Of Bones and Always Fragments

A manuscript in which the poet, generously assisted by the muse, explores the unity of fear-death and whole-love through series of visitations and visions of the apocalypse.Bachelor of Art

Endocytic uptake of particles by mononuclear phagocytes and the penetration of obligate intracellular parasites

As William Trager pointed out some time ago in a review in 'Science', all obligate intracellular parasites--be they viral, bacterial, or protozoan--face a common dilemma. That dilemma is to invade their host cells in a way that is not destructive of the host cell upon whose metabolic hospitality and functional well-being their own reproduction depends. Simply stated, these organisms must penetrate the plasma membranes of their host and take up residence in a suitable location in the cell's cytoplasm. Since many of the speakers in this session will address them selves to the issues of penetration and intracellular location of specific organisms, I view my task as one of trying to place these issues into a general conceptual framework

THE PENETRATION OF REOVIRUS RNA AND INITIATION OF ITS GENETIC FUNCTION IN L-STRAIN FIBROBLASTS

Reovirus type 3 is phagocytized by L cells and rapidly sequestered inside lysosomes. Hydrolases within these organelles are capable of stripping the viral coat proteins, but they fail to degrade the double-stranded RNA genome. These observations support the view that sojourn of reovirus in lysosomes, when the lytic enzymes uncoat its genome, is an obligatory step in the sequence of infection. Although the mechanism for transferring the uncoated RNA out of lysosomes remains to be elucidated, evidence is presented suggesting that progeny genomes are bound to site(s) possessing the fine structure of viral inclusions or factories. It appears that both the synthesis of single- and double-stranded viral RNA and the morphogenesis of progeny virus particles occur in such factories

How Teaching Matters

Silverstein writes a letter to the editor of CBE Life Science Education in response to Harold Wenglinsky's paper “How Teaching Matters: Bringing the Classroom Back into Discussions of Teacher Quality” (www.ets.org/research/pic) which analyzes how the attributes and classroom practices of teachers affect the performance of eighth-grade students on standardized tests in science. Wenglinsky identified teacher attributes and practices that are highly correlated with superior student achievement. Two of the four attributes and practices identified by Wenglinsky (i.e., teacher laboratory skills and implementation of hands-on classroom exercises) are the central focus of Columbia University's Summer Research Program for Science Teachers (www.scienceteacherprogram.org) and of other Science Work Experience Programs for Teachers. Data to be published elsewhere show that teacher participation in Columbia's program has a very positive impact on their students' success in passing a New York State Regents exam in science. Confirmation of Wenglinsky's postulates could greatly simplify the task of improving middle and high school science education. For this reason alone, it is important to test Wenglinsky's conclusions rigorously and soon

Tumor-promoting phorbol esters stimulate C3b and C3b' receptor-mediated phagocytosis in cultured human monocytes

Monocytes were isolated in high yield (approximately 80%) and purity (greater than 90%) by Percoll gradient centrifugation and incubated in Teflon culture vessels. Using this culture method, we routinely recovered 80% of the cells originally placed into culture. Studies of the C3b and C3b' receptors of these monocytes showed that the function of both receptors could be dramatically altered by treating the cells with tumor-promoting phorbol esters. Both C3b and C3b' receptors of human monocytes efficiently mediate attachment of erythrocytes coated with the corresponding ligands, but do not promote their ingestion. However, monocytes treated with phorbol myristate acetate (PMA) or phorbol didecanoate ingest C3b- and C3b'-coated erythrocytes. Phorbol esters that are inactive as tumor promoters do not stimulate C3 receptor-mediated phagocytosis. The ability of monocytes to respond to PMA by activation of C3 receptors is developmentally regulated. Freshly isolated monocytes do not take up C3b- or C3b'-coated erythrocytes in response to PMA, but after 3 d of culture they show strong PMA-stimulated uptake. The stimulatory effect of PMA on monocyte C3b and C3b' receptor function occurs within minutes, is stable for hours, is cycloheximide insensitive, and can be inhibited with colchicine. Several lines of evidence indicates that phagocytosis of C3b or C3b'-coated erythrocytes is specifically mediated by the monocytes' C3b and C3b' receptors. First, erythrocytes attached to monocytes with concanavalin A are not ingested when the monocytes are treated with PMA. Second, monocytes plated on IgG-bearing substrates lose Fc receptor activity on their nonadherent surfaces but retain the capacity to ingest C3b- or C3b'-coated erythrocytes after PMA treatment. Third, PMA-treated monocytes plated on C3b-coated surfaces lose C3b receptor activity on their nonadherent surfaces but retain the capacity to ingest C3b'-coated erythrocytes. Conversely, PMA-treated monocytes plated on C3b'-coated surfaces show reduced C3b' receptors activity on their nonadherent surfaces but retain the capacity to ingest C3b-coated erythrocytes

Receptors for C3b and C3bi promote phagocytosis but not the release of toxic oxygen from human phagocytes

We have measured the release of H2O2 from granulocytes, monocytes, and macrophages during spreading on ligand-coated culture surfaces. While IgG-coated surfaces stimulate vigorous release of H2O2, neither C3b- nor C3bi-coated surfaces promoted appreciable release of H2O2 despite full ligation of C3b and C3bi receptors. We also measured release of H2O2 from cultured monocytes spreading on surfaces coated with both fibronectin and C3. Under such circumstances, the C3 receptors elicit a strong phagocytic response, but no H2O2 release was recorded. We conclude that the C3b and C3bi receptors of monocytes and granulocytes do not signal the generation of toxic oxygen intermediates from these cells

How many neutrophils are enough (redux, redux)?

Many chemotherapeutic regimens produce neutropenia, which predisposes to microbial infection. However, not all neutropenic individuals develop infections, so the ability to predict this outcome would be a powerful clinical tool. In this issue of the JCI, Malka et al. describe a dynamic system model of neutrophil bactericidal activity that confirms and extends the concept of critical neutrophil concentration. The authors demonstrate that when the neutrophil concentration approaches the critical concentration, bacterial populations in contact with them exhibit bistability. Their experimental findings raise the intriguing possibility of greater variability in bactericidal activity of neutrophils from healthy adults than heretofore recognized; their model predicts that this could have life-and-death consequences

Fibronectin and serum amyloid P component stimulate C3b- and C3bi-mediated phagocytosis in cultured human monocytes

Fibronectin (FN) and serum amyloid P component (SAP) markedly enhance phagocytosis mediated by the C3b and C3bi receptors of cultured human monocytes but not of granulocytes. (The C3b and C3bi receptors of granulocytes can be activated by treatment of these phagocytes with PMA.) Activation of monocyte C3 receptors by FN is developmentally regulated: Freshly explanted monocytes respond to FN with a small increase in C3 receptor-mediated phagocytosis while monocytes matured in culture exhibit a much greater response. The mechanism of action of FN on C3 receptors of cultured monocytes is unique in two respects. First, while substrate-bound FN or SAP activate monocyte C3 receptors, soluble FN does not. Second, stimulation of the basal surface of monocyte plasma membranes by substrate-bound FN activates C3b and C3bi receptors on the apical surface of the plasma membrane, i.e., at sites remote from the segments of membrane in contact with the FN or SAP

Interaction of the legionnaires' disease bacterium (Legionella pneumophila) with human phagocytes...

In an accompanying paper (13), we reported that human polymorphonuclear leukocytes kill only a limited proportion (0.5 log) of an inoculum of Legionella pneumophila (Philadelphia 1 strain) in the presence of human anti-L. pneumophila antibody and complement. We now report on the effect of anti-L. pneumophila antibody on L. pneumophila-monocyte interaction. The studies were carried out under antibiotic-free conditions. Monocytes bind more than three times as many viable L. pneumophila bacteria in the presence of both antibody and complement than in the presence of complement alone. Monocytes requires both antibody and complement to kill any L. pneumophila: however, even then, monocytes kill only a limited proportion (0.25 log) of an inoculum. The surviving bacteria multiply several logs in the monocytes and multiply as rapidly as when the bacteria enter monocytes in the absence of antibody. These findings suggest that humoral immunity may not be an effective host defense against L. pneumophila. Consequently, a vaccine that resulted only in antibody production against the Legionnaires' disease bacterium may not be efficacious