Age-related effects of ectopic pituitary transplants on the activation of Ames dwarf mouse lymphocytes in vitro

Prolactin (PRL), one of the anterior pituitary hormones, has been implicated in the development and maintenance of immune system function. The following experiments were conducted to evaluate age-related effects of PRL on immune system activity in a PRL-deficient mouse model, the Ames dwarf. Two- and ten-month-old dwarf and phenotypically normal male mice were used. Six dwarf mice from each age group received a surgically implanted pituitary (under the kidney capsule) from a normal donor female mouse. Six different dwarfs were similarly operated but had no pituitary graft inserted and will be referred to as sham-operated dwarfs. Three weeks following surgery, spleens were removed from the dwarfs and age-matched normal mice and splenocytes isolated. The two age groups will subsequently be referred to as "3-month-old" and "11-month-old", respectively, The splenocytes were used in mitogen-induced (concanavalin A (Con A); phytohemagglutinin (PHA); lipopolysaccharide (LPS)) proliferation assays, and histopaque isolated lymphocytes were used for T cell surface marker determination. Pituitary grafting increased body weights of dwarf mice although the weights were less than control mice independent of age. A similar pattern was observed for total number of splenocytes per spleen. In young animals, the relative number of splenocytes per gram of body weight increased in pituitary grafted dwarfs reaching values of control mice, whereas much smaller differences were observed in older animals. The relative percentage of CD4+ cells was reduced (P<0.01) in 3-month-old pituitary-grafted mice, compared with sham-operated dwarf mice, while no differences were observed between sham- operated dwarf and normal mice. Pituitary grafting did not affect the numbers of CD8+ cells. In 11-month-old animals, the relative percentages of CD4+ and CD8+ cells were greater (P<0.05) in sham-operated dwarf than in normal mice but not affected by pituitary grafting. At 3 months of age, proliferation of splenocytes in response to Con A was increased (P<0.05) in sham-operated dwarfs and reduced (P<0.05) in pituitary-grafted dwarfs compared with normal mice. In contrast, PHA stimulation of splenocytes was decreased (P<0.05) in sham-operated compared with normal, and was still lower in mice receiving an ectopic pituitary. Substantially different responses were obtained in 11-month-old animals. In response to Con A, splenocytes from sham-operated dwarfs exhibited a reduced (P<0.05) proliferative capacity as compared with normals, and proliferation was increased in pituitary-grafted as compared with sham-operated dwarfs. In the presence of PHA, the proliferative capacity of splenocytes was greater (P<0.05) in sham-operated dwarfs as compared to normals and pituitary grafting normalized this parameter. These results demonstrate differential effects of PRL deficiency (sham-operated dwarfs versus normal) and of PRL replacement (pituitary-grafted versus sham-operated) in young as compared with old dwarf mice on immune system activation.