Well it's a pleasure to be here and I thank the organizers for inviting me. One of the aspects that we've heard is that there are a number of cells and mediators that conceivably play a role in allergic inflammation and asthma. And one of the hard parts is to try and understand what is going on in various models of disease and particularly the hereditarity of the disease. What I'd like to do this morning is to focus on a single mediator an old mediator, and that is histamine and to see some of the actions of histamine in allergic inflammation. The question I'd like to address with you this morning is, "Is there a basis for histamine driven physiology in asthma"? I think all of you are well aware of terms of histamine and the implication of the role of histamine in both the early and late phase. In the early theories histamine is clearly implicated as a result from a number of cells that infiltrate the acute phase of the response but there also is accumulating evidence that histamine may also play a role in the late phase of the response. Well what about the role of antihistamines in asthma? Are there anti-allergic effects that can be expressed by some of the antihistamines? Are there anti-inflammatory properties of some of these drugs? Well, I think that it is abundantly clear from the literature, that histamine does play a role in asthma, more recently it is shown that stage 1 receptors expressed in the lung in asthma, although histamine has limited bronchodilatory effects, it may play a role in decreasing airway hyper responsiveness and I think many of you are aware of the ability of antihistamines to decrease symptoms in seasonal asthma. Furthermore for some of the large multi centered studies, particularly in Europe, antihistamines may delay asthma onset in high-risk allergic infants and they may have additional or synergistic properties with a number of other drugs.

In fact, there are a number of studies that have suggested particularly with other antihistamines such as terfenadine, that the use of terfenadine can in fact have some effects in various forms of asthma. And you can see on this slide, that the use in this case of terfenadine can decrease symptoms, may decrease nighttime awakening, may decrease reason, one of the aspects that comes clearly in any of the literature, is that the differences that are often used to exhibit these effects may be higher than are conventionally used in the treatment for example of rhinitis. Furthermore, I think all of us are still in search of one drug that can target both the upper and lower airways. I was always intrigued with the poll we heard recently, that the name we should use is United Airways disease, but I didn't find any frequent flier points, so I like one airway, one disease better. Well what I would like to address are three particular points, in terms of considering the role of histamine in asthma. One is, is histamine a mediator of asthma? Secondly, are histamine effects in asthma mediated through H1 receptors, and I think you all are aware now that there are at least 4 subtypes of histamine receptors, cleverly named 1,2,3 and 4. And finally, are there subsets of asthmatic's where histamine may play a more dominant role in the pathophysiology of the disease? Well first and foremost, there are a number of immune inflammatory activities of histamine. Histamine can elicit virtually all of the pathologic processes involved in immediate allergic reactions including vasodilatations, smooth muscle contraction, mucous hypersecretion and edema, many of the features that Dr. Frew just reviewed with you. Secondly, histamine can induce the expression of a number of pivotal adhesion molecules namely E-selectin, ICAM-1 and LFO-1. In various cell types histamine can trigger the production of IL-6 and IL-8 by endothelial cells, IL-1, IL-8, IL-18, interferon gamma by peripheral blood mononuclear cells, IL-10 and macrophages, IL-6 and macrophages, IL-1 beta, IL-6, IL-8 MCP1 in dendritic cells. What about then the anti-inflammatory effects, particularly now with H1 receptor blockers? Well the antihistamines that block the H1 receptor can reduce the expression in release of soluble ICAM-1. In terms of antigen receptor mediated responses, in gene knock out mice an H1 receptors deficient T-cells, their low proliferative responses were a number of signaling lygams, H1 receptor deficient B-cells at low proliferative responses, to B-cell and receptor cross linking and the H1 receptor deficient mice, had very significant decreases in antibody production. In terms of the macrophage IL-6 production and exocytosis can be inhibited by H1 receptor antagonists and dendritic cell expression of accessory molecules and chemokine production can be decreased. This is a study from Johnny Marrone where he looked at stimulation of beta -glucuronidase by histamine in macrophages, a similar graph can be shown if you look at IL-6 release from these macrophages. But, importantly as you can see on this slide, if you look at the effects fexofenadine in this case, you can see that fexofenadine exhibits a very profound inhibitory activity on the release of beta glucuronidase or IL-6 again in a dose dependent fashion. You can see on the bottom line, where nizatidine an H2 receptor antagonist has no effect in this response. Well what I would like to do is move to some studies that we have carried out using an animal model a primary and secondary sensitization. To directly demonstrate the effects of antihistamine on T-cell function. This slide just illustrates the protocol for our primary challenge model and that is the animals are initially sensitized to ovalbumin with adjuvant and later on, on days 26, 27 and 28 they are exposed to inhalation challenge with ovalbumin and then various studies are carried out. Well this graph shows you that in this response, in this response to inhaled methacholine, measuring airway responsiveness, that the treatment of animals with fexofenadine as shown in the red line, markedly inhibits the increases in airway hyper responsiveness in a dose dependent fashion to inhaled methacholine. You can see that animals that are sensitized and challenged developed a marked increase in airway responsiveness to inhaled methacholine and that response is completely attenuated by pre-treatment of the animals with fexofenadine. Surprisingly, if we look at the numbers of eosinophils in the bowel fluid, treatment with fexofenadine had absolutely no effect on the accumulation of the amount of eosinophils in the bowel fluid. If we look at the number of cells in the lung digest, again treatment of the animals had no effect. But, if you look at the number of tissue eosinophils now accumulating in the tissue itself, not in the bowel fluid, treatment with the drug markedly inhibited the accumulation of eosinophils in the tissue. But perhaps more impressively, if you look at the effects on eosinophil-peroxidase you can see that treatment with fexofenadine markedly inhibited the amount of eosinophil-peroxidase released from these eosinophils. As you can see here, fexofenadine had a very significant effect on the release of IL-4 into the bowel fluid, effects on IL-5, and in our minds a very important phenomenon was the normalization of IL-10 levels, a pivotal regulatory molecule, there were no effects as shown on here on interferon gamma. In terms of IgE, the treatments of the animals with fexofenadine had no effect on total IgE in the serum, but in fact if you now look at allergen specific IgE, you can see a 60-70% reduction. Well this just tells us that treatment with the H1 receptor antagonist can have effects on the primary challenge model.

What I'd like to do is now prove that this is in fact due to effects directly on the T-cells. And I apologize for the complexity of the slide and also the fact that I can't point out certain details to you but, I'll try to describe it. And that is the upper part of the panel, the animals are sensitized and challenged as I showed you in the primary challenge model but after the period of challenge, lung digests are prepared, T-cells are then isolated from the lung digests and then adoptively transferred into naive animals in the lower panel who are then exposed to inhalational challenge with ovalbumin and then are ultimately they are assayed. This now shows you that the animals in the upper graph, the animals that received lung digest sols from untreated animals and then exposed to 6 days of ovalbumin challenge developed a marked increase in airway responsiveness to inhaled methacholine. The lower graph shows both the controls but, also if the lung digests were prepared from fexofenadine treated animals, there is no capacity now for those T-cells to induce airway hyper-responsiveness to inhaled methacholine on an allergen challenge.

The bottom 2 panels to the left show that the animals that received T-cells from the fexofenadine treated animals, accumulate far fewer lymphocytes in the bowel fluid and on the right lower panel, far few eosinophils from the fexofenadine treatment. Similarly, if the animals were treated with fexofenadine, adoptive transfer of T-cells did not induce IL-4 in the recipient animals and slightly lowered levels of IL-5 in the recipient animals. Most impressively, as you can see in the middle bar, the orange bar, that sensitization and treatment or sensitization and challenge of donor mice and then T-cells adoptively transferred into naïve recipients are triggered to develop a marked increase in the number of goblet cells. Pre-treatment of these donor mice with fexofenadine markedly decreased the ability to develop goblet cell hyperplasia, as shown on the far right panel. So, it appears that T-cells transferred from fexofenadine treated mice in non-sensitized, but challenged animals significantly reduced airway hyper responsiveness to methacholine challenge, the eosinophils and lymphocytes in the bowel fluid are markedly decreased and finally that IL-4 and IL-5 also are decreased. So is there a role for histamine in asthma? I hope I've been able to convince you that histamine is indeed a mediator of asthma and certainly based on the data illustrated with use of an H1 specific receptor antagonist that we could block many of the histamine mediator effects in asthma that are mediated through these receptors. And finally the issue that is, are there subsets of asthmatics where histamine does indeed play a predominant role? And I think indeed there is a window of opportunity, if you will in considering the role of antihistamines in asthma, both as monotherapy or as a combination therapeutic approach. Many of these studies, both in vitro and in vivo require a dose of an H1 receptor antagonist that tends to exceed the conventional doses used for the treatment of for example allergic rhinitis and we now know that we can really increase the dose with certain of the H1 receptor antagonist without incurring any of the adverse events. Particularly sleepiness and other aspects that may be induced with certain of these compounds, there clearly is in practice an unmet need for a drug that can target both the upper and lower airways, so that perhaps we can consider the use of one of these drugs in the disease states or asthmatic states where histamine does play a predominant role, for example one may be in seasonal versus perennial asthma and importantly in mild or moderate asthma, antihistamines particularly the H1 receptor antagonist may in fact serve the purpose. So in summary, let me conclude by saying I think that there is abundant evidence that histamine can elicit virtually a pile of pathophysiological processes in allergic asthma that H1 receptors play a major role in mediating some of these pathophysiologic processes and importantly that H1 receptors antagonists can indeed antagonize some of these effects.

Thank you very much.