Entamoeba histolytica: effect of growth conditions and bacterial associates on isoenzyme patterns and virulence

In xenic culture, isolates of Entamoeba histolytica from asymptomatic carriers are characterized, with rare exception, by possession of a nonpathogenic zymodeme. During the process of axenizing such an isolate, strain CDC:0784:4, a change in the pattern of the isoenzymes from nonpathogenic zymodeme I to pathogenic zymodeme II was observed 40 days after the amebae had been transferred from a medium for xenic cultivation to one used for axenic cultivation, but before axenization of the amebae had actually occurred. Axenization was accomplished by feeding the amebae lethally irradiated bacteria while suppressing and finally eradicating with antibiotics the bacterial flora accompanying the amebae in the original xenic culture. The change in zymodeme was accompanied by a change in virulence as evidenced by the ability of the amebae to produce hepatic abscesses in hamsters and to destroy monolayers of tissue culture cells. Two explanations are offered for the observed changes in zymodeme and virulence: a zymodeme is not a stable inherent property of the ameba. Alternatively, the original isolate consisted of two zymodeme populations and the conditions of growth selected for one or the other of the populations. In either case, our results suggest that the finding of a particular zymodeme in a culture of E. histolytica isolated from an asymptomatic carrier of the parasite cannot be used to predict a clinical condition or serve as a basis for the recommendation of therapy.     

Diminished Reovirus Capsid Stability Alters Disease Pathogenesis and Littermate Transmission

Reovirus is a nonenveloped mammalian virus that provides a useful model system for studies of viral infections in the young. Following internalization into host cells, the outermost capsid of reovirus virions is removed by endosomal cathepsin proteases. Determinants of capsid disassembly kinetics reside in the viral σ3 protein. However, the contribution of capsid stability to reovirus-induced disease is unknown. In this study, we found that mice inoculated intramuscularly with a serotype 3 reovirus containing σ3-Y354H, a mutation that reduces viral capsid stability, succumbed at a higher rate than those infected with wild-type virus. At early times after inoculation, σ3-Y354H virus reached higher titers than wild-type virus at several sites within the host. Animals inoculated perorally with a serotype 1 reassortant reovirus containing σ3-Y354H developed exaggerated myocarditis accompanied by elaboration of pro-inflammatory cytokines. Surprisingly, unchallenged littermates of mice infected with σ3-Y354H virus displayed higher titers in the intestine, heart, and brain than littermates of mice inoculated with wild-type virus. Together, these findings suggest that diminished capsid stability enhances reovirus replication, dissemination, lethality, and host-to-host spread, establishing a new virulence determinant for nonenveloped viruses.     

Attachment of Entamoeba histolytica to glass in a defined maintenance medium: specific requirement for cysteine and ascorbic acid

Cysteine and ascorbic acid were previously shown to be required by Entamoeba histolytica trophozoites for attachment to glass, elongation, and ameboid movement as well as for short-term (12-24 h) survival in a balanced salt solution containing bovine serum albumin and a vitamin solution (Maintenance Medium 1). If the only function of cysteine and ascorbate was to decrease the redox potential, other reducing agents should be effective. However, the requirement for cysteine in the presence of ascorbic acid was highly specific. Equally effective were D- and L-cysteine; however, of many other compounds tested, only thioglycolic acid, ascorbic acid, or L-cystine (in decreasing order) were somewhat active. Under N2 atmosphere, cysteine and ascorbic acid were still required, although their concentrations could be halved. The ability to attach in the maintenance medium was irreversibly lost after only 5 min of cysteine-ascorbic acid deprivation; however, there was no decrease in viability when the amebae were transferred to growth medium within 30 min. Cysteine thiol groups in the medium were oxidized rapidly regardless of the concentration of ascorbic acid or the presence of amebae; however, ascorbic acid prolonged attachment of amebae.     

Mercuric chloride-induced nephrotoxicity in the rat following unilateral nephrectomy and compensatory renal growth

The nephropathy induced by mercuric chloride was assessed in unilaterally nephrectomized (NPX) and sham-operated (SO) rats using histological and urinalysis techniques. This assessment was carried out in order to test whether or not rats are more susceptible to the nephrotoxic effects of mercuric chloride after unilateral nephrectomy and a period allowing for compensatory renal growth. Twelve days after surgery both NPX and SO rats were given a single 1.5, 2.0 or 2.5 mumol/kg dose of mercuric chloride (i.v.). Twenty-four hours after the 1.5 or 2.0 mumol/kg dose of mercuric chloride was administered, cellular and tubular necrosis in the pars recta segments of proximal tubules in the outer medulla was more severe in NPX rats than in SO rats. Moreover, the urinary excretion of a number of cellular enzymes (e.g. lactate dehydrogenase) and plasma solutes (e.g. albumin) was greater in NPX rats than in SO rats. At the 2.5 mumol/kg dose of mercuric chloride, renal tubular damage was quite extensive in both groups of rats; to such an extent that possible differences in renal tubular damage between the NPX and SO rats could not be determined histologically. However, the urinary excretion of alanine aminopeptidase was greater in the NPX rats than in the SO rats. Therefore, based on the aforementioned findings, rats that have undergone and adapted to a reduction in renal mass (i.e. unilateral nephrectomy) appear to be more vulnerable to the nephrotoxic effects of mercuric chloride than rats with two normal kidneys.     

Complement Factor H-Related Protein 3 Serum Levels Are Low Compared to Factor H and Mainly Determined by Gene Copy Number Variation in CFHR3

The major human complement regulator in blood, complement factor H (FH), has several closely related proteins, called FH-related (FHR) proteins. As all FHRs lack relevant complement regulatory activity, their physiological role is not well understood. FHR protein 3 (FHR-3) has been suggested to compete with FH for binding to Neisseria meningitidis, thereby affecting complement-mediated clearance. Clearly, the in vivo outcome of such competition greatly depends on the FH and FHR-3 concentrations. While FH levels have been established, accurate FHR-3 levels were never unequivocally reported to date. Moreover, CFHR3 gene copy numbers commonly vary, which may impact the FHR-3 concentration. Hence, we generated five anti-FHR-3 mAbs to specifically measure FHR-3 in human healthy donors of which we determined the gene copy number variation at the CFH/CFHR locus. Finally, we examined the acute-phase response characteristics of FHR-3 in a small sepsis cohort. We determined FHR-3 levels to have a mean of 19 nM and that under normal conditions the copy number of CFHR3 correlates to a very large extent with the FHR-3 serum levels. On average, FHR-3 was 132-fold lower compared to the FH concentration in the same serum samples and FHR-3 did not behave as a major acute phase response protein.     

A Correspondence between Individual Differences in the Brain's Intrinsic Functional Architecture and the Content and Form of Self-Generated Thoughts

Although neural activity often reflects the processing of external inputs, intrinsic fluctuations in activity have been observed throughout the brain. These may relate to patterns of self-generated thought that can occur while not performing goal-driven tasks. To understand the relationship between self-generated mental activity and intrinsic neural fluctuations, we developed the New York Cognition Questionnaire (NYC-Q) to assess the content and form of an individual''s experiences during the acquisition of resting-state fMRI data. The data were collected as a part of the Nathan Kline Rockland Enhanced sample. We decomposed NYC-Q scores using exploratory factor analysis and found that self-reported thoughts clustered into distinct dimensions of content (future related, past related, positive, negative, and social) and form (words, images, and specificity). We used these components to perform an individual difference analysis exploring how differences in the types of self-generated thoughts relate to whole brain measures of intrinsic brain activity (fractional amplitude of low frequency fluctuations, regional homogeneity, and degree centrality). We found patterns of self-generated thoughts related to changes that were distributed across a wide range of cortical areas. For example, individuals who reported greater imagery exhibited greater low frequency fluctuations in a region of perigenual cingulate cortex, a region that is known to participate in the so-called default-mode network. We also found certain forms of thought were associated with other areas, such as primary visual cortex, the insula, and the cerebellum. For example, individuals who reported greater future thought exhibited less homogeneous neural fluctuations in a region of lateral occipital cortex, a result that is consistent with the claim that particular types of self-generated thought depend on processes that are decoupled from sensory processes. These data provide evidence that self-generated thought is a heterogeneous category of experience and that studying its content can be helpful in understanding brain dynamics.