Why do you think it's highly cited?

Chemokines and their receptors are turning out to be important in a wide range of disease processes so a lot of people are doing research on them.

  Does it describe a new discovery or new methodology that's useful to others?

See above—it's a whole new(ish) area of immunology that's growing fast.

  Is it a condensation of previous literature on the subject?

Yes.

  Could you summarize the significance of your paper in laymen's terms?

Chemokines are small proteins that regulate the movement of cells—particularly white blood cells, but other cell types too. They are soluble proteins (cytokines) and they act by binding to receptors on target cells. They are involved in lots of different processes like growth and differentiation of tissues and in the immune responses seen in infections and autoimmune diseases. Some infectious agents (including HIV) infect cells by pretending to be chemokines. It turns out that there are lots of different chemokines and lots of different receptors. The way they all interact is still being figured out. Knowing about them is certain to help find new ways to treat and to prevent a wide range of illnesses.