Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably
all play important functions in the modulation of host defense mechanisms. The current
review considers the assumption that tick proteins have functional relevance during
feeding. The feeding site may be described as a closed system and could be treated
as an ideal equilibrium system, thereby allowing modeling of tick–host interactions in
an equilibrium state. In this equilibrium state, the concentration of host and tick proteins
and their affinities will determine functional relevance at the tick–host interface. Using this
approach, many characterized tick proteins may have functional relevant concentrations
and affinities at the feeding site. Conversely, the feeding site is not an ideal closed
system, but is dynamic and changing, leading to possible overestimation of tick protein
concentration at the feeding site and consequently an overestimation of functional
relevance. Ticks have evolved different possible strategies to deal with this dynamic
environment and overcome the barrier that equilibrium kinetics poses to tick feeding.
Even so, cognisance of the limitations that equilibrium binding place on deductions
of functional relevance should serve as an important incentive to determine both the
concentration and affinity of tick proteins proposed to be functional at the feeding site.