DNA polymorphism of schistosomes and their snail hosts

Analysis of the genomes of schistosomes and one of their intermediate hosts, Biomphalaria glabrata, using Random Amplified Polymorphic DNA (RAPD) demonstrated that intraspecific genetic polymorphism in the parasite is limited but in the snail is highly pronounced. This suggests an important role for the snail in the determination of the epidemiology of the disease. In addition to their intraspecific stability, schistosome derived RAPDs exhibit a high level of interspecific polymorphism and are thus ideal for the construction of phylogenetic trees. For the detection of intraspecific polymorphisms extensive variation in the mitochondrial DNA is being exploited for the development of a PCR based test for Schistosoma mansoni. Gene level polymorphisms are being analyzed by Low Stringency Single Specific Primer PCR.

On the maintenance of sex-chromosome polymorphism by sex-antagonistic selection

Complex sex-determination systems are a priori unstable and require specific selective forces for their maintenance. Analytical derivations have suggested that sex-antagonistic selection may play such a role, but this assumed absence of recombination between the sex-determining and sex-antagonistic genes. Using individual-based simulations, and focusing on the sex chromosome and coloration polymorphisms of platy fishes as a case study, we show that the conditions for polymorphism maintenance induce female-biases in primary sex ratios, so that sex-ratio selection makes the system collapse towards male- or female heterogamety as soon as recombinant genotypes appear. However, a polymorphism can still be maintained under scenarios comprising strong sexual selection against dull males, mild natural selection against bright females, and low recombination rates. Though such conditions are plausibly met in natural populations of fishes harbouring such polymorphisms, quantitative empirical evaluations are required to properly test whether sex-antagonistic selection is a causal agent, or if other selective processes are required (such as local mate competition favouring female biased sex ratios).

MHC-II-independent CD4+ T cells induce colitis in immunodeficient RAG-/- hosts.

CD4(+) alpha beta T cells from either normal C57BL/6 (B6) or MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice engrafted into congenic immunodeficient RAG1(-/-) B6 hosts induced an aggressive inflammatory bowel disease (IBD). Furthermore, CD4(+) T cells from CD1d(-/-) knockout (KO) B6 donor mice but not those from MHC-I(-/-) (homozygous transgenic mice deficient for beta(2)-microglobulin) KO B6 mice induced a colitis in RAG(-/-) hosts. Abundant numbers of in vivo activated (CD69(high)CD44(high)CD28(high)) NK1(+) and NK1(-) CD4(+) T cells were isolated from the inflamed colonic lamina propria (cLP) of transplanted mice with IBD that produced large amounts of TNF-alpha and IFN-gamma but low amounts of IL-4 and IL-10. IBD-associated cLP Th1 CD4(+) T cell populations were polyclonal and MHC-II-restricted when derived from normal B6 donor mice, but oligoclonal and apparently MHC-I-restricted when derived from MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice. cLP CD4(+) T cell populations from homozygous transgenic mice deficient for beta(2)-microglobulin KO B6 donor mice engrafted into RAG(-/-) hosts were Th2 and MHC-II restricted. These data indicate that MHC-II-dependent as well as MHC-II-independent CD4(+) T cells can induce a severe and lethal IBD in congenic, immunodeficient hosts, but that the former need the latter to express its IBD-inducing potential.

Pro-opiomelanocortin gene and melanin-based colour polymorphism in a reptile

Colour polymorphism is widespread among vertebrates and plays important roles in prey-predator interactions, thermoregulation, social competition, and sexual selection. However, the genetic mechanisms involved in colour variation have been studied mainly in domestic mammals and birds, whereas information on wild animals remains scarce. Interestingly, the pro-opiomelanocortin gene (POMC) gives rise to melanocortin hormones that trigger melanogenesis (by binding the melanocortin-1-receptor; Mc1r) and other physiological and behavioural functions (by binding the melanocortin receptors Mc1-5rs). Owing to its pleiotropic effect, the POMC gene could therefore account for the numerous covariations between pigmentation and other phenotypic traits. We screened the POMC and Mc1r genes in 107 wild asp vipers (Vipera aspis) that can exhibit four discrete colour morphs (two unpatterned morphs: concolor or melanistic; two patterned morphs: blotched or lined) in a single population. Our study revealed a correlation between a single nucleotide polymorphism situated within the 3-untranslated region of the POMC gene and colour variation, whereas Mc1r was not found to be polymorphic. To the best of our knowledge, we disclose for the first time a relationship between a mutation at the POMC gene and coloration in a wild animal, as well as a correlation between a genetic marker and coloration in a snake species. Interestingly, similar mutations within the POMC 3-untranslated region are linked to human obesity and alcohol and drug dependence. Combined with our results, this suggests that the 3-untranslated region of the POMC gene may play a role in its regulation in distant vertebrates.

Structural prediction of peptides bound to MHC class I.

An ab initio structure prediction approach adapted to the peptide-major histocompatibility complex (MHC) class I system is presented. Based on structure comparisons of a large set of peptide-MHC class I complexes, a molecular dynamics protocol is proposed using simulated annealing (SA) cycles to sample the conformational space of the peptide in its fixed MHC environment. A set of 14 peptide-human leukocyte antigen (HLA) A0201 and 27 peptide-non-HLA A0201 complexes for which X-ray structures are available is used to test the accuracy of the prediction method. For each complex, 1000 peptide conformers are obtained from the SA sampling. A graph theory clustering algorithm based on heavy atom root-mean-square deviation (RMSD) values is applied to the sampled conformers. The clusters are ranked using cluster size, mean effective or conformational free energies, with solvation free energies computed using Generalized Born MV 2 (GB-MV2) and Poisson-Boltzmann (PB) continuum models. The final conformation is chosen as the center of the best-ranked cluster. With conformational free energies, the overall prediction success is 83% using a 1.00 Angstroms crystal RMSD criterion for main-chain atoms, and 76% using a 1.50 Angstroms RMSD criterion for heavy atoms. The prediction success is even higher for the set of 14 peptide-HLA A0201 complexes: 100% of the peptides have main-chain RMSD values < or =1.00 Angstroms and 93% of the peptides have heavy atom RMSD values < or =1.50 Angstroms. This structure prediction method can be applied to complexes of natural or modified antigenic peptides in their MHC environment with the aim to perform rational structure-based optimizations of tumor vaccines.

Redirecting anti-viral CTL against cancer cells by surface targeting of monomeric MHC class I-viral peptide conjugated to antibody fragments.

To combine the advantage of both the tumor targeting capacity of high affinity monoclonal antibodies (mAbs) and the potent killing properties of cytotoxic T lymphocytes (CTL), we investigated the activity of conjugates made by coupling single Fab' fragments, from mAbs specific for tumor cell surface antigens, to monomeric HLA-A2 complexes containing the immunodominant influenza-matrix peptide 58-66. In solution, the monovalent 95 kDa Fab-HLA-A2/Flu conjugates did not activate influenza-specific CTL. However, when targeted to tumor cells expressing the relevant tumor-associated antigen, the conjugates induced CTL activation and efficient tumor cell lysis, as a result of MHC/peptide surface oligomerization. The highly specific and sensitive in vitro cytotoxicity results presented suggest that injection of Fab-MHC/peptide conjugates could represent a new form of immunotherapy, bridging antibody and T lymphocyte attack on cancer cells.

The separate and combined effects of MHC genotype, parasite clone, and host gender on the course of malaria in mice.

BACKGROUND: The link between host MHC (major histocompatibility complex) genotype and malaria is largely based on correlative data with little or no experimental control of potential confounding factors. We used an experimental mouse model to test for main effects of MHC-haplotypes, MHC heterozygosity, and MHC x parasite clone interactions. We experimentally infected MHC-congenic mice (F2 segregants, homo- and heterozygotes, males and females) with one of two clones of Plasmodium chabaudi and recorded disease progression. RESULTS: We found that MHC haplotype and parasite clone each have a significant influence on the course of the disease, but there was no significant host genotype by parasite genotype interaction. We found no evidence for overdominance nor any other sort of heterozygote advantage or disadvantage. CONCLUSION: When tested under experimental conditions, variation in the MHC can significantly influence the course of malaria. However, MHC heterozygote advantage through overdominance or dominance of resistance cannot be assumed in the case of single-strain infections. Future studies might focus on the interaction between MHC heterozygosity and multiple-clone infections.

The intensity of human body odors and the MHC: should we expect a link?

It is now well established that genes within the major histocompatibility complex (MHC) somehow affect the production of body odors in several vertebrates, including humans. Here we discuss whether variation in the intensity of body odors may be influenced by the MHC. In order to examine this question, we have to control for MHC-linked odor perception on the smeller's side. Such a control is necessary because the perception of pleasantness and intensity seem to be confounded, and the causalities are still unsolved. It has previously been found that intense odors are scored as less pleasant if the signaler and the receiver are of MHC-dissimilar type, but not if they are of MHC similar type. We argue, and first data suggest, that an effect of the degree of MHC-heterozygosity and odor intensity is likely (MHC-homozygotes may normally smell more intense), while there is currently no strong argument for other possible links between the MHC and body odor intensity.

Molecular identification of similar species of the genus Biomphalaria (Mollusca: Planorbidae) determined by a polymerase chain reaction-restriction fragment length polymorphism

The freshwater snails Biomphalaria straminea, B. intermedia, B. kuhniana and B. peregrina, are morphologically similar; based on this similarity the first three species were therefore grouped in the complex B. straminea. The morphological identification of these species is based on characters such as vaginal wrinkling, relation between prepuce: penial sheath:deferens vas and number of muscle layers in the penis wall. In this study the polymerase chain reaction restriction fragment length polymorphism technique was used for molecular identification of these molluscs. This technique is based on the amplification of the internal transcribed spacer regions ITS1 e ITS2 of the ribosomal RNA gene and subsequent digestion of these fragments by restriction enzymes. Six enzymes were tested: Dde I, Mnl I, Hae III, Rsa I, Hpa II e Alu I. The restriction patterns obtained with DdeI presented the best profile for separation of the four species of Biomphalaria. The profiles obtained with all the enzymes were used to estimate the genetic distances among the species through analysis of common banding patterns.

LILRB2 interaction with HLA class I correlates with control of HIV-1 infection.

Natural progression of HIV-1 infection depends on genetic variation in the human major histocompatibility complex (MHC) class I locus, and the CD8+ T cell response is thought to be a primary mechanism of this effect. However, polymorphism within the MHC may also alter innate immune activity against human immunodeficiency virus type 1 (HIV-1) by changing interactions of human leukocyte antigen (HLA) class I molecules with leukocyte immunoglobulin-like receptors (LILR), a group of immunoregulatory receptors mainly expressed on myelomonocytic cells including dendritic cells (DCs). We used previously characterized HLA allotype-specific binding capacities of LILRB1 and LILRB2 as well as data from a large cohort of HIV-1-infected individuals (N = 5126) to test whether LILR-HLA class I interactions influence viral load in HIV-1 infection. Our analyses in persons of European descent, the largest ethnic group examined, show that the effect of HLA-B alleles on HIV-1 control correlates with the binding strength between corresponding HLA-B allotypes and LILRB2 (p = 10(-2)). Moreover, overall binding strength of LILRB2 to classical HLA class I allotypes, defined by the HLA-A/B/C genotypes in each patient, positively associates with viral replication in the absence of therapy in patients of both European (p = 10(-11)-10(-9)) and African (p = 10(-5)-10(-3)) descent. This effect appears to be driven by variations in LILRB2 binding affinities to HLA-B and is independent of individual class I allelic effects that are not related to the LILRB2 function. Correspondingly, in vitro experiments suggest that strong LILRB2-HLA binding negatively affects antigen-presenting properties of DCs. Thus, we propose an impact of LILRB2 on HIV-1 disease outcomes through altered regulation of DCs by LILRB2-HLA engagement.

Restriction fragment length polymorphism of 195 bp repeated satellite dna of Trypanosoma cruzi supports the existence of two phylogenetic groups

The restriction fragment length polymorphism of the 195 bp repeated DNA sequence of Trypanosoma cruzi was analyzed among 23 T. cruzi stocks giving a reliable picture of the whole phylogenetic variability of the species. The profiles observed with the enzymes Hinf I and Hae III were linked together and supported the existence of two groups. Group 1 shows a 195 bp repeated unit (Hinf I) and high molecular weight DNA (Hae III), while group 2 presents a ladder profile for each enzyme, which is a characteristic of tandemly repeated DNA. The two groups, respectively, clustered stocks pertaining to the two principal lineages evidenced by isoenzyme and RAPD markers. The congruence among these three independent genomic markers corroborates the existence of two real phylogenetic lineages in T. cruzi. The specific monomorphic profiles for each major phylogenetic lineage suggest the existence of ancient sexuality and cryptic biological speciation.

Polymorphism in Trypomastigotes of Trypanosoma (Megatrypanum) minasense in the blood of experimentally infected squirrel monkey and marmosets

Experimental infections by Trypanosoma (Megatrypanum) minasense were performed in primates - Saimiri sciureus and Callithrix penicillata - with the objective of searching for morphological variations of the blood trypomastigotes with respect to hosts and time of infection. We carried out morphological and morphometric analysis of blood trypomastigotes. Illustrations are given. Both the squirrel monkey and marmoset became infected after the injection of blood trypomastigotes of T. minasense , although the parasitaemia were briefer in the squirrel monkey. The parasites detected in the later host were narrower and shorter than those found in the inoculated marmoset. In the marmoset, the blood stream parasites derived from culture metacyclic trypomastigotes were considerably smaller than those derived from the inoculation of infected blood. Stronger evidence of polymorphism was found when, at the same time of infection, the blood trypomastigotes found in squirrel monkey had smaller length, body width and the distance from posterior end of the body to the kinetoplast almost four times smaller than the parasite found in the marmoset. Therefore, conflicting results on morphology and morphometry of T. minasense obtained by previous investigators could be due to polymorphism.