[AndrewGSW]

Well, in outline, if you had a checkbox next to the article

<input type="checkbox" name="subscribe">

you could use its onclick event:

if (this.checked) {
    // send ajax request with somepage.php?art=idnumber&subs=1
    // and possibly include the userid
} else {
    // send ajax request with somepage.php?art=idnumber&subs=0
}

then somepage.php could:

PHP Code:

<?php
if (isset($_GET['subs']) && !empty($_GET['subs'])) {
    $subs = (int) $_GET['subs'];
    if ($subs == 1) {
        // check and sanitize the userID and articleID
        // execute SQL to insert userID and articleID
    } else {
        // check and sanitize the userID and articleID
        // execute SQL to delete userID and articleID
    }
}
?>

Of course, this assumes that you are using PHP.