HLA-linked control of susceptibility to tuberculoid leprosy and association with HLA-DR types

Characterization of two MHC II genes (DOB, DRB) in white-tailed deer (Odocoileus virginianus)

BACKGROUND

The major histocompatibility complex (MHC) is responsible for detecting and addressing foreign pathogens inside the body. While the general structure of MHC genes is relatively well conserved among mammalian species, it is notably different among ruminants due to a chromosomal inversion that splits MHC type II genes into two subregions (IIa, IIb). Recombination rates are reportedly high between these subregions, and a lack of linkage has been documented in domestic ruminants. However, no study has yet examined the degree of linkage between these subregions in a wild ruminant. The white-tailed deer (Odocoileus virginianus), a popular ruminant of the Cervidae family, is habitually plagued by pathogens in its natural environment (e.g. Haemonchus contortus, Elaeophora). Due to the association between MHC haplotypes and disease susceptibility, a deeper understanding of MHC polymorphism and linkage between MHC genes can further aid in this species' successful management. We sequenced MHC-DRB exon 2 (IIa) and MHC-DOB exon 2 (IIb) on the MiSeq platform from an enclosed white-tailed deer population located in Alabama.

RESULTS

We identified 12 new MHC-DRB alleles, and resampled 7 alleles, which along with other published alleles brings the total number of documented alleles in white-tailed deer to 30 for MHC-DRB exon 2. The first examination of MHC-DOB in white-tailed deer found significantly less polymorphism (11 alleles), as was expected of a non-classical MHC gene. While MHC-DRB was found to be under positive, diversifying selection, MHC-DOB was found to be under purifying selection for white-tailed deer. We found no significant linkage disequilibrium between MHC-DRB and MHC-DOB, suggesting that these loci are unlikely to be closely linked.

CONCLUSIONS

Overall, this study identified 12 new MHC-DRB exon 2 alleles and characterized a new, non-classical, MHC II gene (MHC-DOB) for white-tailed deer. We also found a lack of significant linkage between these two loci, which supports previous findings of a chromosomal inversion within the MHC type II gene region in ruminants, and suggests that white-tailed deer may have a recombination hotspot between these MHC regions similar to that found for Bos taurus.

Human leukocyte antigen class I and class II alleles are associated with susceptibility and resistance in borderline leprosy patients from Southeast Brazil

BACKGROUND

Evidence suggests that human leukocyte antigen (HLA) alleles influence the host immune response against Mycobacterium leprae. However, the association between HLA alleles and borderline (B) leprosy has not been studied. The aim of this study was to determine whether HLA class I and II molecules are associated with susceptibility or resistance to B leprosy including borderline-tuberculoid (BT), borderline-borderline (BB), and borderline-lepromatous (BL).

METHODS

DNA was obtained by the salting-out technique from the blood samples of 202 patients with B leprosy and 478 control subjects. HLA class I (A*, B*, and C* loci) and class II (DRB1* and DQB1* loci) genotypes were determined by polymerase chain reaction amplification and reverse hybridization with sequence-specific oligonucleotide probes and sequence-specific primers.

RESULTS

The case-controlled analysis results showed a significant association between B leprosy and HLA-C*05 (5.94% vs. 14.02%; p = 0.002, OR = 0.38, 95% CI = 0.20-0.73, pc = 0.032) and HLA-DRB1*07 (16.34% vs. 26.77%; p = 0.003, OR = 0.53, 95% CI = 0.3-0.8, pc = 0.039). A protective association was observed between BL leprosy and HLA-DQB1*02 (18.18% vs. 39.53%; p = 0.005, OR = 0.34, 95% CI = 0.15-0.75, pc = 0.025). In reactional patients, a significant association was observed between HLA-B*15 (28.72% vs. 12.76%; p = 0.011, OR = 2.75, 95% CI = 1.30-5.85, pc = 0.352) and predisposition to reversal reaction. Haplotype analysis showed that A*02-B*07-C*07-DRB1*15-DQB1*06 (2.97% vs. 1.04%; p = 0.015) and A*02-B*40-C*03-DRB1*13-DQB1*06 (1.73% vs. 0.10%; p = 0.0011) were associated with susceptibility to the B form. The presence of the HLA-DRB1*02 or HLA-DRB1*03/HLA-DQB1*01 haplotypes in B patients (22.05% vs. 33.0%; p = 0.005) suggested the involvement of these haplotypes in this clinical form of the disease.

CONCLUSIONS

The results indicate the involvement of HLA class I and class II molecules in B leprosy and reversal reactions; it also suggest a role for HLA in polarization of the disease in this group of patients.

Genetic evidence of TAP1 gene variant as a susceptibility factor in Indian leprosy patients

The heterodimeric transporter associated with antigen processing (TAP) gene loci is known to play a vital role in immune surveillance. We investigated a possible association of gene polymorphisms both in TAP1 and TAP2 in a cohort of clinically classified leprosy patients (n=222) and in ethnically matched controls (n=223). The TAP1 and TAP2 genes were genotyped for four single nucleotide polymorphisms TAP1 (rs1057141 Iso333Val and rs1135216 Asp637Gly) and TAP2 (rs2228396 Ala565Thr and rs241447 Ala665Thr) by direct sequencing and ARMS-PCR. The minor allele of TAP1 637G contributes to an increased risk to leprosy compared to controls (OR: 1.68, 95% CI 1.2-2.36, P=0.0057). An increased risk for the variant minor allele of the TAP1 637G to multibacillary (BL+LL) or paucibacillary (BT+TT) infections was also observed [multibacillary vs. controls (OR: 1.56, 95% CI 1.07-2.28, P=0.054); paucibacillary vs. controls (OR: 1.92, 95% CI 1.21-3.01, P=0.013)]. In the dominant model, the genotypes of the TAP1 rs1135216AG+GG additionally contributed to an increased risk. Overall our findings demonstrate that the TAP1 gene variant (rs1135216 Asp637Gly) influences the susceptibility to clinically classified leprosy patients in Indian population.

Leprosy susceptibility: genetic variations regulate innate and adaptive immunity, and disease outcome

The past few years have been very productive concerning the identification of genes associated with leprosy. Candidate gene strategies using both case-control and family-based designs, as well as large-scale approaches such as linkage and gene-expression genomic scans and, more recently, genome-wide association studies, have refined and enriched the list of genes highlighting the most important innate and adaptive immune pathways associated with leprosy susceptibility or resistance. During the early events of host-pathogen interaction identified genes are involved in pattern recognition receptors, and mycobacterial uptake (TLRs, NOD2 and MRC1), which modulate autophagy. Another gene, LTA4H, which regulates the levels of lipoxin A4 and possibly interacts with lipid droplet-related events, also plays a role in the early immune responses to Mycobacterium leprae. Together, the activation of these pathways regulates cellular metabolism upon infection, activating cytokine production through NF-κB and vitamin D-vitamin D receptor pathways, while PARK2 and LRRK2 participate in the regulation of host-cell apoptosis. Concomitantly, genes triggered to form and maintain granulomas (TNF, LTA and IFNG) and genes involved in activating and differentiating T-helper cells (HLA, IL10, as well as the TNF/LTA axis and the IFNG/IL12 axis) bridge immunological regulation towards adaptive immunity. Subtle variations in these genes, mostly single nucleotide polymorphisms, alter the risk of developing the disease or the severity of leprosy. Knowing these genes and their role will ultimately lead to better strategies for leprosy prevention, treatment and early diagnosis. Finally, the same genes associated with leprosy were also associated with autoimmune (Crohn's disease, rheumathoid arthritis, psoriasis) or neurodegenerative diseases (Parkinson's and Alzheimer's). Thus, information retrieved using leprosy as a model could be valuable to understanding the pathogenesis of other complex diseases.

Human genetic susceptibility to intracellular pathogens

Intracellular pathogens contribute to a significant proportion of infectious disease morbidity and mortality worldwide. Increasing evidence points to a major role for host genetics in explaining inter-individual variation in susceptibility to infectious diseases. A number of monogenic disorders predisposing to infectious disease have been reported, including susceptibility to intracellular pathogens in association with mutations in genes of the interleukin-12/interleukin-23/interferon-γ axis. Common genetic variants have also been demonstrated to regulate susceptibility to intracellular infection, for example the CCR5Δ32 polymorphism that modulates human immunodeficiency virus-1 (HIV-1) disease progression. Genome-wide association study approaches are being increasingly utilized to define genetic variants underlying susceptibility to major infectious diseases. This review focuses on the current state-of-the-art in genetics and genomics as pertains to understanding the genetic contribution to human susceptibility to infectious diseases caused by intracellular pathogens such as tuberculosis, leprosy, HIV-1, hepatitis, and malaria, with a particular emphasis on insights from recent genome-wide approaches. The results from these studies implicate common genetic variants in novel molecular pathways involved in human immunity to specific pathogens.

Mycobacterial infections:PARK2andPACRGassociations in leprosy

An overview of investigations indicating an important role of host genetics, both major histocompatibility complex (MHC) and non-MHC, in leprosy.

Stepwise replication identifies a low-producing lymphotoxin-alpha allele as a major risk factor for early-onset leprosy

Host genetics has an important role in leprosy, and variants in the shared promoter region of PARK2 and PACRG were the first major susceptibility factors identified by positional cloning. Here we report the linkage disequilibrium mapping of the second linkage peak of our previous genome-wide scan, located close to the HLA complex. In both a Vietnamese familial sample and an Indian case-control sample, the low-producing lymphotoxin-alpha (LTA)+80 A allele was significantly associated with an increase in leprosy risk (P = 0.007 and P = 0.01, respectively). Analysis of an additional case-control sample from Brazil and an additional familial sample from Vietnam showed that the LTA+80 effect was much stronger in young individuals. In the combined sample of 298 Vietnamese familial trios, the odds ratio of leprosy for LTA+80 AA/AC versus CC subjects was 2.11 (P = 0.000024), which increased to 5.63 (P = 0.0000004) in the subsample of 121 trios of affected individuals diagnosed before 16 years of age. In addition to identifying LTA as a major gene associated with early-onset leprosy, our study highlights the critical role of case- and population-specific factors in the dissection of susceptibility variants in complex diseases.

Genetic susceptibility to mycobacterial disease in humans

Mycobacterial disease remains a serious global health problem. Tuberculosis causes more than 2 million deaths a year, and leprosy is still a cause of severe disability in many parts of the world. As a result of the study of individuals with marked susceptibility to usually nonpathogenic mycobacteria, as well as case-control studies with candidate genes and genome-wide screens of affected populations, there is substantial evidence for the role of genetic factors in the susceptibility to mycobacterial disease. These studies have defined immunological processes essential for the control of mycobacteria infections in humans.

Molecular mechanisms of MHC linked susceptibility in leprosy: towards the development of synthetic vaccines

Tuberculoid (TT) and lepromatous leprosy (LL) develop in the human host depending on his ability to trigger a specific cellular immune response(CIR). Different genes have been demonstrated in susceptibility/protection and may explain the forms of leprosy. The major histocompatibility complex (MHC) play an important role. The aim of the study was to explore the contribution of human leukocyte antigen (HLA) DRB1, DQA1, DQB1 and DQ promoter genes in LL Mexican patients. Six families (26 LL, three TT patients and 27 controls) were analyzed; 114 unrelated patients were compared with 204 controls. Class I typing was done by the standard microlymphocytotoxicity and class II typing using PCR-SSOP. Haplotype segregation correlated with specific CIR in vivo and in vitro using lepromin. Haplotype sharing was significantly deviated in the affected sibs (p=0.01). Six healthy sibs were non-responders to lepromin and four of them were DQ1 homozgotes. DQ1 was significantly associated with LL and with non-responders. We set up macrophage activation experiments after infecting these cells with 5x10(6) bacilli to demonstrate if elimination occurred in the context or DQ1. When DQ1 was present on macrophages and on T cells, bacteria were poorly eliminated from the cell (32%) while when absent, 76% of the individuals were able to eliminate the bacilli (p=0.03). DRB1*1501 DQA1*0102-DQB1*0602 (DQ1 subtype) was significantly increased in the patients, indicating its participation in susceptibility. QBP 5.11/5.12 promoter present in the mentioned haplotype, and QAP 1.4, linked to DRB1*1301/02 haplotypes were also associated. Two mechanisms are suggested: the promoter polymorphisms may influence allele expression and thus the amount of peptides presented to the T-cell receptor, leading to a deficient CIR: HLA restriction is important for vaccine design; the way peptides anchor the DRB1*1501 groove may be relevant to the activation of TH1 cells, which contribute to an efficient presentation of peptides inducing a protective T-cell response.

Segregation of HLA/TNF region is linked to leprosy clinical spectrum in families displaying mixed leprosy subtypes

Each year an estimated 600000 new leprosy cases are diagnosed worldwide. The spectrum of the disease varies widely from limited tuberculoid forms to extensive lepromatous forms. A measure of the risk to develop lepromatous forms of leprosy is provided by the extent of skin reactivity to lepromin (Mitsuda reaction). To address a postulated oligogenic control of leprosy pathogenesis, we investigated in the present study linkage of leprosy susceptibility, leprosy clinical subtypes, and extent of the Mitsuda reaction to six chromosomal regions carrying known or suspected leprosy susceptibility loci. The only significant result obtained was linkage of leprosy clinical subtype to the HLA/TNF region on human chromosome 6p21 (P(corrected)=0.00126). In addition, we established that within the same family different HLA/TNF haplotypes segregate into patients with different leprosy subtypes directly demonstrating the importance of this genome region for the control of clinical leprosy presentation.

Genetics of susceptibility to leprosy

The ancient disease of leprosy can cause severe disability and disfigurement and is still a major health concern in many parts of the world. Only a subset of those individuals exposed to the pathogen will go on to develop clinical disease and there is a broad clinical spectrum amongst leprosy sufferers. The outcome of infection is in part due to host genes that influence control of the initial infection and the host's immune response to that infection. Identification of the host genes that influence host susceptibility/resistance will enable a greater understanding of disease pathogenesis. In turn, this should facilitate development of more effective therapeutics and vaccines. So far at least a dozen genes have been implicated in leprosy susceptibility and a genome-wide linkage study has lead to the identification of at least one positional candidate. These findings are reviewed here.

Genetic dissection of immunity to mycobacteria: the human model

Humans are exposed to a variety of environmental mycobacteria (EM), and most children are inoculated with live Bacille Calmette-Guérin (BCG) vaccine. In addition, most of the world's population is occasionally exposed to human-borne mycobacterial species, which are less abundant but more virulent. Although rarely pathogenic, mildly virulent mycobacteria, including BCG and most EM, may cause a variety of clinical diseases. Mycobacterium tuberculosis, M. leprae, and EM M. ulcerans are more virulent, causing tuberculosis, leprosy, and Buruli ulcer, respectively. Remarkably, only a minority of individuals develop clinical disease, even if infected with virulent mycobacteria. The interindividual variability of clinical outcome is thought to result in part from variability in the human genes that control host defense. In this well-defined microbiological and clinical context, the principles of mouse immunology and the methods of human genetics can be combined to facilitate the genetic dissection of immunity to mycobacteria. The natural infections are unique to the human model, not being found in any of the animal models of experimental infection. We review current genetic knowledge concerning the simple and complex inheritance of predisposition to mycobacterial diseases in humans. Rare patients with Mendelian disorders have been found to be vulnerable to BCG, a few EM, and M. tuberculosis. Most cases of presumed Mendelian susceptibility to these and other mycobacterial species remain unexplained. In the general population leprosy and tuberculosis have been shown to be associated with certain human genetic polymorphisms and linked to certain chromosomal regions. The causal vulnerability genes themselves have yet to be identified and their pathogenic alleles immunologically validated. The studies carried out to date have been fruitful, initiating the genetic dissection of protective immunity against a variety of mycobacterial species in natural conditions of infection. The human model has potential uses beyond the study of mycobacterial infections and may well become a model of choice for the investigation of immunity to infectious agents.

Influence of HLA-DR phenotype on the risk of hepatitis C virus-associated mixed cryoglobulinemia

OBJECTIVE

Circumstances predisposing hepatitis C virus (HCV)-infected patients to develop mixed cryoglobulinemia (MC), which may manifest as a small-vessel systemic vasculitis (MC vasculitis), remain unclear. Previous studies have failed to demonstrate a clear role of either viral factors (genotype, viral load) or host factors (lymphocytes or immunoglobulin subsets). This study was undertaken to examine a possible role of HLA class II alleles in HCV-associated MC.

METHODS

One hundred fifty-eight HCV-infected patients, of whom 76 had MC (56 with type II MC and 20 with type III MC) and 82 did not have MC, were studied prospectively. MC vasculitis was noted in 35 HCV-infected patients with type II IgMkappa-containing cryoglobulins. HLA-DRB1 and HLA-DQB1 polymorphism was analyzed by hybridization using allele-specific oligonucleotides, after gene amplification. The odds ratio (OR) was calculated with Woolf's method. Then, using multivariate analysis, demographic, biologic, immunologic, virologic, and liver histologic factors associated with the presence of MC and MC vasculitis were investigated.

RESULTS

HLA-DR11 was significantly more frequent in patients with type II MC than in those without MC (41.1% versus 17.1%; OR 3.4, corrected P [Pcorr] = 0.017), regardless of the presence of vasculitis accompanying the MC (37.1% of those with MC vasculitis, 34.1% of those with MC but no vasculitis). HLA-DR7 was less frequent in HCV-infected patients with MC than in those without MC (13.2% versus 30.5%; OR 0.34, P = 0.012, Pcorr not significant), with a particularly lower frequency in those with type II MC and those with MC vasculitis (12.5% and 8.6%, respectively). There was no significant difference in HLA-DQB1 distribution between the different patient groups. By univariate and multivariate analysis, HLA-DR11 was the only positive predictive factor, besides female sex and advanced age, for the presence of MC and HCV-associated MC vasculitis (OR 2.58).

CONCLUSION

Our results indicate that the presence of the DR11 phenotype is associated with a significantly increased risk for the development of type II MC in patients with chronic HCV infection. In contrast, HLA-DR7 appears to protect against the production of type II MC. These results suggest that the host's immune response genes may play a role in the pathogenesis of HCV-associated MC.

Host genes and infectious diseases. HIV, other pathogens, and a public health perspective

INTRODUCTION

The global impact of infectious diseases is tremendous. In 1996, the 17 million deaths from infectious diseases accounted for one third of all deaths worldwide, while the acute and chronic morbidity from infectious diseases adds an additional great burden on global health. Multiple factors, host and nonhost, influence the susceptibility of individuals and populations to infectious diseases, as well as the severity of the illness once infected.

METHODS

We review the influence of host genes on the susceptibility to and severity of viral, bacterial, parasitic and fungal infectious diseases, on vaccine responsiveness and on treatments for infections. HIV/AIDS is discussed in detail because it is an example of an infectious disease influenced by multiple host genes and because of its impact. Although the HIV/AIDS pandemic dates only since the late 1970s, it has claimed the lives of 11 million people worldwide and, today, more than 30 million people are estimated to be HIV infected.

CONCLUSION

Our greater understanding of the genetic factors that influence morbidity and mortality of infectious disease leads to new avenues of prevention and treatment that can improve the health of individuals and populations.

Distinct HLA class II alleles determine antibody response to vaccination with hepatitis B surface antigen

Major histocompatibility complex (MHC) determinants control antibody production in response to protein antigens. Vaccination with hepatitis B surface antigen (HBsAg) frequently fails in hemodialyzed patients, but the genetic factors that modulate humoral responsiveness are poorly characterized. We studied the distribution of HLA class II alleles in 415 hemodialyzed Caucasian patients who received a full course of HBsAg vaccination, using class II oligotyping after genomic amplification of the DRB1 and DQB1 loci. Phenotype frequencies were compared in 114 non responders (anti-HBs antibodies < or = 10 SI units/liter), 301 responders (anti-HBs antibodies > 10 units/liter) and 471 healthy controls. DRB1*01 (DR1) and DRB1*15 (DR15) frequencies were lower in nonresponders than in responders and controls (DR1, 12.3% vs. 22.9% and 24.8%, respectively; DR15, 14% vs. 22.9% and 25.1%), while DRB1*03 (DR3) and DRB1*14 (DR14) frequencies were higher (DR3, 32.5% vs. 16.6% and 25.3%, respectively; DR14, 9.6% vs. 3% and 6.6%). Overall, 44.5% of DR3 or DR14 patients were nonresponders, compared to 18.1% of DR1 or DR15 patients (P = 0.0001). In conclusion the humoral response to HBsAg vaccine is influenced by class II allelic variants, which differ in their capacity to bind and present peptides to T lymphocytes.

HLA-DR2 haplotypic diversity in populations of South-East Asia, northern China, Melanesia and Australian aborigines using PCR-RFLP for DRB1, DRB5, DQA1 and DQB1. A novel DRB1 allele: DRB1*16022

The polymorphism of the human leucocyte antigen HLA-DR2 and the heterogeneity of HLA-DR2 class II-related haplotypes (HLA-DRB1-DRB5-DQA1-DQB1) were investigated in four populations of east and south-east Asia (SEA) and five Melanesian populations using TaqI restriction fragment length polymorphism (RFLP) analysis, and the polymerase chain reaction (PCR) amplification-based techniques PCR-RFLP and sequence-specific oligonucleotide (SSO) typing. The haplotype DRB1*1502-DRB5*0101-DQA1*0102-DQB1*0601 was common in Malaysians, Javanese, Thursday Islanders, Madang, Goroka and the Australian Aborigines, while DRB1*16021-DRB5*0101-DQA1*0102-DQB1*0502 was common in the Thai and Thursday Islanders. DRB1*1501-DRB5*0101-DQA1*0102-DQB1*0602 was present at a high frequency in Northern Chinese, Goroka, Watut and Australian Aborigines. The study describes four rare or unusual haplotypes: HLA-DRB1*1501-DRB5*0101-DQA1*0101-DQB1*0601, DRB1*1502-DRB5*0101-DQA1*0101-DQB1*0502, DRB1*1502-DRB5*0102-DQA1* 0102-DQB1*0502 and DRB1*1501-DRB5*0101-DQA1*0101/2-DQB1*0503; the latter two were confirmed by segregation in two Javanese families. A new DR2 allele, initially detected by PCR-RFLP and confirmed by DNA sequencing as DRB1*16022 (previously designated DRB1*16Madang), was seen in a Madang individual. A new HLA-DR2 TaqI RFLP subtype, locally designated as DR15U, is also described. This RFLP subtype segregated in a Javanese family and correlated with a typically SEA haplotype, DRB1*1502-DRB5*0102-DQA1*0101-DQB1*0501. The allele HLA-DR16Thai, determined by TaqI DRB RFLP, was found by PCR-RFLP and SSO typing to correlate with a unique SEA haplotype, HLA-DRB1*16021-DRB5*0101-DQA1*0102-DQB1*0502, and was observed in the Thai, Malaysian, Thursday Islander, Javanese and Northern Chinese populations.

Arginine at positions 13 or 70-71 in pocket 4 of HLA-DRB1 alleles is associated with susceptibility to tuberculoid leprosy

Evaluation of human histocompatibility leukocyte antigen (HLA) class II genes in 54 cases of tuberculoid leprosy (TL) and 44 controls has shown a positive association with HLA-DRB1 alleles that contain Arg13 or Arg70-Arg71. Among TL patients, 87% carry specific alleles of DRB1 Arg13 or Arg70-Arg71 as compared to 43% among controls (p = 5 x 10(-6)) conferring a relative risk of 8.8. Thus, susceptibility to TL involves three critical amino acid positions of the beta chain, the side chains of which, when modeled on the DR1 crystal structure, line a pocket (pocket 4) accommodating the side chain of a bound peptide. This study suggests that disease susceptibility may be determined by the independent contribution of polymorphic residues participating in the formation of a functional arrangement (i.e., pocket) within the binding cleft of an HLA molecule.

HLA-linked susceptibility to rheumatoid arthritis. A study of forty-one multicase families from northern India

OBJECTIVE

To analyze segregation of rheumatoid arthritis (RA) with HLA-DR4 and/or other alleles in multicase RA families and to compare the segregation patterns among affected and unaffected sibs.

METHODS

Forty-one multicase families (22 multiplex and 19 simplex) of northern Indian origin were studied for HLA haplotype segregation.

RESULTS

HLA haplotype sharing among affected sibs was observed more often than expected in families in which both parents were healthy (P < 0.05). RA cosegregated with a DR4 haplotype among offspring only in multiplex families in which both parents were unaffected (P < 0.05), while in simplex families, the disease segregated with DR4 only when the allele was from the affected DR4-heterozygous parent. In DR4-negative affected sib pairs, DR1, DR6, and DR10 were inherited from healthy parents more often than expected.

CONCLUSION

Dissimilar modes of inheritance are seen among multiplex and simplex RA families. The results of segregation analysis are compatible with the hypothesis that an epitope, rather than an individual DR antigen(s), is responsible for increased risk for development of RA.

Do human leukocyte antigens have a role to play in differential manifestation of multibacillary leprosy: a study on multibacillary leprosy patients from north India

118 multibacillary leprosy patients with differential manifestations were studied for the antigens they expressed at MHC loci to investigate the role of human leukocyte antigens in the differential response to the same causative agent. While the lepromatous leprosy (LL) patients showed a significant increase of Bw60, DR2, DRw8 and DQw1, borderline lepromatous (BL) patients had Bw52, DR9 and DQw7 significantly more often as compared to the normal controls. A comparison of LL, BL and mid-borderline (BB) patients showed a significantly higher frequency of Bw60 in LL patients as compared to the BL. However, Bw52, Bw53, DR9 and DQw7 were found significantly more often in the BL patients as compared to the LL patients but the difference failed to reach significance after pc. A comparison of HLA antigens in BB patients with those of either the LL or BL patients did not show any significant differences.

Leishmaniasis epidemiology: all down to the DNA

Application of quantitative methods to the study of leishmaniasis epidemiology has allowed Dye (1992) to pinpoint important biological parameters which, if they could be accurately measured in the field, would contribute most to our knowledge of the spread of disease and key targets for control. Three areas in which laboratory-based research could impact most on leishmaniasis epidemiology were highlighted by Dye (1992): (i) the development of accurate diagnostic tools which can distinguish between current and past infection; (ii) to determine the underlying molecular/genetic basis to virulence polymorphisms in the parasite and study these in the context of field epidemiological studies; and (iii) to provide the molecular tools to measure genetic variation in resistance to infection in humans and in reservoir hosts of disease. This paper describes current progress in attaining these goals, highlighting first the work on isolation and field application of genomic and kDNA probes for species-specific diagnosis, and the development of PCR-based assays which can be performed under field conditions. At a more preliminary stage, studies are described in which variability in the major molecular determinants of virulence (lipophosphoglycan, GP63, and members of the HSP70 family of stress proteins) identified through studies of laboratory models of infection, is being measured in primary field isolates of Leishmania peruviana. To complete the picture, current progress in identifying and cloning the genes which control host resistance to leishmanial infection is described, along with field studies of multicase families of human disease in which linkage analysis using marker genes from the chromosomal regions bearing these genes can be used to find evidence for their role in determining disease phenotypes in man. The projected view from these studies is that the future of leishmaniasis epidemiology will be all down to the DNA.

Analysis of HLA-DR2-associated polymorphisms by oligonucleotide hybridization in an Asian Indian population

Among major histocompatibility complex class II antigens, HLA-DR2 appears to have a much larger degree of polymorphism than usually recognized by routine serology or restriction fragment length polymorphisms. We have utilized oligonucleotide probes to further identify the DR2 specificity and its molecular subtypes on the basis of specific DNA sequences as they occur in a select sample from the Asian Indian population. In addition, oligonucleotide typing of HLA-DQA1 and -DQB1 genes allowed us to determine specific associations of DRB1, DRB5, DQA1, and DQB1 alleles in DR2 individuals. A set of 60 oligonucleotide probes were hybridized to polymerase chain reaction (PCR)-amplified DNA from DR2 homozygous or heterozygous individuals. The most common DR2 subtypes that occurred in this selected population are: DRB1*1501 (60%), DRB1*1502 (33.8%), and DRB1*1602 (6.2%). No example of DRB1*1601 was detected. By combining these results with the allelic variations at DQA1 and DQB1, we were able to detect at least seven different haplotypes, the most common being DRB1*1502-DRB5*0102-DQA1*0103-DQB1*0601 and DRB1*1501-DRB5*0101-DQA1*0102-DQB1*0502. At least five unexpected combinations, not reported among Western Caucasians, were noticed in this sample. Thus oligonucleotide typing is a valuable tool for defining further polymorphisms in the HLA-D region as exemplified by its applications to typing DR2-positive patients with tuberculoid leprosy and pulmonary tuberculosis.

Genetic regulation of macrophage priming/activation: the Lsh gene story

This paper describes functional and genetic studies on the macrophage resistance gene Lsh/Ity/Bcg first described almost two decades ago. Working in vitro with resident peritoneal, liver (Kupffer cells) and bone marrow derived macrophages from congenic B10 (LshS) and B10.L-LshR mice it has been possible to demonstrate that the final effector mechanism for the gene in regulating antileishmanial activity involves production of reactive nitrogen rather than reactive oxygen intermediates. This in turn is dependent upon priming/activation of macrophages for enhanced TNF-alpha release which acts back on the macrophage in an autocrine manner to increase nitric oxide production. The precise point at which Lsh acts to control macrophage priming/activation has not been identified, but studies of early response gene expression show differences in KC mRNA levels at 2 h after LPS stimulation, and in c-fos mRNA as early as 20 min after stimulation with PMA plus ionophore, in peritoneal macrophages from congenic LshS and LshR mice. Data available suggest that both negative and positive signals may be involved in macrophage priming/activation, with LshS macrophages down-regulating their capacity for continued response to the autocrine loop. Work in progress will examine the role of TPA and cAMP response element-binding proteins in regulating gene expression in Lsh congenic mice. A major new initiative has also commenced to clone the Lsh gene by reverse genetics using yeast artificial chromosomes to walk towards Lsh from the closet proximal and distal markers on mouse chromosome 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitization in vitro of human peripheral blood mononuclear cells to phenolic glycolipid 1 of Mycobacterium leprae in liposomes

Study of primary immune responses in leprosy has been limited, since disease becomes manifest long after infection or is not detectable. To study primary immune responses, we immunized in vitro human peripheral blood mononuclear cells from unexposed individuals using phenolic glycolipid 1 (PGL-1), an important water-insoluble antigenic constituent of Mycobacterium leprae. PGL-1, encapsulated in liposomes, induced lymphoproliferation or, less frequently, suppression of lymphoproliferation in 11-day lymphocyte cultures. The primary lymphocyte responses resembled those elicited with keyhole limpet hemocyanin (KLH). HLA-DR2 expression, associated with tuberculoid leprosy, did not influence the outcome of in vitro sensitization. The association of HLA-DR2 and tuberculoid leprosy is not explained by differential ability to generate primary lymphoproliferative responses to PGL-1 or KLH. We have extended in vitro sensitization methodology to include a water-insoluble antigen in antigen-bearing liposomes. This methodology is potentially useful for studies of immunogenetics and immunopathology, and for vaccine research.

Testing for haplotype sharing by siblings with incomplete information of parental haplotypes

Testing for the inheritance of a disease susceptibility gene by analysis of haplotype sharing among affected siblings has been well established for the case where all four parental haplotypes have been ascertained. This paper presents a modification of a published method to cover the situation where there is incomplete information concerning parental haplotypes and this new test is applied in a worked example.

Genetic control of innate resistance to mycobacterial infections

The Mendelian segregation of resistance to infection in different strains of mice infected with mycobacteria, Salmonella and Leishmania spp, all of which live in macrophages, is currently under close scrutiny. Here, Erwin Schurr and colleagues review the nature and function of the Bcg gene in controlling innate resistance to mycobacterial infection in mice and speculate on the occurrence of a possible human equivalent.

Implications of genetics for the epidemiology and control of leprosy

This paper reviews the rationale and history of genetic studies related to leprosy, and considers their implications for the epidemiology and control of the disease. A long tradition of genetic studies in leprosy was initiated by early impressions that the disease clusters within families. Investigations were first motivated by an attempt to understand population patterns, and the focus shifted from investigations of racial differences to investigations of families, of twins and ultimately of genetic markers. The strongest evidence for genetic influence has come from studies of HLA segregation patterns within families, and this has led to elegant in vitro work demonstrating the role of HLA-DR alleles in mediating T-cell reactions in conjunction with antigens of Mycobacterium leprae. The epidemiological implications of this work are not yet clear. The emphasis on family-segregation studies may have given a biased impression because of their requirement for multi-case families. There is evidence that the genetic mechanisms underlying leprosy differ within and between populations. One possible application of the current work would be the use of HLA-DR-specific reactions to identify epitopes of M. leprae which should be excluded from future vaccine preparations.

Leprosy and immunity: genetics and immune function in multiple case families

Genetic susceptibility to infection with M. leprae was studied in 10 multiple case families of Australian Aborigines. Of the 87 members available for study, 24 had proven stable clinical leprosy which had been or was still being treated with diamino diphenyl sulphone. Evidence of contact with M. leprae in the remaining 63 members as assessed by ELISA to M. leprae sonicate and phenolic glycolipid (PGL) or by indirect immunofluorescence antibody assay was found in 78%, 64% and 71%, respectively. By contrast, in vitro assays of T cell function (LMAT and LTT) were less reliable indicators of exposure. Evidence was sought for possible linkages between human leucocyte antigen (HLA) or non-HLA genes and four marker phenotypes including clinical leprosy, clinical subtype of leprosy and lymphocyte transformation or leucocyte migration inhibition factor (LIF) production in response to M. leprae antigen. No associations were found with any particular HLA or non-HLA gene. On the other hand, sequential analysis of the data from the 10 families was strongly suggestive of a linkage between HLA haplotype and non-responsiveness to M. leprae as manifest by lack of LIF production but not lymphocyte transformation. The model which best fits the data is for a gene on chromosome 6 in close linkage with the HLA haplotype, with two alleles, autosomal recessive inheritance and penetrance of 90%. On this basis, it can be suggested that disease type (lepromatous leprosy) rather than disease susceptibility may be controlled by genes within or closely linked to the major histocompatibility gene complex.

A test statistic for the affected-sib-set method

This paper discusses generalizations of the affected-sib-pair method. First, the requirement that sib identity-by-descent relations be known unambiguously is relaxed by substituting sib identity-by-state relations. This permits affected sibs to be used even when their parents are unavailable for typing. In the limit of an infinite number of marker alleles each of infinitesimal population frequency, the identity-by-state relations coincide with the usual identity-by-descent relations. Second, a weighted pairs test statistic is proposed that covers affected sib sets of size greater than two. These generalizations make the affected-sib-pair method a more powerful technique for detecting departures from independent segregation of disease and marker phenotypes. A sample calculation suggests such a departure for tuberculoid leprosy and the HLA D locus.

Leprosy associated with HLA-DR2 and DQw1 in the population of northern Thailand

A study of the frequency of HLA-DR2 and DQw1 was performed in leprosy patients and controls in northern Thailand. HLA-DR2 was found in 100% (17/17) of patients with sporadic tuberculoid leprosy and in over 90% (30/32) of all tuberculoid leprosy patients, as compared to 62% (20/32) of controls (p = .02). These strong associations had relative risks of 21.4 for sporadic and 7.4 for all tuberculoid leprosy, and etiologic fractions of 1.0 and 0.84, respectively. There was also a statistically significant and strong association between tuberculoid leprosy and DQw1. These data add to the growing body of evidence that products of HLA class II determinants or closely linked genes may play a role in determining the clinical manifestations of M. leprae infection.

Strain variation of lymphokine production and specific antibody secretion in mice infected with Mycobacterium lepraemurium

Mice from strains showing either phenotypical expression of Bcg gene (C57BL/6, BALB/c, DBA/1, and (C57BL/6 X DBA/2)/F1, CBA, A/J, DBA/2) were infected intravenously with 10(7) Mycobacterium lepraemurium (MLM). The number of acid-fast bacilli (AFB) within the spleens, the ability of spleen cells to produce in vitro interleukin 1 and 2, and the serum levels of specific anti-MLM antibodies were assessed 3 months later. The number of AFB recovered from the spleens of various strains followed the strain distribution of genetically controlled innate resistance established for Mycobacterium bovis infection. A decrease of interleukin 2 production by spleen cells could be detected in C57BL/6, DBA/1, DBA/2 and (C57BL/6 X DBA/2)F1 mice only. The level of anti-MLM antibodies was found to be higher in C57BL/6, BALB/c and A/J mice than in the other strains tested. Thus no evidence appeared of a direct influence of the Bcg gene on lymphokine production and antibody secretion.

Association between leprosy and immunoglobulin allotypes: Gm-A2m and Km frequencies in Vietnamese

The relationship between immunoglobulin allotypes and leprosy was studied in 91 unrelated patients and 100 healthy controls from Vietnam. Twenty Vietnamese patients with tuberculosis were also typed for the Gm, A2m and Km allotypes. The results were compared with those from the healthy controls. No significant association was found for the allotypes G1m(z,a,x,f) G2m(n), G3m(g,b), A2m(1,2) and Km(1,3) between the two groups of patients and the controls. Heterogeneity in the distribution of G2m(n), G3m(b), A2m(2) and Km(3) was found when 60 polar-lepromatous (LL) patients and 27 borderline-tuberculoid (BT) patients were separated out of the 91 leprosy patients. In the LL patients there appeared to be a significantly higher frequency of G2m(n), G3m(b) and A2m(2) in comparison with the BT patients (P less than 0.05). A significantly lower frequency of Km(3) was found in the LL patients in comparison with the healthy control group (P less than 0.05). The frequencies of the Gm-A2m haplotypes and of the occurrence of the Km(1) and Km(3) in the Vietnamese population were calculated on the basis of the results in the 100 samples of healthy controls. The main haplotype is Gmaf;n;b (frequency 0.676), occurring with A2m1 (0.200), as well as with A2m2 (0.476).

Monocyte-derived soluble suppressor factor(s) in patients with lepromatous leprosy

Peripheral blood monocytes from polar lepromatous leprosy (LL) patients were unable to support Mycobacterium leprae-induced in vitro lymphoproliferation of HLA-D-matched T cells from tuberculoid leprosy subjects, whereas those from responder individuals were able to do so. Monocyte-rich adherent cells from untreated LL patients released de novo soluble factors which inhibited antigen-induced lymphoproliferation to a greater extent and mitogenic responses to a lesser extent. Suppressive activity varied in different LL patients. However, the degree of suppression was similar in soluble factors obtained de novo and after treatment of adherent cells with heat-killed and freshly extracted, cryopreserved M. leprae. Treated patients showed less inhibition with de novo released soluble factors (27 +/- 7.7%) as compared to parallel soluble factors obtained after antigen treatment (44 +/- 4.8%) or with de novo soluble factors from untreated LL patients (62 +/- 14.2%). Similar supernatants from tuberculoid individuals showed no or insignificant effects on antigen-induced lymphoproliferation. The suppressive activity of LL soluble factors was produced for up to 72 h, was heat stable at 56 degrees C for 30 min, was indomethacin resistant, and resided in the greater than 25,000 molecular weight fraction.

H-2-linked gene(s) influence the granulomatous reaction to viable Mycobacterium lepraemurium in the mouse

The genetic control of the granulomatous response to viable Mycobacterium lepraemurium (MLM) was studied in C3H and C57BL/6 inbred strains, BXH recombinant inbred strains, (C3H X C57BL) F1 hybrids, and backcross mice. The results indicate that an autosomal dominant gene, or linked complex of genes, has a marked influence on the footpad reaction to viable MLM. The distribution of responders and non-responders among 12 BXH recombinant inbred strains and linkage analysis in C3H X (C3H X C57BL)F1 backcross mice indicated that the response gene(s) are linked to the H-2 complex on chromosome 17. The same gene(s) also influence host restriction of MLM multiplication and thus appear to be the first H-2-linked gene(s) influencing resistance to a bacterial infection.

HLA-A, -B, -C and -DR antigen profile in pulmonary tuberculosis in North India

Investigations for the HLA-A, -B, -C and -DR antigens were conducted on 124 random North Indian patients with confirmed diagnosis of pulmonary tuberculosis by the demonstration of acid fast bacilli in the sputum. 109 appropriately matched controls from the same ethnic background were also tissue typed. No significant deviation was observed in the HLA-A, -B, and -C locus antigens. With the HLA-DR typing, there was a marginal increase in DR2 and a concurrent significant decrease in DRw6 in the patient group. These deviations were, however, insignificant when correction for the P value was made. ABO blood group typing results indicate that blood group 'O' may afford protection against TB. The involvement of both DR2 and DRw6 is interesting as it is also implicated in leprosy, another mycobacterial disease. The results suggest the possibility of a common gene in the MHC for both tuberculosis and leprosy.

An approach to study in vitro the expression of HLA-encoded genetic factors predisposing to tuberculoid leprosy

The existence of HLA-encoded genetic factors controlling susceptibility to tuberculoid leprosy in humans has been firmly established. Furthermore HLA-DR2 has been recognized as a marker for tuberculoid leprosy in India. At this moment, however, the gene products involved and the mechanism by which they confer susceptibility to tuberculoid leprosy remain only speculative. In an attempt to detect in vitro the expression of these HLA-encoded factors, we studied 12 tuberculoid leprosy patients and 22 healthy family members in a lymphocyte transformation test (LTT). All individuals were derived from multi-case Indian families, previously reported to show the presence of HLA-linked susceptibility genes. Although the responder-status of the healthy contact siblings was shown to behave independently from the fact whether they were HLA-identical with the patient-siblings or not, some evidence for in vitro expression of HLA-DR2 associated factors could be obtained. Nevertheless, it is concluded that the standard LTT seems not to be a test-system of first choice to detect the in vitro expression of the genes under study.

HLA and susceptibility to leprosy

This review examines the evidence for involvement of MHC-associated factors in host immune response to Mycobacterium leprae, by collating HLA studies of sporadic and familial leprosy and discussing possible HLA-related immunological mechanisms in determining host response. Formal linkage analysis of 109 multiple-case families with data available for HLA haplotype segregation showed that under a three-allele recessive model for susceptibility to leprosy, linkage was observed between the HLA complex and a leprosy susceptibility locus at a recombination fraction of 20%. The significance of the linkage relationship was confined to families with at least two tuberculoid leprosy offspring and neither parent affected. When one parent was affected, with leprosy of any clinical type, lod scores could neither implicate nor exclude linkage between HLA and leprosy susceptibility and this apparent paradox can be explained by the presence of an additional, non-HLA linked susceptibility locus for leprosy.

Leprosy, an overview

Leprosy is both a public health problem and a model for host-parasite relationship. There is much progress in many areas, and in most, hurdles are not only scientific but also social and financial. The following are goals to reach: 1) progress of growth of M. leprae in animals (to be able to breed armadillos in captivity or to substitute them with other animals); 2) to develop methods for in vitro culture of M. leprae; 3) to obtain antigens from M. leprae and characterize them immunologically; 4) to achieve techniques for objective diagnosis of infection with M. leprae and of leprosy (these techniques will most likely be serologic); 5) to develop methods to direct and manipulate immune response. This should include a better definition of immunologically active cells, their characterization by reliable methods, and an understanding of their functions. Immune control mechanisms and ways to channel them should also be understood; and 6) to have better methods of treatment including flexible adaptable schedules. It will be clear that "solving" the problem of leprosy requires "solving" the social problems in developing countries, as well as unraveling the mystery of the precise control of immune response. As I pointed out, the problems that we face are basically similar to those of autoimmune disorders and of cancer immunology. Research in autoimmune diseases or cancer might provide answers to questions posed by leprosy. It may also be that research in leprosy could supply answers to questions concerning cancer and autoimmunity.

HLA-DR-associated genetic control of the type of leprosy in a population from surinam

The relationship between HLA phenotype and leprosy classification was studied in 73 unrelated patients and 92 healthy controls from a mixed Negroid-Caucasoid population originating from Surinam, South America. Heterogeneity in the distribution of HLA-DR (but not A, B, and C) was detected between tuberculoid (TT* + BT*) leprosy and lepromatous (BL* + LL*) leprosy patients (p = 0.024). This heterogeneity appeared to be caused almost exclusively by DR3. Most significantly, the frequency of DR3 was increased among polar tuberculoid (TT) leprosy patients as compared to the rest of the patients (p = 0.0003). Compared with healthy controls the frequency of DR3 was increased among TT patients (p = 0.006), unchanged in BT patients, and decreased among lepromatous (BL + LL) patients (p = 0.027). These data indicate that in this population an DR3-associated factor controls the type of the disease that develops after infection with Mycobacterium leprae.

HLA and sporadic tuberculoid leprosy: a population study in Maharashtra, India

A population study to test whether associations between HLA and sporadic--i.e. non-familial--tuberculoid leprosy exist was undertaken in a hyperendemic area in India. Since previous family studies in the same area had shown both non-random haplotype segregation in the family members affected with tuberculoid leprosy and the preferential segregation of HLA-DR2 into tuberculoid leprosy patients, an increased frequency of DR2 among the "sporadic" patients was expected. However, no heterogeneity for HLA was detected between patients and controls. These findings could indicate that tuberculoid leprosy is a heterogeneous disease with regard to genetic background.