SummaryThe B lymphocyte-induced maturation protein (Blimp-1) upregulates the expression of syndecan-1 and J chain and represses that of c-myc. We have transfected Blimp-1 into two sublines of the BCL1 B cell lymphoma that represent distinct stages of B cell development in secondary lymphoid tissues. After interleukin (IL)-2 and IL-5 stimulation, the BCL1 3B3 cells differentiate into centrocyte-like cells, whereas the BCL1 5B1b cells blast and appear to be blocked at the centroblast stage. This blasting effect and the increase in IgM secretion that follows it can be blocked by a dominant negative form of Blimp-1. At the same time, the ectopic expression of Blimp-1 in these partially activated cells induces an apoptotic response that also can be suppressed by the same dominant negative protein. A similar effect was noticed when Blimp-1 was expressed in the mature L10A and the immature WEHI-231 lines, indicating this may be a general effect at earlier stages of the B cell development, and distinct from the ability of Blimp-1 to induce maturation in late stages of differentiation. Truncation mutants indicate that the induction of the apoptotic response relies mainly on 69 amino acids within Blimp-1's prolinerich domain. We propose that Blimp-1 expression defines a checkpoint beyond which fully activated B cells proceed to the plasma cell stage, whereas immature and partially activated cells are eliminated at this point.

Possible antiinflammatory effects of dehydroevodiamine (1) and evodiamine (2) were examined by assessing their effects on NO production in the murine macrophage-like cell line RAW 264.7. The results indicated that both 1 and 2 inhibited the IFN-gamma/LPS-stimulated NO production in a concentration-dependent manner. However, 1 appeared to inhibit NO production by interfering not only with the priming signal initiated by IFN-gamma but also with iNOS protein synthesis, while 2 affected the former only.

We studied the mechanisms by which the plant alkaloid tetrandrine (TTD) inhibits Mac-1-dependent neutrophil adhesion to fibrinogen. TTD (0.1-10 microM) significantly inhibited Mac-1 up-regulation and neutrophil adhesion, as induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol-myristate-acetate (PMA). Treatment of neutrophils with fMLP or PMA caused a rapid influx of Ca++ and accumulation of reactive oxygen species (ROS), both of which have been shown to enhance neutrophil adhesion via Mac-1 up-regulation. Because TTD antagonizes Ca++ influx and abrogates ROS, we examined the relationship between Ca++ influx, ROS formation, and Mac-1 expression in TTD-inhibited neutrophil adhesion. TTD alone caused a slight but statistically significant increase in [Ca++]i with no effect on adhesion. In contrast, TTD as well as two Ca++ channel antagonists, verapamil and nifedipine, markedly diminished fMLP- and PMA-induced Ca++ influx, Mac-1 up-regulation, and adhesion. TTD also inhibited increases in [Ca++]i and adhesion induced by the ionophore A23187 but failed to inhibit those induced by thapsigargin, an agent mobilizing Ca++ from intracellular stores. Thus, TTD impeded Ca++ influx from outward to avert neutrophil adhesion. Similarly, TTD and two ROS scavengers, superoxide dismutase and catalase, abolished ROS production, Mac-1 up-regulation, and neutrophil adhesion. Ca++ and ROS, therefore, represent two essential signals for Mac-1 up-regulation upon fMLP or PMA stimulation. Our data suggest that the antiadherent effect of TTD is mediated, in part, by the inhibition of Ca++ influx and ROS formation, resulting in suppressed up-regulation of Mac-1 and, in turn, neutrophil adhesion to fibrinogen.

L-arginine-dependent production of reactive nitrogen intermediates (RNIs: nitric oxide, nitrite, and nitrate) by mammalian macrophages has been proposed to occur via an L-arginine oxidative deimination pathway and is known to be responsible for certain antineoplastic and antimicrobial effector functions. The present study represents the first examination of this pathway in a non-mammalian vertebrate. Because chickens, unlike mammals, lack a urea cycle and are incapable of de novo synthesis of L-arginine, the possible existence of an avian macrophage pathway for production of RNIs is questionable. We have defined conditions under which chicken macrophages are able to produce nitrite. Sephadex-elicited chicken peritoneal macrophages required a bacterial lipopolysaccharide (LPS from Escherichia coli) signal to produce nitrite during 24 hour cultures in the presence of L-arginine. As little as 5 ng/ml LPS resulted in significant nitrite production in culture. The relationship of nitrite production to both LPS and L-arginine levels was dose-dependent. D-arginine was unable to substitute for L-arginine but also produced no inhibitory effect. In contrast, L-NG-monomethyl arginine showed a significant inhibitory effect on nitrite production. A virus-transformed chicken macrophage cell line, HD11, also produced nitrite in a dose-dependent manner relative to both LPS and L-arginine concentration. Concentrations as low as 5 ng/ml LPS and 0.1 mM L-arginine resulted in significant nitrite production, while maximum levels of nitrite production were obtained using greater than or equal to 0.5 micrograms/ml LPS and greater than or equal to 0.4 mM L-arginine. These results indicate that chicken macrophages can produce RNIs. This production is dependent upon activation and is influenced by local L-arginine concentration. Moreover, because the chicken does not possess the ability to synthesize arginine and has an absolute nutritional requirement for this amino acid, the chicken represents a highly controllable system to examine the in vivo effects of L-arginine on macrophage-related immune functions.