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Pollen Allergy

Ragweed’s Rule

The Problem Grows

Ragweed eradication seems a long way off. The United States undertook a massive program in the 1950s to get rid of the weed entirely, but the effort proved costly and ineffective. With many cities today banning pesticides and herbicides, ragweed may flourish even more widely, says Cowbrough. This, of course, is bad news for a continent full of hay fever sufferers.

Creticos explains that many consider ragweed pollen to be the most allergenic pollen around. Although a ragweed pollen grain contains about 30 different proteins, a single protein among them, called “Amb a 1,” is responsible for 95 per cent of the grain’s allergenicity. This potent protein appears to activate the immune system’s Th2-type helper T cells in an allergic person. They then cause the persistent nasal inflammation associated with chronic exposure to ragweed.

Even the shape of the pollen grain may have a role in exacerbating allergies, as it looks under a microscope like a medieval mace. The pointy protuberances allow the grain to cling to the mucous membrane while the protein triggers the allergic and often asthmatic response. In the end, however, Creticos says “we just don’t know why ragweed is such a potent allergen, but certainly Amb a 1 is the dominant allergen protein.”

Promising Vaccine On Hold – For Now

Creticos and his colleagues developed a new ragweed vaccine, called AIC, which they reported on in the New England Journal of Medicine in 2006. By chemically attaching a synthetic DNA sequence to the potent Amb a 1 protein, they mobilized a whole new sector of the immune system’s allergic suppression arsenal.

Simply put, this conjugate actually kept the body from recognizing ragweed pollen as an allergen. The ultimate goal?  A vaccine that would be effective for at least two years and require only six weekly injections, rather than today’s standard four to six years of allergy shots.

Unfortunately, clinical development of the vaccine has been rocky. Pharmaceutical manufacturer Dynavax began clinical trials on its version of the vaccine, called Tolamba, but announced last year that it was discontinuing its development.

However, Creticos told Allergic Living that other clinical trials are ongoing and that he is pursuing this area of research with other companies. He remains optimistic the original vaccine concept will prove fruitful. “Obviously, the ability to provide long-term disease remission (or cure), and as importantly, prevention of progression of rhinitis to asthma, are key therapeutic end points in vaccine development,” he said.

In the meantime, until Creticos and his fellow scientists can report some hopeful clinical progress towards a vaccine, millions of ragweed sufferers will just have to accept the smirking weed’s reputation as an unrivaled misery-maker.

First published in Allergic Living magazine; last updated September 2009.
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Allergic Living acknowledges the assistance of the OMDC Magazine Fund, an initative of the Ontario Media Development Cooperation.