Thank you for your recent inquiry.
We know that rennet can be a potent allergen based on respiratory reactions attributed to the inhalation of rennet (see abstract copied below). However, I am not aware of any anaphylactic reactions to rennet, and was not able to find any reports in the literature of allergic reactions to the ingested product. Nonetheless, it is certainly possible, based upon allergic reactions to inhalation of this agent that such could occur.
It should also be noted that all rennets are not from the same source. Calf rennets are used in some cheeses. In this case, the rennet is extracted from the fourth stomach chamber of the calf. Rennet is also obtained from other ruminants such as kid goats and lambs. In addition, there are microbial-produced rennets that are added to cheese. These are used by vegetarians. Finally, there is genetically engineered rennet.
Rennets regardless of source all contain enzymes. The exact amount of the various enzymes may differ depending on the rennet employed. The major enzyme is called chymosin, but other proteases are contained in rennet preparations as well.Protease are as you know are well recognized allergens.
One thing you can do, to help you discern whether or not rennet is the culprit, is simply to purchase rennet and make a slurry as you did for the cheese, and perform an epicutaneous test to rennet itself. Rennet for purchase is readily available online and also in many grocery stores. It can be obtained in a powder form or a pill form.
If you do confirm that rennet is the culprit, two questions arise. The first is whether or not the rennet responsible was from a calf or a vegetable source. More than likely it would be from a calf. If so, it is possible that your patient may be able to eat cheese containing vegetable rennets that are from microbial sources or genetically engineered. However, I am not certain of this since the specific agent responsible for the reaction due to the rennet may be contained in both sources.
Soft cheeses (e.g., cream cheese and cottage cheese) are manufactured totally without rennet. Some health food stores also provide a rennet-free cheese list upon request. Such a list is available on the Trader Joe's Market website. According to this website, soy cheeses are also often free of rennet, and their cream cheese and whipped cream cheese as noted above is rennet-free. They also list on the website those cheeses which have animal rennet sources, microbial rennet sources, and vegetable rennet sources.
In summary, the information that might be helpful to you is as follows:
We know from respiratory sensitization that rennet is a potential allergen; nonetheless, I am personally not aware of, nor could I find via a literature search, any reported cases of anaphylaxis due to rennet ingestion.
There are different types of rennet, and if the rennet was the cause of your patient's reaction, the responsible component may vary according to the source.
You can obtain rennet for testing via an online purchase or at many grocery and health food stores.
There are cheeses, as noted, that are free of rennet, and there are cheeses, as noted, that have varying sources that may not cause a reaction depending on the content of the responsible enzyme producing the reaction (if rennet was indeed the culprit).
I would therefore suggest that you do the following:
Try to obtain the cheeses that the patient has eaten without problem, and look to see if the rennet contained within the cheese was of animal or other sources. Then, do the same for the responsible cheese. This may give you a clue as to whether or not the patient is able to eat microbial or synthesized rennet, but not, for example, calf rennet.
Try to obtain more refined information as to whether or not rennet was the culprit by doing a test to rennet itself as you did to the cheese preparations.
There are rennet-free cheeses, as noted above, and reading labeling would help also if your patient was able to eat one source (but not another) of rennet.
Thank you again for your inquiry and we hope this response is helpful to you.
Respiratory complaints and high sensitization rate at a rennet-producing plant
Anker Jensen, MD 1 2 *, Søren Dahl, MD 1, David Sherson, MD 3, Birgitte Sommer, MD 1
1. Department of Occupational and Environmental Medicine, Haderslev Hospital, Haderslev, Denmark
2. Occupational Health Center South, Danish Defence, Fredericia, Denmark
3. Department of Occupational and Environmental Medicine, Vejle Hospital, Vejle, Denmark
email: Anker Jensen (email@example.com)
*Correspondence to Anker Jensen, FA-SYD, Bülows Kaserne, DK 7000 Fredericia, Denmark.
This research performed at: Department of Occupational and Environmental Medicine, Haderslev Hospital, Denmark.
rennet • allergy • rhinitis • skin prick test • enzymes
Workers in a rennet producing plant reported airway symptoms, mainly rhinitis. Rennet was produced as fluid and powder with proteolytic enzymes as the active component.
Data on airway symptoms and known allergies were collected and skin prick tests (SPTs) with the rennet types produced in the plant and standard allergens were carried out on 35 plant employees. An identical SPT was carried out on 28 controls without known exposure to rennet.
Twenty-one employees (60%) had hay fever-like symptoms, 10 cases mainly at work. Nine had mild to moderate asthma-like symptoms, in six cases related to the work place. Fourteen had a positive SPT to one or more rennets. The sensitization rate was highest among employees with regular contact to rennet powder.
Rennet is a potent allergen. Respiratory symptoms and sensitization can occur in connection with rennet exposure, especially as a powder. Am. J. Ind. Med. 2006. © 2006 Wiley-Liss, Inc
Phil Lieberman, M.D.