Combination of irinotecan (CPT11) and 5-fluorouracil with an analysis of cellular determinants of drug activity

Historical population collapses caused by rinderpest epidemics are hypothesized to have resulted in notable genetic losses in populations of the African buffalo. Polymorphism in the major histocompatibity complex (MHC) DRB3 gene was probed by means of restriction analysis of the sequence encoding the peptide-binding region. Nucleotide substitution patterns agreed with a positive selection acting on this fitness-relevant locus. Buffalo populations from four National Parks, situated in eastern and southern Africa, each revealed a surprisingly high allelic diversity. Current high levels of heterozygosity may be reconciled with historical bottlenecks by assuming that local extinctions were followed by fast recolonization, in accordance with the high dispersive capabilities of buffalo. The specific amplification of DRB3 alleles also enabled the assignment of individual genotypes. For each population sample a deficiency in the expected number of heterozygous animals was found. As overdominant selection on the MHC is predicted to yield an excess of heterozygous individuals, this may not be a locus-specific effect. Several other explanations are discussed, of which increased homozygosity caused by nonrandom mating of buffalo in populations seems the most probable.     

Host movement and the genetic structure of populations of parasitic nematodes

Mitochondrial DNA (mtDNA) sequence data were used to compare the population genetic structures of five species of parasitic nematodes from three different hosts: Ostertagia ostertagi and Haemonchus placei from cattle, H. contortus and Teladorsagia circumcincta from sheep, and Mazamastrongylus odocoilei from white-tailed deer. The parasites of sheep and cattle showed a pattern consistent with high gene flow among populations. The parasite of deer showed a pattern of substantial population subdivision and isolation by distance. It appears that host movement is an important determinant of population genetic structure in these nematodes. High gene flow in the parasites of livestock also indicates great opportunity for the spread of rare alleles that confer resistance to anthelmintic drugs. All species, including the parasite of deer, had unusually high within-population diversities (averages of 0.019-0.027 substitutions per site between pairs of individuals from the same population). Large effective population sizes (Ne), perhaps in combination with rapid mtDNA evolution, appear to be the most likely explanation for these high within-population diversities.     

The population genetic structure of the facultatively sexual parasitic nematode Strongyloides ratti in wild rats

We have investigated the population genetic structure of the parasitic nematode Strongyloides ratti in wild rats. In the UK, S. ratti reproduces predominantly by mitotic parthenogenesis, with sexual forms present at a rate of less than 1%. S. ratti was found to be a prevalent parasite and substantial genetic diversity was detected. Most rats were infected with a genotypic mixture of parasites. A hierarchical analysis of the genetic variation found in S. ratti sampled across Britain and Germany showed that 73.3% was explained by variation between parasites within individual hosts and 25.3% by variation between rats within sample sites. Only a small proportion (1.4%) of the total genetic variation was attributable to genetic subdivision between sample sites, suggesting that there is substantial gene flow between these sites. Most parasites sampled were found to exist in Hardy-Weinberg equilibrium and this population genetic structure is discussed in view of the virtual absence of sexual reproduction.     

Trade-off associated with selection for increased ability to resist parasitoid attack in Drosophila melanogaster

Costs of resistance are widely assumed to be important in the evolution of parasite and pathogen defence in animals, but they have been demonstrated experimentally on very few occasions. Endoparasitoids are insects whose larvae develop inside the bodies of other insects where they defend themselves from attack by their hosts' immune systems (especially cellular encapsulation). Working with Drosophila melanogaster and its endoparasitoid Leptopilina boulardi, we selected for increased resistance in four replicate populations of flies. The percentage of flies surviving attack increased from about 0.5% to between 40% and 50% in five generations, revealing substantial additive genetic variation in resistance in the field population from which our culture was established. In comparison with four control lines, flies from selected lines suffered from lower larval survival under conditions of moderate to severe intraspecific competition.     

Laparoscopic adrenalectomy for nonmalignant disease: improved safety, morbidity, and cost-effectiveness

The genetic diversity displayed by Plasmodiumfalciparum field isolates, the occurrence of variant forms of the parasite at different frequencies in different geographic areas, and the complexity of the infections represent major obstacles for the development of effective malaria control measures. However, since most of the existing studies have been performed in regions where P. falciparum transmission is high, little is known about the diversity and complexity of parasite populations circulating in areas of low malaria endemicity. We investigated the extent of genetic polymorphism in P. falciparum field isolates from Honduras, a region where its transmission is low and seasonal. Allelic diversity was analyzed in the highly polymorphic parasite genes encoding the merozoite surface proteins- (MSP-1) and -2 (MSP-2) and the glutamate-rich protein (GLURP) by the polymerase chain reaction. Gene polymorphism was also assessed in the EB200 region derived from the highly size polymorphic Pf332 gene. Limited size polymorphism was detected in all genes analyzed, with four and three variants for the MSP-1 and MSP-2 alleles, respectively, and two size variants for the GLURP and Pf332 genes. Moreover, based on the studied genetic markers, most infections consisted of only a few genetically distinct parasite clones. These results suggest that the P. falciparum parasite populations circulating in this region are genetically homogeneous and point to an association between the extent of parasite genetic diversity and the intensity of malaria transmission.     

Invasion genetics of the Mediterranean fruit fly: variation in multiple nuclear introns

Biological invasions generally start from low initial population sizes, leading to reduced genetic variation in nuclear and especially mitochondrial DNA. Consequently, genetic approaches for the study of invasion history and population structure are difficult. An extreme example is the Mediterranean fruit fly, Ceratitis capitata (Medfly), for which successive invasions during this century have resulted in a loss of 60% of ancestral genetic variation in isozymes and 75% of variation in mitochondrial DNA. Using Medflies as an example, we present a new approach to invasion genetics that measures DNA sequence variation within introns from multiple nuclear loci. These loci are so variable that even relatively recently founded Medfly populations within California and Hawaii retain ample genetic diversity. Invading populations have only lost 35% of the ancestral genetic variation. Intron variation will allow high-resolution genetic characterization of invading populations in both natural and managed systems, although non-equilibrium methods of analysis may be necessary if the genetic diversity represents sorting ancestral polymorphism.     

Recurrence of major depressive disorder in hospitalized children and adolescents

Global studies of within-group genetic variation have revealed a tendency for some traits, but not all, to show higher heterozygosity in sub-Saharan African populations. Although excess African diversity has been interpreted as reflecting a greater "age" of sub-Saharan African populations, more recent research has shown that this excess is more likely a consequence of a larger African long-term effective population size. The observation that certain traits, particularly classic genetic markers and RFLPs, do not show this pattern has been interpreted as ascertainment bias. Here, I examine another possible factor: that excess African heterozygosity is in part a function of mutation rate. Simple equilibrium and nonequilibrium models of absolute excess heterozygosity are examined. The results indicate that there is little excess African heterozygosity for traits with low mutation rates and greater excess heterozygosity for traits with moderate to high aggregate mutation rates. Observed data are consistent with these models. Also, depending on population size and time depth, traits with high levels of mutation might show less excess heterozygosity than those with moderate to high mutation rates. Another measure of diversity, mean sequence divergence, shows an increase in excess diversity for traits with high mutation rates.     

Fc epsilon receptor-positive cells are a major source of antigen-induced interleukin-4 in spleens of mice infected with Schistosoma mansoni

When cultured in vitro with either mitogen or parasite antigens, spleen cells from mice infected with Schistosoma mansoni produce significantly higher levels of IL-4 than splenocytes from control animals. Previous studies suggested that this increase in IL-4 production occurs because of a selective expansion of T helper type 2 (Th2) cells in infected mice. However, these experiments employed unfractionated spleen populations rather than purified T lymphocytes. Here we demonstrate that T-depleted spleen cells from infected animals synthesize high levels of interleukin-4 (IL-4), but no IL-5 when stimulated with parasite antigen in vitro. Nevertheless, when purified by sorting, T cells and non-B, non-T (NBNT) populations produced similar amounts of IL-4 in response to parasite antigen. The IL-4 producing NBNT cells were found to belong to an Fc epsilon receptor (Fc epsilon R)-positive population which after sort purification produced high levels of IL-4 (between 1000 and 2000 U of per 5 x 10(3) cells). FACS analysis revealed that these Fc epsilon R+ cells make up 0.53% of splenic NBNT cells in control animals while in 8-9-week-infected animals they increase to 3.8% of that population. In contrast, in mice with 8-week unisexual worm infections these cells comprise only 1.71% of NBNT cells, indicating that eggs are a major stimulus of the response. The expansion of Fc epsilon R+ cells and their production of IL-4 could be an important factor regulating the selection and induction of different CD4+ subsets in schistosome-infected hosts.     

Antigenic variation and the murine immune response to Giardia lamblia

The protozoan parasite Giardia lamblia is an important causative agent of acute or chronic diarrhoea in humans and various animals. During infection, the parasite survives the host's reactions by undergoing continuous antigenic variation of its major surface antigen, named VSP (variant surface protein). The VSPs form a unique family of cysteine-rich proteins that are extremely heterogeneous in size. The relevance of antigenic variation for the survival in the host has been most successfully studied by performing experimental infections in a combined mother/offspring mouse system and by using the G. lamblia clone GS/M-83-H7 (human isolate) as model parasite. In-vivo antigenic variation of G. lamblia clone GS/M-83-H7 is characterised by a diversification of the intestinal parasite population into a complex mixture of different variant antigen types. It could be shown that maternally transferred lactogenic anti-VSP IgA antibodies exhibit cytotoxic activity on the Giardia variant-specific trophozoites in suckling mice, and thus express a modulatory function on the proliferative parasite population characteristics. Complementarily, in-vitro as well as in-vivo experiments in adult animals indicated that non-immunological factors such as intestinal proteases may interfere into the process of antigen variation in that they favour proliferation of those variant antigen-type populations which resist the hostile physiological conditions within the intestine. These observations suggest that an interplay between immunological and physiological factors, rather than one of these two factor alone, modulates antigenic diversification of a G. lamblia population within an experimental murine host and thus influences the survival rate and strategy of the parasite.     

Gene-pool variation in caledonian and European Scots pine (Pinus sylvestris L.) revealed by chloroplast simple-sequence repeats

We have used polymorphic chloroplast simple-sequence repeats to analyse levels of genetic variation within and between seven native Scottish and eight mainland European populations of Scots pine (Pinus sylvestris L.). Diversity levels for the Scottish populations based on haplotype frequency were far in excess of those previously obtained using monoterpenes and isozymes and confirmed lower levels of genetic variation within the derelict population at Glen Falloch. The diversity levels were higher than those reported in similar studies in other Pinus species. An analysis of molecular variance (AMOVA) showed that small (3.24-8.81%) but significant (p < or = 0.001) portions of the variation existed between the populations and that there was no significant difference between the Scottish and the mainland European populations. Evidence of population substructure was found in the Rannoch population, which exhibited two subgroups. Finally, one of the loci studied exhibited an allele distribution uncharacteristic of the stepwise mutation model of evolution of simple-sequence repeats, and sequencing of the PCR products revealed that this was due to a duplication rather than slippage in the repeat region. An examination of the distribution of this mutation suggests that it may have occurred fairly recently in the Wester Ross region or that it may be evidence of a refugial population.     

Different patterns of variation at the X- and Y-chromosome-linked microsatellite loci DXYS156X and DXYS156Y in human populations

We compared the global pattern of variation at two homologous microsatellites mapping to the long arm of the X chromosome (DXYS156X) and to the short arm of the Y chromosome (DXYS156Y) in humans. A single pair of oligonucleotide primers amplifies these two nonallelic loci, each of which contains polymorphism in the number of pentanucleotide units. We observed 11 alleles in a sample of 2290 X chromosomes and 2006 Y chromosomes from 50 populations representing 6 major geographic regions. The overlapping size range of the X- and Y-chromosome alleles indicated a more complex distribution of alleles at these two loci than previously reported. Contrasting patterns of X-chromosome-linked and Y-chromosome-linked variation were reflected in statistically significant differences in genetic diversity values among geographic regions and between X and Y chromosomes. Higher levels of diversity characterized the DXYS156X locus in Africa (0.799 +/- 0.004) and the DXYS156Y locus in East Asia (0.700 +/- 0.006) compared with populations from other regions. These different patterns of variation can be explained by a combination of processes at both the molecular and population levels, including variable mutation rates, different effective population sizes, and genetic drift.     

Implications of spatial aggregation of parasites for the population dynamics in host-parasite interaction

Some aspects of the widely observed over-dispersed pattern of the distribution of parasites within the host population are examined. It has been established in the parasitological literature that most hosts usually harbour few parasites, while only few hosts harbour a large proportion of the parasite population. Factors that may influence the pattern of distribution of parasites, the relation between the level of parasite aggregation and the prevalence of infection, and changes in this level of aggregation as a function of host age are analysed. Factors which determine the diversity of species in parasite communities are presented, and aspects of exploitative and interference competition among parasites and their relations with biological control procedures are also considered. Attention is also focused on the regulatory and destabilizing processes influencing the dynamic behaviour of host-parasite population interactions.     

Cytoskeletal sheets of mammalian eggs and embryos: a lattice-like network of intermediate filaments

The interaction between Leishmania parasites and Th1 cells is investigated using a simple mathematical model of immunological responses and parasite population growth within the host. The model generates patterns of resistance and susceptibility to infection that mirror observed trends in experimental infections of mice and of humans exposed to infection in areas of endemic transmission. The heterogeneity in outcome predicted by the model can arise either through differences in the values of the parameters that characterize the genetic background of the host or as a consequence of differences in the size of the infecting inoculum of the parasite. Detailed analyses of equilibrium states and of the time course of infection within a host suggest that a limitation in the availability of precursor T-cells, as a consequence of high levels of recruitment into the activated pool, may play a significant role in the progression of infection in susceptible hosts. A brief discussion is presented of the implications of model prediction for therapeutic intervention.     

Transgenic mice in the study of polyglutamine repeat expansion diseases

We investigated the genetic heterogeneity of 2354 individuals from the 9 provinces of Sicily. The genetic markers we used were HP, GC, TF, PI, and AK1 plus other previously tested polymorphisms, for a total of 24 independent markers. Distinct multivariate statistics were applied to verify the claimed genetic distinctiveness between extant eastern and western Sicilian populations. Our hypothesis stated that any diversity found between the two subpopulations would represent the signature of early colonization of the island by Greek and Phoenician peoples. Correspondence analysis showed that there was no clear geographic clustering within Sicily. The genetic distance matrix used for identifying the main genetic barriers revealed no east-west differences within the island's population, at least at the provincial level. FST estimates proved that the population subdivision did not affect the pattern of gene frequency variation; this implies that Sicily is effectively one panmictic unit. The bulk of our results confirm the absence of genetic differentiation between eastern and western Sicilians, and thus we reject the hypothesis of the subdivision of an ancient population in two areas.     

Extended major histocompatibility complex haplotypes in celiac patients in the west of Ireland

The highest reported prevalence of celiac disease (gluten-sensitive enteropathy) is found in the West of Ireland. Recent genetic data have suggested that major histocompatibility complex-linked loci may have a dominant genetic effect for disease susceptibility in this population compared with a recessive effect in other groups. To further understand the role of the MHC in celiac disease in the West of Ireland, we analyzed markers for 22 MHC haplotypes from celiac patients and compared them with 18 nontransmitted haplotypes found in the parents of celiac children, and with reported haplotypes from other populations. An extended MHC haplotype including [HLA-B8, DR3, DQw2, Bf*S, C4A*Q0, and C4B*1] accounted for 50% of celiac haplotypes but only 27% of nontransmitted parental haplotypes. Compared with other reported haplotypes in celiacs, patients from the West of Ireland show a higher prevalence of HLA-A1 as a component of this extended haplotype, suggesting that although the core haplotype is similar between Irish patients and others, the celiac population in the West of Ireland differs at other HLA loci. We did not observe any other common haplotypes among our patients unlike the situation in other populations. These differences may underlie the possible dominant effect of HLA-linked loci and the unusually high prevalence of celiac disease in the Irish population. We also found that the serum levels of complement components C3c, C4, and factor B were significantly lower among celiac patients than nonceliacs. The lower serum level of C4 appears to be related to the presence of deletions and null alleles at the C4A and C4B loci in celiacs.     

Class II major histocompatibility complex-deficient mice initially control an infection with Leishmania major but succumb to the disease

Class II major histocompatibility complex (MHC)-deficient (H-2b) mice do not express I-A or I-E molecules and, as a result, do not develop CD4 cells. Thus, they represent the ideal model for examining the importance of CD4 cells and MHC class II molecules in resistance to infection with Leishmania major and the capacity of MHC class I-restricted T cells to mediate resistance to L. major. Class II MHC-deficient mice and control (C57BL/6, normal and nude) mice were infected with L. major. Although MHC class II-deficient mice were able to control infection more effectively than nude mice, cutaneous lesions on the mice eventually progressed, and parasite replication became uncontrolled. These results suggest that CD4 cells and MHC class II molecules are essential for resistance to L. major and that in the absence of these cells and molecules, such mice can transiently control infection with L. major but are unable to resolve such infections.     

Population-based study of pelvic lymph node positivity in clinically localized prostate cancer: a study comparing African Americans and whites

Host genetic factors including major histocompatibility complex (MHC) polymorphisms influence both susceptibility to leprosy per se and also to leprosy type. Non-MHC genes may play an important role, but such genes remain undefined. The influence of two non-MHC candidate genes was assessed in a case-control study of Bengali leprosy patients from Calcutta. Recent studies have implicated variation in the vitamin D receptor (VDR) gene in susceptibility to several diseases, including osteoporosis and pulmonary tuberculosis. In this population, homozygotes for the alternate alleles of the VDR polymorphism are associated, respectively, with lepromatous and tuberculoid leprosy. The NRAMP1 (natural resistance associated macrophage protein 1) gene may influence human mycobacterial disease susceptibility based on studies with the murine homologue Nramp1. However, no significant association was found between NRAMP1 and leprosy susceptibility. This study suggests that the VDR polymorphism may influence susceptibility to some diseases by affecting the type and the strength of the host immune response.     

Assessing olfactory performance in an Old World primate, Macaca nemestrina

Viral quasispecies are closely related (but nonidentical) mutant and recombinant viral genomes subjected to continuous genetic variation, competition, and selection. Quasispecies structure and dynamics of replicating RNA enable virus populations to persist in their hosts and cause disease. We review mechanisms of viral persistence in cells, organisms, and populations of organisms and suggest that the critical interplay between host and viral influences (including in some cases the quasispecies organization) is the main driving force for long-term survival of viruses in nature.     

Levels of genetic polymorphism: marker loci versus quantitative traits

Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species.     

The Concerted Action ''Heart'' European registry on clinical application of mechanical circulatory support systems: bridge to transplant. The Registry Scientific Committee

Endemic helminthic infection is a major public-health problem and affects a large proportion of the world's population. In Australia, helminthic infection is endemic in Aboriginal communities living in tropical northern regions of the continent. Such infection is associated with nonspecific (polyclonal) stimulation of IgE synthesis and highly elevated total serum IgE levels. There is evidence that worm-infection variance (i.e., human capacity of resistance) and total serum IgE levels may be related to the presence of a major codominant gene. The beta chain of the high-affinity IgE receptor, Fc epsilon R1-beta, has been previously identified as a candidate for the close genetic linkage of the 11q13 region to IgE responses in several populations. We show a biallelic RsaI polymorphism in Fc epsilon R1-beta to be associated with total serum IgE levels (P = .0001) in a tropical population of endemically parasitized Australian Aborigines (n = 234 subjects). The polymorphism explained 12.4% of the total residual variation in serum total IgE and showed a significant (P = .0000) additive relationship with total serum IgE levels, across the three genotypes. These associations were independent of familial correlations, age, gender, racial admixture, or smoking status. Alleles of a microsatellite repeat in intron 5 of the same gene showed similar associations. The results suggest that variation in Fc epsilon R1-beta may regulate IgE-mediated immune responses in this population.