Loss of Resistance to Angiotensin II-Induced Hypertension in the Jackson Laboratory Recombination-Activating Gene Null Mouse on the C57BL/6J Background.

Resistance to angiotensin II (Ang II)-induced hypertension in T-cell-deficient male mice with a targeted mutation in the recombination-activating gene-1 (Rag1) on the C57BL/6J background (B6.Rag1-/- -M), which was reported by 5 independent laboratories including ours before 2015, has been lost. In mice purchased from Jackson Laboratory in 2015 and 2016, the time course and magnitude increase in mean arterial pressure induced by 2 weeks of Ang II infusion at 490 ng/kg per minute was identical between B6.Rag1-/- -M and male wild-type littermates. Moreover, there were no differences in the time course or magnitude increase in mean arterial pressure at the lowest dose of Ang II (200 ng/kg per minute) that increased mean arterial pressure. This loss in Ang II resistance is independent of T cells. Angiotensin type 1-receptor binding was 1.4-fold higher in glomeruli isolated from recently purchased B6.Rag1-/- -M suggesting an increase in renal angiotensin type 1-receptor activity masks the blood pressure protection afforded by the lack of T cells. The phenotypic change in B6.Rag1-/- -M has implications for investigators using this strain to study mechanisms of T-cell modulation of Ang II-dependent blood pressure control. These findings also serve as a reminder that the universal drive for genetic variation occurs in all animals including inbred mouse strains and that spontaneous mutations leading to phenotypic change can compromise experimental reproducibility over time and place. Finally, these observations illustrate the importance of including experimental details about the location and time period over which animals are bred in publications involving animal studies to promote rigor and reproducibility in the scientific literature.

Effects of nicotine exposure on T cell development in fetal thymus organ culture: arrest of T cell maturation.

There is evidence for both physiological functions of the natural neurotransmitter, acetylcholine, and pharmacological actions of the plant alkaloid, nicotine, on the development and function of the immune system. The effects of continuous exposure to nicotine over a 12-day course of fetal thymus organ culture (FTOC) were studied, and thymocytes were analyzed by flow cytometry. In the presence of very low concentrations of nicotine many more immature T cells (defined by low or negative TCR expression) and fewer mature T cells (intermediate or high expression of TCR) were produced. In addition, the numbers of cells expressing CD69 and, to a lesser extent, CD95 (Fas) were increased. These effects took place when fetal thymus lobes from younger (13-14 days gestation) pups were used for FTOC. If FTOC were set up using tissue from older (15-16 days gestation pups), nicotine had little effect, suggesting that it may act only on immature T cell precursors. Consistent with an increase in immature cells, the expression of recombinase-activating genes was found to be elevated. Nicotine effects were partially blocked by the simultaneous addition of the nicotinic antagonist d-tubocurarine. Furthermore, d-tubocurarine alone blocked the development of both immature and mature murine thymocytes, suggesting the presence of an endogenous ligand that may engage nicotinic acetylcholine receptors on developing thymocytes and influence the course of normal thymic ontogeny.

The thymus does not mediate 2,3,7,8-tetrachlorodibenzo-p-dioxin-elicited alterations in bone marrow lymphocyte stem cells.

Our previous studies have shown that bone marrow lymphocyte stem cells are affected following perinatal or adult exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). These alterations may, in part, be responsible for thymic atrophy that is also observed following TCDD exposure. However, other investigators have suggested that the thymus or thymic-derived lymphocytes can affect bone marrow stem cell development. The purpose of these studies was to determine whether the TCDD-elicited effects that we have observed on lymphocyte stem cells in bone marrow were secondary to the actions of this chemical on the thymus. A single intraperitoneal dose of TCDD (30 micrograms/kg) to sham-operated or neonatally thymectomized female BALB/c mice reduced the levels of mRNA in the bone marrow for the lymphocyte stem cell-specific enzymes terminal deoxynucleotidyl transferase (TdT) and recombinase activating gene (RAG-1). TdT biosynthesis was also reduced by TCDD treatment. Thus, neonatal thymectomy had no effect on the TCDD-elicited reduction of TdT or RAG-1 mRNAs or TdT biosynthesis. Genetically athymic (nu/nu) mice were used to further determine if the actions of TCDD on the thymus or long-lived T-cells altered lymphocyte stem cell development. As observed in BALB/c mice, TCDD treatment decreased the expression of TdT and RAG-1 mRNAs in bone marrow from athymic nu/nu and intact nu/+ littermates. We conclude that TCDD-elicited alterations in bone marrow lymphocyte stem cells are not secondary to any actions, direct or indirect, that TCDD has on the thymus or thymic-derived T-cells.