Possibly keratinocytes in the epidermis as well. These have such a high turnover rate and the skin is our largest organ in the body. This is definitely an interesting questions I'd like to research further.
This is a really interesting question that I've never thought about. If you were fighting off a virus that you've already been exposed to, then I would definitely think B cells. The number of antibodies they're producing in that situation is tremendous. However, I'm not sure it would be B cells in a normal, resting state with no immune response happening.
I would also mention the plasma cells and the ongoing antibody production and secretion, but also hepatocytes which generate albumin and coagulation factors in high amounts.