Inhibition of antigen-induced cutaneous responses of ponies with insect hypersensitivity by the histamine-1 receptor antagonist chlorpheniramine.

This article investigates how the histamine-1 receptor antagonist chlorpheniramine affects the skin responses in ponies with insect hypersensitivity (allergies), specifically those induced by Culicoides impunctatus antigens. It demonstrates that chlorpheniramine substantially reduces oedema (swelling) and the accumulation of certain white blood cells in response to these allergens.

Background and Objectives

• The research explores how a common antihistamine, known as chlorpheniramine, can inhibit the allergic reactions in ponies suffering from hypersensitivity to insects, specifically the species Culicoides impunctatus.
• The objectives were to assess the ability of chlorpheniramine to control the cutaneous (skin) responses, namely oedema formation (fluid build-up causing swelling), and accumulation of specific types of white blood cells (eosinophils and neutrophils), after exposure to these insect antigens.

Methodology

• The scientists used a whole-body extract of Culicoides impunctatus to induce an allergic reaction in the ponies with a known hypersensitivity to the insect.
• A control group of ponies, without a history of the disease, were also tested for responses to the same antigen.
• In the hypersensitive ponies, chlorpheniramine was locally administered and the responses to histamine and the Culicoides antigen were then observed and recorded after one and eight hours.

Findings

• The Culicoides impunctatus antigen caused a two-phase increase in swelling – once after one hour, and then again after eight hours. This occurred only in the group of ponies with a history of insect hypersensitivity, not in those in the control group.
• Chlorpheniramine was found to completely prevent the swelling response to both histamine and the Culicoides antigen one hour after exposure, in the hypersensitive group of ponies.
• The eight-hour swelling response to the antigen was inhibited by 63 percent using chlorpheniramine.
• Furthermore, chlorpheniramine partially inhibited the accumulation of eosinophils and neutrophils, types of white blood cells usually seen during an allergic response, two hours after exposure to the Culicoides antigen.

Conclusions

• The research concludes that chlorpheniramine is effective in substantially reducing the allergic reactions induced by Culicoides impunctatus in ponies with hypersensitivity to the insect.
• This is indicated by the reduced swelling and the controlled accumulation of specific white blood cells in response to the antigen. The study suggests this drug could have potential to manage insect hypersensitivities in ponies.