An update on molecular cat allergens: Fel d 1 and what else? Chapter 1: Fel d 1, the major cat allergen

Abstract

Background: 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.

Main body: 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.

Keywords: CRD; Cat allergy; Fel d 1; Immunotherapy.

Fig. 1

Fel d 1 crystallographic structure highlighting the location of the calcium ions. From Ligabue-Braun et al. [16] reprints in open access

Fig. 2

Specific IgE levels (≥ 0.3 ISU-E) to cat allergens in children with (white box plots) or without (gray box plots) symptoms to cat at 4, 8, and 16 years of age. From Asarnoj et al. [58] reprinted with permission from the publisher

Fig. 3

Difference in bronchial responsiveness (lower values show more responsiveness, a) and % difference of fraction of exhaled nitric oxide (FeNO) (b) between subjects sensitized to cat extract or both extract and components vs. subjects not sensitized to cat. Results are from a multiple linear regression model and adjusted for age, BMI, sex, smoking at baseline. Reference group are the subjects negative to both extract and any cat component. From Patelis et al. [60] reprinted with permission from the publisher

Fig. 4

Possible mechanism of immune modulation in intralymphatic immunotherapy. From Kim et al. [87] reprints in open access