Reconnecting With Old Friends

Hi all! I've been dealing with depression for a number of years now and during this time, especially through uni, I have felt more and more lonely and isolated and I've lost contact with a lot of people. I would like to reach out to some of my old friends but am unsure how to go about it, I don't want to just pop up out of the blue and act like everything has been okay. I'm also nervous that some won't be interested in talking to me anymore. Does anyone have any advice?