The HLA system and leprosy in Thailand

Role of HLA, KIR, MICA, and cytokines genes in leprosy

Many genes including HLA, KIR, and MICA genes, as well as polymorphisms in cytokines have been investigated for their role in infectious disease. HLA alleles may influence not only susceptibility or resistance to leprosy, but also the course of the disease. Some combinations of HLA and KIR may result in negative as well as positive interactions between NK cells and infected host cells with M. leprae, resulting in activation or inhibition of NK cells and, consequently, in death of bacillus. In addition, studies have demonstrated the influence of MICA genes in the pathogenesis of leprosy. Specifically, they may play a role in the interaction between NK cells and infected cells. Finally, pro- and anti-inflammatory cytokines have been influencing the clinical course of leprosy. Data from a wide variety of sources support the existence of genetic factors influencing the leprosy pathogenesis. These sources include twin studies, segregation analyses, family-based linkage and association studies, candidate gene association studies, and, most recently, genome-wide association studies (GWAS). The purpose of this brief review was to highlight the importance of some immune response genes and their correlation with the clinical forms of leprosy, as well as their implications for disease resistance and susceptibility.

HLA and disease

Association of HLA and diseases is well known. Several population studies are available suggesting evidence of association of HLAs in more than 40 diseases. HLA found across various populations vary widely. Some of the reasons attributed for such variation are occurrence of social stratification based on geography, language and religion, consequences of founder effect, racial admixture or selection pressure due to environmental factors. Hence certain HLA alleles that are predominantly associated with disease susceptibility or resistance in one population may or may not show any association in other populations for the same disease. Despite of these limitations, HLA associations are widely studied across the populations worldwide and are found to be important in prediction of disease susceptibility, resistance and of evolutionary maintenance of genetic diversity. This review consolidates the HLA data on some prominent autoimmune and infectious diseases among various ethnic groups and attempts to pinpoint differences in Indian and other population.

Insights into the role of host genetic and T-cell factors in resistance to HIV transmission from studies of highly HIV-exposed Thais

Studies of resistance to HIV-1 transmission are likely to be valuable for the design of vaccines and other efforts to prevent HIV. Here, we review the T-cell and genetic factors associated with resistance to HIV-1 transmission in studies of highly exposed but persistently seronegative (HEPS) women from northern Thailand. Women were enrolled in two sex-worker studies and in a discordant couple study. We performed Cr51 cytotoxic T lymphocyte (CTL), interferon-gamma (IFN-gamma) ELISPOT, and proliferation assays as well as genetic studies, including HLA-class I typing. CTL and ELISPOT studies showed a skewing of T-cell responses to conserved HIV-1 proteins in HEPS, but not in HIV-1-seropositive women. T-cell responses were extremely long-lived in some HEPS women. In the two sex-worker studies, HLA-A11 was associated with resistance to HIV-1 transmission. These data provide promise for the ability of CTL to control HIV and emphasize the importance of developing HIV vaccines that stimulate strong, long-lasting Tcell responses.

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.

HIV-specific cytotoxic T lymphocytes, HLA-A11, and chemokine-related factors may act synergistically to determine HIV resistance in CCR5 delta32-negative female sex workers in Chiang Rai, northern Thailand

Understanding how highly HIV-exposed individuals remain HIV uninfected may be useful for HIV vaccine design and development of new HIV prevention strategies. To elucidate mechanisms associated with resistance to HIV infection, immunologic and genetic factors were examined in 14 HIV-exposed but persistently seronegative (HEPS) female sex workers from Chiang Rai, northern Thailand and in ethnically matched, HIV-positive (n = 9) and HIV-negative women (n = 9). The HEPS women were identified in a study of commercial sex workers who had an HIV-1 incidence of 20.3 per 100 person-years. A high frequency of HLA-A11 was observed in HEPS women (86%) compared with northern Thai controls (56%). HIV-specific cytotoxic T lymphocyte (CTL) lytic responses were detected in cryopreserved peripheral blood mononuclear cells (PBMCs), using HLA-A-matched subtype E HIV-1 peptides in four of seven (57%) HEPS women, eight of eight HIV-positive women, and zero of nine HIV-negative unexposed controls (p = 0.019 HEPS women vs. HIV-negative controls). CTL lysis levels were low, but responses were detected to peptides from Nef, Pol, Gag, and Env. Nef responses predominated in HEPS women. Compared with controls, HEPS women tended to have higher frequencies of CCR5 promotor 59402GG and SDF-1 3'UTR 801A genotypes known to influence HIV transmission or course of disease. HEPS women also had higher levels of spontaneous RANTES production by PBMCs than other groups. Each of these factors could potentially contribute to HIV resistance. As most HEPS women had one or more of these factors, they may prevent HIV infection synergistically by blocking HIV cell entry, delaying its dissemination, or killing HIV-infected cells.

HLA and leprosy: segregation and linkage study

BACKGROUND

The presence of a genetic factor in the determination of leprosy has long been debated. This study tests whether the HLA-linked control of susceptibility to leprosy and/or for the types of leprosy could be confirmed.

MATERIALS AND METHODS

In 15 multicase families, the method of DeVries et al., 1976, was used to detect nonrandom segregation of parental HLA haplotypes in their affected and healthy siblings. Linkage analyses, for two and three alleles were performed by the computer program LIPED:

RESULTS

For the affected siblings, the segregations of the parental HLA haplotype were significantly nonrandom from the healthy parents and random from the affected parents, indicating that affected siblings were sharing their HLA haplotypes (segregated from the healthy parents) more than expected. The segregations to the healthy siblings from both the healthy and affected parents were random. Healthy siblings inherited the haplotypes shared among the leprosy siblings randomly as expected. There were excess DR2/DR2 homozygote individuals among tuberculoid siblings. The highest lod score was achieved when we considered our suggested three-alleles model for the susceptibility to the different types of leprosy.

CONCLUSIONS

A closely HLA-linked gene on chromosome number 6 with multiple alleles (3 or more) in recombination fraction between 0.05 and 0.1 with 70 to 100% penetrance may be responsible for the susceptibility to the different types of leprosy, whereas the susceptibility to leprosy per se maybe the responsibility of non-HLA linked gene/s. DR2/DR2 homozygote individuals may be relatively at high risk of developing leprosy or tuberculoid leprosy.

The HLA association of lepromatous leprosy and borderline lepromatous leprosy in Turkey. A preliminary study

Among 50 patients with lepromatous leprosy and borderline lepromatous leprosy in Turkey, the prevalence of HLA-DR2 was 25/50 (50%). The prevalence of the same alleles among 50 healthy controls was 13/50 (26%).

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.

Analysis of the immunogenetic background of Japanese leprosy patients by the HLA system

295 lepromatous and 74 tuberculoid leprosy patients were typed for HLA-A, -B and -C and compared to 110 healthy controls. It was found that frequency of HLA-B7 was significantly high and that of Bw54 was significantly low in lepromatous leprosy. HLA-DR and MT types were investigated in 84 lepromatous and 28 tuberculoid patients and compared to 55 controls. Both lepromatous and tuberculoid patients showed a marked increase in DR2 frequency. The relative risk is 8.7 and 5.9. Lepromatous leprosy showed an increase in frequency of MT1 and decreases in those of DRw9 and MT3 too.

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.

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

In an attempt to confirm an HLA-linked effect on the course of Mycobacterium leprae infection observed in families from Surinam (South America), we conducted a similar family study in an endemic area in India. We observed a significant (P less than .05) excess of identical HLA-GLO haplotypes only from healthy parents among siblings affected with tuberculoid leprosy. Compared with healthy controls, unrelated patients with tuberculoid leprosy (n = 15) showed a significant heterogeneity at the HLA-DR locus (P less than .05). This heterogeneity was caused by an increased frequency of HLA-DRw2 (.93 versus .53, P less than .05), particularly of DRw2 homozygotes (.53 versus .11, P less than .005), and a decreased frequency of HLA-DRw6 (.07 versus .58, P less than .005). We observed a significant (P = .03) preferential segregation of DRw2 from DRw2 heterozygous parents not affected with tuberculoid leprosy to children with the tuberculoid type of the disease. These data confirm an HLA-linked control of susceptibility to tuberculoid leprosy only, and suggest a recessive inheritance of this trait for which HLA-Drw2 appears to be a genetic marker.

The HLA antigens and leprosy in Thailand

HLA-A and -B locus antigens were determined in 170 unrelated patients with leprosy and 100 healthy controls. There were no statistically significant deviations from expected antigen distribution in patients with any of the various forms of leprosy, though the number of patients studied is relatively small. There were some interesting trends, particularly a possible decrease in the number of tuberculoid patients with A9, and an increase in the proportions of lepromatous patients with B18 and B40. Limited evidence of a genetically controlled pre-disposition to the clinical manifestations of leprosy suggests that further studies with extended typing should be carried out on the HLA haplotype segregation in informative leprosy families. These should provide a clearer indication of the relevance of the HLA (including DR) and possibly of other non-HLA loci to the possible mechanism(s) of disease susceptibility.

The genetic hypothesis for susceptibility to lepromatous leprosy

Evidence for genetic influence of the host response to infection with Mycobacterium leprae is reviewed. A complex segregation analysis is performed on data for 91 families from Mactan, Philippines, in each of which at least one offspring developed lepromatous leprosy. The data are not found to be inconsistent with an autosomal recessive hypothesis for susceptibility to lepromatous leprosy. Heritability estimates in the range of 80% were calculated for sib-sib pairs under the multifactorial hypothesis for susceptibility. It is argued that the multifactorial hypothesis is more in keeping with available immunologic, epidemiologic, and demographic data than is the single gene hypothesis.