Date Published: April 10, 2018
Publisher: BioMed Central
Author(s): B. Bonnet, K. Messaoudi, F. Jacomet, E. Michaud, J. L. Fauquert, D. Caillaud, B. Evrard.
Cats are the major source of indoor inhalant allergens after house dust mites. The global incidence of cat allergies is rising sharply, posing a major public health problem. Ten cat allergens have been identified. The major allergen responsible for symptoms is Fel d 1, a secretoglobin and not a lipocalin, making the cat a special case among mammals.
Given its clinical predominance, it is essential to have a good knowledge of this allergenic fraction, including its basic structure, to understand the new exciting diagnostic and therapeutic applications currently in development. The recent arrival of the component-resolved diagnosis, which uses molecular allergens, represents a unique opportunity to improve our understanding of the disease. Recombinant Fel d 1 is now available for in vitro diagnosis by the anti-Fel d 1 specific IgE assay. The first part of the review will seek to describe the recent advances related to Fel d 1 in terms of positive diagnosis and assessment of disease severity. In daily practice, anti-Fel d 1 IgE tend to replace those directed against the overall extract but is this attitude justified? We will look at the most recent arguments to try to answer this question. In parallel, a second revolution is taking place thanks to molecular engineering, which has allowed the development of various forms of recombinant Fel d 1 and which seeks to modify the immunomodulatory properties of the molecule and thus the clinical history of the disease via various modalities of anti-Fel d 1-specific immunotherapy. We will endeavor to give a clear and practical overview of all these trends.
Worldwide, the domestic cat, Felis domesticus, is one of the most frequently encountered pets. It is a major source of allergens in the indoor environment and is placed in second position after dust mites for its involvement in the incidence of allergic respiratory diseases. In Western countries, the prevalence of sensitization to allergens of cat has increased dramatically to 10–30% in the general population . A significant proportion of atopic subjects (about 20–40%) are sensitized to cat allergens [2, 3]. The severity of induced symptoms varies widely and cat allergy is thus a main risk factor of both rhinitis and asthma, including severe asthma, which can develop into a life-threatening condition.
The appearance of the recombinant forms of Fel d 1 has led to the development of a CRD for cat allergy, which is very useful for the practitioner. Compared to the cat-specific IgE (whole extract), anti-Fel d 1 specific IgE have an equivalent or slightly lower sensitivity in terms of positive diagnosis and are correlated with disease severity and the risk of asthma occurrence. Molecular engineering has contributed to the emergence of multiple forms of Fel d 1 specific immunotherapy that are still being improved to optimize the induction of a tolerogenic immune profile. They open up great therapeutic prospects for patients in the years to come. However, it is becoming clear that the multisensitized profiles correspond to particular phenotypes of the disease, of more severe evolution. It is therefore important to carry out a complete evaluation of the cat molecular allergen, including minor fractions, to correctly characterize the patient profile, including the likely course of the disease, the potential cross-reactions and, finally, the expected immunotherapeutic response. We will deal with these aspects in the second part of this review, focusing on the less known molecular allergens of the cat, such as Fel d 2 or Fel d 4.