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