Polymorphisms at the 3′ untranslated region of SLC11A1 gene are associated with protection to Brucella infection in goats

New insights into the genetic predisposition of brucellosis and its effect on the gut and vaginal microbiota in goats

Goats contribute significantly to the global food security and industry. They constitute a main supplier of meat and milk for large proportions of people in Egypt and worldwide. Brucellosis is a zoonotic infectious disease that causes a significant economic loss in animal production. A case-control genome-wide association analysis (GWAS) was conducted using the infectious status of the animal as a phenotype. The does that showed abortion during the last third period of pregnancy and which were positive to both rose bengal plate and serum tube agglutination tests, were considered as cases. Otherwise, they were considered as controls. All animals were genotyped using the Illumina 65KSNP BeadChip. Additionally, the diversity and composition of vaginal and fecal microbiota in cases and controls were investigated using PCR-amplicone sequencing of the V4 region of 16S rDNA. After applying quality control criteria, 35,818 markers and 66 does were available for the GWAS test. The GWAS revealed a significantly associated SNP (P = 5.01 × 10-7) located on Caprine chromosome 15 at 29 megabases. Four other markers surpassed the proposed threshold (P = 2.5 × 10-5). Additionally, fourteen genomic regions accounted for more than 0.1% of the variance explained by all genome windows. Corresponding markers were located within or in close vicinity to several candidate genes, such as ARRB1, RELT, ATG16L2, IGSF21, UBR4, ULK1, DCN, MAPB1, NAIP, CD26, IFIH1, NDFIP2, DOK4, MAF, IL2RB, USP18, ARID5A, ZAP70, CNTN5, PIK3AP1, DNTT, BLNK, and NHLRC3. These genes play important roles in the regulation of immune responses to the infections through several biological pathways. Similar vaginal bacterial community was observed in both cases and controls while the fecal bacterial composition and diversity differed between the groups (P < 0.05). Faeces from the control does showed a higher relative abundance of the phylum Bacteroidota compared to cases (P < 0.05), while the latter showed more Firmicutes, Spirochaetota, Planctomycetota, and Proteobacteria. On the genus level, the control does exhibited higher abundances of Rikenellaceae RC9 gut group and Christensenellaceae R-7 group (P < 0.05), while the infected does revealed higher Bacteroides, Alistipes, and Prevotellaceae UCG-003 (P < 0.05). This information increases our understanding of the genetics of the susceptibility to Brucella in goats and may be useful in breeding programs and selection schemes that aim at controlling the disease in livestock.

Cytokine expression profile of B. melitensis-infected goat monocyte-derived macrophages

Brucella parasitize the macrophage where is able to replicate and modulate the immune response in order to establish a chronic infection. The most adequate response to control and eliminate Brucella infection is a type 1 (Th1) cell-mediated effector immunity. Research in immune response of B. melitensis-infected goats is relatively scarce. In this study, we first evaluated changes in the gene expression of cytokines, a chemokine (CCL2) and the inducible nitric oxide synthase (iNOS) of goat macrophage cultures derived from monocytes (MDMs) infected for 4 and 24 h with Brucella melitensis strain 16 M. TNFα, IL-1β and iNOS, and IL-12p40, IFNγ and also iNOS were significantly expressed (p < 0.05) at 4 and 24 h respectively, in infected compared to non-infected MDMs. Therefore, the in vitro challenge of goat MDMs with B. melitensis promoted a transcriptional profile consistent with a type 1 response. However, when the immune response to B. melitensis infection was contrasted between MDM cultures phenotypically restrictive or permissive to intracellular multiplication of B. melitensis 16 M, it was observed that the relative IL-4 mRNA expression was significantly higher in permissive macrophage cultures with respect to restrictive cultures (p < 0.05), independently of the time p.i. A similar trend, although non-statistical, was recorded for IL-10, but not for pro-inflammatory cytokines. Thus, the up-expression profile of inhibitory instead of pro-inflammatory cytokines could explain, in part, the difference observed in the ability to restrict intracellular replication of Brucella. In this sense, the present results make a significant contribution to the knowledge of the immune response induced by B. melitensis in macrophages of its preferential host species.

Evaluation of the goat cellular immune response to rBtuB-Hia-FlgK peptides from Brucella melitensis

Brucellosis is a zoonosis caused by Brucella; B. melitensis is the most prevalent species in goats and humans. Previously, three B. melitensis peptides, rBtuB-Hia-FlgK showed antigen-specific immune responses in rodent models. The goal of this study was to evaluate the goat Th1/Th2 immune response to B. melitensis peptides. Twenty-eight animals were separated into four groups and were immunized with the rBtuB-Hia-FlgK peptides cocktail, adjuvant, PBS and Rev-1 vaccine, respectively. Peripheral blood samples were collected on days 0, 15, and 80 post-inoculation. The CD4+ and CD8+ T cells proliferation, and cytokine production of the Th-1 (IL-2, IL-12, TNF-α, and IFN-γ) and Th-2 profiles (IL-4, IL-5, and IL-10) were evaluated. An increase of CD4+/CD8+ at 15 days post-vaccination was observed and continued until the 80th. In addition, the IFN-γ, TNF-α, and IL-2 mRNA expression were typically induced by the 15th day, but only IFN-γ levels were observed at day 80 post-immunization. Brucella pathogenesis is distinguished by the presence of a large amount of Th-1 cytokines. Although a reduced amount of IFN-γ in the culture supernatant was accurately detected compared with Rev-1 after 15 days, it could be influenced by the sampling schedule, as a higher cytokine production might be induced as early as the first-week post-vaccination. The results indicate that rBtuB-Hia-FlgK induced an immune response similar to the Rev-1 vaccine. The possible use of inert molecules with the unique ability to typically induce cellular response similar to attenuated vaccine represents an attractive option that should not be ruled out.

Comparative Review of Brucellosis in Small Domestic Ruminants

Brucella melitensis and Brucella ovis are the primary etiological agents of brucellosis in small domestic ruminants. B. melitensis was first isolated in 1887 by David Bruce in Malta Island from spleens of four soldiers, while B. ovis was originally isolated in Australia and New Zealand in early 1950's from ovine abortion and rams epididymitis. Today, both agents are distributed worldwide: B. melitensis remains endemic and associated with an extensive negative impact on the productivity of flocks in -some regions, and B. ovis is still present in most sheep-raising regions in the world. Despite being species of the same bacterial genus, B. melitensis and B. ovis have extensive differences in their cultural and biochemical characteristics (smooth vs. rough colonial phases, serum and CO2 dependence for in vitro growth, carbohydrate metabolism), host preference (female goat and sheep vs. rams), the outcome of infection (abortion vs. epididymitis), and their zoonotic potential. Some of these differences can be explained at the bacterial genomic level, but the role of the host genome in promoting or preventing interaction with pathogens is largely unknown. Diagnostic techniques and measures to prevent and control brucellosis in small ruminants vary, with B. melitensis having more available tools for detection and prevention than B. ovis. This review summarizes and analyzes current available information on: (1) the similarities and differences between these two etiological agents of brucellosis in small ruminants, (2) the outcomes after their interaction with different preferred hosts and current diagnostic methodologies, (3) the prevention and control measures, and (4) alerting animal producers about the disease and raise awareness in the research community for future innovative activities.

The Paratuberculosis Paradigm Examined: A Review of Host Genetic Resistance and Innate Immune Fitness in Mycobacterium avium subsp. Paratuberculosis Infection

Paratuberculosis, or Johne's Disease (JD) is a debilitating chronic enteritis mainly affecting ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). This organism causes worldwide economic losses to the livestock industry, and is of public health importance due to the potential zoonotic risk between MAP and Crohn's disease (CD) in humans. Without economical treatments, or a vaccine capable of preventing infection without causing cross-reactions with bovine tuberculosis, test-and-cull methods for disease control are imperative. Unfortunately, difficulties in diagnostics and long subclinical stage hinder adequate control and is further complicated by variation in MAP exposure outcome. Interestingly, the majority of infections result in asymptomatic presentation and never progress to clinical disease. One contributing factor is host genetics, where polymorphisms in innate immune genes have been found to influence resistance and susceptibility to disease. Candidate genes identified across studies overlap with those found in CD and tuberculosis including; Solute carrier family 11 member 1 gene (SLC11A1), Nucleotide-binding-oligomerization domain containing gene 2 (NOD2), Major histocompatibility complex type II (MHC-II), and Toll-like receptor (TLR) genes. This review will highlight evidence supporting the vital role of these genes in MAP infection outcome, associated challenges, and implications for the future of JD research.

Characterization of innate immune response to Brucella melitensis infection in goats with permissive or restrictive phenotype for Brucella intramacrophagic growth

Caprine brucellosis is a chronic, world-wide distributed disease which causes reproductive failure in goats and Brucella melitensis, its causative agent, bears a great zoonotic potential. There is evidence suggesting that some cattle and pigs have an innate ability to resist Brucella infection, but this has not yet been investigated in goats. In this study, we compared caprine macrophages that exhibit extreme restriction and permissiveness to B. melitensis' intracellular growth in vitro. Monocyte derived macrophages (MDMs) from 110 female goats were cultured and challenged in vitro with B. melitensis 16 M. After initial screening, 18 donor goats were selected based on their macrophages ability to restrict or allow bacterial intracellular growth and some elements of humoral and cellular immunity were studied in depth. MDMs that were able to restrict the pathogen's intracellular growth showed enhanced bacterial internalization, although there were no differences between groups in the production of reactive oxygen and nitrogen intermediates following 48 h treatment with heat-killed B. melitensis. Moreover, there were no differences between groups in the level of antibodies reacting with keyhole limpet hemocyanin (natural antibodies, NAbs) or with Brucella LPS antigens (cross-reacting antibodies, CrAbs), although a strong positive correlation between individual levels of IgM NAbs and IgM CrAbs was detected. Altogether, these results represent an initial step in understanding innate primary host response to B. melitensis, and deciphering which mechanisms may determine a successful outcome of the infection in goats.

Microsatellite markers reveal polymorphisms at the 3′ untranslated region of the SLC11A1 gene in Zhongdian Yellow cattle (Bos taurus)

Solute carrier family 11-member A1 (SLC11A1) gene encodes natural macrophage resistance-associated protein which regulates activity of macrophages against intracellular pathogens. The objective of this study was to study the polymorphism in the microsatellites present at 3′ untranslated region (UTR) of the SLC11A1 gene in 113 Zhongdian Yellow cattle (Bos taurus). Using DNA bi-directional sequencing, we detected seven alleles (GT10–16) for the first microsatellite (MS1), five alleles (GT12–16) for MS2, and four alleles (GT4–7) for MS3. MS3 is studied for the first time and revealed four novel variants (alleles GT4–7). Alleles GT12 (45.1%), GT13 (59.3%), and GT5 (85.4%) were the most frequent alleles at MS1, MS2, and MS3, respectively, Genotypes G12/12, G13/13, and G5/5 had the highest frequency 0.239, 0.540, and 0.743 at MS1, MS2, and MS3, respectively. Haplotypic data revealed that GT12/GT13 was the most frequent haplotype observed followed by GT12/14 haplotype. Three nucleotide variations were observed in MS1 and MS2. Comparative analysis of GT12/GT12 and GT13/GT13 genotype with other bovine genotypes showed significant difference (P > 0.05). Our results suggest that the homozygous genotypes GT12/GT12 and GT13/GT13 in Zhongdian Yellow cattle might be related to disease resistance. The findings reported in this study would be helpful in cattle breeding programs.

Association of TNF rs668920841 and INRA111 polymorphisms with caprine brucellosis: A case-control study of candidate genes involved in innate immunity

Caprine brucellosis is an infectious, contagious zoonotic disease caused by Brucella melitensis. Multiple factors, including host genetics, can influence the outcome of the exposure to Brucella; and it is expected that genetic variants that affect the host innate immune response could have a key role in Brucella infection and pathogenesis. In this study, we evaluated if polymorphisms in innate immunity-related genes are associated with results of Brucella infection in goats. Nine polymorphisms within interferon gamma (IFNG), tumor necrosis factor (TNF), MyD88 innate immune signal transduction adaptor (MYD88), interleukin 10 (IL10) and IL-10 receptor subunit alpha (IL10RA) genes and two molecular markers (BMS2753 and INRA111) were resolved by PCR-capillary electrophoresis in samples from 81 seronegative and 61 seropositive goats for brucellosis. A heterozygous genotype at INRA111, a microsatellite near the VRK serine/threonine kinase 2 (VRK2) gene, was associated with absence of Brucella-specific antibodies in goats naturally exposed to the pathogen (P = .004). Conversely, variants in the TNF gene (rs668920841) and near the IFN gamma receptor 1 (IFNGR1) gene (microsatellite BMS2753) were significantly associated with presence of Brucella-specific antibodies at allelic (P = .042 and P = .046) and genotypic level (P = .012 and P = .041, respectively). Moreover, an in silico analysis predicted a functional role of the insertion-deletion polymorphism rs668920841 on the transcriptional regulation of the caprine TNF gene. Altogether, these results contribute to the identification of genetic factors that have a putative effect on the resistance / susceptibility phenotype of goats to Brucella infection.

Genetic epidemiology of the Alpine ibex reservoir of persistent and virulent brucellosis outbreak

While it is now broadly accepted that inter-individual variation in the outcomes of host-pathogen interactions is at least partially genetically controlled, host immunogenetic characteristics are rarely investigated in wildlife epidemiological studies. Furthermore, most immunogenetic studies in the wild focused solely on the major histocompatibility complex (MHC) diversity despite it accounts for only a fraction of the genetic variation in pathogen resistance. Here, we investigated immunogenetic diversity of the Alpine ibex (Capra ibex) population of the Bargy massif, reservoir of a virulent outbreak of brucellosis. We analysed the polymorphism and associations with disease resistance of the MHC Class II Drb gene and several non-MHC genes (Toll-like receptor genes, Slc11A1) involved in the innate immune response to Brucella in domestic ungulates. We found a very low neutral genetic diversity and a unique MHC Drb haplotype in this population founded few decades ago from a small number of individuals. By contrast, other immunity-related genes have maintained polymorphism and some showed significant associations with the brucellosis infection status hence suggesting a predominant role of pathogen-mediated selection in their recent evolutionary trajectory. Our results highlight the need to monitor immunogenetic variation in wildlife epidemiological studies and to look beyond the MHC.

Association of an IRF3 putative functional uORF variant with resistance to Brucella infection: A candidate gene based analysis of InDel polymorphisms in goats

Brucellosis is an important zoonotic disease caused by infection with Brucella spp. It generates major economic losses in livestock production worldwide. Goats are the principal hosts of B. melitensis, the main infection agent of caprine and human brucellosis. The selection of resistance-related genes is considered one of the best long-term means to improve control to bacterial infection in domestic ruminants. We performed a candidate gene association study to test if six short insertion/deletion polymorphisms (InDels) at bacterial-infection related genes influence the resistance to Brucella infection in female creole goats. InDels (IRF3-540: rs660531540, FKBP5-294: rs448529294, TIRAP-561: rs657494561, PTPRT-588: rs667380588, KALRN-989: rs667660989 and RAB5a-016: rs661537016) were resolved by PCR-capillary electrophoresis in samples from 64 cases and 64 controls for brucellosis. Allelic frequencies were significantly different between cases and controls at IRF3-540 and KALRN-989 (p = 0.001 and 0.005). Indeed, the minor alleles (a and k) at InDels IRF3-540 and KALRN-989 were more frequent among controls than cases, providing evidence that these alleles confer protection against Brucella infection. Moreover, IRF3-540 a-containing genotypes (Aa and aa) were associated with absence of Brucella-specific antibodies in goats (p = 0.003; OR = 3.52; 95% CI = 1.55-7.96), and more specifically, a-allele was associated with resistance to Brucella infection in a dose-dependent manner. Also, we observed that the IRF3-540 deletion (a-allele) extends a conserved upstream ORF by 75 nucleotides to the main ORF, and thus it may decrease gene expression by reducing translation efficiency from the main ORF. These results suggest a potential functional role of IRF3-540 deletion in genetic resistance to Brucella infection in goats.