Is depression an inflammatory disease?
There certainly isn't a single cause of depression. Wikipedia does not list inflammation, so that seems to be sufficient disproof of universal acceptance, and at least one candidate for representative of mainstream opinions. Berk and colleagues (2013) make a pretty convincing case though, so it may only be a matter of time, exposure to the evidence, and someone bothering to update Wikipedia.

For another, partially independent (probably cites some of the same studies), preexisting reference on the matter, check out Psychology Today's article, "The Brain on Fire: Inflammation and Depression: Inflammation and Its Effects on Mood" (Greenblatt, 2011, November 23). It too supports the potentially causal relationship, though I don't see any direct evidence of inflammation causing depression here. You may want to scrutinize it more closely than I have; if you find anything, please comment or edit!