Fel d 1

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Major allergen I polypeptide chain 2
Fel d 1.png
Crystallographic structure of the Fel d 1 dimer, the primary allergen present in cat saliva.[1]
Alt. symbolsFel d I, AG4, Allergen Cat-1
NCBI gene677879
Allergen Fel d I-B chain
PDB 2ejn EBI.jpg
structural characterization of the tetrameric form of the major cat allergen fel d 1
Pfam clanCL0370

Fel d 1 is a protein that in cats is encoded by the CH1 (chain 1/Fel d 1-A) and CH2 (chain 2/Fel d 1-B) genes.[2][3]

Fel d 1, produced largely in cat saliva and sebaceous glands, is the primary allergen present on cats and kittens.[1] Fel d 1 is also produced by cat skin itself.[4] The protein is of an unknown function to the animal but causes an IgG or IgE reaction in sensitive humans (either as an allergic or asthmatic response). Kittens produce less Fel d 1 than adult cats. Female cats produce a lower level of Fel d 1 than (unneutered) males.[5], while neutered males produce levels similar to those of females; both intact and spayed females produce similar levels.

Even though females and neutered males produce Fel d 1 in lower levels, they still produce enough to cause allergic symptoms in sensitive individuals. Removal of soft surfaces in the home (carpet, furniture), frequent washings of bed linens, HEPA filters and even washing cats has been proven to reduce the amounts of Fel d 1 present in the home[citation needed].

Researchers have been investigating reports from cat owners that certain breeds of cats either do not produce Fel d 1 or do so at significantly lower levels than other breeds. For instance, individual Siberian cats from naturally occurring breed native to the Siberian region for which it is named, have been shown to have genetic variants that result in a lower production of Fel d 1.[6] Another breed thought to have a possible genetic disposition not to produce this allergen or to produce less is the Balinese, an offshoot of the Siamese breed.[7] Research continues, hampered by the lack of a reliable genetic test for Fel d 1 production.

A variant of Fel-D1 is present in the venom of the slow loris (Primate: Nycticebus). Slow lorises are one of only a few venomous mammals and the only known venomous primate, possessing a dual-composite venom of saliva and brachial gland exudate (BGE).[8] The BGE possesses a protein resembling Fel-D1, which may affect host species as an allergen as a constituent of the venom, and possess a communicative function.


The complete quaternary structure of Fel d 1 has been determined.[1] The allergen is a tetrameric glycoprotein consisting of two disulfide-linked heterodimers of chains 1 and 2. Fel d 1 chains 1 and 2 share structural similarity with uteroglobin, a secretoglobin superfamily member; chain 2 is a glycoprotein with N-linked oligosaccharides. Both chains share an all alpha-helical structure.[1]

See also[edit]


  1. ^ a b c d PDB: 1PUO​; Kaiser L, Grönlund H, Sandalova T, Ljunggren HG, van Hage-Hamsten M, Achour A, Schneider G (September 2003). "The crystal structure of the major cat allergen Fel d 1, a member of the secretoglobin family". J. Biol. Chem. 278 (39): 37730–5. doi:10.1074/jbc.M304740200. PMID 12851385.
  2. ^ Morgenstern JP, Griffith IJ, Brauer AW, Rogers BL, Bond JF, Chapman MD, Kuo MC (November 1991). "Amino acid sequence of Fel dI, the major allergen of the domestic cat: protein sequence analysis and cDNA cloning". Proc. Natl. Acad. Sci. U.S.A. 88 (21): 9690–4. Bibcode:1991PNAS...88.9690M. doi:10.1073/pnas.88.21.9690. PMC 52784. PMID 1946388.
  3. ^ Griffith IJ, Craig S, Pollock J, Yu XB, Morgenstern JP, Rogers BL (April 1992). "Expression and genomic structure of the genes encoding FdI, the major allergen from the domestic cat". Gene. 113 (2): 263–8. doi:10.1016/0378-1119(92)90405-E. PMID 1572548.
  4. ^ DABROWSKI, A; VANDERBREMPT, X; SOLER, M; SEGURET, N; LUCCIANI, P; CHARPIN, D; VERVLOET, D (1990). "Cat skin as an important source of Fel d I allergen". Journal of Allergy and Clinical Immunology. 86 (4): 462–465. doi:10.1016/S0091-6749(05)80200-3. PMID 2229808.
  5. ^ Sex difference in Fel d 1 allergen production. http://www.jacionline.org/article/S0091-6749(96)70238-5/fulltext . Accessed 31 Oct 2016.
  6. ^ Sartore, Stefano; Landoni, Eleonora; Maione, Sandra; Tarducci, Alberto; Borrelli, Antonio; Soglia, Dominga; Rasero, Roberto; Sacchi, Paola (2017-12-01). "Polymorphism Analysis of Ch1 and Ch2 Genes in the Siberian Cat". Veterinary Sciences. 4 (4): 63. doi:10.3390/vetsci4040063. PMC 5753643. PMID 29194349.
  7. ^ "Allergy to Cats - Cat DNA Test Kit | Basepaws". Allergy to Cats - Cat DNA Test Kit | Basepaws. Retrieved 2018-08-07.
  8. ^ Nekaris, K. Anne-Isola; Moore, Richard S.; Rode, E. Johanna; Fry, Bryan G. (2013-09-27). "Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom". Journal of Venomous Animals and Toxins Including Tropical Diseases. 19 (1): 21. doi:10.1186/1678-9199-19-21. ISSN 1678-9199. PMC 3852360. PMID 24074353.
This article incorporates text from the public domain Pfam and InterPro: IPR015332