Prolactin regulation of the expression of TNF-α, IFN-γ and IL-10 by splenocytes in murine multiple low dose streptozotocin diabetes

Previously, the hormone prolactin (PRL) has been found to protect against development of type 1 diabetes induced by multiple injections of streptozotocin (STZ) in mice. To further investigate this effect of PRL, C57BL/Ks mice were injected intraperitoneally with STZ (40 mg/kg body weight) or NaCl for 5 days and PRL (4 mg/kg body weight) or NaCl for 14 days. On day 15, splenocytes were isolated from the in vivo treated mice. Spleen cell preparations depleted in erythrocytes and macrophages were stained for cytoplasmic TNF-α, IFN-γ and IL-10 and analyzed with flow cytometry. Isolated spleen cells were also cultured (RPMI 1640 + 10% fetal bovine serum) for 24 h. Thereafter, cytokine mRNA expression by the spleen cells was measured by real-time PCR and cytokine secretion determined by enzyme linked immunosorbent assay (ELISA). Freshly isolated spleen cell preparations from PRL and STZ + PRL treated animals seemed to have an increased frequency of IL-10 positive cells compared to controls. In cultured spleen cells isolated from STZ treated mice, IFN-γ and IL-10 mRNA expression was up-regulated. PRL treatment down-regulated the mRNA expression of these cytokines and also TNF-α in the splenocytes obtained from animals treated with STZ. The accumulation of these cytokines in the cultures of the explanted splenocytes showed only minor differences between the experimental groups. Overall, the data seems to favor the view that PRL enhanced a Th2 response, which may reflect the preventive effect of PRL against development of multiple low dose STZ diabetes in mice.