Others release enzymatic granules that damage pathogenic invaders. Leukocytes also release inflammatory mediators that develop and maintain the inflammatory response. In general, acute inflammation is mediated by granulocytes, whereas chronic inflammation is mediated by mononuclear cells such as monocytes and lymphocytes. Leukocyte extravasation
Various leukocytes, particularly neutrophils, are critically involved in the initiation and maintenance of inflammation. These cells must be able to move to the site of injury from their usual location in the blood, therefore mechanisms exist to recruit and direct leukocytes to the appropriate place. The process of leukocyte movement from the blood to the tissues through the blood vessels is known as extravasation and can be broadly divided up into a number of steps:

Leukocyte margination and endothelial adhesion: The white blood cells within the vessels which are generally centrally located move peripherally towards the walls of the vessels. Activated macrophages in the tissue release cytokines such as IL-1 and TNFα, which in turn leads to production of chemokines that bind to proteoglycans forming gradient in the inflamed tissue and along the endothelial wall. Inflammatory cytokines induce the immediate expression of P-selectin on endothelial cell surfaces and P-selectin binds weakly to carbohydrate ligands on the surface of leukocytes and causes them to "roll" along the endothelial surface as bonds are made and broken. Cytokines released from injured cells induce the expression of E-selectin on endothelial cells, which functions similarly to P-selectin.
Recent data suggest that, in the United States, the rates of daily smoking and the number of cigarettes smoked per day are declining, suggesting a reduction in population-wide dependence among current smokers. However, there are different groups of people who are more likely to smoke than the average population, such as those with low education or low socio-economic status and those with mental illness. There is also evidence that among smokers, some subgroups may be more dependent than other groups. Men smoke at higher rates than do women and score higher on dependence indices; however, women may be less likely to be successful in quitting, suggesting that women may be more dependent by that criterion. There is an increased frequency of nicotine dependence in people with anxiety disorders. 6% of smokers who want to quit smoking each year are successful at quitting. Nicotine withdrawal is the main factor hindering smoking cessation. A 2010 World Health Organization report states, "Greater nicotine dependence has been shown to be associated with lower motivation to quit, difficulty in trying to quit, and failure to quit, as well as with smoking the first cigarette earlier in the day and smoking more cigarettes per day." E-cigarettes may result in starting nicotine dependence again. Greater nicotine dependence may result from dual use of traditional cigarettes and e-cigarettes. Like tobacco companies did in the last century, there is a possibility that e-cigarettes could result in a new form of dependency on nicotine across the world.