Inflammation of the synovial membranes that line the joints is coupled with increased release of synovial fluid, producing a thickening of the synovial membrane, swelling of the joints, and in severe cases, soft tissue tumors and bone and cartilage destruction. This is a recently discovered virus, the pathogen of the disease erythema infectiosum, an acute viral disease characterized by mild constitutional symptoms and a spreading rash that begins on the cheeks. Localized outbreaks of the disease are common among children and adolescents. Macrophages are amoeba-like leukocytes that are able to surround and digest foreign entities such as bacteria and protozoa.
Dendritic cells are mononuclear cells with long cytoplasmic processes.
Certain cytokines are endogenous, and need to be controlled by cell regulatory mechanisms. As a promoter of cell growth and division, a cytokine acts as a messenger to cells, and the transmission of the message requires a binding of the cytokine molecule to a cytokine-specific receptor on the cell surface.