Potential effect of the administration of substance P and allergen therapy on immunoglobulin E-mediated allergic reactions in human subjects

Functional, Diagnostic and Therapeutic Aspects of Gastrointestinal Hormones

Gastrointestinal (GI) hormones are essential to many physiologic functions in our body. They have many GI and extra-GI functions. Some of the functions of these hormones, which have GI and extra-GI sources, are still unknown. Specific GI hormones can affect the brain to control food intake, while others can proliferate normal and neoplastic tissue when their receptors are expressed in certain neoplasms. GI hormones also have many diagnostic and therapeutic roles. Physiologic and pathophysiologic aspects as well as the diagnostic and therapeutic values of GI hormones are elaborated in this review.

Substance P downregulates expression of the high affinity IgE receptor (FcepsilonRI) by human mast cells

The effect of the neuropeptide substance P (SP) on human mast cell (MC) phenotype is poorly understood. In this study, SP effects on human MC expression of the high affinity IgE receptor (FcepsilonRI) were characterized. SP downregulated expression of FcepsilonRI mRNA and protein by approximately 50% and in a concentration dependent manner, the effect was partially mediated by engagement of the neurokinin-1 receptor (NK1R) and resulted in reduced mast cell activation. Sensitization of MC with IgE prior to SP exposure protected MC from SP-mediated FcepsilonRI downregulation. SP release may inhibit MC responses to allergens and these results may have implications in neuroinflammatiion and stress.

Immunologically induced histamine release from rat peritoneal mast cells is enhanced by low levels of substance P

Although direct activation of mast cells by high concentrations (>10(-6) M) of substance P is well established, the effect of sub-micromolar concentrations of the neuropeptide on mast cell activation has not been reported. We hence investigated if substance P would modulate immunologic activation of mast cells by studying the effect of the neuropeptide on anti-rat immunologlobulin E antibody (anti-IgE)-induced histamine release from purified rat peritoneal mast cells. We observed that substance P could dose-dependently potentiate anti-IgE-induced histamine release from rat peritoneal mast cells at concentrations (3x10(-9) M to 3x10(-7) M) which alone induced insignificant or low level of histamine release. While the potentiating effect of substance P was not suppressed by any of the non-peptide tachykinin receptor antagonists CP99994 ((2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine), SR48968 ((S)-N-methyl-N-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl) butyl-benzamide) and SR142801 ((S)-(N)-(1-[3-(1-benzoyl-3(3,4-dichlorophenyl)piperidine-3-yl)propyl]-4-phenylpiperidin-4-yl)-N-methyl-acetamide), it was mimicked by compound 48/80 and suppressed by benzalkonium chloride. Hence, substance P enhanced anti-IgE-induced histamine release through a similar receptor-independent mechanism as the direct mast cell activating action of polybasic compounds. Since high concentrations of substance P required for directly activating mast cells may not be achievable physiologically, the enhancing actions of the neuropeptide on the immunologic activation of mast cells may be more clinically relevant in the pathogenesis of various inflammatory conditions.

Rush immunotherapy in a dog with severe ragweed and grass pollen allergy

BACKGROUND

Forty years of study of naturally occurring IgE-mediated allergy in animals is briefly reviewed. These studies provided models for study of bioactive mediators and innovative pharmacologic therapies for IgE-mediated asthma.

OBJECTIVE

Based on our experience with canine allergy we evaluated and treated a dog with severe grass and ragweed allergy whose allergic dermatitis was uncontrolled by H1 blockers and topical corticosteroids. The dog was miserable during the Chicago grass and ragweed pollen seasons.

METHODS

Rush immunotherapy was initiated during the ragweed season of 1997.

RESULTS

Dramatic improvement was seen which persisted through the grass and ragweed seasons of 1998 after maintenance immunotherapy.

CONCLUSION

The case is presented not as a model for canine immunotherapy but as an example of how animal research can be of value to both animals and humans.