[Biophysics] chemical pinging mechanism?

[Tom Chou]

Dear all,

I am wondering if anyone knows any biological examples of the following 
mechanism, or something close to it:


A cell emits a chemical A that diffuses outward and comes in contact 
with another cell (or target). The target is then triggered to produce
another chemical B, that diffuses back to the cell that prodiced A. This 
cell then uses B as a chemoattractant/repellent to move towards or away 
from the target. Are there any examples of
such chemical pinging mechanisms in Nature? I think bacterial 
aggregation is different from what I have in mind.

Thank you,

Tom