The cytokine receptors started to attract the  attention of more and more  investigators, even more than cytokines themselves. This is  partly because of the remarkable characteristics of the receptors, and partly because a deficiency of cytokine receptors have now been directly linked to certain debilitating immunodeficiency states.
The redundancy and pleiomorphism of cytokines are in fact a consequence of their homologous receptors, we therefore have chosen a classification of cytokines according to their cytokine receptors.