Circulating Leukocyte Populations Research Articles

Apoptotic Death of Peripheral Leukocytes in Channel Catfish: Effect of Confinement-Induced Stress

Abstract Channel catfish Ictalurus punctatus were stressed by net confinement for 0–12 h, and the percentages of apoptotic peripheral leukocytes were determined. The frequency of apoptosis was lower in stressed animals than in nonstressed controls, and the degree of reduction was dependent on the duration of stress. Leukocytes isolated from control fish were incubated in autologous plasma or plasma from stressed fish. The cells cultured in plasma from stressed fish showed decreased apoptosis, indicating a direct effect of stress on the individual cells rather than redistribution or cell lysis. Hydrocortisone (0.l mg/mL) had no effect in vitro on apoptosis in leukocytes. The mechanism, as well as the significance, of stress-induced changes in apoptosis in circulating leukocyte populations remains to be explained.

Activated pulmonary vascular neutrophils as early mediators of endotoxin-induced lung inflammation.

Pulmonary vascular sequestration of leukocytes has been reported to increase in some models of lung injury, including that induced by gram-negative bacterial lipopolysaccharide (LPS). Neutrophils recruited to the lung likely participate in LPS-induced lung inflammation and associated injury, but the functional activities of these pulmonary vascular neutrophils have not been directly assessed. In the current study, cells were recovered by pulmonary vascular lavage (PVL) of isolated rat lungs, harvested 2 h after intravenous infusion of LPS (3 mg/kg) or saline in intact rats, at which time LPS-induced neutrophil recruitment to the lung could be appreciated histologically but not by airway lavage. Relative concentrations of leukocytes recovered from the pulmonary vasculature by PVL were compared with those present in circulating blood, normalizing for lavage dilution on the basis of erythrocyte counts. Excess neutrophils, lymphocytes, monocytes, and eosinophils were recovered from the pulmonary vasculature of controls, and LPS infusion increased recovery of neutrophils (most prominently), lymphocytes, and monocytes. Compared with cells recovered from controls, PVL neutrophils from LPS-infused animals were primed for increased zymosan-stimulated superoxide generation, determined by ferricytochrome C reduction, and were more adherent to nylon wool columns. Northern blots of extracted RNA demonstrated that LPS infusion also upregulated interleukin-1 beta (IL-1 beta) mRNA expression in PVL leukocyte samples, but not BAL or circulating blood samples. Ficoll-hypaque separation demonstrated that the LPS-induced IL-1 beta signal in PVL leukocytes was derived primarily from polymorphonuclear rather than mononuclear leukocytes. In conclusion, all circulating leukocyte populations are sequestered in rat lungs, and LPS increases pulmonary vascular sequestration of leukocytes, recruiting most prominently an activated pool of neutrophils that are more adherent, primed for increased oxygen radical production, and expressing increased IL-1 beta message. These findings suggest a more prominent role than previously appreciated for sequestered neutrophils in sepsis-induced lung inflammation.

IL-8 in septic shock, endotoxemia, and after IL-1 administration.

Much effort has been directed toward elucidating the host response to sepsis and inflammation, resulting in the definition of a cascade of endogenous mediators that direct metabolic and immunological responses. Here we report that IL-8, a novel cytokine produced by a variety of cells in vitro in response to stimulation with bacterial LPS and the proinflammatory cytokines, appears in the circulation of primates in vivo during septic shock, sublethal endotoxemia, and after the administration of IL-1 alpha. The magnitude of the IL-8 response correlates with the severity of the insult, and levels of IL-8 peak relatively late, after those of TNF-alpha and IL-1 beta, and simultaneously with those of IL-6. IL-8 has been primarily defined as a selective activator and chemoattractant of neutrophils, and we demonstrate that after LPS or IL-1 alpha infusion, circulating neutrophil numbers rapidly recover from an initial neutropenia while IL-8 concentrations are maximal, supporting the hypothesis that IL-8 influences circulating leukocyte populations in vivo. We conclude that IL-8 is another participant in the cytokine cascade elicited by sepsis and inflammation and, as such, may play a significant role in host defense and disease.

Tumor necrosis factor-induced alterations in circulating leukocyte populations

Tumor necrosis factor is a potent agent possessing diverse biological functions. We investigated the effects of intravenous administration of human recombinant tumor necrosis factor (TNF) on immune cell populations in CBA/J mice. The animals developed a significant lymphopenia and neutrophilia both reaching a maximum at 4 hours post-injection with a trend towards resolution to normal values by 6 hours. The lymphopenia was both relative and absolute. Similarly, the neutrophilia was both relative and absolute and was due to the presence of both immature and mature neutrophils. As the neutrophilia and lymphopenia occurred concomitantly, there was no difference at any time point in the total number of peripheral blood white cells. Extensive controls were done to rule out LPS contamination in the TNF preparation. These data demonstrate the potent effects of intravenous administration of human recombinant tumor necrosis factor on peripheral blood constituents.

Effects of acute endotoxemia and glucose administration on circulating leukocyte populations in normal and diabetic subjects

Effects of intravenous endotoxin and glucose administration on circulating leukocyte populations were compared in seven normal subjects and seven patients with juvenile-onset diabetes by means of automated cytochemical differential counting to quantitate each cell type. Both groups had comparable control cell counts that were unaffected by glucose tolerance testing but altered significantly by endotoxin. Different patterns of response to endotoxin were observed for different circulating cell types. The response of diabetics was parallel to that of normals but showed lower neutrophil and monocyte rebound, longer lasting depression of lymphocytes and eosinophils, and greater rebound of basophils on the day following endotoxin exposure. Characterization of distinctive normal response patterns of circulating leukocyte populations to endotoxin and comparison with responses in diabetics revealed abnormalities under conditions of stress that may impair the diabetic's ability to cope with acute infection.

Immune Status in Crohn's Disease

Proportions and absolute numbers of circulating leukocyte populations and lymphocyte subpopulations (T- and B-cells) were determined in 33 patients with Crohn's disease (group CD), and were compared with those of age- and sex-matched healthy subjects. Group CD comprised 15 patients with newly diagnosed, short-standing, and untreated CD (group CD 1) and 18 patients with long-standing, previously drug treated CD (group CD 2). All CD groups showed a significant absoulte leukocytosis, based on a significant absolute and relative increase of the neutrophils, and, as far as group CD and CD 1 were concerned, also of the absolute number of monocytes. In group CD 1, absolute lymphocyte and relative as well as absolute T-cell numbers were close to normal. In contrast, in group CD 2 absolute as well as relative numbers of lymphocytes and absolute numbers of T-cells were highly significantly reduced, whereas the reduction of the relative T-cell concentration barely reached significance. The proportion of B-cells was significantly above normal in all patient groups, the absolute number in group CD only. Also group CD 1 showed considerably, though statistically insignificantly, higher than normal absolute B-cell numbers. In group CD 1 , there was an inverse correlation between absolute T-cell numbers and disease activity, and between absolute lymphocyte numbers and duration of disease. These data indicate that there is no gross numerical reduction of the carriers of the cell-mediated immunity as a primary predisposing factor for CD, but that a reduction of these cells occurs in the circulation after the disease has started.