Answer
You can have up to 14 mesh groups per VPLS on MX Series routers. For example, for a given VPLS instance, if you need LDP-BGP interworking, there must be one mesh group for every LDP-VPLS cloud that is connected to the BGP-VPLS cloud, at the interworking router.
For more information, click Layer 2 VPNs and VPLS Feature Guide.