Which cells release inflammatory mediators?
There are several kinds of inflammatory mediators. You can broadly classify them as cytokines (including interferons) and chemokines. 

Cells which sense antigens (or pathogen associated molecular patterns) do secrete cytokines, as you said but infected cells also secrete some cytokines like interferons- α and β. Infected/injured cells also secrete chemokines that attract leukocytes to the site of infection/injury (Saiman and Freidman, 2012).