The quest to fend off cat allergies

This exercise is a part of Educator Guide: How to Lick Cat Allergies / View Guide

Directions for teachers: After your students read “How to lick cat allergies,” ask them to answer the following questions.

1. How many people are allergic to cats? How does that compare to the number of people with airborne allergens?

Approximately 10 to 20 percent of people are allergic to cats. By some estimates three times that number, up to 30 percent, have airborne allergies.

2. What protein triggers cat allergies in people? What genes are responsible for making the protein?

Two genes, Ch1 and Ch2, make the Fel d1 protein, the main culprit in cat allergies.

3. Do scientists know the protein’s role in cats? What evidence do scientists have that might suggest a possible function of the protein?

Scientists don’t know what Fel d1 does in cats. Evidence from unneutered male cats and similarity to other molecules suggests the protein may be a pheromone, a chemical that cats use to communicate through scent.

4. What does finding a version of the protein in lions indicate to scientists about its importance?

Lions and other big cats have versions of Fel d1 as well, suggesting it stuck around through cat evolution and so may be important.

5. Describe one approach currently used to treat people who are allergic to cats. What are some drawbacks of the treatment?

One treatment for cat allergies is desensitization therapy, which trains a person’s immune system to be less sensitive to allergens by slowly introducing small amounts of allergens. The treatment can require a lot of time and money, and doesn’t provide permanent relief for all symptoms.

6. Describe one approach to treat people who are allergic to cats that is still in testing. What are the advantages and drawbacks of that potential approach? 

Some researchers are testing a cat vaccine that uses a virus fragment coated in Fel d1 to trick a cat’s immune system into thinking that Fel d1 is an invader. The cat’s immune system then makes antibodies that bind to the protein, rendering Fel d1 invisible to human immune systems. The advantages are that humans don’t have to get shots to prevent their allergies and the vaccine doesn’t seem to harm cats, but the approach doesn’t eliminate all Fel d1.

7. Based on the graph titled “Cat food’s effects on allergen levels,” what is the baseline level of active Fel d1 in cat fur (be sure to include units and define “baseline” levels in your answer)? What does early evidence suggest about a treatment approach that relies on cat food? 

The graph shows that the baseline level was about 220 micrograms of active Fel d1 per gram of cat fur. All levels of active Fel d1 in the fur of cats that ate the experimental food over 10 weeks dropped below baseline levels. In some weeks, the level of active Fel d1 was one-third baseline levels. In theory, that should calm symptoms of people with mild to moderate allergies. 

8. What does the graph titled “Total nasal symptom score” show (be sure to define the x- and y-axes and their units)? How does the experimental allergy shot compare with the placebo at 29 days after the injection (be sure to explain what a negative percentage indicates)?

The graph shows data from an experiment testing the effectiveness of injections of a Fel d1-binding antibody at reducing nasal symptoms in people with cat allergies versus a placebo shot. The y-axis shows the average percent change in nasal symptom scores from baseline, and the x-axis shows time, measured in days. On day 29, people who received an injection of the antibody saw their nasal symptoms decrease by up to 60 percent. Comparatively, people who received the placebo shot saw about a 30 percent reduction of their nasal symptoms after 29 days. Negative percentages are used to indicate that nasal symptoms have decreased relative to the baseline symptom levels. 

9. What does it mean for a cat to be hypoallergenic? Why is this a goal for some researchers?

Cats that are hypoallergenic produce very little to no Fel d1 protein. Breeding such a cat is a goal because some people may not be able to tolerate even small amounts of Fel d1.

10. Why does breeder Tom Lundberg advise people who need low-allergen cats to get potential pets tested and meet them in person?

Even with two low-allergen cats as parents, there’s no guarantee that a kitten will be hypoallergenic — not all kittens in a litter will end up with Fel d1 levels. The only way to determine a cat’s hypoallergenic status is to test its protein levels, and the only way to be sure how a person with allergies will react to a specific cat is to meet it in person.

11. What tool is Indoor Biotechnologies using to eliminate Fel d1 in cats and how does it work? Do researchers know whether the approach will be harmful to cats? Explain.

Indoor Biotechnologies is using the gene-editing tool CRISPR/Cas9 to delete the genes for making Fel d1 in cat cells. The next step is to delete the genes in cat tissues so that Fel d1 is no longer made. Scientists don’t yet know if editing the genes for Fel d1 would be harmful to cats. Some cats that produce very little Fel d1 still appear to be healthy, but the idea needs to be tested.

12. Why might the techniques described for alleviating cat allergies also work for people with other airborne allergies? Give an example.

Since airborne allergies trigger the immune reaction in a similar way, a treatment that is proved to be safe and effective for cat allergies might inspire treatments for other allergies. For example, if a vaccine works in cats, it might also work to fight an allergen in dog dander.