Mannose-binding Lectin Promoter Research Articles

5588568 ASSOCIATION OF MANNOSE-BINDING LECTIN SERUM LEVEL AND PROMOTER GENE VARIANTS RS7096206 AND RS10031251 WITH FREQUENCY OF VASO-OCCLUSIVE EVENTS IN SICKLE CELL DISEASE PATIENTS; AN EGYPTIAN CROSS-SECTIONAL STUDY

Background: Sickle cell disease (SCD) is a genetic blood disorder involving hemoglobin alterations, in addition to endothelial adhesion, thrombosis and inflammation. Low serum Mannose-binding lectin (MBL) levels can enhance SCD-related blood vessel inflammation as well as reduction of phagocytic activity, leading to sickled erythrocyte accumulation on vessel walls and impaired ability to combat infections. This may contribute to the vaso-occlusive (VOC) episodes. Aim: This work aimed to investigate serum MBL level and MBL promoter gene variants distribution among a cohort of Egyptian SCD patients and to describe their association with VOC events frequencies in the studied patients. Methods: This cross-sectional study included 88 steady-state Egyptian SCD patients aged 6-18 years diagnosed and followed up at Pediatric Hematology Unit, Cairo University Children Hospital. Informed consent was obtained willingly from all subjects or their guardians before enrolment in the study. MBL promoter (-221) (rs7096206) X/Y and (-550) (rs10031251) H/L gene variants were studied by Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) technique. Serum MBL level was assayed by ELISA technique with values <500ng/ml considered deficient. Results: The median serum MBL level in SCD patients was 130.9 ng/ml (IQR 71.2-323.9 ng/ml). Patients with serum MBL levels <500ng/ml were significantly older, had longer disease duration and higher rate of VOCs per year, VOCs per lifetime and a higher VOC index (p= 0.039, 0.034, 0.047, 0.040 and 0.008 respectively). Levels <500ng/ml predominated in SS (89.4%) than Sβ groups (70%) (p= 0.023) and in patients with high frequency of VOCs (91.4%) (p=0.008). Serum MBL level correlated negatively with patients’ age, disease duration, hydroxyurea total treatment duration, blood transfusions per lifetime and steady-state HbS level (p= <0.001, <0.001, 0.011, 0.014, 0.031 respectively) but correlated positively with steady-state HbF level (p=0.002). MBL (-221) X/Y both alleles were more associated with (H) allele of MBL (-550) than with L allele (p=0.048), however, with no statistically significant genotype distribution between the studied variants. There was no statistically significant difference in genotype distribution or allele frequencies between MBL (-221) and MBL (-550) in SCD patients regarding serum MBL level, sickle cell type (SS and Sβ), VOCs frequencies or disease severity classes. Conclusion: Serum MBL level rather than studied MBL gene variants is more likely to contribute to the clinical outcomes of SCD; patients with lower MBL levels had a higher rate of VOC per year, per lifetime and a higher VOC index. Meanwhile, the variant genotypes and alleles of the studied MBL promotor gene variants were not associated with MBL deficiency, VOCs, infection events, and disease severity.Further studies to investigate other polymorphisms in MBL gene; MBL exon-1 (codons 52,54 and 57) are recommended. Keywords: MBL, Polymorphism, Sickle cell disease, Vaso-occlusive crises, Egypt

Association between -221 X/Y polymorphism of mannose-binding lectin (MBL) gene and susceptibility to HTLV-1 infection among people from an endemic region in the Northeast of Iran

The role of (MBL) gene single nucleotide polymorphisms (SNPs) has been well documented in susceptibility to several infectious diseases. This study aimed to investigate the association between two MBL promoter variants, -550 H/L and -221 X/Y, and susceptibility to HTLV-1 infection. A total of 153 subjects infected with HTLV-1 and 169 healthy controls were recruited. SSP-PCR method was applied to genotype -550 H/L and -221 X/Y polymorphisms. Associations between genotypes or alleles and susceptibility to HTLV-1 infection were analyzed by Pearson's Chi-Square. p ≤ .05 was considered statistically significant. Statistical analysis revealed significant differences between the two groups in the -221 position (χ2 = 19.709; p = .000). The MBL YX genotype was significantly associated with increased susceptibility to HTLV-1 (OR = 2.73, %95 CI = 1.74-4.30). Combined genotype of the two loci showed that the HYHX genotype (OR = 2.20, 95% CI = 1.95-2.48) and LYLX (OR = 1.97, 95% CI = 1.13-3.45) were associated with an increased risk of HTLV-1 infection. Our results represent the importance of -221 X > Y variants in acquisition of HTLV-1 as this is the case for several other viral and bacterial infections.

Genetic association between mannose-binding lectin polymorphisms and viral hepatitis: a meta-analysis.

Some previous genetic association studies have tried to investigate potential associations between mannose-binding lectin (MBL) polymorphisms and viral hepatitis. However, the results of those studies were not consistent. Therefore, we performed the current meta-analysis to explore associations between MBL polymorphisms and viral hepatitis in a large pooled population. A systematic literature research of PubMed, Web of Science, Embase and CNKI was performed to identify eligible studies for pooled analyses. We used Review Manager version 5.3.3 to conduct statistical analyses. In total, 27 studies were included for analysis (4840 cases and 5729 controls). The pooled analyses showed that MBL promoter (-211C/G, dominant model: P=0.0002, I2=40%; over-dominant model: P=0.0001, I2=22%) and exon 1 (codon 52, 54 and 57, dominant model: P=0.04, I2=49%; allele model: P=0.01, I2=48%) polymorphisms were both significantly associated with viral hepatitis in the overall population. Further subgroup analyses revealed similarly significant findings for MBL promoter polymorphism in HBV and HCV, but no positive results were detected in subgroup analyses for MBL exon 1 polymorphism. These results suggested that MBL promoter and exon 1 polymorphisms could be used to identify individuals at higher susceptibility to HBV and HCV.

Broilers with low serum Mannose-binding Lectin show increased fecal shedding of Salmonella enterica serovar Montevideo

Mannose-binding lectin (MBL) is a key molecule in innate immunity. MBL binds to carbohydrates on the surface of pathogens, initiating the complement system via the lectin-dependent pathway or facilitates opsonophagocytosis. In vivo studies using inbred chicken lines differing in MBL serum concentration indicate that chicken MBL affects Salmonella resistance; further studies are imperative in conventional broiler chickens. In this study 104 conventional day-old chickens (offspring from a cross between Cobb 500 male and female parent breeders) were orally infected with Salmonella enterica subsp. enterica serovar Montevideo. The chickens were divided into two groups based on polymorphisms in their MBL promoter region, designated L/L for low serum concentrations of MBL and L/H for medium serum concentrations of MBL. A semi-quantitative real-time PCR method for detection of Salmonella in cloacal swabs was used, the log10 CFU quantification was based on a standard curve from artificially spiked cloacal swab samples pre-incubated for 8h with known concentrations of Salmonella ranging from 10(1) to 10(6) CFU/swabs, with an obtained amplification efficiency of 102% and a linear relationship between the log10 CFU and the threshold cycle Ct values of (R(2) = 0.99). The L/L chickens had significantly higher Log10 CFU/swab at week 5 post infection (pi) than the L/H chickens. A repetition of the study with 86L/L and 18L/H chickens, also gave significantly higher log10 CFU ± SEM in cloacal swabs, using the semi-quantitative real-time PCR method from L/L chickens than from the L/H chickens at week 5 pi. These results indicate that genetically determined basic levels of MBL may influence S. Montevideo susceptibility.

Transcription efficiency of different chicken mannose-binding lectin promoter alleles.

The serum collectin mannose-binding lectin (MBL) plays a major role in innate immunity by activation of the lectin complement pathway or by acting as an opsonin. The serum levels of human and animal MBL are associated with susceptibility to a wide range of infections, and the variation of MBL in serum is genetically determined. In the chicken, 14 single nucleotide polymorphisms (SNPs) have so far been found in the MBL promoter region. In this study, the transcription activity of a 670-bp promoter region covering all 14 SNPs from the four MBL promoter alleles A1 to A4 was assessed using a dual-luciferase assay. Of the analysed alleles, A1 showed the highest transcription activity although this allele is frequently found in chickens with low MBL mRNA expression.

SAT0213 Association of mannose-binding lectin gene polymorphisms with intima-media thickness (IMT) in primary antiphospholipid syndrome

BackgroundSerum mannose-binding lectin (MBL) is a recognition molecule of the lectin pathway of complement with antimicrobial and anti-inflammatory actions. Several polymorphisms have been reported for the MBL2 gene. These variants...

Mannose-binding lectin promoter polymorphisms and gene variants in pulmonary tuberculosis patients from cantabria (northern Spain).

Mannose-binding lectin is a central molecule of the innate immune system. Mannose-binding lectin 2 promoter polymorphisms and structural variants have been associated with susceptibility to tuberculosis. However, contradictory results among different populations have been reported, resulting in no convincing evidence of association between mannose-binding lectin 2 and susceptibility to tuberculosis. For this reason, we conducted a study in a well genetically conserved Spanish population in order to shed light on this controversial association. We analysed the six promoter and structural mannose-binding lectin 2 gene variants in 107 patients with pulmonary tuberculosis and 441 healthy controls. Only D variant and HYPD haplotype were significantly more frequents in controls which would indicate that this allele could confer protection against pulmonary tuberculosis, but this difference disappeared after statistical correction. Neither the rest of alleles nor the haplotypes were significantly associated with the disease. These results would indicate that mannose-binding lectin promoter polymorphisms and gene variants would not be associated with an increased risk to pulmonary tuberculosis. Despite the slight trend of the D allele and HYPD haplotype in conferring protection against pulmonary tuberculosis, susceptibility to this disease would probably be due to other genetic factors, at least in our population.

Effects of Mannose-Binding Lectin Polymorphisms on Irinotecan-Induced Febrile Neutropenia

Mannose-binding lectin (MBL) is important in the innate immune response. MBL2 gene polymorphisms affect MBL expression, and genotypes yielding low MBL levels have been associated with an elevated risk for infections in hematological cancer patients undergoing chemotherapy. However, these reported associations are inconsistent, and data on patients with solid tumors are lacking. Here, we investigated the effects of MBL2 genotypes on irinotecan-induced febrile neutropenia in patients with solid tumors. Irinotecan-treated patients were genotyped for the MBL2 gene. Two promoter (-550 H/L and -221 X/Y) and three exon polymorphisms (52 A/D, 54 A/B, and 57 A/C) were determined, together with known risk factors for irinotecan-induced toxicity. Neutropenia and febrile neutropenia were recorded during the first course. Of the 133 patients, 28% experienced severe neutropenia and 10% experienced febrile neutropenia. No associations were found between exon polymorphisms and febrile neutropenia. However, patients with the H/H promoter genotype, associated with high MBL levels, experienced significantly more febrile neutropenia than patients with the H/L and L/L genotypes (20% versus 13% versus 5%). Moreover, patients with the HYA haplotype encountered significantly more febrile neutropenia than patients without this high MBL-producing haplotype (16% versus 4%). In the subgroup with wild-type exon polymorphisms (A/A), patients with the high MBL promoter phenotype had the highest incidence of febrile neutropenia, regardless of known risk factors. Patients with high MBL2 promoter genotypes and haplotypes seem more at risk for developing febrile neutropenia. If confirmed, these preliminary findings may contribute to more individualized approaches of irinotecan treatment.

Mannose-binding lectin in high-risk human papillomavirus infection

Mannose-binding lectin (MBL) is a serum lectin that mediates phagocytosis and activates complement. We investigated the association of mbl-2 functional polymorphisms with human papillomavirus (HPV) infection, which is a primary etiologic factor for cervical cancer. The frequencies of haplotypes and genotypes of mbl-2 exon1 and promoter region variants were analyzed in 150 patients with HPV and 277 control subjects with no HPV. Unconditional logistic regression analysis was performed to evaluate an association between specific mbl-2 alleles and susceptibility to HPV infection. The frequency of high-producer mbl-2 genotypes was higher in patients with HPV than in control subjects with no HPV (P = .001). The genotype of the mbl-2 gene polymorphisms represented the least significant risk for the group with HPV. Certain polymorphisms in the MBL promoter region are increased among cervical samples that demonstrate HPV infection. This finding suggests a potential link between MBL and high-risk HPV infection.

Association Between Donor MBL Promoter Haplotype and Graft Survival and the Development of BOS After Lung Transplantation

Lung transplantation is a well accepted therapy for end-stage lung disease, despite high mortality rates. Mortality after transplantation is mainly caused by allograft failure in the first years after transplantation. Mannose binding lectin (MBL), a recognition molecule of innate immunity, has been associated with transplant outcome in other solid organ transplantation. In this study, the effect of donor- and recipient-MBL genotype on lung transplant outcome was investigated. All lung transplantations performed in our center, except from retransplantations and combined lung-liver or heart-lung transplantations, were included. Genotyping of the MBL2 variants (promoter: L/H, Y/X, and P/Q allele and exon 1: A/D, A/B, and A/C allele) was performed in donor and recipient DNA. Analyses on graft survival and the development of bronchiolitis obliterans syndrome were performed with Kaplan-Meier (log rank) survival analysis. Of the 277 included cases, DNA was available from 189 donors and 200 recipients and genotyping of the promoter single nucleotide polymorphisms was successful in 184 donors and 198 recipients and of the exon 1 single nucleotide polymorphisms in 181 donors and 193 recipients. Patients who received a graft from a donor with an X-allele had better graft survival (P=0.007) and bronchiolitis obliterans syndrome free survival (P=0.007). Recipient MBL genotype was not associated with transplant outcome. The donor X-allele, which corresponds to the LXPA haplotype is associated with superior lung transplant outcome. Our findings might prove to be important in finding ways to optimize outcome after lung transplantation.

Mannose-Binding Lectin Serum Levels are Low in Persons with Clinically Active Coccidioidomycosis

Mannose-binding lectin (MBL) is a circulating collectin that is part of the innate immune response. We explored the serum levels of MBL in persons with different forms of coccidioidomycosis. Serum MBL was measured by ELISA from samples obtained from healthy donors with immunity to Coccidioides, and those with various forms of active coccidioidomycosis. Blood cell specimens from a subgroup of subjects with active coccidioidomycosis were examined for single nucleotide polymorphisms of the MBL gene and promoter regions. The control group comprised 29 healthy immune subjects. Patient groups with active coccidioidomycosis consisted of 20 patients with symptomatic primary pulmonary coccidioidomycosis, 26 with non-meningeal disseminated coccidioidomycosis, and nine with coccidioidal meningitis. The group with active coccidioidomycosis was significantly older and more likely to be male than the control group (for both, P < 0.001). The mean +/- SEM level of serum MBL in the healthy controls was 169.4 +/- 28.6 ng/ml, significantly higher than the 79.2 +/- 10.9 ng/ml for all active groups (P < 0.001). Moreover, the active coccidioidomycosis group was significantly more likely to have serum MBL level <or=70 ng/ml compared to the control group (P = 0.001). Genetic analysis in 27 subjects with active coccidioidomycosis revealed marked variation based on race and ethnicity. Among a subgroup of 10 white, non-hispanic men with active coccidioidomycosis, there was a significant association between the H and P haplotypes and MBL levels <or=70 ng/ml (P < 0.036 and P < 0.035, respectively). These data suggest that there is an association between low serum MBL levels and symptomatic coccidioidomycosis.

RESEARCH OF MANNOSE-BINDING LECTIN AND INTERLEUKINS 10, 12, AND 18 IN CHILDREN WITH HENOCH-SCHÖNLEIN PURPURA

INTRODUCTION: Henoch-Schönlein Purpura (HSP) is a common vasculitis in children, and the unbalance of T-helper 1/T-helper 2 plays an important part in its pathogenesis. Mannose-binding lectin (MBL) is an important component of innate immunity and related with a lot of diseases with immunologic derangement. However, we do not know the relationship between MBL and HSP. OBJECTIVE: We aimed to explore the serum level and gene polymorphisms of MBL and the levels of interleukin 10 (IL-10), IL-12, and IL-18 in supernatant of peripheral blood mononuclear cells of children with HSP and HSP nephritis (HSPN) and of healthy children. METHODS: The concentrations of MBL and IL-10, IL-12, and IL-18 were measured by enzyme-linked immunosorbent assay: MBL gene polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism and polymerase chain reaction with sequence-specific primers. RESULTS: The serum MBL levels in the 23 children with HSP were not significantly different from 27 children with HSPN (P = .95) or 18 normal children. The levels of IL-18 in the supernatant of peripheral blood mononuclear cells in the 3 groups were not significantly different from each other (P = .47, .15, and .14). The levels of IL-10 in children with HSP and HSPN were not different from each other (P = .70), but both were significantly different from those in the normal children (P = .04 and .01). The levels of IL-12 in children with HSP were different from those in the children with HSPN (P = .04). The MBL promoter genotype and the frequency of alleles were not different between the children with HSP and HSPN or between those 2 groups compared with the normal group. CONCLUSIONS: IL-12 probably plays an important role in the renal involvement in HSP. The position of MBL in the pathogenesis of HSP and HSPN remains to be confirmed.

Mannose-binding lectin gene polymorphisms in a cohort study of ANCA-associated small vessel vasculitis

To investigate whether single nucleotide polymorphisms (SNPs) within the mannose-binding lectin (MBL) gene are associated with small vessel vasculitis (SVV) and are a risk factor for intercurrent infection, as described previously in other autoimmune diseases. Six SNPs in the MBL promoter and coding region were genotyped by sequence-specific polymerase chain reaction or restriction fragment length polymorphism assay in 170 white Caucasians with SVV and 372 ethnically matched controls in a case-control association study. Serum MBL levels were measured by ELISA. The genotype and protein concentrations were correlated to clinical details retrieved from hospital records. No differences in allelic and genotypic frequencies were detected between patients with SVV and control subjects. MBL deficiency did not increase the susceptibility to infection (P = 0.6, Fisher's exact test) or the duration of hospital stay. Our data suggest that MBL polymorphisms are not associated with SVV and do not influence the incidence of concomitant infections. These results raise doubts about the usefulness of MBL polymorphisms as a predictive marker for infection in SVV.

P962 Mannose-binding lectin promoter gene variants in Korean patient with bacteraemia

P962 Mannose-binding lectin promoter gene variants in Korean patient with bacteraemia

Increased frequency of mannose-binding lectin promoter LX haplotype among Filipinos with systemic lupus erythematosus

Sir—Mannose-binding lectin (MBL) is structurallyhomologous to C1q, and low serum MBL has beenshown to cause defective activation of the complementsystem, leading to impaired complement-mediatedclearance of immune complexes, characteristic ofautoimmune diseases like systemic lupus erythemato-sus (SLE).

Mannose-Binding Lectin Genotype and Invasive Pneumococcal Infection

Invasive pneumococcal disease is a serious infection that primarily affects young children and elderly or immunocompromised persons, but it also can affect healthy persons. Mannose-binding lectin (MBL) is a mediator of innate host immunity that activates the complement pathway and directly opsonizes pathogens. Variant structural codon and promoter MBL alleles have been associated with susceptibility to infections. Sixty-three Belgian patients with invasive pneumococcal disease and 162 healthy Belgian controls were genotyped for MBL alleles. We found a nonsignificant increased risk between the MBL structural codon variants (52, 54, and 57) and invasive pneumococcal disease. Combining our data with similar data from Kronberg et al. (J Infect Dis 2002;185:1517-20) indicated that MBL structural variants contributed to a small but significant increased risk of invasive pneumococcal disease. On the other hand, the -221 and -550 promoter allele distribution and the prevalence of the combined MBL structural and promoter -221 variant alleles were not significantly different between the patient group and the control group.

Association between familial deficiency of mannose-binding lectin and mutations in the corresponding gene and promoter region.

In a recent report, our group presented clinical research data supporting the role of mannose-binding lectin (MBL) deficiency in susceptibility to meningococcal disease (W. A. Bax, O. J. J. Cluysenaer, A. K. M. Bartelink, P. C. Aerts, R. A. B. Ezekowitz, and H. van Dijk, Lancet 354:1094-1095, 1999). This association was reported earlier by Hibberd et al. (M. L. Hibberd, M. Sumiya, J. A. Summerfield, R. Booy, M. Levin, and the Meningococcal Research Group, Lancet 353:1049-1053, 1999) but was not based on family data. Our study included three members of one family who had acquired meningococcal meningitis in early adulthood. The objective of the present study was to investigate whether the genotypes of the MBL gene in this family, analyzed by PCR, correlate with MBL concentrations. We found that genotype variants in the MBL gene and promoter region match the low functional MBL levels (<0.25 microg of equivalents/ml) in the sera of the three patients in this family and that a significant correlation between genotype MBL deficiency and meningococcal disease existed.

Mannose-binding lectin deficiency—revisited

There is an emerging interest for mannose-binding lectin (MBL) due to its role in innate immunity. In this survey we present a mixture of old and new data describing the effect MBL polymorphisms may have on the level and function of the molecule. Three single nucleotide substitutions in exon 1 of the mbl2 gene cause a dominant decrease of functional MBL in the circulation. Additionally, promoter variants influence expression of MBL. It has been assumed that the structural variant alleles may disrupt the assembly of MBL trimers or accelerate the degradation of the protein, thereby causing the decrease in MBL serum concentrations. We have analysed 1183 different sera in a double sandwich antibody ELISA using the same antibody to capture and detect MBL and find the same results as have been presented previously showing that different MBL promoter alleles have profound effect of on the MBL serum concentration. The use of a new anti-MBL monoclonal antibody, however, has shown that the amount of MBL in the circulation is less dependent on the presence of structural variant alleles than previously anticipated. Molecular characterisation of MBL revealed that sera from donors homozygous for the normal MBL genotype predominantly contained high molecular weight MBL, while sera from individuals heterozygous for the variant alleles contained both high and low molecular weight MBL. The ratio between high and low molecular weight MBL was dependent on the MBL promoter type on the normal haplotype. Sera deriving from individuals homozygous for MBL variant alleles contained mainly low molecular weight MBL. Of the different oligomers of MBL only the high molecular weight forms bound mannan efficiently and activated complement. In contrast to a previous notion, we demonstrate that variant alleles give rise to relatively high levels of MBL in the circulation. However, the variant MBL has lower molecular weight and is dysfunctional compared to normal MBL. The physiological relevance of variant MBL remains to be established.

Analysis of the relationship between mannose-binding lectin (MBL) genotype, MBL levels and function in an Australian blood donor population.

The mannose-binding lectin (MBL) pathway of complement activation is an important component of innate host defence. Numerous studies have described associations between the MBL genotype, MBL levels and disease susceptibility. However, genotyping and quantitative assays used in these studies have frequently been limited, and comprehensive data examining the interaction between structural and coding MBL genetic variants, MBL antigenic levels and MBL functional activity are lacking. Such data may be important for accurate planning and interpretation of studies of MBL and disease. This study has examined MBL in a cohort of 236 Australian blood donors. Five MBL promoter and coding single nucleotide polymorphisms were genotyped using polymerase chain reaction-sequence-specific priming (PCR-SSP). Plasma levels of MBL antigen were quantified using a double-antibody enzyme-linked immunosorbent assay (ELISA), and functional MBL levels were quantified using a mannan-binding assay. Activation of the complement pathway by MBL was measured in a C4-deposition assay. Significant associations were found between both coding and promoter polymorphisms and MBL antigenic and functional levels. There was significant correlation between the results of MBL double-antibody, mannan-binding and C4-deposition assays. Comprehensive MBL genotyping and functional MBL quantitation using mannan-binding and C4-deposition assays have the potential to be highly informative in MBL disease association studies.

Restricted polymorphism of the mannose-binding lectin gene of indigenous Australians.

Mannose-binding lectin (MBL) is an important complement-activating protein of the human innate immune system. Deficiency of MBL is associated with an increased risk of various infections and arises from three structural gene mutations in exon 1 (variants B, C and D) and/or the presence of a low efficiency promoter. The C allele is found in sub-Saharan Africa whereas the B allele is found elsewhere, suggesting that these mutations occurred after the suggested hominid migration out of Africa [100-150 000 years before present (BP)]. Paradoxically, these alleles may have a selective advantage in protection against intracellular pathogens and occur at particularly high frequencies in sub-Saharan Africa (C variant) and South America (B variant). Since hominids reached Australia at least 50 000 years ago, a study of MBL polymorphisms in the indigenous population was of interest. Using heteroduplex technology we found a paucity of MBL structural gene mutations in two population groups from geographically distinct regions. Of 293 individuals tested, 289 were wild-type and four were heterozygous for either the B or D allele. In each individual with an MBL mutation the HLA haplotype profile suggested some Caucasian admixture. We also found a restricted range of MBL promoter haplotypes and the serum MBL levels were higher than those of any other ethnic group studied to date (median 3.07 microg/ml). Our data suggest that the B mutation probably arose between 50 000 and 20 000 BP. Its absence from the founder gene pool of indigenous Australians may also partly explain their vulnerability to intracellular infections such as tuberculosis.