MS defender for office 365 license

Hi All,

• We are using MS defender for office 365 license-Plan 2 and like to downgrade the license to plan 1
• https://learn.microsoft.com/en-us/office365/servicedescriptions/office-365-advanced-threat-protection-service-description#feature-availability-across-advanced-threat-protection-atp-plans As per the above article,in the last line(comparison between plan 2 and plan1),it says "integration with MS defender" is not available on plan 1. What it means? Please explain.