Biochemestry
Serum albumins are multifunctional proteins with very flexible structures that can change conformation easily to bind with many diverse ligands (4). Can f 3 is a mammalian serum albumin allergen with a molecular weight of 67–70 kDa (4-6, 13). Can f 3, previously known as Can d 3, is considered to be an intermediate dog allergen component (4, 14).
Cross-reactivity
Table: Amino acid identities (%) between allergenic serum albumins. Figures in bold indicate documented IgE cross-reactivity between albumins. HSA: human serum albumin. (15)
| Sus s 1 | HSA | Fel d 2 | Equ c 3 | Cav p 4 | Can f 3 | Bos d 6 | |
|---|---|---|---|---|---|---|---|
| Bos d 6 | 79 | 76 | 78 | 74 | 70 | 76 | 100 |
| Can f 3 | 78 | 80 | 87 | 76 | 73 | 100 | |
| Cav p 4 | 72 | 72 | 76 | 72 | 100 | ||
| Equ c 3 | 76 | 76 | 78 | 100 | |||
| Fel d 2 | 79 | 82 | 100 | ||||
| HSA | 75 | 100 | |||||
| Sus s 1 | 100 |
Can f 3 displays a high hom*ology to other mammalian albumins (9), and mono-sensitization to Can f 3 seems to be very rare (16). In a study of 200 animal-allergic patients, 30% reacted with albumins from different animals (3). In this study, despite a high degree of sequence hom*ology among the albumins, recombinant Can f 3 bound IgE from all of the 15 patients allergic to albumin from dog, cat, guinea pig or horse (3). Similarly, other studies have demonstrated significant sequence hom*ologies ranging from 75–90% between dog-specific IgE directed against dog albumin and albumins from mammals including human, pig, cattle, cat, sheep, mouse, and rat (2, 4, 14). A high degree of sequence hom*ologies among albumins explains the extensive cross-reactivity of patient IgE antibodies with albumins from many species (4, 14).
In a study of 10 patients with IgE antibodies to cat dander and pork, all patients allergic to cat serum albumin also had high IgE titers to dog serum albumin, even if they had no contact with dogs (17). Boutin et al. showed that anti-cat albumin monoclonal antibodies recognized both cat and dog albumin equally, as did anti-dog albumin monoclonal antibodies, confirming cross-reactivity between cat and dog (13). Furthermore, as histamine release can be induced from basophils derived from dog-albumin-allergic patients on incubation with albumins from rat, mouse, and chicken, albumins from different species represent functional cross-reactive allergens (2).
