[Histamine as an immunomodulator]

Histamine in cancer immunology and immunotherapy. Current status and new perspectives

Cancer is the second leading cause of death globally and its incidence and mortality are rapidly increasing worldwide. The dynamic interaction of immune cells and tumor cells determines the clinical outcome of cancer. Immunotherapy comes to the forefront of cancer treatments, resulting in impressive and durable responses but only in a fraction of patients. Thus, understanding the characteristics and profiles of immune cells in the tumor microenvironment (TME) is a necessary step to move forward in the design of new immunomodulatory strategies that can boost the immune system to fight cancer. Histamine produces a complex and fine-tuned regulation of the phenotype and functions of the different immune cells, participating in multiple regulatory responses of the innate and adaptive immunity. Considering the important actions of histamine-producing immune cells in the TME, in this review we first address the most important immunomodulatory roles of histamine and histamine receptors in the context of cancer development and progression. In addition, this review highlights the current progress and foundational developments in the field of cancer immunotherapy in combination with histamine and pharmacological compounds targeting histamine receptors.

TRPV1 and TRPA1 Channels Are Both Involved Downstream of Histamine-Induced Itch

Two histamine receptor subtypes (HR), namely H1R and H4R, are involved in the transmission of histamine-induced itch as key components. Although exact downstream signaling mechanisms are still elusive, transient receptor potential (TRP) ion channels play important roles in the sensation of histaminergic and non-histaminergic itch. The aim of this study was to investigate the involvement of TRPV1 and TRPA1 channels in the transmission of histaminergic itch. The potential of TRPV1 and TRPA1 inhibitors to modulate H1R- and H4R-induced signal transmission was tested in a scratching assay in mice in vivo as well as via Ca²⁺ imaging of murine sensory dorsal root ganglia (DRG) neurons in vitro. TRPV1 inhibition led to a reduction of H1R- and H4R- induced itch, whereas TRPA1 inhibition reduced H4R- but not H1R-induced itch. TRPV1 and TRPA1 inhibition resulted in a reduced Ca²⁺ influx into sensory neurons in vitro. In conclusion, these results indicate that both channels, TRPV1 and TRPA1, are involved in the transmission of histamine-induced pruritus.

H2-antagonist in IgE-mediated type I hypersensitivity reactions: what literature says so far?

Histamine is a monoamine synthesized from the amino acid histidine that is well-known for its role in IgE-mediated anaphylaxis but has shown pleiotropic effects on the immune system, especially in order to promote inflammatory responses. H₁-receptor antagonist are common drugs used in mild/moderate allergic reactions whereas H₂-receptor antagonist are commonly administered in gastric ulcer but showed some properties in allergy too. The EAACI guidelines for diagnosis and treatment of anaphylactic reactions recommend their use as third-line therapy in adjunct to H₁-antagonists. The purpose of this article is to produce a complete summary of findings and evidence known so far about the usefulness of H₂-receptor antagonist in allergic reactons.

Impact of histamine H4 receptor deficiency on the modulation of T cells in a murine breast cancer model

BACKGROUND

The histamine H4 receptor (H4R) is preferentially expressed in immune cells and is a potential therapeutic target for inflammatory and autoimmune diseases. This study aimed at further exploring the role of H4R in the immunobiology of breast cancer.

METHODS

We used wild type (WT) and H4R deficient mice (KO) to evaluate whether H4R genotypes show a different distribution of T cell subsets in spleens, tumours and tumour draining lymph nodes (TDLN) in a syngeneic ErbB2-positive breast cancer model developed orthotopically with LM3 cells and its impact on tumour growth.

RESULTS

The presence of tumours had a differential impact on the distribution of T cells in TDLN from KO mice compared to WT ones. At day 21 post-inoculation (p.i.) of cells, despite no significant changes in the tumour weight, TDLN from KO mice showed a significantly increased proportion of CD8⁺ T cells compared to WT mice. At day 38 p.i. of cells a reduced tumour weight was evident in KO mice. This was accompanied by a decreased proportion of CD4⁺CD25⁺FoxP3⁺ regulatory T cells in TDLN of KO compared to WT mice. Tumour-bearing KO mice showed a better survival compared to WT mice.

CONCLUSIONS

H4R-mediated mechanisms may modulate the immune tumour microenvironment, promoting an immunosuppressive milieu. Results suggest that H4R could be explored as an immunotherapeutic target with potential benefit in combination with immunotherapy. Further preclinical and clinical studies are necessary to confirm this hypothesis.