Immune Regulation by Various Facets of Histamine in Immunomodulation and Allergic Disorders

Histamine has tremendous biological role, mediated by four types of histamine receptors (H1R–H4R) on secretion by effector cells (mast cells and basophils) through various immunological and non-immunological stimuli. Their patho-physiological implication in all facets of biomedical areas have been reported extensively. It shows proinflammatory or anti-inflammatory effects, depending on the predominance of the types of histamine receptors. It had proinflammatory activity through the H1R, and is involved in the development of various aspects of antigen-specific immune response including the maturation of dendritic cells and the modulation of the balance of type 1 helper (Th1) T cells and type 2 helper (Th2) T cells. Histamine blocks humoral immune responses by means of a specific mechanism in which it induces an increase in the proliferation of Th1 cells and in the production of interferon-γ. Histamine stimulates the release of proinflammatory cytokines and lysosomal enzymes from human macrophages and shows the capacity to influence the activity of immune cells including mast cells, basophils, eosinophils, fibroblasts, lymphocytes, neutrophils, epithelial and endothelial cells, and plays a pivotal role in allergic inflammation which is a complex network of cellular events and involves redundant mediators and signals. In this chapter, we tried to elaborate the newer discoveries of histamine H1–H4-receptors in immunomodulation and allergic conditions, and effect of histamine in immune cells with respect to allergic diseases. We hope that this article would stimulate discussions and active research on this important aspect.