In the antibody-mediated immune response, when the helper T cell gets activated by the costimulus (IL-2 and TNF-α secreted by the APC) which in turn produces IL-2, IL-2 acts in an autocrine manner. I'm just wondering why does IL-2 have to be secreted? Why doesn't it just exert an affect while it's already inside the helper T cell? What's the point of autocrine signalling?
I hope the answer isn't going to be, "Well, that's just the way it is..." because paracrine and endocrine make sense and have advantages, but autocrine just seems a bit extra.