Biology of neurotensin: revisited study

The tridecapeptide neurotensin (NT) acts in the mammalian brain as a primary neurotransmitter or neuromodulator of classical neurotransmitters. Morphological and functional in vitro and in vivo studies have demonstrated the existence of close interactions between NT and dopamine both in limbic and in striatal brain regions. Additionally, biochemical and neurochemical evidence indicates that in these brain regions NT also plays a crucial role in the regulation of the aminoacidergic signalling. Immune cells, such as lymphocytes, macrophages and mast cells are reported to be activated by neuropeptides, such as neurotensin; this activation leads to cytokine and immunoglobulin production. In addition, neurotensin increases calcium level and the production of nitric oxide. Therefore neurotensin is deeply involved in immunity and inflammation but its real function still remains to be elucidated.

Mast cells and chemokines

Chemokines are small proteins (8-12 kD polypeptides) secreted by the cells of innate and adaptive immunity that mediate many of the functions of these cells, including recruitment of other cells. They are classified into families: CC, CXC and CX3C. CXC chemoattract mainly on neutrophils and CC act mainly on monocytes, eosinophils and mast cells. Mast cells are important cells in the modulation of allergic and inflammatory diseases. Activation of mast cells with specific IgE antibody and antigens or other active compounds such as Substance P and corticotrophin releasing hormone causes transcription and translation of several different cytokines/chemokines such as tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-1 (MIP-1) and GM-CSF, RANTES, MCP-1, CXCL8, along with other proinflammatory compounds, proteases (chymase and tryptase), histamine, leukotrienes and prostaglandin D2. Neutralization of chemokines may reduce inflammatory cell accumulation and may protect against allergy, toxic shock syndrome and inflammatory diseases.

Impact of substance P on cellular immunity

Much evidence suggests a cross-talking between nerve fibers and the immunity system. The immunomodulation by substance P includes cell activation and proliferation of human cells, with cytokine and chemokine generation and release. Substance P was first isolated by Leeman et al. as an undecapeptide with important neurotransmitter-neuromodulator effects. In addition, substance P was shown to induce and mediate inflammation, angiogenesis, infections, intestinal mucosal immunity and stress. Substance P is able to activate several immune cells, such as CD4+ and CD8+ T lymphocytes, mast cells, NK cells and macrophages. In recent studies we have shown that substance P can activate interleukin-8, a CXC chemokine, demonstrating its involvement in immune cell chemoattraction. We believe that substance P is important in understanding the pathophysiology of inflammation.