Complement proteins are generated in various tissues and by different cell types. The majority of complement proteins found in the bloodstream are produced and released by liver cells, specifically by hepatocytes. Endothelial and epithelial cells also contribute to this production, as well as immune cells such as monocytes, macrophages, fibroblast and lymphocytes. C3, C4 and MBL are all produced by hepatocytes. Epithelial cells, monocytes and fibroblasts have been shown to produce C1qin vitro. Monocytes have the capability to generate nearly all complement proteins. The complement system and monocytes, along with their derivatives like macrophages and dendritic cells (DCs), form crucial interactions that link the innate and adaptive immune responses.