Cytokines act on other cells by bonding to cytokine receptors on the surface of cells. We assume that each cytokine has its own particular cytokine receptor, but only some of the cytokine receptors have been identified so far. The difficulty in finding cytokine receptors is that there are so few of them on each cell, between 10 and 10,000. With so few it is difficult to purify them and identify their structure. Cytokine binding to cell receptors can induce a significant change in cell activity and production of proteins.
Different cytokines have different actions on the same cell.
However, there is a large degree of overlap between the action of one cytokine and another. Cytokines interact first to stimulate and regulate production of more cytokines and then by altering cell activity. Attempting to work out how all the different cytokines work together is practically impossible. The functions of each cytokine is generally worked out by isolating each one in a cell culture and monitoring the effects on cells. We supplement this information with observations on cytokine concentrations in people with different disease states, using antibodies to neutralize different cytokines in animals and monitoring the results, administering injections of individual cytokines and observing their effects, and using drugs that knock out production of cytokines.