Nano Server 2016 does not come with an Antivirus client by default in contrast to Server with Desktop Experience and Server Core which both come with Windows Defender installed.
Nano Server also uses Windows Defender, however, it's a more lightweight version compared to other versions of Windows.
As we have seen in this book, all the roles and features for Nano Server come as additional packages that can be added on demand.
There are many different options that you can use to install Windows Defender on Nano Server. You could use the New-NanoServerImage cmdlet to create a Nano Server image and add the Defender package as part of the image in offline mode. You could also use Nano Server ...