Sensory potentials and sural nerve biopsy: a model evaluation

Compound action potentials (CAPs) were recorded from the sural nerve prior to nerve biopsy in patients with various kinds of polyneuropathy. A previously developed volume conductor model for the CAP is applied to analyze the recorded CAPs in close relation with the morphological findings in the biopsy. First, the fiber diameter histograms obtained from the biopsy are used to simulate CAPs, by assuming a linear relation between fiber diameter and propagation velocity. It is concluded that the simulated CAPs deviate systematically from the recorded CAPs. Next, the assumption of a linear diameter-velocity relation is left, and the assumed fiber velocity distribution is adapted to obtain optimal model reconstructions of the recorded CAPs. It is concluded that the model is capable of reconstructing the recorded CAPs, including slow components and small polyphasic potentials in the case of severe fiber loss. It is demonstrated how the diameter histogram and the optimal velocity distribution can be combined to an empirical estimate of the diameter-velocity relation.     

The depolarizing effect of suxamethonium on the membrane potential of striated muscle fibres at endplate-free regions

The depolarizing effect of suxamethonium (Sch) on the muscle fibre membrane of the isolated diaphragm of the rat was studied. The existence of Sch-sensitive loci other than postsynaptic receptors was confirmed. These loci, non-endplate receptors (distal side), could be separated from the endplate (proximal side) with a partition so that the two parts of the muscle on either side of the partition could be perfused separately. Two types of partition were used. The first type permitted conduction of the action potentials from one part of the muscle to the other, without leakage of perfusion fluid (physiological continuity); the second type of partition applied sufficient pressure to prevent conduction of action potentials (physiological discontinuity). Suxamethonium (10^?4.8M) applied to the distal side under the condition of physiological discontinuity depolarized this part of the muscle fibre membrane. However, when there was physiological continuity, the distal side showed no response to Sch. However, when in this situation (physiological continuity) the endplates were blocked with tubocurarine, the distal receptors responded to Sch in the same way as in the condition of discontinuity. It is suggested that under physiological conditions the sensitivity to choline-like agents of the distal receptors is masked by activity at the endplate.     

The contribution of calcium and potassium to the alpha-action of adrenaline on smooth muscle cells of the portal vein, pulmonary artery and taenia caeci of the guinea-pig

The role of calcium and potassium in the alpha-action of adrenaline in pulmonary artery and portal vein was compared with that in taenia caeci by measuring changes in membrane potential, muscle contraction and ion fluxes in quiescent preparations from guinea-pigs (23 degrees C). The depolarization evoked by adrenaline (5 x 10(-8)-3 x 10(-5) M) was sustained in portal vein; in pulmonary artery it declined to a constant level after reaching an initial maximum. In calcium-free medium (20 min) containing EGTA (0.4 mM) and high magnesium (6.2 mM) adrenaline did not affect the membrane potential or the contractile state of the portal vein. Under these conditions the sustained phase of the response was abolished in the pulmonary artery; the remaining transient depolarization and contraction could be evoked only once. Adrenaline (3 x 10(-5) M) caused an increased 45Ca loss and 86Rb loss from the pulmonary artery and taenia caeci in calcium-free solution; a second addition of adrenaline to the calcium-free solution did not enhance the 45Ca loss from these tissues. The portal vein responded with an enhanced 86Rb loss on addition of the alpha-agonist. The bee toxin apamin (3 x 10(7) M) did not modify the depolarization, the contraction or the 45Ca and 86Rb fluxes evoked by adrenaline in the blood vessels. Enhancement of the 86Rb loss from taenia in the presence of adrenaline was prevented by apamin, but the excess loss of 45Ca was not abolished. It is concluded that adrenaline enhances cytoplasmic calcium by promoting calcium entry from the extracellular space in portal vein. In pulmonary artery and taenia caeci this is accompanied by mobilization of calcium from a cellular structure. Calcium entry facilitates triggering of the contractile proteins in vascular smooth muscle and is associated with membrane depolarization; in taenia caeci the mobilization of calcium caused by alpha-receptor activation is associated with the opening of potassium channels producing hyperpolarization and accordingly relaxation of the smooth muscle cells.     

Deciphering the message broadcast by tumor-infiltrating dendritic cells

Human dendritic cells (DCs) infiltrate solid tumors, but this infiltration occurs in favorable and unfavorable disease prognoses. The statistical inference is that tumor-infiltrating DCs (TIDCs) play no conclusive role in predicting disease progression. This is remarkable because DCs are highly specialized antigen-presenting cells linking innate and adaptive immunity. DCs either boost the immune system (enhancing immunity) or dampen it (leading to tolerance). This dual effect explains the dual outcomes of cancer progression. The reverse functional characteristics of DCs depend on their maturation status. This review elaborates on the markers used to detect DCs in tumors. In many cases, the identification of DCs in human cancers relies on staining for S-100 and CD1a. These two markers are mainly expressed by Langerhans cells, which are one of several functionally different DC subsets. The activation status of DCs is based on the expression of CD83, DC-SIGN, and DC-LAMP, which are nonspecific markers of DC maturation. The detection of TIDCs has not kept pace with the increased knowledge about the identification of DC subsets and their maturation status. Therefore, it is difficult to draw a conclusion about the performance of DCs in tumors. We suggest a novel selection of markers to distinguish human DC subsets and maturation states. The use of these biomarkers will be of pivotal importance to scrutinize the prognostic significance of TIDCs.     

Antibodies and carbohydrate ligands binding to DC-SIGN differentially modulate receptor trafficking

DCs are regarded as key APCs that initiate humoral and cellular immune responses. Consequently, targeted delivery of Ag toward DC-specific receptors enhances vaccine efficacy. DC-SIGN is a C-type lectin receptor that facilitates DC-specific delivery of Ag. This is accomplished by conjugating Ag to receptor-specific Ab or carbohydrate ligands that bind to its carbohydrate recognition domain. Here, we investigated the fate of DC-SIGN following receptor triggering with Ab. Both whole and single-chain Ab induced rapid internalization of about half of the surface receptor molecules. Biochemical studies showed that about half of the receptor molecules were still intracellular after 3 h, while minimal or no resurfacing of internalized or newly synthesized unbound DC-SIGN molecules was observed. Prolonged exposure of DCs to DC-SIGN Ab, but not carbohydrate ligands, resulted in reduced receptor expression levels, which lasted up to 2 days following removal of the Ab. In addition, exposure to DC-SIGN Ab reduced the ability of the receptor to internalize. Consequently, DC-SIGN showed a poor ability to accumulate targeting Abs within DCs. Vaccine efficacy may therefore be enhanced by strategies increasing the amount of Ag entering via a single receptor molecule, such as the use of targeting moieties allowing DC-SIGN recycling or Ab-coated vaccine carriers.     

Ascorbic acid neutralizes reactive oxidants released by hyperactive phagocytes from cigarette smokers

During exposure to the leukoattractant FMLP (N-formyl-l-methionyl-l-leucyl-l-phenylalanine) human polymorphonuclear leukocytes (PMNL) exhibit a bimodal pattern of luminol-enhanced chemiluminescence (LECL) with distinct early extracellular and later-occurring intracellular membrane-associated oxidative responses [4, 7, 14]. With the primary objective of measuring the effects of oral administration of the antioxidant ascorbate on the generation of reactive oxidants by circulating phagocytes from cigarette smokers and nonsmokers, we have developed a method for the measurement of FMLP-activated LECL in whole blood. With this method definite bimodal LECL responses, similar to those obtained with pure PMNL, were observed with FMLP-activated whole blood. No LECL responses were observed when whole blood from 3 children with chronic granulomatous disease was stimulated with FMLP, which shows that the FMLP-activated LECL responses are exclusively phagocyte-derived in blood from normal individuals. The whole blood method was used to compare the FMLP-activated LECL responses in blood from 30 asymptomatic smokers and 30 nonsmokers and to investigate the effects of co-incubation of whole blood from smokers and nonsmokers with ascorbate (2.5 × 10⁻⁵ M-2.5 × 10⁻⁴ M), as well as the effects of oral administration of the antioxidant on FMLP-activated LECL. Increased generation of both extracellular (58% mean increase,P < 0.005) and intracellular (75% mean increase,P < 0.005) phagocyte-derived oxidants was observed with FMLP-activated blood from smokers relative to nonsmokers. Co-incubation of blood with ascorbate in vitro caused a dose-dependent selective neutralization of extracellular oxidants. Similar effects were observed following the oral administration of a single dose of ascorbate (1 g). The whole blood method may be useful in identifying smokers at risk for smoking-related diseases.     

Interaction of acute lymphopblastic leukemia cells with C-type lectins DC-SIGN and L-SIGN

The C-type lectins DC-SIGN (CD209) and L-SIGN (CD299) recognize defined carbohydrates expressed on pathogens and cells. Those lectins are expressed on dendritic cells (DC) and/or on liver-sinusoidal endothelial cells. Both cell types modulate immune responses. In acute lymphoblastic leukemia (ALL), aberrant glycosylation of blast cells can alter their interaction with the C-type lectins DC-SIGN and L-SIGN, thereby affecting their immunological elimination. We investigated whether recombinant DC-SIGN and L-SIGN bind to blood or bone marrow cells from B- and T-ALL patients and compared that with binding of peripheral blood lymphocytes from healthy donors. It was found that increased binding of ALL cells to DC-SIGN and L-SIGN was observed compared to cells from healthy donors. Furthermore, L-SIGN bound a higher percentage of leukemic and normal cells than DC-SIGN. B-ALL bone marrow cells showed the highest binding to L-SIGN. DC-SIGN bound equally well to B-ALL and T-ALL cells. Within ALL subtypes, DC-SIGN binding was higher with mature T-ALL. Interestingly, our data demonstrate that increased binding of DC-SIGN and L-SIGN to peripheral leukemic cells from B-ALL patients is associated with poor survival. These data demonstrate that high binding of B-ALL peripheral blood cells to DC-SIGN and L-SIGN correlates with poor prognosis. Apparently, when B-ALL cells enter the blood circulation and are able to interact with DC-SIGN and L-SIGN the immune response is shifted toward tolerance. Additional studies are necessary to ascertain the possible role of these results in terms of disease pathogenesis and their potential as target to eradicate leukemic cells.