The earliest manifestation of cell injury is:

Vasodilation is one of the earliest manifestations of acute inflammation; sometimes it follows a transient constriction of aerioles, lasting a few seconds. Vasodilation first involves the aerioles and then leads to opening of new capillary beds in the area. The result is increased blood flow, which is the cause of heat and redness (erythema) at the site of inflammation. Vasodilation is induced by the action of several mediators, notably histamine and nitric oxide (NO), on vascular smooth muscle. Ref: Robbins 8th edition, Chapter 2