We and others have identified luteinizing hormone-releasing hormone (LHRH) in cells of the immune system in both animals and humans. LHRH is an immunostimulant, and testosterone is an immunosuppressant. Because testosterone is known to modulate the concentrations of hypothalamic LHRH, we wondered whether testosterone might also alter the concentrations of rat thymic LHRH. Two weeks after castration or sham castration, adult male rats were implanted with either vehicle or testosterone capsules. All animals were killed 4 days after capsule implantation. Thymic LHRH concentration increased significantly in castrated animals. Testosterone replacement prevented this increase. The concentration of the LHRH precursor, proLHRH, decreased significantly, but testosterone replacement prevented this decrease. Steady-state concentrations of LHRH mRNA were not changed by castration or by hormonal replacement. In contrast to the post-castration increase in thymic LHRH, LHRH content of the hypothalamus decreased significantly. Whereas concentrations of LHRH were lower in the thymus than in the hypothalamus, proLHRH concentrations were much greater in the thymus. These data suggest that gonadal manipulation modulates LHRH molecular processing and its tissue concentration in the thymus in addition to those in the hypothalamus, and that the regulation of LHRH molecular processing by testosterone in the hypothalamus is different from that in the thymus.

Abstract

Jurkat cells were used to study the immunomodulatory role of luteinizing hormone-releasing hormone (LHRH) in immune cells. The Jurkat cell, a human mature leukemic cell line, phenotypically resembles resting human T lymphocytes and has been widely used to study T cell physiology. The data from this study demonstrate that the Jurkat cell concentration of immunoreactive LHRH was 210 ± 36 pg/10⁶ cells and that of proLHRH was 188 ± 27 pg/10⁶ cells (means ± s.e.m.). The authenticity of this LHRH immunoreactivity is documented in two ways. First, both Jurkat LHRH and proLHRH immunoreactivity demonstrate dilutional parallelism with hypothalamic LHRH and proLHRH. Second, Jurkat lysates show LHRH bioactivity by releasing luteinizing hormone from rat anterior pituitary cells in culture. The presence of substantial amounts of LHRH in medium in which Jurkat cells were cultured for 72 h indicated that LHRH can be released from the cells. Using specific primers to exons 2 and 4 of the LHRH gene, we have found that Jurkat cells (like human T cells) express LHRH mRNA.

The LHRH agonist, des-Gly¹⁰,d-Trp⁶-LHRH ethylamide, significantly increases the proliferative activity of Jurkat cells, as assessed by tritiated thymidine incorporation, from 15 980 ± 1491 c.p.m. in controls to 28 934 ± 3395, 30 457 ± 3861 (P=0·05 vs control) or 35 299 ± 5586 c.p.m. (P<0·01 vs control) with 10⁻¹¹, 10⁻⁹ or 10⁻⁷ m agonist respectively. LHRH antagonist, [d-pGlu¹,d-Phe²,d-Trp^3,6]-LHRH, at a concentration of 10⁻⁸ m decreases Jurkat cell proliferative activity from 17 145 ± 526 c.p.m. in control medium to 10 653 ± 1323 c.p.m. (P=0·05). Co-incubation with the LHRH antagonist completely inhibits the proliferative stimulation induced by the LHRH agonist. Furthermore, applying monoclonal LHRH antibody to Jurkat cells inhibits the cell proliferative activity assessed by tritiated thymidine incorporation from 19 900 ± 2675 c.p.m. in controls to 15 680 ± 2254, 15 792 ± 1854 and 9700 ± 908 c.p.m. in media with 1:40, 1:20 and 1:10 dilution of purified antibody respectively (P<0·01, 1:10 dilution compared with control). In addition, the cAMP level in LHRH-stimulated Jurkat cells is decreased to 74, 27 and 57% of control levels after 15, 30 and 45 min respectively of exposure to 10⁻⁷ m LHRH agonist.

In summary, Jurkat cells produce, process and release immunoreactive and bioactive LHRH, as do normal human T cells. Endogenous and exogenous LHRH increase Jurkat cell proliferative activity, and cAMP may be involved in LHRH-induced Jurkat cell proliferation. The Jurkat cell may be a useful model with which to study the role of LHRH in human T cell function.

Journal of Endocrinology (1997) 153, 241–24