Molecular diagnosis in cat allergy

Table 1 Characteristics of cat molecular allergens[7-11] mentioned in the World Health Organization/International Union of Immunological Societies database[4]

Allergen	Biochemical designation	Source of exposure	MW in kDa
Fel d 11,2	Secretoglobin4	Saliva, dander	38
Fel d 21,3	Serum albumin	Dander, serum, urine	69
Fel d 3	Cystatin5	Dander	11
Fel d 41,2	Lipocalin5	Saliva	22
Fel d 5	Immunoglobulin A4	Saliva, serum	400
Fel d 6	Immunoglobulin M4	Saliva, serum	800-1000
Fel d 72	Lipocalin, von Ebner gland protein	Saliva	17.5
Fel d 8	Latherin-like protein	Saliva	24

The World Health Organization/International Union of Immunological Societies is commonly known by its acronym, WHO/IUIS. Fel d 1, Fel d 2, Fel d 4 and Fel d 7 allergens are available in commercial immunoglobulin E immunoassays:

¹Available in singleplex immunoassays as recombinant allergen.

²Available in multiplex immunoassays as recombinant allergen.

³Available in multiplex immunoassays as native purified component.

⁴Presence of glycosylation.

⁵Glycosylation deduced from sequence analysis. MW: Molecular weight.

Table 2 Cat Fel d 1 and other cross-reactive Fel d 1-related allergens from big cats (Felidae family)[11,22-25]

Subfamily	Species	Common name	Allergen
Felinae	Felis domesticus (Felis catus)	Domestic cat	Fel d 1
	Leopardus pardalis	Ocelot	Leo p 1
	Leptailurus serval	Serval	Lep s 1
	Puma concolor	Puma/cougar	Pum c 1
Pantherinae	Panthera leo	Lion	Pan l 1
	Panthera onca	Jaguar	Pan o 1
	Panthera pardus	Leopard	Pan p 1
	Panthera tigris longipilis	Siberian tiger	Pan t 1
	Panthera uncia (Uncia uncia)	Snow leopard	Unc u 1

Table 3 Allergens used in singleplex and multiplex immunoglobulin E immunoassays in patients with cat allergy[7,8,10,28,29]

Protein family	Allergen	IgE sensitization biomarker
Secretoglobins	rFel d 1	Major cat allergen, species-specific biomarker of primary sensitization to cat, as efficient as or even superior compared to natural cat extract in diagnosis
Lipocalins	rFel d 4	Major cat allergen, biomarker of cross-sensitization to other animal lipocalins, cross-reactive with lipocalins dog rCan f 6, horse rEqu q 1, and mouse nMus m 1
	rFel d 7	Minor cat allergen, biomarker of cross-sensitization to dog lipocalin, cross-reactive with lipocalin dog rCan f 1
Serum albumins	n/rFel d 2	Minor cat allergen, biomarker of sensitization to non-human serum albumin, cross-reactive with pork rSus d1/nSus s1 (cat-pork syndrome) and other serum albumins bovine nBod d 6, dog nCan f 3, and horse nEqu c 3
Immunoglobulins	nFel d 5	Minor cat allergens IgA Fel d 5 and IgM Fel d 6 carry α-Gal epitopes involved in the α-Gal syndrome and in impairing cat allergy in vitro diagnostics in parasite-infected patients; α-Gal biomarker: nBos d TG

Major cat allergen: Allergen recognized by immunoglobulin E antibodies of > 50% of cat allergic patients; Minor allergen: Allergen recognized by < 50% of the allergic population; IgA: Immunoglobulin A; IgM: Immunoglobulin M; α-Gal: Galactose-α-1,3-galactose; TG: Thyroglobulin, bovine.