CD44 and Splenomegaly: As shown in Fig. 5, compared to the slight immunostimulatory effect of rhIL-15, the treatment of the two IL-15/SuIL-15Rα-IgG4 Fc complexes led to the appearance of splenomegaly (Fig. 5a, b), and significantly elevated the percentages of NK cells, NKT cells, and CD8+ CD44+ T memory cells to a much higher level in spleens (Fig. 5c) and blood (Fig. 5d), in line with previous studies [10, 11].