Kinetics and differential expression of heat-stable antigen and GL7 in thenormal and Toxoplasma gondii-infected murine brain

The co-expression of various cell surface molecules by cells of the nervous system and the immune system is a remarkable feature. To identify novel mo lecules that are shared between cells of the neural and hematopoietic linea ge, the expression and regulation of heat-stable antigen (HSA, CD24, nectad rin) and GL7, two hematolymphoid differentiation antigens that are involved in antigen presentation, cell adhesion, signal transduction and activation , was studied in the adult normal and Toxoplasma gondii-infected murine bra in by immunohistochemistry and flow cytometry of isolated cerebral leukocyt es. In the normal brain ependymal cells, plexus macrophages and a fraction of blood vessel endothelial cells were HSA positive (C), whereas the choroi d plexus epithelium was GL7(+). This basal expression of HSA and GL7 was no t further modified on these cell populations in Toxoplasma encephalitis (TE ). In acute and chronic TE, HSA and GL7 were strongly induced on resident b rain cells, and activated astrocytes were the predominant HSA(+) and GL7(+) cell type. FACS analysis additionally identified a minor fraction of HSA() microglia in the normal brain with a small, but significant increase in T E. The differential expression pattern of HSA and GL7 on distinct resident cell populations in various anatomic compartments of the normal adult brain and their up-regulation in TE may indicate that their intracerebral role i s diverse and may include both immunological as well as non-immunological f unctions.