WPP, the world’s largest adverting holding company is upping its investment in ad tech company AppNexus with a $25 million investment and will use the AppNexus technology to sell ads, the companies announced today.

In an interview with the Wall Street Journal, WPP CEO Martin Sorrell says, “The only alternative to AppNexus is to align with Facebook or Google. At least we’re agnostic,” he said.

Last month, we interviewed AppNexus President Michael Rubenstein about the company’s growth. We have republished that interview today.