Malaria in humans: Plasmodium falciparum blood infection levels are linked to chromosome 5q31-q33

Plasmodium falciparum malaria remains a major cause of morbidity and mortality in many tropical countries, especially those in sub-Saharan Africa. Human genetic control of malaria infection is poorly understood; in particular, genes controlling P. falciparum blood infection levels remain to be identified. We recently evidenced the existence of complex genetic factors controlling blood infection levels in an urban population living in Burkina Faso. We performed, on 153 sibs from 34 families, sib-pair linkage analyses between blood infection levels and chromosome 5q31-q33, which contains numerous candidate genes encoding immunological molecules. Our results, obtained by means of the two-point Haseman-Elston (HE) method and a nonparametric (NP) approach, show linkage of parasitemia to D5S393 (P=.002) and D5S658 (P=.0004). Multipoint analyses confirmed linkage, with a peak close to D5S658 (P=.0013 and P=.0007 with the HE and NP methods, respectively). The heritability of the locus was .48, according to the two-point results, and .43, according to the multipoint results; this indicates that its variation accounted for approximately 45% of the variance of blood infection levels and that the locus plays a central role in the control of parasitemia. The identification of the gene is, therefore, of major interest in understanding the mechanisms controlling P. falciparum parasitemia.

Efficacy of anti-influenza peptide vaccine in aged mice

Influenza infections may cause serious morbidity, as well as mortality in the elderly. In the present study we vaccinated old and young mice of two strains with three synthetic recombinant constructs (Levi and Arnon, 1995. In: Chanock, R.M. et al. (Eds.), Vaccines 95. CSHL Press, New York, pp. 311-316) and examined their capacity to eliminate a challenge of virus. Virus clearance from the lungs in the aged was very efficient, although the immune response in the aged was comparatively reduced. The data demonstrate that an intranasal administration of peptide-based anti-influenza vaccine without any adjuvant can be efficient and protective in old mice. Further studies are needed to determine whether such constructs will provide an effective vaccine for elderly human subjects.

Linkage analysis of blood Plasmodium falciparum levels: interest of the 5q31-q33 chromosome region

There is accumulating evidence for the involvement of genetic factors in the human response to malaria infection, mostly based on results obtained in studies of severe clinical malaria. The role of major gene(s) controlling blood parasitemia levels in human malaria has also been detected by means of segregation analysis. To confirm and to localize such gene(s), we performed a sib-pair linkage analysis investigating the role of five candidate chromosomal regions: 6p21 (HLA-tumor necrosis factor region), 2q13-q21 (genes coding for interleukin-1 alpha and beta), 14q11 (locus coding for the alpha chain of T cell antigen receptor), 7q35 (gene cluster for the beta subunit of T cell receptor), and 5q31-q33, which includes several candidate genes and was recently linked to a locus controlling infection levels by Schistosoma mansoni, denoted as SM1. The analysis was carried out on nine families from a southern Cameroon village, and the phenotype under study was blood infection levels with Plasmodium falciparum. No linkage was found with any of the four markers outside the 5q31-q33 region. A trend in favor of linkage was observed in the distal part of the 5q31-q33 region, especially with the marker D5S636 (P < 0.05 using the Monte Carlo P value), which was the marker that provided the highest evidence for linkage with SM1. These results suggest that a locus influencing P. falciparum levels in malaria could be located in the same genetic region as that containing SM1, indicating that the 5q31-q33 region may be critical in the control of different parasite infections.

Checkpoints in thymocytopoiesis in aging: expression of the recombination activating genes RAG-1 and RAG-2

The study was designed to establish whether the ability to rearrange the T cell receptor (TCR) Vbeta genes is altered with age. We examined the expression of recombinase activating genes, RAG-1 and RAG-2, in the thymus of mice at different ages (2-24 months). A significant age-related decrease in RAG-1 and RAG-2 expression was observed in the thymocytes from the age of 12 months and over. To find out if this decrease is determined in the thymocyte progenitors or induced by the thymic microenvironment, we co-cultured lymphoid depleted fetal thymus (FT) explants with bone marrow cells, or immature thymocytes, from young and old mice. The developing thymocytes were examined at different time intervals during the first week of culture. Whereas cells derived from the immature thymocytes of the old donors failed to express RAG-1 and RAG-2, compared to the young, the bone marrow derived cells of both age groups did show this expression, and there was no difference in Vbeta rearrangement of the TCR. Our study indicates that T cell progenitors in the aging bone marrow retain the potential to give rise to T cells with TCR rearrangements, and the expression is determined by the thymic stroma.

Absence of linkage between MHC and a gene involved in susceptibility to human schistosomiasis

Six hundred million people are at risk of infection by Schistosoma mansoni. MHC haplotypes have been reported to segregate with susceptibility to schistosomiasis in murine models. In humans, a major gene related to susceptibility/resistance to infection by S. mansoni (SM1) and displaying the mean fecal egg count as phenotype was detected by segregation analysis. This gene displayed a codominant mode of inheritance with an estimated frequency of 0.20-0.25 for the deleterious allele and accounted for more than 50% of the variance of infection levels. To determine if the SM1 gene segregates with the human MHC chromosomal region, we performed a linkage study by the lod score method. We typed for HLA-A, B, C, DR and DQ antigens in 11 informative families from an endemic area for schistosomiasis in Bahia, Brazil, by the microlymphocytotoxicity technique. HLA-DR typing by the polymerase chain reaction with sequence-specific primers (PCR-SSP) and HLA-DQ were confirmed by PCR-sequence-specific oligonucleotide probes (PCR-SSOP). The lod scores for the different theta values obtained clearly indicate that there is no physical linkage between HLA and SM1 genes. Thus, susceptibility or resistance to schistosomiasis, as defined by mean fecal egg count, is not primarily dependent on the host's HLA profile. However, if the HLA molecule plays an important role in specific immune responses to S. mansoni, this may involve the development of the different clinical aspects of the disease such as granuloma formation and development of hepatosplenomegaly.

Genetic control of blood infection levels in human malaria: evidence for a complex genetic model

There is now accumulating evidence for the involvement of genetic factors in the control of immune response against malaria. These arguments come from numerous animal models, from population studies showing associations of red blood cell genetic defects as well as HLA antigens with severe malaria, and from familial studies including a recent segregation analysis, which led to detection of a major gene effect predisposing to high infection levels. The heterogeneity and complexity of this genetic control is one of the main findings of these previous studies, and probably a major cause of the difficulty in developing an effective malaria vaccine. A segregation analysis of blood infection levels is performed here in 44 pedigrees living in the tropical rain forest of southern Cameroon and exposed to high vectorial transmission intensity. The results confirm the existence of complex genetic factors controlling blood infection levels in human malaria but are not consistent with the parent-offspring transmission of a single Mendelian gene. This study also shows the dramatic effect of age on infection levels and its interaction with a putative major gene suggesting that genetic related differences are much more important in children than in adults. Further genetic studies focused on children may help to identify the nature of the genetic factors involved in the expression of human malaria, by means of linkage analyses using both familial information and genetic markers.

Susceptibility to leprosy is linked to the human NRAMP1 gene

Leprosy is a debilitating infectious disease of human skin and nerves. Genetic factors of the host play an important role in the manifestation of disease susceptibility. The human NRAMP1 gene is a leprosy susceptibility candidate locus since its murine homologue Nramp1 (formerly Lsh/Ity/Bcg) controls innate resistance to Mycobacterium lepraemurium. In this study, 168 members of 20 multiplex leprosy families were genotyped for NRAMP1 alleles and 4 closely linked polymorphic markers. Highly informative haplotypes overlapping the NRAMP1 gene were constructed, and the haplotype segregation into leprosy-affected offspring was analyzed. It was observed that the segregation of NRAMP1 haplotypes into affected siblings was significantly nonrandom. This finding is consistent with the hypothesis that NRAMP1 itself is a leprosy susceptibility locus.

Genetic epidemiology of infectious diseases in humans: design of population-based studies

The spread and clinical manifestations of an infection in human populations depend on a variety of factors, among them host genetics. Familial linkage studies used in genetic epidemiology to identify host genes test for nonrandom segregation of a trait with a few candidate chromosomal regions or any regions in the genome (genomewide search). When a clear major gene model can be inferred and reliable epidemiologic information is collected (e.g., in schistosomiasis), parametric linkage studies are used. When the genetic model cannot be defined (e.g., in leprosy and malaria), nonparametric linkage studies (e.g., sibling-pair studies) are recommended. Once evidence of linkage is obtained, the gene can be identified by polymorphisms strongly associated with the trait. When the tested polymorphism is in strong linkage disequilibrium with the disease allele or is the disease allele itself (e.g., in HIV infection and malaria), association studies can directly identify the disease gene. Finally, the role of the detected polymorphism in causing the trait is validated by functional studies.

Cytokine production profile of heart-infiltrating T cells in Chagas' disease cardiomyopathy

The hallmark of chronic Chagas' disease cardiomyopathy (CCC) is the finding of a T cell-rich inflammatory mononuclear cell infiltrate in the presence of extremely few parasites in the heart lesions. The scarcity of parasites in affected heart tissue casts doubt on the direct participation of Trypanosoma cruzi in CCC heart tissue lesions, and suggests the possible involvement of autoimmunity. The cells in the infiltrate are presumably the ultimate effectors of tissue damage, and there is evidence that such cells recognize cardiac myosin in molecular mimicry with T. cruzi proteins rather than primary reactivity to T. cruzi antigens (Cunha-Neto et al. (1996) Journal of Clinical Investigation, 98: 1709-1712). Recently, we have studied heart-infiltrating T cells at the functional level. In this short review we summarize the studies about the role of cytokines in human and experimental T. cruzi infection, along with our data on heart-infiltrating T cells in human Chagas' cardiomyopathy. The bulk of evidence points to a significant production of IFN-gamma and TNF-alpha which may be linked to T. cruzi-induced IL-12 production.

Estrogen-receptor expression and function in thymocytes in relation to gender and age

The expression of estrogen receptor (ER) in thymocytes was studied in young, middle-aged, and old (2, 12, and 24 months, respectively) female and male C57BL/6J mice. Western immunoblots prepared from the thymocytes of females of all age groups showed the presence of a 67-kD protein band, which has been associated with the apparent MW of denatured ER. Flow cytometry analysis of cells stained with a monoclonal anti-ER antibody (clone 13H2) disclosed ER expression in both females and males of all age groups. In vivo treatment with estradiol (E2) led to an increase in the specific activity of thymic creatine kinase (CK) in the female mice, whereas the male thymocytes responded with an increase in CK activity only on treatment with dihydrotestosterone (DHT). The data show no differences in ER expression between male and females, but the receptor appears not to be functional in males. Interestingly, when estradiol was applied to co-cultures of lymphoid-depleted fetal thymus (FT) explants and bone-marrow cells, or thymocytes, from young and old females, it resulted in increased cellularity of cultures containing cells of the young, and not those of the old. The proportion of CD4/CD8 phenotypes of the developing cells in these cultures was not affected by E2 treatment. These observations provide a new insight into ER expression and function in T-cell development in relation to gender and age.

Evidence for a major gene controlling susceptibility to tegumentary leishmaniasis in a recently exposed Bolivian population

Tegumentary leishmaniasis due to Leishmania braziliensis is a parasitic disease that occurs in two stages after the infected sandfly bite: (1) a primary cutaneous lesion followed by (2) a secondary mucosal involvement generally resulting in severe facial deformities. In order to investigate the genetic and environmental factors involved in the development of the cutaneous lesion, a familial study was performed in a region of Bolivia in which the disease is endemic. Complete selection of 118 nuclear families (703 subjects, with 241 patients), each with at least one cutaneous affected subject, was achieved; 41 families were of native origin, and 77 (herein designated "migrant") recently had settled in the area. For the analysis, the trait under study was the time to onset of the primary cutaneous lesion. The start of the follow-up was birth, for native population, or date of arrival in the endemic area, for migrant population. Segregation analysis was performed by use of a model based on survival analysis methods that allows joint estimation of genetic and environmental effects and accounts for gene x covariate interactions. A significant effect of gender, home-forest distance, and forest-related activity was found. In the 77 migrant families there was evidence for a recessive major gene controlling the onset of the primary cutaneous lesion, with residual familial dependences and age x genotype interaction. Penetrance estimations show that young subjects are genetically more susceptible than older subjects, suggesting that this genetic component could concern mechanisms involved in the development of individual protection during childhood. There was also a significant genetic heterogeneity of the sample according to the native/migrant origin of the families, and no major-gene effect was found in the native subsample.

The impact of host genetics on susceptibility to human infectious diseases

The development of genetic epidemiology methods using recent human genetic mapping information, together with the growing availability of candidate genes, has led to major advances in the identification of host genes involved in human infectious diseases. Within the past year, highlights include the mapping of a locus controlling the intensity of infection by Schistosoma mansoni, the demonstration that mutations in the interferon-gamma receptor 1 gene are causative of disseminated infection due to weakly pathogenic mycobacteria, and the identification, in the CCR5 gene, of a deletion which provides high protection against HIV-1 infection. The impact of these findings on the understanding of infectious disease pathogenesis and on the design of future preventive and therapeutic strategies should be considerable.

Risk factors for onset of cutaneous and mucocutaneous leishmaniasis in Bolivia

A survival analysis was performed on data from an endemic area of Bolivia where two populations, natives and highland migrants, were living, to investigate risk factors for onset of cutaneous leishmaniasis (CL) and its mucosal form (MCL). In a first data set (703 subjects with 242 CL patients), significant risk factors for CL were gender, native/migrant status, activity, and home-forest distance. The instantaneous risk of CL increased until adolescence in both populations, and rapidly decreased thereafter. This risk was 3-10 times higher in migrants than in natives until 20 years of age, and became similar thereafter. Environmental and behavioral factors did not seem sufficient to explain this contrast between the two populations, and this evolution with age may suggest differences in the mechanisms involved in the development of individual protection during childhood. In a second data set (446 CL patients with 34 mucosal forms) the native/migrant status was the main factor associated with the onset of mucosal form.

Thymocyte progenitors and T cell development in aging

Dysfunction of T lymphocytes in aging has been causally related to a gradual loss of the thymic microenvironmental function. However, in view of the fact that T cells are generated from bone marrow-derived stem cells that settle in the thymus, we have investigated the possibility that aging effects on the bone marrow have an impact on T cell development. Our approach was based on seeding of bone marrow cells, from young and old mice, onto lymphoid-depleted fetal thymus explants, and examining the patterns of T lymphocyte development under organ culture conditions. The results indicate multifactorial effects of aging, on pre-thymic and intra-thymic development processes, as well as on feedback regulation by mature T cells.

Effect of sertraline on regional metabolic rate in patients with affective disorder

Seventeen patients with major affective disorder completed a 10-week, placebo-controlled, randomized trial of the serotonin reuptake inhibitor sertraline. Patients underwent positron emission tomography with 18F-deoxyglucose and were assessed with the Hamilton Depression Rating Scale at baseline and 10 weeks after treatment with sertraline or placebo. The middle frontal gyrus, an area previously characterized by decreased metabolic activity in depressive patients, showed relatively increased activity on both sides after sertraline when contrasted with temporal and some occipital areas. Sertraline was associated with a significantly increased relative metabolic rate in right parietal lobe and in left occipital area 19, and a decreased metabolic rate in right occipital area 18. Other areas that differed between controls and a larger cohort of 39 depressive patients--including medial frontal lobe, cingulate gyrus, and thalamus--also showed a normalization of metabolic rate after sertraline.

Genetic localization of a locus controlling the intensity of infection by Schistosoma mansoni on chromosome 5q31-q33

Three hundred million individuals are at risk of infection by schistosomes and around 200,000 die each year of this disease. Severe clinical disease in schistosomiasis is often the consequence of heavy infection which, in several endemic areas, are determined largely by the susceptibility/resistance of individuals. Previously, we reported evidence, based on a segregation analysis in Brazilian pedigrees, that intensity of infection by Schistosoma mansoni was influenced by a major gene, indicating that host genetic factors are probably critical in controlling schistosome infection and disease development. To localize this gene, referred to as SM1, we performed a genome-wide study on 142 Brazilian subjects belonging to 11 informative families Our results show a linkage to only one region, on chromosome 5q31-q33, with maximum two-point lod scores of +4.74 and +4.52 for D5S636 and the colony stimulating factor-1 receptor marker (CSF1R), respectively. This was corroborated by multipoint analysis, indicating a close proximity to CSF1R as the most likely location of SM1. This region contains several candidate genes encoding immunological molecules that were shown to play important roles in human protection against schistosomes.

Segregation analysis indicates a major gene in the control of interleukine-5 production in humans infected with Schistosoma mansoni

The interleukine-5 (IL-5) is a hormone of the immune system that is the main regulator of eosinopoiesis, eosinophil maturation and activation, and immunoglobulin A production. Thus, IL-5 contributes in several ways to human immune defenses against various pathogens, including helminths and infectious agents of the digestive and respiratory tracts. On the other hand, the increase in eosinophil number and the activation of these cells, which both have been related to elevated IL-5 production, are the cause of severe pathological disorders, as in asthma or hypereosinophilic syndromes. Although the immunological pathways leading to IL-5 synthesis have been identified, the reasons for the large variability observed in IL-5 production among subjects exposed to comparable antigenic stimulation are unknown. To investigate the role of genetic factors in this variability, we conducted a segregation analysis in a Brazilian population infected by the helminth parasite Schistosoma mansoni. The analysis was performed on IL-5 levels produced by blood mononuclear cells of these subjects after in vitro restimulation with either parasite extracts (IL-5/schistosomula sonicates [SS] phenotype) or a T-lymphocyte mitogen (IL-5/phytohemagglutin [PHA]). The results provide clear evidence for the segregation of a codominant major gene controlling IL-5/SS and IL-5/PHA production and accounting for 70% and 73% of the phenotypic variance, respectively; the frequency of the allele predisposing to low IL-5 production was approximately .22 for both phenotypes. No significant relationship was found between these genes and the gene controlling infection intensities by S. mansoni detected in a previous study. Linkage studies are ongoing to locate those genes that would help to characterize the genetic factors involved in pathological conditions such as severe helminth infections and allergic diseases.