Up-regulation of surface antigens on epiplexus cells in postnatal rats following intraperitoneal injections of lipopolysaccharide.

Epiplexus cells in postnatal rats exhibited a remarkable up-regulation of major histocompatibility complex class I and II antigen expression after intraperitoneal administration of bacterial lipopolysaccharide; other surface antigens, i.e. complement type 3 receptors and leukocyte common antigens, were also vigorously elevated when compared with those of the corresponding control rats. The immunostaining of epiplexus cells with OX-42, OX-18 and OX-1 for the detection of complement type 3 receptors, major histocompatibility class I and leukocyte common antigens, respectively, was noticeably enhanced with a drastic increase in their numbers. The most significant finding was the upsurge of OX-6-positive epiplexus cells exhibiting major histocompatibility class II antigens, especially in rats receiving two intraperitoneal injections of lipopolysaccharide and killed at the age of 14 days. Immunoelectron microscopy confirmed the above findings and added the fact that the immunoreactive site was confined to the plasma membrane. An interesting feature was the occurrence of OX-6-positive macrophage-like cells in transit across the choroid epithelium. It is concluded from this study that the upsurge of immunopositive epiplexus cells after lipopolysaccharide injections was partly attributed to the infiltration of stromal macrophages which migrated across the epithelium. The up-regulation of major histocompatibility complex class I and II antigen expression on epiplexus cells by lipopolysaccharide would enable them to carry out self-recognizing and antigen-presenting function in the ventricular system.