Fel d1-neutralizing cat food may be less useful than a cursory glance at the idea would suggest.
The idea: Cat food that tries to neutralize the cat allergen Fel d1 at its source in the cat’s saliva itself
Fel d1-specific IgE antibodies in allergic humans need to bind free Fel d1 to trigger their allergy. Feed cats food that contains chicken antibodies against Fel d1 to bind and neutralize it. Such cats would then deposit not free but rather antibody-bound Fel d1 on their fur and surroundings while grooming themselves. Lower free Fel d1 levels, lower the chance of triggering allergy or at least that’s the idea.
No harm to cats and no provocation of allergy in cat parents. Cats themselves would suffer no deleterious effects from eating such food while Fel d1-allergic humans would be protected from exposure to free Fel d1. Win-win idea in theory.
Cute idea on paper but the reality’s a lot harder to digest. Plenty of crucial unanswered questions for starters,
- Does this method of reducing free Fel d1 levels on cats reduce frequency and severity of allergy symptoms in those around them? No evidence for that yet.
- What is the minimum amount of free Fel d1 necessary and sufficient to trigger allergy in someone already allergic to it? Not known.
- Does this antibody-laden food consistently reduce the amount of free Fel d1 below such levels on and around cats fed this food? Not possible to know at this point.
- How much Fel d1-specific antibody should be present in food to consistently reduce its amount below such levels? Not clear.
- What’s the point of this dubious intervention if free Fel d1 levels remain above such levels even after cats eat this food, especially considering the fact that Fel d1 levels tend to vary greatly between cats? Some cats are shown to secrete <10µg while others >500µg of Fel d1 per gram of hair. How could one set dose of antibody in cat food possibly reduce Fel d1 levels sufficiently across such a broad concentration range to effectively reduce allergy in those exposed to cats fed this food?
- Antibodies are highly complex biological molecules that are also highly sensitive to environmental conditions. How stable could they be inside cat food designed for extended shelf-life?
- Would daily long-term intake of such antibody levels be safe for the cat itself? Not known.
How much Fel d1 secreted by a cat is likely to get bound by antibody in cat food? Not much. Definitely not all. And maybe not enough to prevent allergy in those already allergic to Fel d1.
And therein lies another proverbial fly in the ointment.
Fel d1-specific antibody present in cat food would bind what’s locally available in the cat’s saliva as it chews the food.
Simply from the mechanics of food intake, the process of chewing and swallowing would lead to some Fel d1+antibody presumably ending up in the cat’s GI tract in and getting digested.
Some unknown remaining amount of Fel d1+antibody would then presumably end up as Purina hopes on the cat’s coat and surroundings as it grooms itself.
What about the Fel d1 that a cat secretes when it’s not eating food? Wouldn’t it remain free to trigger allergy in those already Fel d1-allergic?
One of the main practical drawbacks of this cute sounding approach is thus that it’s likely to neutralize only some and not all Fel d1 present in a cat’s saliva. It’s also unclear at this point whether such reductions are sufficient to prevent allergy trigger.
Brief what and how of common cat allergy; allergy to Fel d1 found in cat hair and dander
Cats synthesize a variety of molecules that are potential allergens to humans, the most common being the protein Fel d1 secreted in their saliva and then deposited on their coats when they groom themselves. It also makes its way into their surroundings as fomites (environmental contamination), found everywhere that cat hair and dander get deposited. It can also remain air-borne for some time, meaning it’s also easy to inhale.
Antibodies are Y-shaped molecules that do business at both ends. The top Y end or Fab binds antigens while the stem portion or Fc binds Fc receptors expressed by a variety of cell types. Antibodies in humans are either IgM, IgG, IgA or IgE and each of these antibody classes binds different Fc receptors expressed by different cell types. Different Fc receptors on different antibody classes is why antibody binding can have very different outcomes for one class versus another.
Individuals are either allergic or not to cat Fel d1, the crucial difference being that when individuals allergic to Fel d1 come in contact with it, they make IgE antibodies against it. The problem in cat allergy comes not from an IgE antibody binding Fel d1 but from what happens when the Fel d1-bound IgE binds FcE receptors expressed by mast cells. Such binding of an IgE’s Fc to the FcE receptor on the mast cell causes the latter to degranulate.
Mast cells are essentially a bag filled with a variety of poison pills that spew their contents out when triggered to do so by an antigen-bound IgE antibody binding the FcE receptor they express abundantly on their cell surface. Mast cell contents include highly potent molecules such as histamine and prostaglandins, molecules useful when their targets are microbial pathogens or parasites in their immediate vicinity but problematic when their targets are otherwise innocuous and commonly found molecules such as Fel d1, so-called allergens that trigger allergy only in those who are allergic.
Such inappropriate release of mast cell degranulation products produces itching, skin reactions, redness, local swelling or edema and other symptoms typical of an allergic reaction.
Unfortunately, data for how effectively and reproducibly antibody-laden cat food reduces Fel d1 in cat hair and saliva is neither rigorous nor convincing enough
Proof of the pudding is in the eating. Published data suggests that the ability of chicken anti-Fel d1 antibodies in cat food to neutralize Fel d1 is highly variable.
Study 1
From 2019 (1). What they did
- In this study 105 cats were first fed a control diet for 2 weeks and then fed a test diet containing chicken antibody to Fel d1 for 10 weeks. The test diet was formulated to contain 8ppm of polyclonal chicken anti-Fel d1 IgY antibody (IgY is an antibody class found in chickens that is considered to be equivalent to mammalian IgG; polyclonal means different antibodies from different B cells, each binding a different piece of Fel d1).
- The authors collected cat hair twice weekly during the 2 week control period and weekly during the 10 week test period. They measured active (that is unbound by antibody) Fel d1 amounts in the hair. They also assessed the cats’ body weights as a surrogate of safety of test diet intake.
Problematic data and premise. The data in this paper reveal a variety of problems, both with the study itself as well as the way the data are presented.
Standard error – Wikipedia is a statistical tool intended to account for natural and expected variations between iterations of the same experiment. To wit,
“the relationship between the standard error of the mean and the standard deviation is such that, for a given sample size, the standard error of the mean equals the standard deviation divided by the square root of the sample size. In other words, the standard error of the mean is a measure of the dispersion of sample means around the population mean.”
Unfortunately abuse of this otherwise quite sensible statistical tool is at epidemic levels in biological sciences and especially in basic biomedical research where it’s now routinely used to artificially minimize within-group variations in order to artificially accentuate between-group differences.
This paper is a case in point.
Table 1 lists the mean weekly body weight, food consumption and active Fel d1 over the 10 weeks the cats were on the test diet (below from 1).
Just one experiment was performed so why are they reporting the data as mean +/- SE (standard error of the mean) if not to artificially suppress the data spread within each week over the 10 weeks of the test diet phase, especially for the active Fel d1 levels (column 3 in the table)?
Notice that the SE numbers for active Fel d1 levels (column 3 in Table 1; Figure 1 shows the same data in the form of a bar graph) are in the teens, which implies that the standard deviations (SDs) from which these SEs are derived must themselves be as high as the means themselves. In practical terms this means that rather than steadily declining over the 10 week course of test diet as the authors would like to suggest, active Fel d1 levels actually varied all over the map.
This data spread would have been clearer to see if the authors had chosen to present the data in the form of a scatter plot but then the cat would have been out of the bag, wouldn’t it?
The reason the authors used SE in Table 1 becomes clear from Table 2 where they show the same data but this time as mean +/- SD (below from 1).
The difference is that in Table 2, they have grouped the data into quartiles based on their mean baseline Fel d1 levels. Turns out Fel d1 levels vary enormously between cats. In fact, the data in Table 2 shows an almost 8-fold difference in baseline Fel d1 levels between cats with the lowest (column 1) versus those with the highest (column 4) levels.
Such tremendous variation in baseline Fel d1 levels between cats introduces another important practical obstacle for this approach. How could a single antibody amount, namely 8ppm, be justified as adequate for neutralizing Fel d1 across such an enormous range? How did the authors even hit upon this number, 8ppm, in the first place? That’s not clear.
It’s also difficult if not impossible to reconcile the implied steady drop in active Fel d1 levels with the fact that the authors also steadily decreased the amount of food offered over the 10 week course of the test diet. How could active Fel d1 levels drop in that manner when steadily lower amounts of antibody were available to bind them over that period?
Study 2
So much for study 1. Let’s look now at study 2, also published in 2019 (2).
Two trials were performed. In one, 6 adult domestic shorthair cats were first fed a control diet for 2 weeks and then the antibody-containing test diet for 6 weeks. Saliva was collected throughout to measure levels of free Fel d1. In the other trial, adult domestic shorthair cats were first fed a control diet for 1 week and then 20 continued to get this diet for another 4 weeks while a test group of 11 got the antibody-containing test diet.
Salivary Fel d1 levels in these groups of cats ranged from 2 to 20µg/ml. While the data is shown as means +/- SD, the variations are high enough to make it difficult to interpret what they even mean (below from 2). Further, actual Fel d1 changes between cats fed control or test diets seem minimal or non-existent (Figure 2) even though the authors cook the data to suggest otherwise (Figure 1).
Foot-notes
1. Satyaraj, Ebenezer, et al. “Reduction of active Fel d1 from cats using an antiFel d1 egg IgY antibody.” Immunity, inflammation and disease 7.2 (2019): 68-73. Reduction of active Fel d1 from cats using an antiFel d1 egg IgY antibody
2. Satyaraj, Ebenezer, et al. “Anti-Fel d1 immunoglobulin Y antibody-containing egg ingredient lowers allergen levels in cat saliva.” Journal of feline medicine and surgery 21.10 (2019): 875-881. Anti-Fel d1 immunoglobulin Y antibody-containing egg ingredient lowers allergen levels in cat saliva – Ebenezer Satyaraj, Qinghong Li, Peichuan Sun, Scott Sherrill, 2019