Restricted secretion of a T-lymphocyte chemotactic cytokine by serotonin-stimulated cultured aortic endothelial cells

Endothelial cell nitric oxide production in acute chest syndrome

Acute chest syndrome (ACS) is the most common form of acute pulmonary disease associated with sickle cell disease. To investigate the possibility that alterations in endothelial cell (EC) production and metabolism of nitric oxide (NO) products might be contributory, we measured NO products from cultured pulmonary EC exposed to red blood cells and/or plasma from sickle cell patients during crisis. Exposure to plasma from patients with ACS caused a 5- to 10-fold increase in S-nitrosothiol (RSNO) and a 7- to 14-fold increase in total nitrogen oxide (NO(x)) production by both pulmonary arterial and microvascular EC. Increases occurred within 2 h of exposure to plasma in a concentration-dependent manner and were associated with increases in endothelial nitric oxide synthase (eNOS) protein and eNOS enzymatic activity, but not with changes in nitric oxide synthase (NOS) III or NOS II transcripts, inducible NOS (iNOS) protein nor iNOS enzymatic activity. RSNO and NO(x) increased whether plasma was obtained from patients with ACS or other forms of vasoocclusive crisis. Furthermore, an oxidative state occurred and oxidative metabolites of NO, particularly peroxynitrite, were produced. These findings suggest that altered NO production and metabolism to damaging oxidative molecules contribute to the pathogenesis of ACS.

Role of serotonin in the immune system and in neuroimmune interactions

Serotonin (5-HT) is one of the most extensively studied neurotransmitters of the central nervous system. 5-HT is, however, also present in a variety of peripheral tissues including in constituents of the immune system. The function of 5-HT in the immune system has received increasing attention since about 1984, but has been reviewed only once, in 1985. In recent years, modern techniques of molecular biology such as reverse-transcriptase polymerase chain reaction and targeted gene disruption have made it possible to study new important aspects of 5-HT in the immune system. In the first part of the review, we explore whether 5-HT is involved in interactions between the central nervous and immune systems. It emerges that 5-HT may mediate interactions of these two systems by four different pathways. In the second part, we dissect the functional roles of 5-HT in the immune system. We describe the distribution of 5-HT receptors and the 5-HT transporter on immune cells and estimate which levels 5-HT may attain in the extracellular space in physiological conditions and under pathological circumstances such as inflammation, thrombosis, and ischemia. At these 5-HT concentrations, four major functions for 5-HT emerge. These include T cell and natural killer cell activation, delayed-type hypersensitivity responses, production of chemotactic factors, and natural immunity delivered by macrophages. Finally, we discuss promising future avenues to further advance knowledge of the role of 5-HT in the immune system and in neuroimmune interactions.

Perforin-secreting killer cell infiltration in the aortic tissue of patients with atherosclerotic aortic aneurysm

Cell-mediated immunity has been implicated in the pathogenesis of vascular cell injury in patients with atherosclerotic aortic aneurysms. To clarify the immunologic mechanisms involved, we examined the expression of a cytolytic factor, perforin, in infiltrating cells from aortic tissue samples taken from 6 patients with atherosclerotic aortic aneurysms. Immunohistochemical studies showed that the infiltrating cells consisted mainly of macrophages, natural killer (NK) cells, cytotoxic T lymphocytes (CTLs), and T helper cells, and that perforin was expressed in NK cells and CTLs. Immunoelectron microscopic studies demonstrated that the infiltrating cells released massive amounts of perforin directly on to the surface of arterial vascular cells. These findings provide the first direct evidence that some of the infiltrating cells in the aortic tissue consist of killer cells, and strongly suggest that these killer cells, especially NK cells and CTLs, may play a critical role in the vascular cell injury caused by atherosclerotic aortic aneurysm by releasing perforin.

Serotonin involvement in the antitumour and host effects of flavone-8-acetic acid and 5,6-dimethylxanthenone-4-acetic acid

The relationship of serotonin (5-HT) receptors to the action of the experimental antitumour drugs flavone-8-acetic acid (FAA) and 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA) was studied. Both FAA and 5,6-MeXAA are known to induce the synthesis of tumour necrosis factor-alpha (TNF) and to stimulate nitric oxide synthesis in vivo, as measured by elevation of plasma nitrate. Serotonin potentiated the effect of a subtherapeutic dose of 5,6-MeXAA (20 mg/kg) as measured both by plasma nitrate increase and by growth delay of s.c. implanted colon 38 tumours. On the other hand, administration of the serotonin 5-hydroxytryptamine-2 (5-HT2) antagonist cyproheptadine (20 mg/kg) inhibited both the plasma nitrate response and, to a lesser extent, the induction of tumour haemorrhagic necrosis by 5,6-MeXAA, FAA and TNF. Reduction of circulating plasma serotonin by pre-treatment with p-chlorophenylalanine and reserpine reduced the plasma nitrate response, but not the tumour necrosis response, to 5,6-MeXAA (30 mg/kg). It is suggested that serotonin is necessary for the induction of nitric oxide synthases and acts, either directly or indirectly, in concert with TNF. Serotonin agonists may have utility in increasing nitric oxide synthesis in response to TNF or to agents that induce TNF as part of their antitumour action.