After you reach level 80 and prestige what do you actually lose?

Basically you just lose all the guns, perks, attachments, and most challenges you have unlocked throughout your CoD:MW3 career. You keep you clan tag, playlists, titles, and emblems. Also, with Prestige Tokens, beside from earning Double XP, Double Weapon XP, but when you prestige, you have the option to unlock any gun or perk or your choosing. And you can do the same thing until you reach 10th Prestige. As a little bonus tip which is only a recommendation, but when you reach 10th Prestige and select the option "Reset All Stats," you go back to Level 1 at no prestige, but you get all pro perks, and every gun you unlocked via Prestige Shop will automatically receive gold camo. The only downside is that you keep all of your losses and deaths and lose all your wins and kills. However, you can stay 10th Prestige if you want to or plan on going that far. That decision is up to you. I hope this was able to assist you!

Great answer dude