HLA and leprosy: segregation and linkage study

Frequencies of MICA alleles in patients from southern Brazil with multibacillary and paucibacillary leprosy

Leprosy is a chronic infectious disease caused by Mycobacterium leprae, which mainly affects the skin and nervous system. The disease has several clinical forms. This study investigated the MICA and HLA-B genes in 223 samples from leprosy patients and 201 samples from healthy individuals matched for age, gender and ethnical background. Of the patients, 153 had multibacillary, 45 paucibacillary and 25 indeterminate leprosy. The aim of this case-control study was to assess whether the MICA alleles influence susceptibility for leprosy or affect the subtype of the disease in a population of southern Brazil. There were significant differences in frequencies of the MICA*027 allele (4.7% vs 1.8%, P-value = 0.01, OR = 0.37; 95% CI = 0.16-0.85) between leprosy patients and controls, and of the MICA*010 (4.5% vs 1.6%, P-value = 0.05, OR = 0.35, 95% CI = 0.13-0.97) and MICA*027 alleles (4.7% vs 1.3%, P-value = 0.01; OR = 0.27; 95% CI = 0.09-0.79) between multibacillary leprosy patients and the control group. There were no significant differences in the frequency of MICA alleles between paucibacillary leprosy patients and controls. Thus, the MICA*027 allele is associated with a protective effect for leprosy per se, while the MICA*010 and MICA*027 alleles are associated with protection against multibacillary leprosy, the most severe clinical subtype.

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.

Genetic host resistance and susceptibility to leprosy

Leprosy is a chronic infectious disease that affects 600,000 new individuals worldwide every year. This article summarizes some of the advances achieved over the past decades towards the description of the exact number, location and nature of the genetic variants responsible for the well established genetic component controlling leprosy susceptibility in humans.

Leprosy in a backpacker

Leprosy is the most common cause of peripheral neuropathy in the developing world. It is not expected to be acquired by visitors traveling through these countries. We present a backpacker who contracted leprosy during brief stays in endemic countries.

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.

Associations between human leukocyte antigens and leprosy in the Turkish population

Leprosy is a chronic infection caused by an intracellular microorganism. Genetic predisposition to both disease susceptibility and to host immunological response has been postulated for many years. The aim of this study was to determine whether there is HLA-linked susceptibility to leprosy and its different types. HLA-class I (A, B, C) and II (DR, DQ) antigen frequencies in 80 patients with leprosy (35 borderline lepromatous, 25 lepromatous, 15 borderline tuberculoid, five tuberculoid) were compared with those in 120 healthy individuals. HLA-class I antigens A9, A10, A32, B5, B21, Bw4, Bw6, Cw1, Cw2 and HLA-class II antigens DR9, DR10, DRw52, DQ1, DQ3 were found to be significantly more frequent in patients with leprosy, whereas HLA-class I antigens A3, B44, B49 and HLA-class II antigen DQ5 were so in controls. However, there was no significant difference in HLA-class I and II antigen frequencies between subtypes of leprosy. HLA-A null antigen was found to have weak expression in patients with leprosy. In conclusion, factors other than HLA-class I and class II antigens may have a more critical role in the pathophysiology of leprosy infection in man.

Association and linkage of leprosy phenotypes with HLA class II and tumour necrosis factor genes

Previous analyses indicate major gene control of susceptibility to leprosy per se and the HLA class II region has been implicated in determining susceptibility and control of clinical phenotype. Segregation analysis using data from 76 Brazilian leprosy multi-case pedigrees (1166 individuals) supported a two locus model as the best fit: a recessive major gene and a recessive modifier gene(s) (single locus vs two locus model, P = 0.0007). Combined segregation and linkage analysis to the major locus, showed strong linkage to HLA class II (HLA-DQB1 P = 0.000002, HLA-DQA1 P = 0.000002, HLA-DRB1 P = 0.0000003) and tumour necrosis factor genes (TNF P = 0.00002, LTA P = 0.003). Extended transmission disequilibrium testing, using multiple affected family members, demonstrated that the common allele TNF*1 of the -308 promoter region polymorphism showed linkage and/or association with disease per se, at a high level of significance (P < 0.0001). Two locus transmission disequilibrium testing suggested susceptibility (TNF*1/LTA*2) and protective (TNF*2/LTA*2) haplotypes in the class iii region. Taken together the segregation and HLA analyses suggest the possibility of more than one susceptibility locus in the MHC.

HLA-DRB1 leprogenic motifs in nigerian population groups

Amino acid residues involved in the peptide binding groove of HLA-DRB1 alleles were examined in three Nigerian ethnic groups with leprosy (n = 287) and 170 controls to determine the role of DRB1 alleles in disease outcome with Mycobacterium leprae. Nine positively charged motifs and two others with neutral charge to the binding groove were detected. These motifs occurred more frequently in leprosy (leprogenic) than was expected by chance (P < 0.0001). In contrast, five motifs with net negative or 'modified' neutral charges to the pocket were negatively associated with leprosy. We conclude that clinical outcome of infection with M. leprae is largely determined by a shared epitope in DRB1 alleles marked by several motifs. These motifs occur in otherwise normal DRB1 alleles, characterized by net positive or neutral charges in the binding groove. We hypothesize that these polarities cause poor binding of DRB1 to M. leprae. On presentation, the signal via the T cell receptor results in muted cell-mediated immunity. The resulting response translates to various forms of leprosy depending on degree of charge consonance between M. leprae and host DRB1 allele. Other factors within or without the HLA complex, such as the T cell receptor repertoire, may also influence the resulting disease.

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.

Human leukocyte antigens in tuberculosis and leprosy

Human mycobacterial infections are characterized by a spectrum of clinical and immunological manifestations. Specific human leukocyte antigen (HLA) factors are associated with the subtypes of leprosy that develop and the course of tuberculosis after infection. The identification of protective mycobacterial antigens presented by a broad variety of HLA molecules will have important implications for the design of vaccines.