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Histamine release from mast cells of EAE rats by Gi protein-dependent and IgE-dependent pathways
1Department of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Abstract:
We investigated both Gi protein-dependent and IgE-dependent pathways that control release of histamine by PMCs derived from EAE or Complete Freund's Adjuvant (CFA) immunized rats. The number and histamine content of MCs per rat were the same between normal and EAE rats. Activation of Gi pathway by substance P (SP), DSA, 48/80, and mastoparan resulted in a dose-dependent increase in release of histamine by PMCs in normal, EAE-, and CFA-immunized rats. In EAE and CFA rats, however, the induction was decreased by 10-20% compared to normal rats. The histamine release induced by MP was decreased at a concentration of 3 microM, but not at 10 microM in severe active EAE rats. Activation of the IgE pathway by MAM and concanavalin A (Con A) in the presence of phosphatidylserine led to dose-dependent histamine release in normal rats, and a 10-25% lower level of induction was observed in EAE rats. In CFA rats, the induction of histamine release was equivalent to normal rats. There was an increase in intracellular calcium stores following activation of both pathways in normal rats, whereas depletion of calcium stores by ryanodine reduced the level of induction by 48/80 and MP by 9-11% in normal rats. In EAE rats, 48/80, Con A, and MAM induced a smaller increase, but SP and MP induced larger or similar increases in calcium stores compared to normal rats. It was unlikely that the calcium stores of the PMCs from EAE rats were depleted, because MP stimulated calcium movement subsequent to the release of histamine. These results suggested that the Gi pathway may not be correlated to clinical manifestation of EAE, but cold be involved in the inflammatory process, and that the IgE pathway is better associated with clinical symptoms of EAE and may be more directly related to disease outcome.
Insights
The IgE pathway, not the Gi pathway, is linked to EAE clinical symptoms. Histamine release via IgE activation is reduced in EAE rats, suggesting a role in disease outcome.
Area of Science:
- Immunology
- Neuroscience
- Cell Biology
Background:
- Mast cells (MCs) play a crucial role in allergic reactions and inflammation.
- Understanding histamine release pathways is vital for inflammatory disease research.
- Experimental Autoimmune Encephalomyelitis (EAE) is a model for multiple sclerosis.
Purpose of the Study:
- To investigate Gi protein-dependent and IgE-dependent histamine release pathways in rat mast cells.
- To correlate these pathways with the clinical manifestations of EAE.
- To examine the role of intracellular calcium stores in histamine release.
Main Methods:
- Isolated peritoneal mast cells (PMCs) from normal, EAE, and Complete Freund's Adjuvant (CFA) immunized rats.
- Stimulated histamine release using Gi pathway activators (Substance P, 48/80, mastoparan) and IgE pathway activators (MAM, Con A).
- Measured intracellular calcium levels and the effect of calcium depletion.
Main Results:
- Gi pathway activation induced histamine release in all groups, but was slightly reduced in EAE/CFA rats.
- IgE pathway activation showed reduced histamine release (10-25%) in EAE rats compared to normal rats.
- Intracellular calcium dynamics differed between pathways and EAE/normal rats, with IgE pathway more affected in EAE.
Conclusions:
- The Gi pathway's role in EAE inflammation is suggested, but not directly correlated with clinical symptoms.
- The IgE pathway is more strongly associated with EAE clinical symptoms and disease progression.
- Differential regulation of intracellular calcium stores contributes to altered mast cell responses in EAE.