Fel d 4, a cat lipocalin allergen.
BACKGROUND
Cat allergy is unique among allergy to mammals in that the major allergen Fel d 1 is a uteroglobin-like protein and not a lipocalin. The biochemical spectrum of the cat allergens is thus uncertain, particularly with regard to the role that a cat lipocalin protein may play in sensitization to cats in allergic individuals.


OBJECTIVE
To analyse cDNA encoding a lipocalin allergen and the corresponding recombinant allergen at both the molecular and immunological levels.


METHODS
A submandibular salivary gland cDNA expression library was constructed and screened for clones producing IgE-binding polypeptides. cDNA encoding a lipocalin allergen and its corresponding recombinant allergen were analysed.


RESULTS
An IgE binding molecule with high sequence identity to the boar salivary lipocalin and the horse lipocalin Equ c 1 allergen was isolated and designated, Fel d 4. Serum from 62.96% of cat-allergic subjects examined had measurable IgE antibody to Fel d 4 but typically at low levels. Despite this in 47% of sera the anti-Fel d 4 IgE titres were higher than the anti-Fel d 1 titres. IgE binding to the lipocalin allergen could be blocked by an allergen extract from cow and to a lesser degree by extracts from horse and dog.


CONCLUSIONS
Fel d 4 is a lipocalin allergen produced by the cat, which binds IgE at relatively high frequency in cat-sensitive individuals. The allergen provides not only a means for investigating differences in the immune response to lipocalin allergens from that found for other mammalian species but also an important reagent for the diagnosis of cat allergy.
Smith
W
W
Telethon Institute for Child Health Research and Centre for Child Health Research, University of Western Australia, West Perth, WA, Australia. wendy@ichr.uwa.edu.au
Butler
A J L
AJ
Hazell
L A
LA
Chapman
M D
MD
Pomés
A
A
Nickels
D G
DG
Thomas
W R
WR
D000485:Allergens / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002415:Cats / Q000276:immunology*; D003429:Cross Reactions; D018076:DNA, Complementary / Q000235:genetics; D015723:Gene Library; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000209:etiology / Q000276:immunology*; D007073:Immunoglobulin E / Q000096:biosynthesis; D054834:Lipocalins; D008322:Mammals / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000276:immunology; D016415:Sequence Alignment; D013045:Species Specificity
D000485:Allergens; D018076:DNA, Complementary; C499337:Fel d 4 allergen, Felis domesticus; D006023:Glycoproteins; D054834:Lipocalins; D011994:Recombinant Proteins; D007073:Immunoglobulin E; C059296:Fel d 1 protein, Felis domesticus