The diverse physiological functions of histamine are mediated through distinct histamine receptors. Mast cells are major producers of histamine, yet effects of histamine on mast cells are currently unclear. The present study shows that histamine induces chemotaxis of mouse mast cells, without affecting mast cell degranulation. Mast cell chemotaxis toward histamine could be blocked by the dual H 3 /H 4 receptor antagonist thioperamide, but not by H 1 or H 2 receptor antagonists. This chemotactic response is mediated by the H 4 receptor, because chemotaxis toward histamine was absent in mast cells derived from H 4 receptor-deficient mice but was detected in H 3 receptor-deficient mast cells. In addition, Northern blot analysis showed the expression of H 4 but not H 3 receptors on mast cells. Activation of H 4 receptors by histamine resulted in calcium mobilization from intracellular calcium stores. Both G␣i/o proteins and phospholipase C (PLC) are involved in histamineinduced calcium mobilization and chemotaxis in mast cells, because these responses were completely inhibited by pertussis toxin and PLC inhibitor 1- [6-[[17␤-3-methoxyestra-1,3,5 (10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122). In summary, histamine was shown to mediate signaling and chemotaxis of mast cells via the H 4 receptor. This mechanism might be responsible for mast cell accumulation in allergic tissues.

Histamine mediates its physiological function through binding to four known histamine receptors. Here, we describe the first selective antagonist of the histamine H 4 receptor, the newest member of the histamine receptor family, and provide evidence that such antagonists have anti-inflammatory activity in vivo.

No abstract

Following the discovery of the human histamine H4 receptor, a high throughput screen of our corporate compound collection identified compound 6 as a potential lead. Investigation of the SAR resulted in the discovery of novel compounds 10e and 10l, which are the first potent and selective histamine H4 receptor antagonists to be described.

In this study we utilized immortalized morphologically and functionally distinct epithelial cell lines from normal human endocervix, ectocervix, and vagina to characterize gonococcal epithelial interactions pertinent to the lower female genital tract. Piliated, but not nonpiliated, N. gonorrhoeae strain F62 variants actively invaded these epithelial cell lines, as demonstrated by an antibiotic protection assay and confocal microscopy. Invasion of these cells by green fluorescent protein-expressing gonococci was characterized by colocalization of gonococci with F actin, which were initially detected 30 min postinfection. In all three cell lines, upregulation of interleukin 8 (IL-8) and IL-6, intercellular adhesion molecule 1 (CD54), and the nonspecific cross-reacting antigen (CD66c) were detected 4 h after infection with piliated and nonpiliated gonococci. Furthermore, stimulation of all three cell lines with gonococcal whole-cell lysates resulted in a similar upregulation of IL-6 and IL-8, confirming that bacterial uptake is not essential for this response. Increased levels of IL-1 were first detected 8 h after infection with gonococci, suggesting that the earlier IL-8 and IL-6 responses were not mediated through the IL-1 signaling pathway. The IL-1 response was limited to cultures infected with piliated gonococci and was more vigorous in the endocervical epithelial cells. The ability of gonococci to stimulate distinct proinflammatory host responses in these morphologically and functionally different compartments of the lower female genital tract may contribute directly to the inflammatory signs and symptoms characteristic of disease caused by N. gonorrhoeae.Cervicovaginal epithelial cells are increasingly recognized as active moderators of both innate and acquired immune functions in the genital tract via the production of a variety of proinflammatory and anti-inflammatory mediators. Increased levels of the cytokines interleukin 1 (IL-1), tumor necrosis factor alpha (TNF-␣), and IL-6 and the chemokines RANTES, MIP-1␣, and MIP-1␤ in cervicovaginal secretions have been associated with human immunodeficiency virus type 1 infection and bacterial vaginosis; however, little is known about the role of locally produced proinflammatory mediators in the pathogenesis of bacterial vaginitis and cervicitis (10). We recently developed three epithelial cell lines from normal human vagina, ectocervix, and endocervix, immortalized by expression of the E6 and E7 genes of human papillomavirus type 16 (8). The morphological and immunocytochemical characteristics of the immortalized lines closely resembled those of their tissues of origin and primary cultures, and all three differed significantly from the HeLa cervical adenocarcinoma cell line, the most commonly used cell line derived from the human female lower genital tract mucosa. The three cell lines constitutively produced distinctive arrays of cytokines (IL-1, IL-6, IL-7, macrophage colony-stimulating factor, and transforming growth factor ␤) and chemokines (IL-8 and RANTES),...

Three series of H(4) receptor ligands, derived from indoly-2-yl-(4-methyl-piperazin-1-yl)-methanones, have been synthesized and their structure-activity relationships evaluated for activity at the H(4) receptor in competitive binding and functional assays. In all cases, substitution of small lipophilic groups in the 4 and 5-positions led to increased activity in a [(3)H]histamine radiolabeled ligand competitive binding assay. In vitro metabolism and initial pharmacokinetic studies were performed on selected compounds leading to the identification of indole 8 and benzimidazole 40 as potent H(4) antagonists with the potential for further development. In addition, both 8 and 40 demonstrated efficacy in in vitro mast cell and eosinophil chemotaxis assays.

No abstract

The histamine H 4 receptor (H 4 R) has been implicated in numerous inflammatory functions. Here it is shown that the receptor can mediate cytokine production from mast cells. Histamine and an H 4 R agonist, JNJ 28610244, induced the production of IL-6 in mouse bone marrow (BM)-derived mast cells. This effect was blocked by two different H 4 R antagonists and was not present in H 4 R-deficient cells. In addition, histamine acting via the H 4 R potentiated LPS-induced IL-6 production. Histamine-induced IL-6 production could be blocked by inhibitors of ERK and phosphoinositide 3-kinase c (PI3Kc) pathways. Furthermore, it was shown that H 4 R activation can induce phosphorylation of ERK, MEK and AKT. H 4 R activation led to a rapid and transient phosphorylation of these kinases, whereas with LPS the activation occurred at later time points. When both histamine and LPS were added, the phosphorylation was evident at 5 min and persisted for at least 60 min suggesting that changes in the kinetics of kinase activation may be one mechanism driving the signaling interaction between the H 4 R and toll-like receptors. These observations suggest that the H 4 R can synergize with other inflammatory signals to potentiate cytokine production and provides mechanistic information on the role of the H 4 R in inflammation.