Richard D. Wells

Human TLR1 deficiency is associated with impaired mycobacterial signaling and protection from leprosy reversal reaction.

Toll-like receptors (TLRs) are important regulators of the innate immune response to pathogens, including Mycobacterium leprae, which is recognized by TLR1/2 heterodimers. We previously identified a transmembrane domain polymorphism, TLR1_T1805G, that encodes an isoleucine to serine substitution and is associated with impaired signaling. We hypothesized that this TLR1 SNP regulates the innate immune response and susceptibility to leprosy. In HEK293 cells transfected with the 1805T or 1805G variant and stimulated with extracts of M. leprae, NF-κB activity was impaired in cells with the 1805G polymorphism. We next stimulated PBMCs from individuals with different genotypes for this SNP and found that 1805GG individuals had significantly reduced cytokine responses to both whole irradiated M. leprae and cell wall extracts. To investigate whether TLR1 variation is associated with clinical presentations of leprosy or leprosy immune reactions, we examined 933 Nepalese leprosy patients, including 238 with reversal reaction (RR), an immune reaction characterized by a Th1 T cell cytokine response. We found that the 1805G allele was associated with protection from RR with an odds ratio (OR) of 0.51 (95% CI 0.29–0.87, p = 0.01). Individuals with 1805 genotypes GG or TG also had a reduced risk of RR in comparison to genotype TT with an OR of 0.55 (95% CI 0.31–0.97, p = 0.04). To our knowledge, this is the first association of TLR1 with a Th1-mediated immune response. Our findings suggest that TLR1 deficiency influences adaptive immunity during leprosy infection to affect clinical manifestations such as nerve damage and disability.

NOD1 and NOD2 regulation of pulmonary innate immunity to Legionella pneumophila

The role of nucleotide‐binding oligomerization domain‐1 (NOD1) and nucleotide‐binding oligomerization domain‐2 (NOD2), cytoplasmic receptors which detect bacterial cell wall molecules, in pulmonary innate immune responses is poorly understood. We determined that both NOD1 and NOD2 detect heat‐killed Legionella and stimulate NF‐κb and IFN‐β promoter activity using an in vitro luciferase reporter system. We next infected NOD1‐ and NOD2‐deficient animals with aerosolized Legionella pneumophila. At 3 days post infection, Nod1−/− mice had impaired bacterial clearance compared to WT controls. In addition, at 4 h and 24 h, Nod1−/− mice had impaired neutrophil recruitment to the alveolar space. In contrast, increased lung neutrophils were seen in the Nod2−/− animals at 24 h. Analysis of cytokine production at 4 h post infection revealed a significant decrease in proinflammatory cytokines in the Nod1−/− animals when compared to WT animals. In contrast, increased 4‐h proinflammatory cytokines were seen in the Nod2−/− animals. Furthermore, the lungs of both Nod1−/− and Nod2−/− mice had significantly increased pro‐inflammatory cytokine levels at 24 h, suggesting possible suppressive roles for later stages of infection. Together, our data suggest that although both NOD1 and NOD2 can detect Legionella, these receptors modulate the in vivo pulmonary immune response differently.

Association of human TLR1 and TLR6 deficiency with altered immune responses to BCG vaccination in South African infants

The development of effective immunoprophylaxis against tuberculosis (TB) remains a global priority, but is hampered by a partially protective Bacillus Calmette-Guérin (BCG) vaccine and an incomplete understanding of the mechanisms of immunity to Mycobacterium tuberculosis. Although host genetic factors may be a primary reason for BCGs variable and inadequate efficacy, this possibility has not been intensively examined. We hypothesized that Toll-like receptor (TLR) variation is associated with altered in vivo immune responses to BCG. We examined whether functionally defined TLR pathway polymorphisms were associated with T cell cytokine responses in whole blood stimulated ex vivo with BCG 10 weeks after newborn BCG vaccination of South African infants. In the primary analysis, polymorphism TLR6_C745T (P249S) was associated with increased BCG-induced IFN-γ in both discovery (n = 240) and validation (n = 240) cohorts. In secondary analyses of the combined cohort, TLR1_T1805G (I602S) and TLR6_G1083C (synonymous) were associated with increased IFN-γ, TLR6_G1083C and TLR6_C745T were associated with increased IL-2, and TLR1_A1188T was associated with increased IFN-γ and IL-2. For each of these polymorphisms, the hypo-responsive allele, as defined by innate immunity signaling assays, was associated with increased production of TH1-type T cell cytokines (IFN-γ or IL-2). After stimulation with TLR1/6 lipopeptide ligands, PBMCs from TLR1/6-deficient individuals (stratified by TLR1_T1805G and TLR6_C745T hyporesponsive genotypes) secreted lower amounts of IL-6 and IL-10 compared to those with responsive TLR1/6 genotypes. In contrast, no IL-12p70 was secreted by PBMCs or monocytes. These data support a mechanism where TLR1/6 polymorphisms modulate TH1 T-cell polarization through genetic regulation of monocyte IL-10 secretion in the absence of IL-12. These studies provide evidence that functionally defined innate immune gene variants are associated with the development of adaptive immune responses after in vivo vaccination against a bacterial pathogen in humans. These findings could potentially guide novel adjuvant vaccine strategies as well as have implications for IFN-γ-based diagnostic testing for TB.

Human CD1a Deficiency Is Common and Genetically Regulated

CD1 proteins evolved to present diverse lipid Ags to T cells. In comparison with MHC proteins, CD1 proteins exhibit minimal allelic diversity as a result of nonsynonymous single nucleotide polymorphisms (SNPs). However, it is unknown if common SNPs in gene regulatory regions affect CD1 expression and function. We report surprising diversity in patterns of inducible CD1a expression on human dendritic cells (DCs), spanning the full range from undetectable to high density, a finding not seen with other CD1 isoforms. CD1a-deficient DCs failed to present mycobacterial lipopeptide to T cells but had no defects in endocytosis, cytokine secretion, or expression of costimulatory molecules after LPS treatment. We identified an SNP in the 5′ untranslated region (rs366316) that was common and strongly associated with low CD1a surface expression and mRNA levels (p = 0.03 and p = 0.001, respectively). Using a CD1a promoter-luciferase system in combination with mutagenesis studies, we found that the polymorphic allele reduced luciferase expression by 44% compared with the wild-type variant (p < 0.001). Genetic regulation of lipid Ag presentation by varying expression on human DCs provides a mechanism for achieving population level differences in immune responses despite limited structural variation in CD1a proteins.

Transcriptional networks are associated with resistance to Mycobacterium tuberculosis infection.

Rationale Understanding mechanisms of resistance to M. tuberculosis (M.tb) infection in humans could identify novel therapeutic strategies as it has for other infectious diseases, such as HIV. Objectives To compare the early transcriptional response of M.tb-infected monocytes between Ugandan household contacts of tuberculosis patients who demonstrate clinical resistance to M.tb infection (cases) and matched controls with latent tuberculosis infection. Methods Cases (n = 10) and controls (n = 18) were selected from a long-term household contact study in which cases did not convert their tuberculin skin test (TST) or develop tuberculosis over two years of follow up. We obtained genome-wide transcriptional profiles of M.tb-infected peripheral blood monocytes and used Gene Set Enrichment Analysis and interaction networks to identify cellular processes associated with resistance to clinical M.tb infection. Measurements and main results We discovered gene sets associated with histone deacetylases that were differentially expressed when comparing resistant and susceptible subjects. We used small molecule inhibitors to demonstrate that histone deacetylase function is important for the pro-inflammatory response to in-vitro M.tb infection in human monocytes. Conclusions Monocytes from individuals who appear to resist clinical M.tb infection differentially activate pathways controlled by histone deacetylase in response to in-vitro M.tb infection when compared to those who are susceptible and develop latent tuberculosis. These data identify a potential cellular mechanism underlying the clinical phenomenon of resistance to M.tb infection despite known exposure to an infectious contact.

Genetic Variation in Toll-Interacting Protein Is Associated With Leprosy Susceptibility and Cutaneous Expression of Interleukin 1 Receptor Antagonist

Leprosy is a chronic disease characterized by skin and peripheral nerve pathology and immune responses that fail to control Mycobacterium leprae. Toll-interacting protein (TOLLIP) regulates Toll-like receptor (TLR) and interleukin 1 receptor (IL-1R) signaling against mycobacteria. We analyzed messenger RNA (mRNA) expression of candidate immune genes in skin biopsy specimens from 85 individuals with leprosy. TOLLIP mRNA was highly and specifically correlated with IL-1R antagonist (IL-1Ra). In a case-control gene-association study with 477 cases and 1021 controls in Nepal, TOLLIP single-nucleotide polymorphism rs3793964 TT genotype was associated with increased susceptibility to leprosy (recessive, P = 1.4 × 10(-3)) and with increased skin expression of TOLLIP and IL-1Ra. Stimulation of TOLLIP-deficient monocytes with M. leprae produced significantly less IL-1Ra (P < .001), compared with control. These data suggest that M. leprae upregulates IL-1Ra by a TOLLIP-dependent mechanism. Inhibition of TOLLIP may decrease an individuals susceptibility to leprosy and offer a novel therapeutic target for IL-1-dependent diseases.

Differential Dermal Expression of CCL17 and CCL18 in Tuberculoid and Lepromatous Leprosy

Background Leprosy is characterized by polar clinical, histologic and immunological presentations. Previous immunologic studies of leprosy polarity were limited by the repertoire of cytokines known at the time. Methodology We used a candidate gene approach to measure mRNA levels in skin biopsies from leprosy lesions. mRNA from 24 chemokines and cytokines, and 6 immune cell type markers were measured from 85 Nepalese leprosy subjects. Selected findings were confirmed with immunohistochemistry. Principal Results Expression of three soluble mediators (CCL18, CCL17 and IL-10) and one macrophage cell type marker (CD14) was significantly elevated in lepromatous (CCL18, IL-10 and CD14) or tuberculoid (CCL17) lesions. Higher CCL18 protein expression by immunohistochemistry and a trend in increased serum CCL18 in lepromatous lesions was observed. No cytokines were associated with erythema nodosum leprosum or Type I reversal reaction following multiple comparison correction. Hierarchical clustering suggested that CCL18 was correlated with cell markers CD209 and CD14, while neither CCL17 nor CCL18 were highly correlated with classical TH1 and TH2 cytokines. Conclusions Our findings suggest that CCL17 and CCL18 dermal expression is associated with leprosy polarity.

A Functional Toll-Interacting Protein Variant Is Associated with Bacillus Calmette-Guérin–Specific Immune Responses and Tuberculosis

Rationale: The molecular mechanisms that regulate tuberculosis susceptibility and bacillus Calmette‐Guérin (BCG)‐induced immunity are mostly unknown. However, induction of the adaptive immune response is a critical step in host control of Mycobacterium tuberculosis. Toll‐interacting protein (TOLLIP) is a ubiquitin‐binding protein that regulates innate immune responses, including Toll‐like receptor signaling, which initiate adaptive immunity. TOLLIP variation is associated with susceptibility to tuberculosis, but the mechanism by which it regulates tuberculosis immunity is poorly understood. Objectives: To identify functional TOLLIP variants and evaluate the role of TOLLIP variation on innate and adaptive immune responses to mycobacteria and susceptibility to tuberculosis. Methods: We used human cellular immunology approaches to characterize the role of a functional TOLLIP variant on monocyte mRNA expression and M. tuberculosis‐induced monocyte immune functions. We also examined the association of TOLLIP variation with BCG‐induced T‐cell responses and susceptibility to latent tuberculosis infection. Measurements and Main Results: We identified a functional TOLLIP promoter region single‐nucleotide polymorphism, rs5743854, which was associated with decreased TOLLIP mRNA expression in infant monocytes. After M. tuberculosis infection, TOLLIP‐deficient monocytes demonstrated increased IL‐6, increased nitrite, and decreased bacterial replication. The TOLLIP‐deficiency G/G genotype was associated with decreased BCG‐specific IL‐2+ CD4+ T‐cell frequency and proliferation. This genotype was also associated with increased susceptibility to latent tuberculosis infection. Conclusions: TOLLIP deficiency is associated with decreased BCG‐specific T‐cell responses and increased susceptibility to tuberculosis. We hypothesize that the heightened antibacterial monocyte responses after vaccination of TOLLIP‐deficient infants are responsible for decreased BCG‐specific T‐cell responses. Activating TOLLIP may provide a novel adjuvant strategy for BCG vaccination.