Autoimmune thrombocytopenia and cat allergy and cat immunotherapy
I have a 25 y/o female with a history of ITP and Fel D 1 sensitivity. In the course of her ITP treatment, it was noticed that after exposures to cat, her platelet count would drop to 15-20K and require treatment. This occurred 20-30 times over the course of her treatment. When levels were checked with no recent cat exposure, she was maintained her platelet levels. Is there any prior report of allergen exposure exacerbating ITP, and what is the mechanism of this reaction if known? Additionally, would a patient like this benefit from ITx or would it potentially exacerbate her thrombocytopenia?
There is no evidence in the literature that atopy or allergy to inhalant allergens increases risk of autoimmune disease in general or specifically of autoimmune thrombocytopenia. There is a Danish population study investigating a potential association between atopy and autoimmunity but hemolytic anemia or thrombocytopenia were not separately investigated (Skaaby). The conclusion of these authors is there is no relationship between inhalant allergy and autoimmunity, although they could not exclude a very small protective or promotive effect. The autoimmune diseases included were any autoimmune disease, thyroid disease, iritis, inflammatory bowel disease, psoriasis, rheumatoid arthritis and polymyalgia rheumatic. There may be a generalized disruption of immune regulation in subjects with autoimmune thrombocytopenia with evidence of decrease in IL-10 production by Treg cells (Hua). Allergen immunotherapy increases Treg activity and IL-10 production with in vitro allergen challenge, but any relationship of immune dyregulation in atopy and autoimmune thrombocytopenia is based on hypotheticals. Likewise, there is no evidence of a beneficial or harmful effect of allergen immunotherapy on autoimmune disease. A quote from the practice parameter for allergen immunotherapy in 2011 is the following:
“Although concern about the safety of allergen immunotherapy in patients with autoimmune disorders has been raised in the past, there is no substantive evidence that such treatment is harmful in patients with these diseases. Therefore the benefits and risks of allergen immunotherapy in patients with HIV infection, other immunodeficiencies, or autoimmune disorders must be assessed on an individual basis.”
Sensitivity to cat, particularly cat albumin, may result in cross-reactivity with other mammalian albumins, notable pig albumin. This cross-reactivity may result in cat allergic subjects having reactions to ingestion of pork (Hilger). There are also reports of cat epithelial sensitivity resulting in reactivity to cow’s milk, beef and pork (Mamikoglu). There is no evidence I can find of a relationship between cat allergy and autoimmune thrombocytopenia.
In summary, I cannot find any information that would explain changes in autoimmune thrombocytopenia due to exposure to cat allergen in a patient with cat sensitivity. Likewise, I cannot relate allergy or allergen immunotherapy with autoimmune thrombocytopenia. I cannot explain the change in platelet count with cat exposure. Although I would not expect any change in the autoimmune thrombocytopenia with cat specific immunotherapy, it is an intriguing question.
I regret I could not provide more insight into your question.
All my best.
Dennis K. Ledford, MD, FAAAAI
Skaaby, Tea, et al. "Specific IgE positivity against inhalant allergens and development of autoimmune disease." Autoimmunity 48.5 (2015): 282-288.
Hua, Fanli, et al. "Aberrant frequency of IL-10-producing B cells and its association with Treg/Th17 in adult primary immune thrombocytopenia patients." BioMed Research International 2014 (2014).
Hilger, C., et al. "Allergic cross‐reactions between cat and pig serum albumin." Allergy 52.2 (1997): 179-187.
Mamikoglu, Bulent. "Beef, pork, and milk allergy (cross reactivity with each other and pet allergies)." Otolaryngology-Head and Neck Surgery 133.4 (2005): 534-537.