Activated lymphocytes depress phagocytosis of latex particles by human monocyte-macrophages

In this study, monocyte-macrophages of normal human donors were cultured with and without lymphocytes and antigen in order to define the effect of antigen-stimulated lymphocytes on phagocytosis by macrophages. Phagocytosis was assessed by uptake of radio-labeled latex particles by macrophage monolayers. Although no effect was noted when purified macrophage monolayers were cultured in the presence of antigen, marked inhibition of phagocytosis was observed when macrophages were cultured in the presence of autochthonous antigen-stimulated lymphocytes. The degree of phagocytic depression correlated with the delayed cutaneous hypersensitivity response of the donor and with the concentration of antigen present in the system.     

Subunit asymmetry in the three-dimensional structure of a human CuZnSOD mutant found in familial amyotrophic lateral sclerosis.

The X-ray crystal structure of a human copper/zinc superoxide dismutase mutant (G37R CuZnSOD) found in some patients with the inherited form of Lou Gehrig's disease (FALS) has been determined to 1.9 angstroms resolution. The two SOD subunits have distinct environments in the crystal and are different in structure at their copper binding sites. One subunit (subunit[intact]) shows a four-coordinate ligand geometry of the copper ion, whereas the other subunit (subunit[broken]) shows a three-coordinate geometry of the copper ion. Also, subunit(intact) displays higher atomic displacement parameters for backbone atoms ((B) = 30 +/- 10 angstroms2) than subunit(broken) ((B) = 24 +/- 11 angstroms2). This structure is the first CuZnSOD to show large differences between the two subunits. Factors that may contribute to these differences are discussed and a possible link of a looser structure to FALS is suggested.     

Mapping of peroxyl radical induced damage on genomic DNA

We have examined the DNA damage produced by reaction of peroxyl radicals with human fibroblast DNA. DNA damage consisted of both strand breaks and base modifications. The extent of strand breaks and base modifications induced as a function of peroxyl radical concentration was determined by quantitation of fragment size distributions using denaturing glyoxal-agarose gel electrophoresis. Both strand breaks and base modifications increased in a log linear fashion with respect to peroxyl radical concentration. Oxidative base modifications were observed to occur to a greater extent than strand breaks at every concentration measured. The sequence-specific distribution of peroxyl radical induced base damage was mapped for 803 nucleotide positions using the method of ligation mediated PCR. A total of 87% of all guanine positions in the examined sequences was found to be significantly oxidized. The order of reactivity of DNA bases toward oxidation by peroxyl radicals was found to be G > C > T. Adenine is essentially unreactive. The yield of oxidative base modifications at guanines and cytosines by peroxyl radicals depends on the exact specification of 5' and 3' flanking bases in a polarity dependent manner. Every guanine in the 5'XGC3' motif was found to be oxidized, where X is any 5' neighbor. In contrast, 5' and 3' purine flanks drastically reduced the extent of peroxyl radical G oxidation. The pattern of base modification and the influence of nearest neighbors differs substantially from that previously reported for hydrogen peroxide damage mediated by low valent transition metal ions for the identical DNA sequences.     

Book Reviews

The Social Fabric of Health: An Introduction to Medical Anthropology. John M. Janzen. New York: McGraw-Hill, 2002. xiv. 313 pp.     

Excision of N-myc from chromosome 2 in human neuroblastoma cells containing amplified N-myc sequences.

Amplification of one of three growth-stimulating myc genes is a common method by which many tumor types gain a proliferative advantage. In metastatic human neuroblastoma, the amplification of the N-myc locus, located on chromosome 2, is a dominant feature of this usually fatal pediatric cancer. Of the many models proposed to explain this amplification, all incorporate as the initial step either disproportionate overreplication of the chromosomal site or recombination across a loop structure. The original locus is retained within the chromosome in the overreplication models but is excised in the recombination models. To test these models, we have used somatic cell hybrids to separate and analyze the chromosomes 2 from a neuroblastoma cell line containing in vivo amplified N-myc. Our results demonstrate that N-myc is excised from one of the chromosomes, suggesting that deletion is a requisite part of gene amplification in a naturally occurring system.     

An ultrahigh-sulphur keratin gene of the human hair cuticle is located at 11q13 and cross-hybridizes with sequences at 11p15

A human hair cuticle ultrahigh-sulphur keratin (UHSK) gene (KRN1) has been mapped by Southern analysis of a somatic cell hybrid panel and by in situ hybridization. A probe containing the coding region of this gene mapped to 11pter->11q21 using the hybrid cell panel and on in situ hybridization mapped to two regions on chromosome 11: the distal part of 11p15, most likely 11p15.5, and the distal part of 11q13, most likely 11q13.5. A probe from the 3 non-coding region of KRN1 mapped to 11q13.5 indicating that this was the map location of the cloned gene. The sequence of 11p15.5 is termed KRN1-like (KRN1L). The results reveal that the cuticle UHSK gene family is clustered in the human genome. Present address: The Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, OX3, 9DU, United Kingdom.     

Temperature dependence of rat diaphragm muscle contractility and fatigue

The diaphragm is a skeletal muscle of mixed fiber type that is unique in its requirement to maintain contractile function and fatigue resistance across a wide range of temperatures to sustain alveolar ventilation under conditions of hypo- or hyperthermia. The direct effect of temperature (15-41 degrees C) on rat diaphragm isometric contractility and fatigue was determined in vitro. As temperature decreased from 37 to 15 degrees C, contraction and relaxation times increased, and there was a left shift of the diaphragm's force-frequency curve, with decreased contractility at 41 and 15 degrees C. Fatigue was induced by 10 min of stimulation with 30 trains/min of 5 Hz at a train duration of 900 ms. Compared with 37 degrees C, fatigue resistance was enhanced at 25 degrees C, but no difference in fatigue indexes was evident at extreme hypothermia (15 degrees C) or hyperthermia (41 degrees C). Only when the fatigue program was adjusted to account for hypothermia-induced increases in tension-time indexes was fatigue resistance evident at 15 degrees C. These findings indicate that despite the diaphragm's unique location as a core structure, necessitating exposure to in vivo temperatures higher than found in limb muscle, the temperature dependence of rat diaphragm muscle contractility and fatigue is similar to that reported for limb muscle of mixed fiber type.     

Activation of human B cells. Comparison of the signal transduced by IL-4 to four different competence signals

The effects of the cytokine IL-4 on resting and activated human B cells were compared with the effects of known "competence" signals able to drive resting B cells into the cell cycle, including anti-Ig, PMA, anti-CD20, and a recently described competence signal, anti-Bgp95. In proliferation assays, IL-4 was costimulatory with anti-Ig and anti-Bgp95 but not with anti-CD20 or PMA. IL-4 alone triggered increases in expression of class II DR/DQ and CD40, but it did not trigger increases in intracellular free calcium [Ca2+]i in resting B cells or induce resting B cells to leave G0 and enter the G1 phase of the cell cycle. Although IL-4 has some characteristics of competence signals, it was most effective if added to B cells up to 12 h after anti-Ig or anti-Bgp95 rather than before, and thus, in this respect, works more like a progression signal. Like IL-4, all four competence signals for B cells triggered increases in class II and CD40, but only IL-4 consistently induced increases in CD23 surface levels. IL-4 was costimulatory only with anti-Ig and anti-Bgp95, each of which can trigger increases in [Ca2+]i and new protein synthesis of the proto-oncogene c-myc, and can increase attachment of protein kinase C to the plasma membrane. IL-4 was not costimulatory with signals that 1) did not affect [Ca2+]i yet induced c-myc protein synthesis (anti-CD20), 2) only stimulated the translocation of protein kinase C (PMA), or 3) only stimulated increases in [Ca2+]i (calcium ionophore). These results suggest that resting human B cells require at least two intracytoplasmic signals before IL-4 can effectively promote B cell proliferation.