Receptor activity on some mesenchymal cells in CNS of normal rabbits. Indications of the monocytic origin of intracerebral perivascular cells, epiplexus cells and mononuclear phagocytes in the subarachnoid space.

The surface receptor activity for various cell types within rabbit CNS was investigated. Sheep red blood cells (E) used as markers were washed, sensitized with the IgG-fraction of E-antibodies (EA) or additionally coated with complement (EAC) and incubated with CNS cells. The inhibitory effect produced by the addition of soluble IgG was investigated. Incubation (1 h) with red cells was undertaken in three ways: 1. Rabbit leptomeninx was stripped and incubated. 2. Rabbits were killed, the brain was perfused with warm buffer and red cell complexes were then injected intracerebrally, intrathecally and intraventricularly into the perfused brains. 3. E, EA and EAC were injected intracerebrally, intrathecally and intra-ventricularly into living rabbits. Using these methods, receptor sites for IgG and complement of mononuclear cells from the subarachnoid space, epiplexus cells and perivascular cells from intracerebral vessels could be demonstrated. In other areas of the body, these receptors have been demonstrated using similar methods only on cells from the monocyte-macrophage series. The common derivation of these three cell types from the monocytes as well as their comparable function within the immune response is discussed.