The prevalence of the variants of the L-ficolin gene (FCN2) in the arctic populations of East Siberia

Ficolin-3 and MASP-2 gene variants in Siberian arctic populations: Summarized evidence of selective pressure for the high frequency of lectin complement pathway deficiency

Herewith, we provide novel original data about the prevalence of FCN3 rs532781899 and MASP2 rs72550870 variants among the newborns of aboriginal Siberian Arctic populations (Nenets and Dolgan-Nganasans) and Russians of East Siberia. This novel data has been analysed along with the genetic data about other proteins of the lectin pathway of the complement system (mannose-binding lectin and ficolin-2) obtained earlier. A total of 926 specimens of dried blood spots of the newborns were genotyped. The newborns represented four populations: Nenets, Dolgan-Nganasans, Mixed aboriginal population, and Russians (Caucasians) to study the prevalence of single nucleotide polymorphisms of FCN3 rs532781899 and MASP2 rs72550870. The prevalence of the deletion allele of the rs532781899 variant in the FCN3 gene associated with the decreased production of ficolin-3 was found to be increased in Russians compared to the Nenets aboriginal populations (P = .002). The prevalence of the rs72550870*G allele in the MASP2 gene associated with low serum protease activity was found to be increased in Russians compared with Nenets and Dolgan-Nganasans (P < .001 and P = .03, respectively). The results of the current study and our previous findings corroborate with a hypothesis that human evolution has been directed toward the accumulation of genotypes associated with low activity of the lectin complement activation pathway.

Proteins of the lectin pathway of the complement system activation: immunobiological functions, genetics and involvement in the pathogenesis of human diseases

The complement system is the most ancient components in the innate immunity, mainly functioning to primarily eliminate bacterial agents intravascularly. Moreover, the complement complex proteins play a role as a bridge between the systems of innate and adaptive immunity providing adequate conditions for maturation and differentiation of B- and T-lymphocytes. The complement system consists of plasma proteins and membrane receptors. Plasma proteins interact with each other via the three described cascade pathways lectin (which is most ancient phylogenetically), alternative and classical. Lectins are proteins comprising a separate superfamily of pattern-recognizing receptors able to sense molecules of oligo- and polysaccharide nature and induce their aggregation. Among all the lectins, ficolins (FCN) (common domain fibrinogen) and collectins (common domain collagen) mannose-binding lectin (MBL), hepatic and renal collectins have exert unique functions by complexing with carbohydrate components of microbial wall. Formation of a compound complex microbial wall polysaccharides + collectin/ficolin + specific mannose-binding lectin-associated serine proteases (MARP) results in the complement system activation, inflammatory reaction and bacterium elimination. Such scenario is proceeded along the lectin pathway compared to the two other pathways called classical and alternative. Examining a role of the complement system and congenital protein defects in the pathogenesis of various diseases is of topical interest because inborn deficiency of the complement components comprises at least 5% out of total primary immunodeficiency rate, whereas the aspects of their prevalence and pathogenesis remain unexplored. Relevance of investigating the complement system components for diverse populations is tremendous, taking into consideration accumulated evidence regarding an important role of the lectin pathway in viral infections. Lectins, the main proteins in the lectin pathway of the complement activation, are encoded by polymorphic genes, wherein single nucleotide polymorphisms (SNPs) result in altered protein conformation and expression, which, in turn, affects functionality and potential to respond to a pathogen. The distribution of the lectin polymorphic gene frequencies and their haplotypes displays extremely marked population differences. According to analyzing available data, population SNP frequencies including those associated with inborn deficiencies for components of the lectin pathway have been currently scarce or unexplored. hence, here we review major lectins and their functions, their functionally significant SNPs in diverse populations and their pathogenetic importance for host defense functions.

Prevalence of the polymorphic H-ficolin (FCN3) genes and mannosebinding lectin-associated serine protease-2 (MASP2) in indigenous populations from the Russian Arctic regions

Lectins, being the main proteins of the lectin pathway activating the complement system, are encoded by polymorphic genes, wherein point mutations cause the protein conformation and expression to change, which turns out to have an effect on the functionality and ability to respond to the pathogen. In the current study, largescale data on the population genotype distribution of the genes for H-ficolin FCN3 rs28357092 and mannose-binding lectin-associated serine protease MASP2 rs72550870 among the indigenous peoples of the Russian Arctic regions (Nenets, Dolgans and Nganasans, a mixed population and Russians: a total sample was about 1000 newborns) have been obtained for the first time. Genotyping was carried out using RT-PCR. The frequency of the homozygous variant del/del FCN3 rs28357092 associated with the total absence of the most powerful activator of the lectin complement pathway, N-ficolin, was revealed; 0 % in the Nenets, 0.8 % in the Dolgans and Nganasans, and 3.5 % among the Russians ( p < 0.01). Analysis of the prevalence of the MASP2 genotypes has shown the predominance of the homozygous variant AA in all studied populations, which agrees with the available world data. The heterozygous genotype AG rs72550870 associated with a reduced level of protease was found to occur rarely in the Nenets, Dolgans and Nganasans compared to newborns of Caucasoid origin from Krasnoyarsk: 0.5 % versus 3.3 %, respectively. Moreover, among 323 examined Nenets, one AG carrier was identified, whereas in Russians, 16 out of 242 examined newborns were found to be AG carriers ( p < 0.001). A homozygous variant (GG) in total absence of protease with impaired binding of both MBL and ficolins was not detected in any of the 980 examined newborns. An additional analysis of infectious morbidity in Arctic populations allows one to find phenotypic characteristics related to a high functional activity of the lectin pathway of complement activation as an most important factor for the first-line of anti-infectious defense, including such new viral diseases as COVID-19.

Polymorphism of the mannose-binding lectin gene in the Arctic indigenous populations of the Russian Federation

Маннозосвязывающий лектин (mannose-binding lectin, MBL) – паттерн-распознающий острофазовый белок, относящийся к системе врожденного иммунитета и активно участвующий в элиминации широкого круга патогенных микроорганизмов посредством активации лектинового пути системы комплемента. Значительная часть человеческой популяции имеет врожденно низкий уровень продукции и/или низкую функциональную активность MBL вследствие носительства различных вариантов гена MBL2, что может модифицировать течение самых разнообразных инфекционных заболеваний. Частота генотипов и гаплотипов полиморфизмов в гене MBL2 имеет значительные популяционные различия. К настоящему времени данные относительно распределения генотипов гена MBL2 в коренных популяциях территорий Арктической зоны Российской Федерации отсутствуют. Цель исследования – изучение частоты и этнической специфики распределения аллельных вариантов полиморфизмов гена MBL2 rs11003125, rs7096206, rs7095891, rs5030737, rs1800450 и rs1800451 и их гаплотипов в популяциях Таймырского Долгано-Ненецкого района Красноярского края (ненцы, долганы-нганасаны, русские). В настоящем исследовании нами впервые получены данные о частотах генотипов и гаплотипов гена MBL2 у коренных народностей, проживающих на территориях Арктической зоны Российской Федерации. Частота встречаемости гаплотипа HYPA, ассоциированного с высокой концентрацией MBL, составила 35.4 % для русских новорожденных Восточной Сибири, что соответствует частотам европейских популяций (27–33 %). У новорожденных арктических популяций частота гаплотипа HYPA была статистически значимо выше, чем у русских, и составила 64 % для ненцев и 56 % для долган-нганасан, что приближается к значениям частот, выявленных для эскимосов и североамериканских индейцев (64–81 %). Популяции ненцев и долган-нганасан демонстрируют существенно более низкие частоты MBL-дефицитных гаплотипов в сравнении с европеоидами Восточной Сибири (3.9, 6.4 и 21.3 % соответственно). Мы предполагаем, что изолированные арктические популяции исторически позже столкнулись с некоторыми внутриклеточными инфекциями (туберкулезом, лепрой) и, в отличие от европеоидных популяций, сохранили сформированную на ранних этапах эволюции человека высокую активность лектинового пути активации комплемента.

Mannose-binding lectin gene polymorphisms in the East Siberia and Russian Arctic populations

Mannose-binding lectin (MBL) encoded by MBL2 gene is a protein with the ability to form carbohydrate complexes with microbial wall promoting their subsequent elimination. Genetically determined levels of MBL can modify the risk and clinical characteristics of many infectious diseases. The frequency of MBL2 genotypes exhibits significant population differences. The data on the distribution of MBL2 genotypes among the aborigines of the Russian Arctic territories have not yet been published. A total of 880 specimens of dried blood spots of the newborns were genotyped. The newborns represented four populations: Nenets, Dolgan-Nganasans, Mixed aboriginal population, and Russians (Caucasians, Krasnoyarsk). Six polymorphisms of the MBL2 gene were studied: rs11003125, rs7096206, rs7095891, rs5030737, rs1800450, and rs1800451. The frequency of the combined rare O allele (composed of the coding region variants rs5030737, rs1800450, and rs1800451) in the homozygous state was significantly higher in Russians: 10% vs 2% in Nenets and 1% in Dolgan-Nganosans (p < 0.001 for Russians vs other populations). The frequency of the high-producing haplotype (HYPA) was 35.4% in the Russian newborns, in keeping with European populations (27-33%); 64% for Nenets and 56% for Dolgan-Nganasans, similar to the estimates obtained for Eskimos and North Amerinds (64-81%). Our study results are in line with the hypothesis that human evolution has been moving in the direction of accumulation of the genotypes associated with low activity of the lectin complement activation pathway because of the prevalence of some intracellular infections such as tuberculosis, whereby low MBL activity may have a protective effect.

Congenitally impaired pattern-recognition receptors in pathogenesis of pediatric invasive and recurrent pneumococcal infection

Here we review currently available data showing that innate immune signs predisposing to recurrent and invasive pneumococcal infections were identified in children. Streptococcus pneumoniae (pneumococcus) belongs to Grampositive bacteria being the major cause of morbidity and mortality in infants, especially in developing countries and in communities with low socioeconomic status. Due to the lack of anti-pneumococcal vaccination, the significant proportion of pneumococcus carriers develop non-invasive (pneumonia, otitis media, sinusitis) and severe invasive (bacteremia/septicemia, meningitis) pneumococcal infection. A great deal of diverse factors related to pneumococcus biological features (virulence factors) as well individualized host-specific immunity are implicated in efficient bacterial penetration across the mucous membranes. The TLR signaling system plays a crucial role in the human nonspecific defense upon the first encounter with the pathogen. Various TLRs comprise the first pattern recognition receptor fami ly ever described which sense ligands derived from the outer bacterial wall. The complement system is the ancient innate immunity component mainly involved in intravascular elimination of bacterial agents. In addition, the complement proteins serve as a bridge between innate and adaptive immunity, ensuring optimal conditions for B- and T-cell maturation and differentiation. Because pneumococcus secretes the IgA protease, a local protective effects related to IgA antibodies might not be so prominent. Therefore, B-cell immunodeficiency and impaired complement system hold a lead place among congenital causes resulting in severe and recurrent pneumococcal infections in children. Thus, based on available data, we concluded that impaired B-cell function, the complement components deficiency as well as receptor-recognition receptors (TLR-2, -9, -4, MYD88 adapter protein, TLR cascade enzymes: IRAK4, NEMO, NOD-like receptors: NOD2, NLRP3; C-type lectins: MBL, Dextin-2, and, possibly, ficoline) play the most important role among congenital immunodeficiencies predisposing to invasive and recurrent pneumococcal infections play the most important role among congenital immunodeficiencies predisposing to invasive and recurrent pneumococcal infections, and should be used as a rationale for immunological surveillance and organizing immunogenetics screening in these patients.