Plasma cytokines refer to small proteins that are secreted by immune cells in response to infection, inflammation, or injury. These cytokines play a crucial role in regulating the immune response and are involved in various biological processes, including inflammation, cell proliferation, and cell communication. Measurement of plasma cytokine levels can provide valuable information about the body's immune response and can be used as biomarkers for various diseases, such as autoimmune disorders, cancer, and infectious diseases. Studying plasma cytokines can help researchers understand the underlying mechanisms of disease and develop new treatments or diagnostic tools.