The number of splenocytes expressing CD25 molecules, but not CD4 molecules on their surface in a specified sample of spleen tissue. The CD4 molecule acts as a coreceptor with the T-cell receptor on the T lymphocyte to recognize antigens displayed by an antigen presenting cell in the context of class II MHC molecules. The CD25 molecule (IL2RA) is normally an integral-membrane protein, but soluble IL2RA has been isolated and determined to result from extracellular proteolysis.