Distribution and characterization of immunoreactive corticostatin in the hypothalamic-pituitary-adrenal axis

Absence of Rac1 and Rac3 GTPases in the nervous system hinders thymic, splenic and immune-competence development

The nervous system influences organ development by direct innervation and the action of hormones. We recently showed that the specific absence of Rac1 in neurons (Rac1(N) ) in a Rac3-deficient (Rac3(KO) ) background causes motor behavioural defects, epilepsy, and premature mouse death around postnatal day 13. We report here that Rac1(N) /Rac3(KO) mice display a progressive loss of immune-competence. Comparative longitudinal analysis of lymphoid organs from control, single Rac1(N) or Rac3(KO) , and double Rac1(N) /Rac3(KO) mutant animals showed that thymus development is preserved up to postnatal day 9 in all animals, but is impaired in Rac1(N) /Rac3(KO) mice at later times. This is evidenced by a drastic reduction in thymic cell numbers. Cell numbers were also reduced in the spleen, leading to splenic tissue disarray. Organ involution occurs in spite of unaltered thymocyte and lymphocyte subset composition, and proper mature T-cell responses to polyclonal stimuli in vitro. Suboptimal thymus innervation by tau-positive neuronal terminals possibly explains the suboptimal thymic output and arrested thymic development, which is accompanied by higher apoptotic rates. Our results support a role for neuronal Rac1 and Rac3 in dictating proper lymphoid organ development, and suggest the existence of lymphoid-extrinsic mechanisms linking neural defects to the loss of immune-competence.

Autonomic denervation of lymphoid organs leads to epigenetic immune atrophy in a mouse model of Krabbe disease

Lysosomal beta-galactosylceramidase deficiency results in demyelination and inflammation in the nervous system causing the neurological Krabbe disease. In the Twitcher mouse model of this disease, we found that neurological symptoms parallel progressive and severe lymphopenia. Although lymphopoiesis is normal before disease onset, primary and secondary lymphoid organs progressively degenerate afterward. This occurs despite preserved erythropoiesis and leads to severe peripheral lymphopenia caused by reduced numbers of T cell precursors and mature lymphocytes. Hematopoietic cell replacement experiments support the existence of an epigenetic factor in mutant mice reconcilable with a progressive loss of autonomic axons that hampers thymic functionality. We propose that degeneration of autonomic nerves leads to the irreversible thymic atrophy and loss of immune-competence. Our study describes a new aspect of Krabbe disease, placing patients at risk of immune-related pathologies, and identifies a novel target for therapeutic interventions.

Neutrophil Defensins Induce Histamine Secretion from Mast Cells: Mechanisms of Action

Defensins are endogenous antimicrobial peptides stored in neutrophil granules. Here we report that a panel of defensins from human, rat, guinea pig, and rabbit neutrophils all have histamine-releasing activity, degranulating rat peritoneal mast cells with EC50 ranging from 70 to 2500 nM, and between 45 and 60% of the total histamine released. The EC50 for defensin-induced histamine secretion correlates with their net basic charge at neutral pH. There is no correlation between histamine release and antimicrobial potency. Degranulation induced by defensins has characteristics similar to those of activation by substance P. The maximum percent histamine release is achieved in <10 s, and it can be markedly inhibited by pertussis toxin (100 ng/ml) and by pretreatment of mast cells with neuraminidase. These properties differ from those for degranulation induced by IgE-dependent Ag stimulation and by the calcium ionophore A23187. GTPase activity, a measure of G protein activation, was induced in a membrane fraction from mast cells following treatment with defensin. Thus, neutrophil defensins are potent mast cell secretagogues that act in a manner similar to substance P and 48/80, through a rapid G protein-dependent response that is mechanistically distinct from Ag/IgE-dependent mast cell activation. Defensins may provide important pathways for communication between neutrophils and mast cells in defenses against microbial agents and in acute inflammatory responses.

Pituitary-adrenal axis function in systemic inflammatory response syndrome

This study characterizes the hypothalamic-pituitary-adrenal axis function in patients with sepsis syndrome now known as systemic inflammatory response syndrome (SIRS). One hundred and thirteen patients with SIRS had their pituitary-adrenal axis tested with the use of a 250 µg IV ACTH stimulation test. No patient received corticosteroids prior to the ACTH stimulation test. Serum cortisol concentrations were measured prior to and 30 and 60 min after ACTH administration. 26% of the patients had bacteremia, 22% bacteruria, 22% AIDS, 17% renal failure, 15% diabetes, 13% severe liver disease, 8% GI bleed, 4% pancreatitis, 3% trauma and 1% classical Addison's disease. Several patients had more than one disorder. The overall mortality was 28%. Multivariate analysis identified that both the baseline cortisol concentration and delta cortisol concentration were significant indicators of mortality. Despite the fact that mortality was double in the bacteremic patients, the baseline cortisol concentrations were similar to the non-bacteremic patients (25.4 ± 1.9vs 25.1 ± 2.5 µg/dl). The only cortisol abnormality noted in the bacteremic patients was a significantly smaller delta cortisol response to ACTH (14.7 ± 2.2vs 18.9 ± 1.2 µg/dl;P<0.05). These data imply that bacteremic processes may alter the adrenal responsiveness to intravenous ACTH administration. Understanding the pathophysiological disturbances responsible for an impaired adrenal reserve may identify new treatment strategies for patients with bacteremia.