CD25 is not restricted to T cells, it is expressed by several other cells including B cells, dendritic cells, eosinophils and macrophages. Because of macrophage CD25 expression, increased sCD25 can be seen in diseases involving macrophage activation (J Allergy Clin Immunol. 1994,94:1057, Arthritis Rheum. 2007;56:965).
although CD62L (L-selectin) is also expressed on other cells, you might look, whether T cell activation in your model is correlated to increased levels of soluble L-selectin, which might be shed from the T cell surface upon activation. You might combine your approaches with simultaneous measurement of surface L-selectin on T cells and on other cell populations (for example, granulocytes, NK cells, B cells).