Deficiency of purine nucleoside phosphorylase activity in thymocytes from the immunodeficient diabetic BB rat.

The spontaneously diabetic BB (BBd) rat displays marked T lymphopenia. The present study was designed to investigate whether the immunodeficiency in this animal may be associated with deficiency of purine nucleoside phosphorylase (PNP) and possibly adenosine deaminase (ADA). The activities of these two enzymes were measured in lymphoid and non-lymphoid cells from both non-diabetes-prone (BBn) and BBd rats as well as from streptozotocin-induced diabetic (STZ) BBn rats. There were no significant differences between BBn and BBd rats in ADA activities in thymocytes, skeletal muscle or brain. However, ADA activity was increased (P less than 0.01) by 50% in BBd mesenteric lymph node lymphocytes and splenocytes as compared with BBn cells, but was not altered in cells from STZ-BBn rats. On the other hand, the PNP activity in BBd thymocytes was only 61% (P less than 0.01) of that observed in BBn cells. This PNP deficiency was not the consequence of diabetes per se, as its activity was normal in thymocytes from STZ-BBn rats. There were no significant differences in PNP activities between BBn and BBd rats in all other cell types examined. The diabetic BB rat may be a novel source of PNP-deficient thymocytes (mainly immature T cells) for studying biochemical mechanisms of immunodeficiency in association with decreased PNP activity. The findings also raise the question of whether a causal relationship exists between PNP deficiency and the recently demonstrated abnormality in T cell maturation in the thymus of the BBd rat.