Kurt D. Ackerman

Noradrenergic Sympathetic Neural Interactions with the Immune System: Structure and Function

Histochemical studies from our (Williams & Felten 1981, Williams et al. 1981, D. Felten et al. 1981, 1984, 1985, 1987a, 1987b, Livnat et al. 1985, Ackerman et al. 1986, S. Felten et al. 1987) and other laboratories (Giron et al. 1980, Bulloch & Pomeranz, 1984, Singh 1984, Walcott & MacLean 1985) have shown the presence of autonomic nerve fibers in specific compartments of both primary and secondary lymphoid organs. These nerve fibers are associated not only with blood vessels but also with lymphocytes and macrophages. We have demonstrated that the neurotransmitter norepinephrine (NE), present in the postganglionic sympathetic fibers that richly innervate lymphoid organs, acts in the spleen as both a paracrine secretion, available to receptors on cells in the white pulp, and a localized neurotransmitter in nerve terminals that directly contact T lymphocytes in the periarteriolar lymphatic sheath (PALS) (S. Felten et al. 1986, S. Felten & Olschowka 1987). We propose that NE in lymphoid organs fulfills the criteria for neurotransmission, estabUshed in more traditional efTector tissues such as the heart, and plays a role in the modulation of immune responses. This review summarizes evidence for neurotransmission, including presence and compartmentation of NE, transmitter release, post-synaptic receptors on cells of the immune system, and functional consequences of denervation and pharmacological manipulation of NE. We also review aspects of development, aging, and plasticity of noradrenergic (NA) fibers that enhance our understanding of their role in organs of the immune system.

Ontogeny and Senescence of Noradrenergic Innervation of the Rodent Thymus and Spleen

Publisher Summary This chapter explores the ontogeny, maturation, and senescence of noradrenergic (NA) sympathetic neurotransmission in two lymphoid organs. Noradrenergic sympathetic nerves provide an anatomical link between the nervous and immune systems throughout the life span of the host. Developmental and age-related changes in NA neurotransmission are complex and continuous, varying with each organ of the immune system. In the rat thymus, a primary lymphoid organ, NA innervation was predominantly vascular during early development, and peak density of innervation was not achieved until after thymic involution. The chapter presents a study in which NA innervation was maintained in some aged rodents and increased in density in the thymus as a result of thymic involution. In contrast, NA innervation of spleen and lymph nodes declined with age, in parallel with a loss of lymphocytes and macrophages from these organs. Noradrenergic neurotransmission is dependent not only on the presence of nerve fibers in appropriate compartments of target organs but also on the rate of release of transmitter, the concentration of transmitter in the vicinity of target cells, the presence of functional receptors, and the ability of target cells to respond to NA signals.

Parallel development of noradrenergic innervation and cellular compartmentation in the rat spleen

By combining neurochemical measurement of norepinephrine (NE) with double-label immunocytochemistry for tyrosine hydroxylase-positive (TH+) noradrenergic nerves and specific lymphoid markers, we have examined the developmental compartmentation of noradrenergic nerves in the rat spleen. TH+ nerve fibers were present in the white pulp of the spleen at birth, among surface IgM-positive (sIgM+) B lymphocytes at the outer border of the periarteriolar lymphatic sheath (PALS), distant from the central artery. During the first 7 days, noradrenergic innervation developed rapidly, forming plexuses of nerve fibers along the central artery and its branches, among T and B lymphocytes of the PALS, and along the developing marginal sinus where ED3+ macrophages accumulate. The splenic concentration of NE (per mg wet wt.) and 3-methoxy-4-hydroxy-phenetheleneglycol (MHPG), a NE metabolite, increased rapidly during this period, suggesting that NE is available and released from these nerves. From 7-14 days, the white pulp expanded to include an inner PALS, outer PALS, marginal sinus, and marginal zone; during this period, TH+ fibers arborized principally among T lymphocytes of the inner PALS and adjacent to macrophages along the marginal sinus. By 14 days of age, NE concentration reached adult levels, although the MHPG/NE ratio (an index of NE turnover) remained higher throughout development than in adulthood. Finally, from 14-28 days, the outer PALS expanded to include follicles containing sIgM+ B lymphocytes. At the earliest stages of follicular development, a parafollicular rim of noradrenergic fibers was present, providing occasional branches which arborized within the follicle. No further changes were observed in either noradrenergic innervation or cellular compartmentation after 28 days of age. These findings suggest that noradrenergic fibers are present in developing compartments of the spleen at the earliest stages of their development, providing norepinephrine for interaction with a variety of adrenoceptor-bearing lymphoid and nonlymphoid cells.

A longitudinal study of age-related loss of noradrenergic nerves and lymphoid cells in the rat spleen

A longitudinal study of sympathetic noradrenergic (NA) innervation of the spleen was carried out in 3-, 8-, 12-, 17-, 21-, and 27-month-old Fischer 344 (F344) rats using (i) fluorescence histochemistry for localization of norepinephrine (NE); (ii) immunocytochemistry (ICC) for localization of tyrosine hydroxylase (TH)-positive nerve fibers alone, and in combination with specific markers for T and B lymphocytes (OX19 and anti-mu respectively), and macrophages (ED3); and (iii) high-performance liquid chromatography with electrochemical detection for quantitation of NE. Fluorescence histochemistry revealed extensive loss of NA nerve fibers in all compartments of the spleen in 21- and 27-month-old rats. With single-label ICC, a decline in TH+ nerve fibers in all compartments of the spleen was observed by 17 months of age and became more severe with advancing age; these findings suggest that both the rate-limiting enzyme and the transmitter itself (NE) are depleted from sympathetic nerves in aged rat spleen. Double-label ICC demonstrated the loss of TH+ nerve fibers in spleen from 17-, 21-, and 27-month-old rats, and a parallel loss of OX19+ T lymphocytes and ED3+ macrophages in these cellular compartments. Neurochemical measurement of NE demonstrated a decline in NE per wet weight at 27 months of age. The age-related decline in NA innervation of spleen and in the density of specific populations of cells of the immune system (T lymphocytes and antigen-presenting ED3+ macrophages), that follow remarkably similar time courses, supports functional evidence for dynamic interactions between the immune system and NA sympathetic nerves in the spleen, and further suggests a causal relationship between these age-related phenomena, i.e., that age-related immunosenescence promotes sympathetic denervation of the spleen which further compromises immune function. This hypothesis, however, requires further testing.

Neonatal sympathetic denervation alters the development of in vitro spleen cell proliferation and differentiation

The ontogeny of spleen cell proliferation to T and B cell mitogens and immunoglobulin secretion, measured in vitro, was examined in neonatally sympathectomized Fischer 344 (F344) rats, administered the neurotoxic drug 6-hydroxydopamine (6-OHDA) from 1 to 3 days of age. Compared to cells from age-matched controls, spleen cells from neonatally sympathectomized animals, aged 7-14 days, exhibited a shift in the proliferative response to the T cell mitogen, concanavalin A (Con A), with reduced proliferation in the presence of low doses of Con A, but increased proliferation with higher doses. During the same period, from 7 to 14 days, the B cell mitogen STM/DxS inhibited proliferation by spleen cells from all rats, and no effect of sympathectomy was observed. As adult-like patterns of mitogen responsiveness emerged from 21 to 42 days of age, neonatally sympathectomized rats showed reduced proliferative responses of both T and B cells. This effect dissipated by 56 days of age. Polyclonal immunoglobulin (Ig) production by B cells was assessed in vitro in the presence or absence of STM/DxS. Neonatal sympathectomy resulted in reduced spontaneous IgM production throughout development. From 28 to 42 days of age, when mitogen-triggered IgM secretion first developed, neonatal sympathectomy decreased the magnitude of the response. By 56 days of age, mitogen-induced IgM secretion was no longer affected by sympathectomy, similar to the proliferative response. Gender influenced the time course of sympathectomy-induced changes in spleen cell proliferation and differentiation; however, the magnitude and direction of these changes were similar in both males and females. Desipramine, administered prior to 6-OHDA, prevented both sympathetic denervation and the 6-OHDA-induced changes in spleen cell responsiveness. This indicates that the alterations in immune function were dependent on NA nerve fiber destruction and were not simply the result of direct 6-OHDA action on other cells. The results of this study suggest that sympathetic innervation may play an important potentiating role in the development of the lymphoid system, through effects on lymphocyte proliferation and differentiation.

Noradrenergic Sympathetic Innervation of Spleen and Lymph Nodes in Relation to Specific Cellular Compartments

Noradrenergic (NE) sympathetic nerve fibers abundantly innervate both the vasculature and parenchyma of primary and secondary lymphoid organs. This innervation is compartmentalized in specific zones of the lymphoid organs. The present study reports simultaneous localization of markers for both NE nerves and specific cell types in rat spleen and lymph nodes (LNs). In spleen, NE nerves distribute in the white pulp in the periarteriolar lymphatic sheath (PALS), the parafollicular zone, and the marginal zone, and travel adjacent to lymphocytes, macrophages, and other cells in these regions. In LNs, NE nerves distribute in the subcapsular cortical and the paracortical zones, the parafollicular zone, and the medullary cords adjacent to the sinuses, and travel adjacent to lymphocytes, macrophages, and other cells in these regions. We review evidence that NE in secondary lymphoid organs fulfills the criteria for neurotransmission of presence, availability, interaction with “postsynaptic” receptors on immune cells, and modulation of immune responses, suggesting that this neurotransmitter may act as in immunomodulator. We further suggest that this abundant innervation of lymphoid organs by NE autonomic nerves provides an anatomical, physiological, and neurochemical basis for interactions between the nervous and immune systems.