Table 3.

Principles of MC biology to keep in mind when assessing the importance of MCs as sources of cytokines, chemokines and growth factors^*.

In vivo, MCs can be heterogeneous in multiple aspects of phenotype and function, depending on animal species, anatomical location, stage of development or maturity, and influence of genetic and microenvironmental factors (reviewed in 381–383). Many other factors also may influence MC phenotype and function in vivo, including effects of age, sex, circadian rhythms, various forms of stress and concurrent metabolic, inflammatory or immune responses, and disease processes. MCs are potentially long-lived and are responsive to diverse systemic or local signals which can influence their phenotype and function, including those related to having undergone prior activation events. Some biological responses are associated with substantial expansion and/or contraction of MC populations, and this may result in tissues containing MCs in various stages of development or maturation and such cells may vary in phenotype and function. MC populations which are generated in vitro may differ in important features from native MC populations in vivo. Processes of purifying MCs from bodily fluids and, especially, tissues may alter aspects of MC phenotype and function, including their ability to make or respond to cytokines, chemokines and growth factors.

^*All of these factors may influence the MC’s ability to produce cytokines, chemokines and growth factors, and/or to produce and secrete proteases and other factors that can influence the structure and bioactivity of these molecules.