Journal of Neu rocytology 20, 609-624 (1991) i Macrophages in human sensory ganglia: an immunohistochemical and ultrastructural study F. SCARAVILLI*, B. GIOMETTO ~, L. CHIMELLP and E. SINCLAIR Department of Neuropathology, Institute of Neurology, The National Hospital, Queen Square, London WC1, UK Received 28 March 1990; revised 16 November 1990 and 16 January 1991; accepted 23 January 1991 Summary The paper describes the immunohistochemical and ultrastructural features of normal posterior root ganglia in a group of humans aged 1 day to 80 years and compares the findings with those seen in the ganglia of normal rats of various ages, some of which underwent permanent traumatic lesions of the sciatic nerve. In humans, cells with the immunohistochemical reactions of macrophages are present in small number at birth, most of them having an endoneurial position. Subsequently, their number increases and more of them are seen around neurons, where their processes intermingle with those of satellite cells. Ultrastructural studies confirm that, in addition to interstitial cells, a small number of cells in satellite position have features of mesenchymal cells. In this respect, human sensory ganglia differ from those of rodents and this difference may explain why no nodules of Nageotte can be found either in ageing animals or after a permanent damage to the nerve has produced considerable cell loss. Other features observed in human ganglia, but absent in rats, are multiple layers of satellite cells surrounding each neuron and desmosome-like structures between satellite cell processes. Previous studies describing maturation of the satellite-nerve cell complex in animals are confirmed. In addition, the present investigation shows that, in human ganglia, satellite cells acquire a more elaborate structure than in rodents. It is also suggested that mesenchymal cells may play a role in the trophism of nerve cells and their removal after irreversible damage. Introduction The components of the PNS include axons, and Schwann, endothelial and perineurial cells. The latter form a barrier preventing free diffusion of substances of high molecular weight (Olsson & Reese, 1971). The nature of perineurial cells has been the subject of many investigations (Key & Retzius, 1876; Harvey & Burr, 1926; Denny-Brown, 1946; Shanthaveerappa & Bourne, 1962; Thomas & Jones, 1967). Works by Thomas and Bhagat (1978) and Scaravilli (1984) and a more recent study by Bunge and co-workers (1989) suggest that perineurial cells originate from cells with morphological features of fibroblasts. In addition, endoneurial cells with functional and ultrastructural features of macrophages have been described by Arvidson (1977) and their role in nerve regeneration stressed by Beuche and Friede (1986). The existence of resident cells with phagocytic function has been recently confirmed by Stevens and co-workers (1989) using an immunohistochemical approach. Sensory root ganglia are part of the PNS and it is accepted that they comprise the same types of cells mentioned above, together with the sensory neurons (see Lieberman, 1976). The endoneurial space of the ganglia contains fibroblasts and scattered mast cells. Cells identifiable as macrophages have been described (Hamburger & Levi-Montalcini, 1949; Pannese, 1978). Furthermore, Esiri and Reading (1989) have reported that a number of cells in normal human ganglia react with antibodies specific for macrophages. In this paper, human sensory ganglia were exam- ined by immunohistochemistry, light and electron microscopy and compared with those of rats in an attempt to identify and localize macrophages and investigate their relationships with ganglion and satel- lite cells. Material and methods LIGHT MICROSCOPY Human sensory ganglia Sensory ganglia were obtained at post mortem from 14 humans of both sexes, between 1 day and 80 years of age. The interval between death and the removal of the specimen * To whom correspondence should be addressed. *Present address: ClinicaMalattieNervosee MentaliII, Universitgt di Padova, Italy. Present address: Departamentode Patologia, HospitalUniversitarioA. Pedro, Niteroi, RJ, Brazil. 0300-4864/91 $03.00 +.12 9 1991 Chapman and Hall Ltd.