Induction of Experimental Allergic Encephalomyelitis in Suckling Lewis Rats: Role of Age and Type of Sensitizing Neuroantigen

Abstract

Despite previous reports to the contrary, experimental allergic encephalomyelitis (EAE) can be induced in a variable proportion of suckling Lewis rats after sensitization with neuroantigen-complete Freund's adjuvant (CFA). Three factors have been identified as essential determinants of EAE in suckling animals: a) sensitization via the intracutaneous route, b) age when sensitized, and c) type of neuroantigen injected. For example, animals as young as 4 days of age regularly developed EAE approximately 2 weeks after injection of highly encephalitogenic emulsions of guinea pig spinal cord homogenate-CFA. In contrast, rats as old as 10 days of age injected with soluble syngeneic myelin basic protein (MBP)-CFA developed no evidence of disease whatsoever. Rat spinal cord homogenates and guinea pig MBP gave intermediate results. Further studies revealed two additional features of EAE induced in suckling rats: a) comparatively less response to the injection of supplemental pertussis vaccine,a known EAE accelerating and potentiating adjuvant in adult animals; and b) a striking paucity of monocytes and histiocytes within the inflammatory reactions at intracutaneous injection sites and the focal nervous tissue cellular infiltrates of animals manifesting typical clinical neurologic signs of the disease. Immaturity of host monocyte-macrophage responses, including processing of soluble antigen, may well account for the contrasting capacities of suckling rats to develop EAE after sensitization to whole cord versus soluble MBP.