Immunization-induced inflammatory infiltration of the central nervous system in transgenic mice expressing a microbial antigen in astrocytes.

Transgenic mice expressing a defined microbial antigen from central nervous system (CNS) cell type-specific promoters can be utilized to investigate the consequences of induction of peripheral immune responses to foreign antigens produced by different CNS cell types. Immunization of mice expressing beta-galactosidase (beta-gal) in astrocytes with this protein resulted in antigen-dependent infiltration of the CNS by mononuclear cells, principally CD4+ T lymphocytes and monocyte/macrophages. The perivascular and intraparenchymal infiltrates, which were located predominantly in the hippocampal formation and cerebellum, the areas of highest beta-gal expression, were associated with astrocytosis, microgliosis, and a generalized increase in blood-brain barrier permeability. The resemblance of these pathological changes to aspects of human immune inflammatory CNS disorders, e.g. multiple sclerosis, suggests that an initiating step in the process by which such complex diseases are produced could be the induction of peripheral immune responses to antigens expressed in astrocytes.