HL-A antigens and susceptibility to diseases. II. Leprosy

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 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%).

HLA and leprosy in Koreans

HLA antigens in 157 unrelated Koreans with leprosy have been identified and compared with 162 healthy Korean controls. The patient group consisted of 124 with lepromatous leprosy and 33 with tuberculoid leprosy. Although no significant differences were detected between the two patient groups, several antigens were found to be increased in the combined patient group compared to healthy controls. Two Class I antigens were increased: HLA-A11 (22% vs 12%) and Aw33 (27% vs 14%). Four Class II antigens were increased: HLA-DR1 (16% vs 7%), DR2 (39% vs 21%), DRw9 (14% vs 6%) and DQw1 (74% vs 55%). HLA-DR4 (28% vs 48%), DRw53 (46% vs 69%) and DQw3 (50% vs 75%) in contrast were significantly decreased in patients. Interaction of DR1, DR2, DRw9 and DQw1 as risk factors was analyzed. HLA-DR2 appeared to be the strongest risk factor. No evidence for synergy between DR1, DR2 and DRw9 was detected. DQw1 was not significantly increased in patients in the absence of DR1 and DR2, and thus it was not apparent in this study that DQw1 was an independent risk factor.

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).

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.

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.

The immunology of mycobacterial infections

Mycobacteria are endowed with substances that profoundly affect the immune system. Leprosy and tuberculosis exemplify broad spectra of useful and detrimental immune responses of mycobacterial infections that range from intense potentiation to severe specific adn nonspecific suppression of humoral and cellular immune elements. The cellular hypersensitivity induced by mycobacteria serves as a classical model for the analysis of specific and nonspecific immune mechanisms. Mycobacterial disease are prevalent worldwide and rank among the most important bacterial diseases. The kaleidoscope of immunologic events induced by injected mycobacteria and during infections will be reviewed from the standpoint of pathogenesis, pathology, in vitro and in vivo effects on cellular and humoral arms of the immune response, diagnosis, classification, potentiation and suppression.

Tuberculoid leprosy and HLA in Japanese

HLA phenotypes of 54 patients with tuberculoid leprosy were compared with those of 167 healthy controls. Frequencies of HLA-A, -B and -C antigens did not differ significantly between the leprosy patients and the controls. However, an increase in the frequencies of DR1, DR2, DRW8 and MT1 antigens and a decrease in the frequencies of DR4 and MT3 antigens were observed in the leprosy patients. Statistical evidence was presented that MT1 antigens were primarily associated with tuberculoid leprosy in Japanese patients rather than DR2.

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.

In-vitro lymphoproliferative response to Mycobacterium leprae of HLA-D-identical siblings of lepromatous leprosy patients

Lymphoproliferative responses to Mycobacterium leprae and P.P.D. were measured in 23 lepromatous and borderline lepromatous leprosy patients and in 27 of their normal siblings. At the same time siblings HLA-D-identical with the patients were identified by the absence of a mixed-lymphocyte reaction. The 7 siblings who were HLA-identical to lepromatous patients responded as well to M. leprae as did the 20 HLA-non-identical normal siblings. In contrast, 22 of the 23 lepromatous patients failed to respond to M. leprae but responded normally to P.P.D. The specific unresponsiveness of lepromatous patients thus does not result from an HLA-linked genetic defect and the defective cell-mediated immune response to M. leprae seems to be acquired, not inherited. Lepromatous patients may be high responders to antigens shared by M. leprae and other microorganisms in whom a strong antibody response has blocked the induction of an M. leprae-specific-cell-mediated immune response.

The HLA system and leprosy in Thailand

To investigate immunogenetics of leprosy, 205 leprosy patients (26 with tuberculoid, 57 with borderline-tuberculoid, 21 with borderline, 31 with borderline-lepromatous, and 70 with lepromatous leprosy) have been typed for HLA antigens, and compared with 183 healthy controls from the same region (Northern Thailand). There was no significant difference between the overall group of leprosy patients or the three borderline classes and the controls. The two polar forms, tuberculoid and lepromatous leprosy, however, showed significant associations: HLA-A2 is decreased and HLA-Bw17 is increased in tuberculoid leprosy; HLA-B7 is increased in lepromatous leprosy. When both polar forms are compared with each other, HLA-A2 is significantly higher, HLA-Bw40 lower in patients with lepromatous than in those with tuberculoid leprosy. The results are discussed with respect to the different immune responsiveness in the two polar forms of leprosy.

HLA and mycobacterial infection: increased frequency of B8 in Japanese leprosy

A total of 60 leprosy patients, 28 of lepromatous and 32 of tuberculoid form, and 70 active tuberculosis patients was compared with a control of 184 for 34 HLA specificities. The most interesting finding was an increased frequency (10.0%) for HLA-B8 (corrected P = 0.062, relative risk = 20.3) in the leprosy patients as compared with the control group, despite the fact that the frequency of HLA-B8 was extremely low in Japanese. Furthermore, all leprosy patients with B8 had leprous member(s) in their family.

The incidence of HLA antigens in leprosy

HLA antigens were studied in 36 patients, with leprosy, 20 cases of lepromatous and 16 cases of tuberculoid type. Eleven out of 36 (30.55%) had BW40 as compared to 9.33% of 150 controls. The frequency of BW40 in tuberculoid patients (31.25%) was not different from that in lepromatous cases (30%).

HLA-linked genetic control of host response to Mycobacterium leprae

Non-random parental HLA-haplotype segregation is demonstrated in siblings with leprosy. A new method is described for the statistical analysis of non-random segregation among sibships of different sizes. Sibs with the same type of leprosy show a significant excess of identical HLA haplotypes. This is also true for families in which only tuberculoid leprosy is found, which is by far the commonest type in the population studied. However, sibs affected with different types of leprosy share a haplotype less often than expected. This indicates that both susceptibility to and type of leprosy are controlled by at least two HLA-linked genes. Our findings suggest that the equivocal results of previous population studies are due to differences of linkage disequilibrium between HLA-linked genes controlling the host response to Mycobacterium leprae and alleles of HLA A and B loci in various populations.

Histocompatibility antigens (HL-A) in leprosy

HL-A antigens of 70 leprosy patients and 40 normal healthy individuals were determined by the standard microlymphocytotoxicity test. Both lepromatous and non-lepromatous leprosy patients were tested for the presence of 11 HL-A antigens, and the frequency of each specificity was compared with that in a normal population of the same ethnic group. Although the statistical significance of HL-A8 specificity was found to be marginal in lepromatous leprosy patients, when using ordinary 2 times 2 statistics, there did seem to be a decreased frequency of HL-A9 among the non-lepromatous type. Other antigens tested did not reveal any significant differences between the two groups of subjects.

Histocompatibility antigens in leprosy

Results of HL-A typing are presented in 82 patients with leprosy and 50 normal Filipinos from Cebu, and 144 normal Filipino immigrants from the Luzon area. Comparisons of HL-A antigen frequencies among the total patients and normals of Cebu showed no statistically significant differences; however, HL-A10 was increased in frequency among the patients with lepromatous disease compared to the normals, and HL-A5 was increased among the tuberculoid patients compared to the lepromatous patients. None of these comparisons was statistically significant when corrected for the number of antigens tested. Comparisons of HL-A antigen frequencies between normal Filipinos of the Cebu and Luzon regions showed increased W-5 in the Luzon population (corrected p smaller than 0.025).