Background: Mannose binding lectin (MBL) has an important role in the activation of the complement system and opsonization of pathogenic microorganisms. Frequent polymorphisms found in theMBL2gene affect the concentration and functionality of the protein and are associated with enhanced susceptibility to severe malaria in African children. MostMBL2typing strategies were designed to the analysis of selected variants, the significance of whole haplotypes is poorly known. In this work, a new typing strategy was developed and validated in an association analysis ofMBL2with adult asymptomatic infection.Methods: MBL2allele-specific fragments of 144 healthy Gabonese adults were amplified by using haplotype-specific sequencing (HSS), a new strategy that combines sequence-specific PCR and sequence-based typing. The Gabonese were investigated for the presence ofPlasmodium falciparumparasitaemia by the amplification of parasite genes, immunochromatographic antigen detection and microscopic analysis. HSS results were also compared with a previously used real-time PCR (RT-PCR) method in 72 Euro-Brazilians.Results: Fourteen polymorphisms were identified beside the commonly investigated promoter (H, L;X, Y;P, Q) and exon 1 (A, O;O=B,CorD) variants. TheMBL2*LYPA/LYPAgenotype was associated with the absence of asymptomatic infection (P = 0.017), whereas theMBL2*LYQChaplotype andYA/YO+YO/YOgenotypes were associated with positive parasite counts in asymptomatic adults (P = 0.033 and 0.018, respectively). The associations were specific toLYPA(identical to the reference sequence Y16577) andLYQC(Y16578) and would not have been revealed by standard genotyping, as there was no association withLYPAandLYQChaplotypes carrying new polymorphisms defined by sequence-based typing. In contrast, HSS and RT-PCR produced very similar results in the less diverse European-derived population.Conclusion: In this work, a new typing strategy for a highly polymorphic gene was developed and validated focusing on the asymptomatic status ofP. falciparum-infected adults. In populations with high nucleotide diversity, it allowed for the identification of associations with fine-scaled haplotypes that would not have been found using common typing techniques. In this preliminary study,MBL2haplotypes or SNPs linked to them were found associated with susceptibility to infection and parasitaemia control of asymptomatic adults.

Leprosy is a chronic inflammatory disease caused by Mycobacterium leprae that mainly affects the skin and peripheral nervous system, leading to a high disability rate and social stigma. Previous studies have shown a contribution of genes encoding products of the lectin pathway of complement in the modulation of the susceptibility to leprosy; however, the ficolin-3/FCN3 gene impact on leprosy is currently unknown. The aim of the present study was to investigate if FCN3 polymorphisms (rs532781899: g.1637delC, rs28362807: g.3524_3532insTATTTGGCC and rs4494157: g.4473C>A) and ficolin-3 serum levels play a role in the susceptibility to leprosy. We genotyped up to 190 leprosy patients (being 114 (60%) lepromatous), and up to 245 controls with sequence-specific PCR. We also measured protein levels using ELISA in 61 leprosy and 73 controls. FCN3 polymorphisms were not associated with disease, but ficolin-3 levels were higher in patients with FCN3 *2B1 (CinsA) haplotype (p = 0.032). Median concentration of ficolin-3 was higher in leprosy per se (26034 ng/mL, p = 0.005) and lepromatous patients (28295 ng/mL, p = 0.016) than controls (18231 ng/mL). In addition, high ficolin-3 levels (>33362 ng/mL) were more common in leprosy per se (34.4%) and in lepromatous patients (35.5%) than controls (19.2%; p = 0.045 and p = 0.047, respectively). Our results lead us to suggest that polymorphisms in the FCN3 gene cooperate to increase ficolin-3 concentration and that it might contribute to leprosy susceptibility by favoring M. leprae infection. Leprosy is considered a neglected disease and still a public health problem in many countries where it was not yet eliminated, leading to a high disability rate and social stigma. The molecular mechanisms of M. leprae infection and immune evasion are still poorly known, raising the need for studies that may contribute to a better understanding of leprosy etiology, as well as improvement in diagnosis and treatment. Ficolin-3 is a soluble molecule of the innate immune system that recognizes a wide range of pathogen-associated molecular patterns leading to complement activation and phagocytosis. We observed high concentration of ficolin-3 in leprosy patients, likely caused by polymorphisms present in intronic regions of FCN3 gene, which may contribute to leprosy susceptibility by favoring M. leprae infection. This is the first study addressing FCN3 polymorphisms and ficolin-3 levels in leprosy, indicating it as a good candidate biomarker associated with the host response against M. leprae.