Saliva allergens and cross-reactivity
The saliva of blood-feeding arthropods contains a complex mixture of anti-platelet, anti-clotting, vasodilatory, anti-complement, and anti-inflammatory compounds some of which have been identified as allergens (Table 6). Recent proteomic and genomic research has provided growing insight into the composition and evolution of the “sialome” (the set of salivary proteins encoded by the salivary glands) in different blood-feeding insects.101 Some saliva proteins represent ubiquitous proteins also found in Hymenoptera venoms (e.g. antigen 5, phospholipases, hyaluronidase), while others are more unique and limited to certain insect orders, families, or even genera. As a consequence, sensitization may be limited to a narrow panel of species in some patients while involving broad cross-sensitization in others.
Mosquitoes (Culicidae)
Relevant mosquito saliva allergens have been successfully identified when using salivary gland extracts or pure saliva instead of whole-body extracts102-105 but to date, only a few have been characterized on a molecular level. Most studies have been carried out on Aedes .106-108 Four Aedes aegyptiallergens (Aed a 1-4, (Table 6) have been cloned and well characterized in clinical studies.109-113 Homologues have also been cloned from Aedes albopictus .114 The allergens from Culex and Anopheles are less well studied.114,115
There is evidence from clinical and laboratory studies of cross-reactivity between different mosquito species.108 In any case, in vitrocross-reactivity may be limited between less closely related mosquito species102,116 and even between congeneric species.117 The similarity between homologous allergens from different mosquito species may be low; for example, identity between the D7 proteins Aed a 2 and Cul q 2 is <35%.114