Nucleic acid composition of bone marrow mononuclear cells in cobalamin deficiency

Recent studies using anion exclusion chromatography have suggested that uracil is misincorporated into the DNA of patients with megaloblastic anemia to levels detectable by nonradioactive methods. We have investigated the nucleotide composition of DNA from the bone marrow mononuclear cells of eight patients with cobalamin deficiency and compared this with that found in normal subjects. The median level of uracil in the megaloblastic group was 0.082 mol% of cytosine (approx. 0.02 mol% of all bases in DNA), which was similar to that found in the control group (median 0.085 mol% of cytosine) and may be attributable, at least in part, to artefactual deamination of deoxycytidine monophosphate during the DNA hydrolysis. Our findings give no support for the view that, by overwhelming the uracil N-glycosidase mechanism, the degree of uracil misincorporation in megaloblastic anemia is sufficient to increase the steady state level of uracil in the DNA by amounts detectable by nonradioactive methods. Using high performance liquid chromatography, we have also demonstrated normal levels of methylcytosine in the DNA of megaloblastic subjects.     

A subset of Ly-1 inducer T cell clones activates B cell proliferation but directly inhibits subsequent IgG secretion

We find that a fraction of Ly-1+2- inducer T cell clones inhibits differentiation of memory B cells into IgG-secreting plaque-forming cells. Inhibition of secondary antibody responses was not the result of induction of Ly-2+ T suppressors. Instead, inducer cells directly inactivated B cells, requiring an antigen bridge as well as identity at the major histocompatibility complex (I-A) locus. The interaction between the inducer T cell clone and hapten-specific B memory cells results in an early proliferative response and subsequent failure of B cells to secrete antibody in response to T helper cell signals. Possible mechanisms for this novel type of B cell inactivation are explored.     

Analysis of mononuclear cell infiltrate and cytokine production in murine autoimmune gastritis

BACKGROUND & AIMS: Murine autoimmune gastritis, induced by day-3 thymectomy, is characterized by cellular infiltrates and circulating autoantibodies to gastric hydrogen/potassium adenosine triphosphatase. The aim of this study was to analyze the cellular infiltrates and cytokines in autoimmune gastritis. METHODS: Stomachs and blood samples from day-3 thymectomized BALB/c mice were obtained from 2 to 12 weeks after thymectomy for analysis. RESULTS: At 4 weeks, the gastritic infiltrates were composed of macrophages and CD4+ T cells, accompanied by major histocompatibility complex class II expression on gastric epithelial cells. Mucosal B cells, scant at 4 weeks, were abundant at 8 weeks, coincident with the peaking of autoantibodies to gastric hydrogen/potassium adenosine triphosphatase. CD8+ T cells increased marginally during the 12 weeks. Mononuclear cells from diseased stomachs transferred gastritis to nu/nu recipients. At 4 weeks, interleukins 2, 3, 5, 6, and 10; interferon gamma; tumor necrosis factor alpha; and granulocyte-macrophage colony-stimulating factor were detected in gastritic mucosa, but interleukin 4 was not. CONCLUSIONS: The early lesion of autoimmune gastritis is composed of macrophages and CD4+ T cells with major histocompatibility complex class II expression in gastric epithelial cells. Autoantibody production is a late event. Our results are consistent with a lesion mediated by CD4+ T cells producing a mix of Th1- and Th2-type cytokines. (Gastroenterology 1996 Jun;110(6):1791-802)     

Cytokine production of in vitro stimulated peripheral lymphocytes during the course of pregnancy and pseudopregnancy in the rat

Problem Does maternal lymphocyte cytokine production after in vitro stimulation vary with the stage of pregnancy in the rat? Method of study Blood samples were taken during the estrus cycle in rats (n = 11). Thereafter, rats were rendered pregnant (n = 6) or pseudopregnant (n = 5) and blood samples were taken at days 4, 8, 11, 15, and 20 of pregnancy and pseudopregnancy. White blood cell (WBC) count was measured and whole blood was stimulated with phorbol 12‐myristate 13‐acetate and calcium ionophore; interferon‐γ (IFNγ) and interleukin‐4 (IL‐4) production as well as (sub)populations of lymphocytes were measured using flow cytometry. Results We observed an increase of WBC in the second week of pregnancy and a slowly decreasing percentage of lymphocytes during the course of pregnancy. The percentage IFNγ producing T‐lymphocytes after in vitro stimulation was increased during pregnancy (for Th‐lymphocytes only in the second week of pregnancy, for Tc‐lymphocytes at all days). This increased IFNγ production in pregnant T‐lymphocytes was accompanied by an increase during pseudopregnancy, and therefore may result from increased sex hormone concentrations. The percentage IFNγ producing natural killer (NK) cells after in vitro stimulation was decreased on day 20 of pregnancy. No effect of pregnancy or pseudopregnancy was seen on percentage IL‐4 producing lymphocytes after in vitro stimulation. Conclusion In the rat the IFNγ production after in vitro stimulation varies during pregnancy and is increased, rather than decreased, during pregnancy.