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The loss of spleen may lead to fatal bacterial infections. To prevent this, splenic autotransplantation has been performed in humans and experimental animals. However, there is still controversy about the protective function of this procedure. Since innervation plays an important role in splenic function, we investigated whether splenic regenerates are re-innervated, and whether this depends on the donor and host age. Splenic tissue (30 mg) was implanted into the greater omentum of either young (2 days) or old (12 months) rats, from either young or old syngeneic animals. After 3 months of regeneration, the weight of the regenerates was determined, PGP + nerve fibers were revealed by immunohistology, and subdivided into nerve fibers of sympathetic (TH + , NPY + ) or sensory (SP + , CGRP + ) origin. In addition, proliferating (Ki-67 proliferation antigen + ) and apoptotic cells (TUNEL technique + ) were likewise investigated. No innervation of splenic regenerates was observed after implantation into old hosts, correlating with poorly developed splenic compartments. In contrast, almost normal re-innervation occurred in young hosts after implantation of both young and old splenic tissue. These regenerates showed well-developed splenic compartments and a normal number and tissue distribution of proliferating and apoptotic cells. However, after the implantation of young tissue, the final size of splenic regenerates was three times larger (140±30 vs. 40±10 mg). Thus, re-innervation of splenic implants is necessary for their subsequent development. It is determined by host age, whereas the final size of the splenic regenerates is regulated by donor age-dependent factors. This model is useful for studying both the process leading to initial innervation and the consequences of this innervation.

Contact hypersensitivity responsiveness to dinitrofluorobenzene is depressed in mice that are sensitized through skin sites exposed to ultraviolet (UV) radiation. Local impairment of contact hypersensitivity by UV has been associated with a reduction in antigen-presenting cell activity within UV-irradiated skin sites marked by a decrease in the density of Ia-positive epidermal Langerhans cells. Our recent studies have demonstrated that neurogenic mediators (e.g. calcitonin gene-related peptide (CGRP) and nitric oxide (NO) contribute to cutaneous inflammation following exposure of rats to high-dose UV radiation. Since CGRP and NO inhibit antigen presentation by dendritic cells in vitro, we have investigated the possible involvement of CGRP and NO in local immunosuppression in UV-irradiated rodents. Hindpaw skin of Sprague-Dawley rats and back skin of UV-susceptible C57BL/6 mice was exposed to acute UV radiation (2.0 J/cm2 and 0.5 J/cm2, respectively). Alterations in cutaneous CGRP content were analyzed by a specific radioimmunoassay (RIA). In separate experiments, the CGRP receptor antagonist CGRP-(8-37) (10-5 M) and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (2 X 10-5 M) were topically applied to UV-exposed skin before induction of contact hypersensitivity with dinitrofluorobenzene. Finally, we examined the effects of UV irradiation and epicutaneous application of CGRP on Ia-positive Langerhans cells by immunohistochemical analysis of epidermal sheets. It was found that UV exposure lead to a decrease in skin CGRP levels starting already 2 h after irradiation and reaching a minimum (less than 40% of non-irradiated control skin) at 6-12 h. Contact hypersensitivity reactions were significantly suppressed by UV radiation in rat skin (by 51%) and murine skin (by 80%). Topical administration of both CGRP-(8-37) and L-NAME before sensitization restored the capacity to respond to haptens applied to UV-exposed skin. Both UV exposure and topical CGRP reduced the density of Ia-positive epidermal cells. Our data indicate that CGRP may be released from sensory neurons following cutaneous UV irradiation and that CGRP and NO contribute of UV-induced local immunosuppression. Moreover, topical administration of CGRP or its antagonist may be able to modulate epidermal Langerhans cell activity in vivo.

The opioidergic innervation of the mammalian spleen and possible species differences were investigated. Light-microscopic immunohistochemistry revealed that splenic nerves of bovine and porcine spleen, but not of rat, mouse, hamster and guinea-pig spleen contained proenkephalin-derived opioidergic innervation. Immunoreactivity to both prodynorphin and pro-opiomelanocortin was absent from splenic nerves. In bovine and porcine spleen, fibers immunoreactive for met-enkephalin, met-enkephalin-Arg-Phe, met-enkephalin-Arg-Gly-Leu, leu-enkephalin and peptide F formed perivascular plexus, traveled in trabecular connective tissue, and extended into the capsule. Spatial relationships with immune cells were apparent in the white and red pulp, excluding lymphoid follicles. Colocalization of enkephalin immunoreactivity with immunoreactivities for tyrosin hydroxylase, dopamin-beta-hydroxylase, and neuropeptide Y, but not for substance P or calcitonin gene-related peptide were found. Our results provide evidence that opioid expression in splenic innervation is strongly species-dependent and exclusively proenkephalin-derived. Colocalization with marker enzymes of noradrenergic neurons indicates a mainly postganglionic sympathetic origin of proenkephalinergic splenic innervation. Opioidergic perivascular nerves probably control the splenic blood flow. A close interrelationship of opioidergic fibers with immune cells provides the anatomical basis for direct effects of neurally released opioids on splenic immune functions.

Light microscopic immunohistochemistry was employed to elucidate and compare the presence, distribution, and coexistence of various peptides, neuroendocrine markers and enzymes of the catecholamine pathway in nerves supplying lymphoid tissues in a variety of mammalian species. All lymphoid organs and tissues receive innervation by fibers containing dopamine-beta-hydroxylase and/or tyrosine hydroxylase, neural markers like protein gene product 9.5, synaptophysin and neurofilament and a varied spectrum of peptides. The prominent peptides were tachykinins (substance P, neurokinin A), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal polypeptide/peptide histidine isoleucine (VIP/PHI). Opioid innervation was variable. Double immunofluorescence revealed coexistence of tachykinins and CGRP and of tyrosine hydroxylase and NPY. A minor proportion of fibers showed coexistence of NPY and tachykinins and of VIP/PHI and tachykinins. The possible importance of the complex peptidergic innervation of lymphoid tissues in inflammation, allergy, inflammatory pain and psycho-neuro-immuno-endocrine network function is discussed. A special immunomodulatory role of the sensory neurons is suggested.