Cytokines are a category of signalling proteins an glycoproteins that, like hormones and neurotransmitters, are used extensively in cellular communication. While hormones are secreted from specific organs to the blood, and neurotransmitters are related to neural acitivity, the cytokines are a more diverse class of compounds in terms of origin and purpose. They are produced by a wide variety of hematopoietic and non-hematopoietic cell types and can have effects on both nearby cells or throughout the organism, sometimes strongly dependent on the presence of other chemicals. The cytokine family consists mainly of smaller, water-soluble proteins and glycoproteins with a mass of between 8 and 30 kDa.