Golli–myelin basic proteins delineate the nerve distribution of lymphoid organs

Abstract

The golli–myelin basic proteins (MBPs) have been known to mark the nerve fiber extensions in both the peripheral nervous system (PNS) and the central nervous system. In this paper, we show that the nerve fibers revealed by neurofilament (NF) antibody staining in thymus and spleen, colocalized with golli in the capsular, trabecular (tr), and vasculature (v) systems. In the thymus, the density of these fibers was greater in the medulla than in the cortex. In the spleen, the golli immunoreactive fibers were seen within the capsule (ca), trabeculae, and along the artery tree, as well as the fine nerve fiber networks in the periarteriolar lymphoid sheath (PALS). Golli immunoreactivity appeared to colocalize with ER-TR7, a putative marker of connective tissue in lymphoid organs. However, further examination by Western blot analysis and immunohistochemistry performed on golli “knock out” mice showed that the antigens recognized by these two antibodies were different. The reason for the apparent colocalization of golli and ER-TR7 appears to be due to the close physical association of nerve fibers with connective tissue in these organs. These results suggest that golli immunoreactivity can visualize the distribution of nerve fibers in these lymphoid organs.

Introduction

Among the most potent autoimmunogens are the classic myelin basic proteins (MBPs), which induce experimental autoimmune encephalomyelitis (EAE) in susceptible animals Bernard and Carnegie, 1975, Hashim, 1978. A second family of proteins, called the golli proteins, is also a product of the MBP gene. The relationship of the golli proteins to the classic MBPs are shown in Fig. 1. The golli proteins are closely related to the classic MBPs in that they contain MBP peptide sequences, some of which include the major encephalitogenic epitopes.

The golli proteins are expressed in several cell types in the lymphatic system, and we have recently shown that quantitatively, their major site of expression in the thymus is in T-cells (Feng et al., 2000). However, golli proteins are also expressed in the peripheral nervous system (PNS). Golli immunoreactivity is found in sensory and motor fibers as early as E11 and persists into postnatal life (Landry et al., 1997). Some regions in which golli immunoreactivity has been found include the terminal sensory fibers of the skin, the celiac sympathetic fibers in the kidney, and the enteric neurons of the gut (Landry et al., 1997). The accumulated evidence shows the existence of crosstalk between the nervous system and the immune system. Direct innervation of lymphoid tissues, through the neuroendocrine humoral outflow via the hypothalamic–pituitary–adrenal (HPA), has been known for some time. Fibers of the autonomic nervous system have been shown to innervate both primary (bone marrow, thymus) and secondary (spleen, lymph nodes, gut-associated lymphoid tissue) lymphoid organs Giron et al., 1980, Williams and Felten, 1981, Singh, 1984, Felten et al., 1987, Felten and Felten, 1988. It has been shown that thymic autonomic nerves include both sympathetic and parasympathetic fibers. These nerves include catecholaminergic (Singh, 1984), dopaminergic (Katz et al., 1987), peptidergic (Felten et al., 1985), as well as cholinergic fibers (Fatani et al., 1986).

Because golli proteins appear to be an excellent marker of peripheral nerve fibers, the aims of this study were to determine whether golli immunoreactivity could be used to visualize nerves within the thymus and spleen, and thus to determine further the localization of this autoantigen within these tissues.