Subject(s)
Depsipeptides , Immunosuppressive Agents/pharmacology , Invertebrates/immunology , Peptides, Cyclic/pharmacology , Animals , Binding Sites , Binding, Competitive , Carrier Proteins/metabolism , Cytosol/metabolism , Heat-Shock Proteins/metabolism , Humans , Immunosuppressive Agents/isolation & purification , Immunosuppressive Agents/metabolism , In Vitro Techniques , Kinetics , Male , Mice , Mice, Inbred BALB C , Peptides, Cyclic/immunology , Peptides, Cyclic/metabolism , Spleen/metabolism , Subcellular Fractions/metabolism , T-Lymphocytes/metabolism , Tacrolimus Binding ProteinsABSTRACT
Recent evidence has demonstrated an important immunoregulatory role for pituitary PRL. Moreover, PRLs have been identified as products of transformed human lymphocyte cell lines and normal murine lymphocytes, and implicated as regulators of their proliferative responses. However, PRL synthesis by normal human lymphocytes has not yet been reported. Here we demonstrate that human thymocytes and peripheral blood lymphocytes (PBL) synthesize PRL in primary culture. The principal form produced by thymocytes is 24 kilodaltons (kDa), essentially the same size as pituitary PRL, while PBL produced a 27-kDa variant. Size heterogeneity was evident, with products detected ranging from 21-29 kDa in various tissue samples, a phenomenon also found to occur in human pituitary and decidual PRL. Thymocytes and PBLs also synthesized a low mol wt form (11 kDa) that was released into culture supernatants concurrently with the larger PRL. The 24- and 11-kDa forms expressed PRL-like bioactivity in the Nb2 node lymphoma bioassay, further supporting their PRL-like nature. Expression of these PRLs was regulated by mitogen stimulation in thymocytes, but was constitutively produced in PBL. Northern blot analysis of thymocyte RNA using a human PRL cDNA probe detected a single PRL-like mRNA, which was significantly larger than human pituitary PRL mRNA. This was constitutively present in unstimulated thymocytes. Taken together, these data demonstrate that normal human lymphocytes synthesize bioactive PRLs similar in size to those produced by the pituitary. The presence of a single PRL mRNA suggests that the size variation observed in these proteins is probably due to posttranslational modification, such as proteolysis and glycosylation.
Subject(s)
Gene Expression , Lymphocytes/metabolism , Prolactin/biosynthesis , Prolactin/genetics , RNA, Messenger/analysis , Thymus Gland/metabolism , Biological Assay , Blotting, Northern , Cells, Cultured , DNA Probes , DNA, Neoplasm/biosynthesis , Humans , Immunosorbent Techniques , Lymphoma/metabolism , Prolactin/pharmacology , Tumor Cells, CulturedABSTRACT
BACKGROUND: Although recent evidence suggests that prolactin is important in the immune response, bidirectional communication between prolactin and the immune system has not been demonstrated previously. We examined our hypothesis that this communication exists during mouse skin allograft rejection. METHODS: Serum prolactin levels were measured by bioassay, and pituitary prolactin mRNA was examined by use of Northern blots, in BALB/c mice receiving skin allografts from C57BL mice, on days 2, 4, and 6 after grafting. The feedback effects of prolactin on splenic lymphocytes were assessed in one-way mixed lymphocyte reactions, with or without added interleukin-2 (IL-2) or IL-4. RESULTS: Prolactin mRNA was increased significantly in grafted animals compared with sham animals (2.4-fold by day 4). Serum prolactin bioactivity was also elevated on all days tested. Prolactin treatment resulted in dose-dependent modulation of the mixed lymphocyte reaction with lymphocytes from grafted animals but not from sham animals. These effects depended on the time points and the presence of IL-2 or IL-4; the maximal enhancement occurred with day-4 lymphocytes cultured with IL-4 (80%). CONCLUSIONS: This report is the first to implicate in vivo immune regulation of prolactin gene expression. Our observations indicate that bidirectional interaction exists between prolactin and the immune system and provide a rationale for altering prolactin levels to treat allograft rejection.
Subject(s)
Gene Expression Regulation , Graft Rejection , Lymphocytes/cytology , Prolactin/genetics , Up-Regulation , Animals , Cell Division , Dose-Response Relationship, Drug , Feedback , Lymphocyte Culture Test, Mixed , Male , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Pituitary Gland/metabolism , Prolactin/blood , Prolactin/pharmacology , RNA, Messenger/metabolism , Time Factors , Transplantation, HomologousABSTRACT
Cultured murine lymphoid cells release a PRL-like immunoreactive (IR) protein which may be important in immunity, as anti-PRL antisera inhibit lymphocyte proliferation in vitro. We examined culture supernatants (SNs) and cell lysates from concanavalin A (Con A) activated murine thymocytes to identify these proteins. Western blot analysis of cell lysates revealed three specifically-stained PRL-IRs. A doublet of bands at 35.6 and 33.6 kDa was associated with the particulate fraction of the cell. These PRL-IRs were present in lymphocytes independently of mitogen stimulation. In contrast, a 22 kDa PRL-IR was only produced in mitogen stimulated cells, and was specifically immunoprecipitated with anti-PRL antiserum. In addition, all three PRL-like IRs incorporated 35S-methionine in vitro, indicating that they are synthesized by these cells. Only the 22 kDa PRL-like protein was present in culture medium from stimulated cells, suggesting that this may be the PRL bioactivity previously demonstrated in SNs from murine lymphocytes.
