Inflammation is one of the first responses of the immune system to infection. Cytokines are a diverse group of non-antibody proteins that act as mediators between cells. Common cytokines, which regulate the inflammatory response, include interleukins that are responsible for communication between white blood cells, chemokines that promote chemotaxis, and interferons that have anti-viral effects. Acute inflammation occurs in response to cell damage resulting from infection or injury. The magnitude of an immune response is determined by the balance between antigen-driven activation of lymphocytes and negative regulatory influences that prevent or dampen the response. The impact factor of the journal provides a quantitative assessment tool for grading, evaluating, sorting, and comparing journals of a similar kind. It reflects the average number of citations to recent articles published in science and social science journals in a particular year or period and is frequently used as a proxy for the relative importance of a journal within its field. It is first devised by Eugene Garfield, the founder of the Institute for Scientific Information. The impact factor of a journal is evaluated by dividing the number of current year citations to the source items published in that journal during the previous two years.