animals developing EAE were found to have greatly elevated levels of corticosterone in the blood. This endogenous increase in steroid production was accompanied by lymphopenia and depressed delayed-type hypersensitivity responses to OVA, indicating that rats with EAE are immunosuppressed in an antigen-nonspecific fashion. Adrenalectomized rats given subcutaneous implants of corticosterone to maintain basal steroid levels invariably died when EAE was induced. However, if the steroid replacement therapy was adjusted to mimic the hormone levels that were observed in intact rats developing EAE, then the disease followed a nonfatal course closely resembling that seen in the nonadrenalectomized controls. Replacement therapy that achieved serum corticosterone levels slightly higher than those found in intact rats with EAE virtually suppressed the disease completely. It is concluded that endogenous corticosterone release in rats with EAE plays an essential role in the spontaneous recovery that is observed in this condition. However, the subsequent refractory phase that is characteristic of rats that have recovered from EAE induced by active immunization with MBP is not associated with chronically elevated corticosterone levels. This finding is discussed in the light of other data that suggest that unlike the spontaneous recovery, the refractory state has an immunological basis rather than an endocrinological basis.

Application of a radiometric ear assay for studies of adjuvant arthritis in rats

A radioisotopic method, originally developed for measuring the cellular response in delayed hypersensitivity lesions in mice, has been evaluated in adjuvant arthritic rats. Focal accumulation of 5-iodo-2'-deoxyuridine-125I (125IUdR) at a site of antigen challenge (left pinna) was measured and expressed as increased radioactivity in the challenged (left) over the unchallenged (right) ear (L/R ear ratio). Immunologic specificity of the assay was established with anti-lymphocyte globulin (ALG)-treated arthritic rats. ALG significantly inhibited the 125IUdR L/R ear ratio; normal rabbit globulin had no effect on this parameter. A significant negative correlation was observed between the 125IUdR ear ratios and subjective arthritic scores in established adjuvant disease. Certain characteristics of the 125IUdR radiometric ear assay in rats were established in several types of experiments: disappearance of the isotope from blood, whole body irradiation studies in turpentine-injected rats, and cyclophosphamide pretreatment in a sheep erythrocyte antigenic system. The results of this study support the utility of the 125IUdR ear assay to quantify cellular accumulation at a site of antigen challenge in adjuvant arthritic rats and possibly other antigenic systems in this species.