Role of collectins and complement protein C1q in pregnancy and parturition

Disruption of the SP-A/SP-R210L (MYO18Aα) pathway prolongs gestation and reduces fetal survival during lipopolysaccharide-induced parturition in late gestation

Prolonged labor can lead to infection, fetal distress, asphyxia, and life-threatening harm to both the mother and the baby. Surfactant protein A (SP-A) was shown to contribute to the maintenance of pregnancy and timing of term labor. SP-A modulates the stoichiometric expression of the SP-R210L and SP-R210S isoforms of the SP-R210 receptor on alveolar macrophages (AMs). Lack of SP-R210L dysregulates macrophage inflammatory responses. We asked whether SP-A alters normal and inflammation-induced parturition through SP-R210 using SP-A- and SP-R210L-deficient mice. Labor and delivery of time-pregnant mice were monitored in real time using a time-lapse infrared camera. Intrauterine injection with either vehicle or Escherichia coli lipopolysaccharide (LPS) on embryonic (E) day 18.5 post coitus was used to assess the effect of gene disruption in chorioamnionitis-induced labor. We report that either lack of SP-A or disruption of SP-R210L delays parturition by 0.40 and 0.55 days compared with controls, respectively. LPS induced labor at 0.60, 1.01, 0.40, 1.00, and 1.31 days earlier than PBS controls in wild type (WT), SP-A-deficient, littermate controls, heterozygous, and homozygous SP-R210L-deficient mice, respectively. Lack of SP-A reduced litter size in PBS-treated mice, whereas the total number of pups delivered was similar in all LPS-treated mice. The number of live pups, however, was significantly reduced by 50%-70% in SP-A and SP-R210L-deficient mice compared with controls. Differences in gestational length were not associated with intrauterine growth restriction. The present findings support the novel concept that the SP-A/SP-R210 pathway modulates timely labor and delivery and supports fetal lung barrier integrity during fetal-to-neonatal transition in term pregnancy.NEW & NOTEWORTHY To our knowledge, this study is the first to report that SP-A prevents delay of labor and inflammation-induced stillbirth through the receptor SP-R210L.

Protective role of complement factor H against the development of preeclampsia

Pregnancy is an immunologically regulated, complex process. A tightly controlled complement system plays a crucial role in the successful establishment of pregnancy and parturition. Complement inhibitors at the feto-maternal interface are likely to prevent inappropriate complement activation to protect the fetus. In the present study, we aimed to understand the role of Factor H (FH), a negative regulator of complement activation, in normal pregnancy and in a model of pathological pregnancy, i.e. preeclampsia (PE). The distribution and expression of FH was investigated in placental tissues, various placental cells, and in the sera of healthy (CTRL) or PE pregnant women via immunohistochemistry, RT-qPCR, ELISA, and Western blot. Our results showed a differential expression of FH among the placental cell types, decidual stromal cells (DSCs), decidual endothelial cells (DECs), and extravillous trophoblasts (EVTs). Interestingly, FH was found to be considerably less expressed in the placental tissues of PE patients compared to normal placental tissue both at mRNA and protein levels. Similar results were obtained by measuring circulating FH levels in the sera of third trimester CTRL and PE mothers. Syncytiotrophoblast microvesicles, isolated from the placental tissues of PE and CTRL women, downregulated FH expression by DECs. The present study appears to suggest that FH is ubiquitously present in the normal placenta and plays a homeostatic role during pregnancy.

The Lung Microenvironment Instructs Gene Transcription in Neonatal and Adult Alveolar Macrophages

Immaturity of alveolar macrophages (AMs) around birth contributes to the susceptibility of newborns to lung disease. However, the molecular features differentiating neonatal and mature, adult AMs are poorly understood. In this study, we identify the unique transcriptomes and enhancer landscapes of neonatal and adult AMs in mice. Although the core AM signature was similar, murine adult AMs expressed higher levels of genes involved in lipid metabolism, whereas neonatal AMs expressed a largely proinflammatory gene profile. Open enhancer regions identified by an assay for transposase-accessible chromatin followed by high-throughput sequencing (ATAC-seq) contained motifs for nuclear receptors, MITF, and STAT in adult AMs and AP-1 and NF-κB in neonatal AMs. Intranasal LPS activated a similar innate immune response in both neonatal and adult mice, with higher basal expression of inflammatory genes in neonates. The lung microenvironment drove many of the distinguishing gene expression and open chromatin characteristics of neonatal and adult AMs. Neonatal mouse AMs retained high expression of some proinflammatory genes, suggesting that the differences in neonatal AMs result from both inherent cell properties and environmental influences.

Changes in Expression of Complement Components in the Ovine Spleen during Early Pregnancy

During early gestation in humans, complement regulation is essential for normal fetal growth. It is supposed that a complement pathway participates in maternal splenic immune regulation at the early stage of gestation in ewes. The aim of this study was to analyze the effects of early pregnancy on the expression of complement components in the maternal spleen of ewes. In this study, ovine spleens were sampled on day 16 of nonpregnancy, and days 13, 16 and 25 of gestation. RT-qPCR, Western blot and immunohistochemical analysis were used to detect the changes in expression of complement components in the ovine maternal spleens. Our results reveal that C1q was upregulated during early gestation, C1r, C1s, C2, C3 and C5b increased at day 25 of gestation and C4a and C9 peaked at days 13 and 16 of gestation. In addition, C3 protein was located in the capsule, trabeculae and splenic cords. In conclusion, our results show for the first time that there was modification in the expression of complement components in the ovine spleen at the early stage of gestation, and complement pathways may participate in modulating splenic immune responses at the early stage of gestation.

Dysregulation of complement system in HELLP syndrome

OBJECTIVE

To investigate the expression of complement system's activation factors in patients with HELLP syndrome.

METHODS

A case-control study was performed. Sixteen HELLP syndrome patients, 32 severe preeclampsia patients, and 48 normal pregnancy women were involved in this studyELISA was used to test C1q, C4d, MBL, Bb, C3a, C5a, sC5b-9, s-Endoglin, and sflt-1 in the plasma.

RESULTS

The levels of C5a (P < 0.01) and sC5b-9 (P = 0.014) in HELLP syndrome were higher than those in severe preeclampsia patients.

CONCLUSIONS

The abnormal activation of the complement system is more significant in the pathogenesis of HELLP syndrome than in severe preeclampsia.

Effects of early pregnancy on the complement system in the ovine thymus

The complement system is crucial for the innate immune system, and complement activation is related to abnormal pregnancy in mice and humans. It is hypothesized that the complement system participates in maternal thymic immune regulation during early pregnancy in sheep. In this study, maternal thymuses were sampled on day 16 of the estrous cycle, and days 13, 16 and 25 of gestation in sheep. Quantitative real-time PCR, Western blot and immunohistochemistry analyses were used to analyze the expression of the complement components C1q, C1r, C1s, C2, C3, C4a, C5b and C9 in the maternal thymus. The results revealed that the mRNA and protein expression of C1r, C1s, C2, C3 and C4a was inhibited by early pregnancy, and the pregnancy recognition signal induced upregulation of C1q, C5b and C9 expression at day 16 of gestation. Furthermore, C3 protein was mostly located in epithelial reticular cells and thymic corpuscles, which may be involved in immune regulation. In summary, early pregnancy inhibits the complement system in the maternal thymus, which may be essential for the maternal immune regulation and successful pregnancy in sheep.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Impact of infections in autoimmune rheumatic diseases and pregnancy

PURPOSE OF REVIEW

To provide an update about the impact of infections in autoimmune rheumatic diseases (ARDs), from the analysis of the role of infections in pregnant women without ARDs, to the identification of maternal-fetal infections and their role in the maternal-fetal outcome of women with ARDs.

RECENT FINDINGS

Recent studies indicate that patients with ARDs and pregnancy are also susceptible to presenting infections of varying degrees, including serious infections, which contribute to the morbidity and mortality observed in pregnancy and postpartum of these patients.Any type of infectious agent will interact with a hormonal, immunological and metabolic environments modified by ARD, treatments, and by the changes inherent in pregnancy. Therefore, infections in the pregnancy of patients with ARDs should be considered as a risk factor for an unfavorable maternal-fetal outcome.

SUMMARY

The recognition of infections in the pregnancy of ARDs as a risk factor is the first step to prevent, identify, and treat them in a timely manner, and thus contribute to the favorable course of pregnancy in these patients. Patients with ARDs and major organ involvement, use of high doses of steroids, immunosuppressant and biological therapies, adolescence, and obesity are populations susceptible to developing infections.

Dysregulation of complement system during pregnancy in patients with preeclampsia: A prospective study

Recent studies have shown that aberrant activation of the complement system plays an important role in the pathogenesis of preeclampsia. There is evidence to suggest that aberrant activation of the complement system may already be present during the first trimester. Here, we performed a prospective study in which peripheral blood samples were collected from 500 women during pregnancy. Twenty-one patients (41 specimens) suffering from preeclampsia later in pregnancy were classified into the study group, and sixty-three gravidas with normal pregnancies (136 specimens) were selected as the control group. The plasma concentrations of complement factor B (CFB), C1q, complement factor H (CFH), C3c, C4, C3a, C5a and soluble C5b-9 (sC5b-9) were measured. The levels of CFB (P = 0.004), CFH (P = 0.002), C1q (P = 0.044), C3c (P = 0.032) and C4 (P = 0.015) were significantly higher in preeclampsia than in normal pregnancy during the first trimester, and these levels became similar to those in normal pregnancy thereafter. Before the onset of preeclampsia, the levels of C3a, C5a and sC5b-9 in the preeclampsia group were similar to those in control group even in late pregnancy. C3a levels showed a significant positive correlation with C5a in normal pregnancy (r=0.658, P<0.01) but not in preeclampsia (r = 0.001, P = 1).Thus, we found that aberrant activation of the complement system in patients with preeclampsia was initiated during the first trimester but returned to normal pregnancy levels in the second trimester. At the same time, there is aberrant regulation of complement activation at the C3a-C5a level in preeclampsia during pregnancy.

Identification, expression profile and analysis of the antimicrobial activity of collectin 11 (CL-11, CL-K1), a novel complement-associated pattern recognition molecule, in half-smooth tongue sole (Cynoglossus semilaevis)

Collectin 11 (CL-11, also known as collectin kidney-1, CL-K1), a new member of the vertebrate C-type lectin superfamily, plays an important role in innate immunity as a pattern recognition molecule of the lectin complement pathway. However, little is known about CL-11 in teleosts. In the present study, a CL-11 homolog was identified and characterized from half-smooth tongue sole (Cynoglossus semilaevis) (designated as CsCL-11). The full-length cDNA of CsCL-11 is 1220 bp long and includes a 5'untranslated region (5'-UTR) of 180 bp, a 3'-UTR of 218 bp and an open reading frame (ORF) of 819 bp encoding 273 amino acids. Multiple sequence alignment revealed that the deduced CsCL-11 protein has the typical modular architecture (EPN and WTD) conserved throughout vertebrates, suggesting a conserved function of CsCL-11. Tissue expression profile analysis by quantitative real-time PCR (qRT-PCR) showed CsCL-11 to be ubiquitously distributed in tissues and highly expressed in the ovary and liver. A pattern of significant upregulation of CsCL-11 expression was observed in the blood, spleen, head kidney and gill at 6 h, 12 h and 24 h after infection with Vibrio anguillarum, and western blotting showed that natural CsCL-11 protein levels in the blood were significantly increased after V. anguillarum infection. Moreover, by binding to various bacteria, recombinant CsCL-11 (rCsCL-11) expressed in HEK-293 T cells displayed strong antibacterial activity. Taken together, these results suggest that CsCL-11 is a unique C-type lectin that is likely involved in host defense against bacterial infection. To our knowledge, this is the first study on CL-11 in marine fish.

Regulation of the complement system and immunological tolerance in pregnancy

Preeclampsia is a serious vascular complication of the human pregnancy, whose etiology is still poorly understood. In preeclampsia, exacerbated apoptosis and fragmentation of the placental tissue occurs due to developmental qualities of the placental trophoblast cells and/or mechanical and oxidative distress to the syncytiotrophoblast, which lines the placental villi. Dysregulation of the complement system is recognized as one of the mechanisms of the disease pathology. Complement has the ability to promote inflammation and facilitate phagocytosis of placenta-derived particles and apoptotic cells by macrophages. In preeclampsia, an overload of placental cell damage or dysregulated complement system may lead to insufficient clearance of apoptotic particles and placenta-derived debris. Excess placental damage may lead to sequestration of microparticles, such as placental vesicles, to capillaries in the glomeruli of the kidney and other vulnerable tissues. This phenomenon could contribute to the manifestations of typical diagnostic symptoms of preeclampsia: proteinuria and new-onset hypertension. In this review we propose that the complement system may serve as a regulator of the complex tolerance and clearance processes that are fundamental in healthy pregnancy. It is therefore recommended that further research be conducted to elucidate the interactions between components of the complement system and immune responses in the context of complicated and healthy pregnancy.

Emerging Roles of Complement Protein C1q in Neurodegeneration

The innate immune system is an ancient and primary component system that rapidly reacts to defend the body against external pathogens. C1 is the initial responder of classical pathway of the innate immune system. C1 is comprised of C1q, C1r, and C1s. Among them, C1q is known to interact with diverse ligands, which can perform various functions in physiological and pathophysiological conditions. Because C1q participates in the clearance of pathogens, its interaction with novel receptors is expected to facilitate apoptosis induction, which could prevent the onset or progression of neurodegenerative diseases and could delay the aging process. Because senescence-associated secreting phenotype determinants are generally inflammatory cytokines or immune factors to activate immune cells. In the central nervous system, C1q has diverse neuroprotective roles against pathogens and inflammation. Most of neurodegenerative diseases show region specific pathology feature in the brain. It has been suggested the evidences that the active site and amount of C1q may be disease specific. This review considers currently the emerging and under-recognized roles of C1q in neurodegeneration and highlights the need for further research to clarify these roles. Future studies on the roles of C1q in regulating disease progression should consider these aspects, including the age-dependent onset time of each neurodegenerative disease progression.

The role of the complement system in HIV infection and preeclampsia

BACKGROUND

The complement system is a key component of the innate immune system that plays a vital role in host defense, maintains homeostasis and acts as a mediator of the adaptive immune response. The complement system could possibly play a role in the pathogenesis of HIV infection and preeclampsia (PE), both of which represent major causes of maternal death in South Africa.

RECENT FINDINGS

The relationship between PE and HIV infection is unclear as PE represents an exaggerated immune response, while HIV infection is associated with a decline in immune activity. Although the complement system works to clear and neutralize HIV, it could also enhance the infectivity of HIV by various other mechanisms. It has been suggested that the dysregulation of the complement system is associated with the development of PE.

CONCLUSION

There is currently a paucity of information on the combined effect of the complement system in HIV-associated PE. This review highlights the role of the complement system in the duality of HIV infection and PE and provides new insights into this relationship whilst also elucidating potential therapeutic targets.

Identification and characterization of a B-type mannose-binding lectin from Nile tilapia (Oreochromis niloticus) in response to bacterial infection

Lectins are a group of carbohydrate-binding proteins, which play an important role in innate immune system against pathogen infection. In this study, a B-type mannose-binding lectin (OnBML) was identified from Nile tilapia (Oreochromis niloticus), and characterized at expression patterns against bacterial infection and capability to promote phagocytosis by macrophages. The open reading frame of OnBML is 354 bp of nucleotide sequence encoding polypeptides of 117 amino acids. The deduced protein is highly homologous to other teleost BMLs, containing two repeats of the conserved mannose-binding motif QXDXNXVXY. Expression of OnBML was widely exhibited in all examined tissues, with the most abundance in spleen and following gill, peripheral blood, and head kidney. The OnBML expressions were significantly up-regulated following two major bacterial infections including a Gram-positive bacterium (Streptococcus agalactiae) and a Gram-negative bacterium (Aeromonas hydrophila) in vivo and in vitro. Recombinant OnBML protein possessed capacities of mannose-binding and calcium-dependent agglutination to S. agalactiae and A. hydrophila, and promoted the phagocytosis by macrophages. Taken together, the present study indicated that OnBML is likely to get involved in host defense against bacterial infection in Nile tilapia.

Expression and functional characterization of collection-K1 from Nile tilapia (Oreochromis niloticus) in host innate immune defense

Collectin-K1 (CL-K1), a multifunctional Ca²⁺-dependent lectin, is able to bind carbohydrates on pathogens and inhibit infection by direct neutralization, agglutination, opsonization and killing, which plays an important role in innate immunity. In this study, a CL-K1 homolog (OnCL-K1) was identified from Nile tilapia (Oreochromis niloticus) and characterized at expression and agglutination functional levels. The open reading frame of OnCL-K1 is 720 bp of nucleotide sequence encoding a polypeptide of 239 amino acids. The deduced amino acid sequence has two characteristic structures, containing a collagen-like region and a carbohydrate recognition domain. Expression analysis revealed that the OnCL-K1 was highly expressed in the liver, and widely exhibited in other tissues including kidney, intestine and spleen. In addition, the OnCL-K1 expression was significantly up-regulated in spleen and anterior kidney following challenges with a Gram-positive bacterial pathogen (Streptococcus agalactiae) and a Gram-negative bacterial pathogen (Aeromonas hydrophila). The up-regulation of OnCL-K1 expression was also demonstrated in hepatocytes and monocytes/macrophages in vitro stimulation with S. agalactiae and A. hydrophila. Recombinant OnCL-K1 protein was able to agglutinate both S. agalactiae and A. hydrophila in vitro, and participate in the regulation of inflammatory, migration reaction and promote the phagocytosis by monocytes/macrophages. Taken together, the results of this study indicated that OnCL-K1, possessing apparent agglutination, opsonization and killing ability to bacterial pathogens and participating in the regulation mechanisms of the non-specific cellular immune, might be involved in host defense of innate immunity against bacterial infection in Nile tilapia.

Potential Marker Pathways in the Endometrium That May Cause Recurrent Implantation Failure

The aim of this prospective cohort study was to identify altered biologic processes in the endometrium that may be potential markers of receptive endometrium in patients with repeated implantation failure (RIF) as compared with fertile controls. The study was conducted in a university-affiliated in vitro fertilization (IVF) gynecology clinic and molecular biology and genetics laboratory. Healthy fertile controls (n = 24) and patients with RIF (n = 24) were recruited. Window of implantation gene profiling associated with RIF was performed. Six hundred forty-one differentially expressed genes were identified, and 44 pathways were found enriched. Upon clustering of the enriched pathways, 9 representative pathways were established. The important pathways that were identified included circadian rhythm, pathways in cancer, proteasome, complement and coagulation cascades, citrate cycle, adherens junction, immune system and inflammation, cell cycle, and renin-angiotensin system. The involvement of the circadian rhythm pathway and other related pathways may alter the endometrium's functioning to ultimately cause RIF. Furthermore, we found that the pathogenesis of RIF was multifaceted and that numerous processes were involved. We believe that a better understanding of the underlying mechanisms of RIF will ultimately give rise to better treatment opportunities and to better outcomes in IVF.

A C-type lectin (CL11X1-like) from Nile tilapia (Oreochromis niloticus) is involved in host defense against bacterial infection

Collectins, a subfamily of the C-type lectins, are able to bind non-self glycoconjugates on the surface of microorganisms and inhibit infection by direct neutralization, agglutination and/or opsonization, which play important roles in innate immunity. In this study, a CL11X1-like collectin (OnCL11X1) was identified from Nile tilapia (Oreochromis niloticus) and characterized at expression and agglutination functional levels. The open reading frame of OnCL11X1 is 840 bp of nucleotide sequence encoding polypeptides of 279 amino acids. The deduced amino acid sequence is highly homology to teleost and similar to mammalian CL11X1, containing a canonical collagen-like region, a carbohydrate recognition domain and a neck region. Expression analysis revealed that the OnCL11X1 was highly expressed in the liver, and widely exhibited in other tissues including kidney, intestines and spleen. In addition, the OnCL11X1 expression was significantly up-regulated in spleen and anterior kidney following challenges with a Gram-positive bacterial pathogen (Streptococcus agalactiae) and a Gram-negative bacterial pathogen (Aeromonas hydrophila). The up-regulation of OnCL11X1 expression was also demonstrated in hepatocytes and macrophages in vitro stimulation with S. agalactiae and A. hydrophila. Recombinant OnCL11X1 protein was able to agglutinate both S. agalactiae and A. hydrophila in vitro and promote the phagocytosis by macrophages. Taken together, the results of this study indicated that OnCL11X1, possessing apparent agglutination and opsonization ability to bacterial pathogens, might be involved in host defense against bacterial infection in Nile tilapia.

Zika virus infection elicits auto-antibodies to C1q

Zika virus (ZIKV) causes mostly asymptomatic infection or mild febrile illness. However, with an increasing number of patients, various clinical features such as microcephaly, Guillain-Barré syndrome and thrombocytopenia have also been reported. To determine which host factors are related to pathogenesis, the E protein of ZIKV was analyzed with the Informational Spectrum Method, which identifies common information encoded by primary structures of the virus and the respective host protein. The data showed that the ZIKV E protein and the complement component C1q cross-spectra are characterized by a single dominant peak at the frequency F = 0.338, suggesting similar biological properties. Indeed, C1q-specific antibodies were detected in sera obtained from mice and monkeys infected with ZIKV. As C1q has been known to be involved not only in immunity, but also in synaptic organization and different autoimmune diseases, a ZIKV-induced anti-C1q antibody response may contribute to the neurological complications. These findings might also be exploited for the design of safe and efficacious vaccines in the future.

Protein-Protein Interaction between Surfactant Protein D and DC-SIGN via C-Type Lectin Domain Can Suppress HIV-1 Transfer

Surfactant protein D (SP-D) is a soluble C-type lectin, belonging to the collectin (collagen-containing calcium-dependent lectin) family, which acts as an innate immune pattern recognition molecule in the lungs at other mucosal surfaces. Immune regulation and surfactant homeostasis are salient functions of SP-D. SP-D can bind to a range of viral, bacterial, and fungal pathogens and trigger clearance mechanisms. SP-D binds to gp120, the envelope protein expressed on HIV-1, through its C-type lectin or carbohydrate recognition domain. This is of importance since SP-D is secreted by human mucosal epithelial cells and is present in the female reproductive tract, including vagina. Another C-type lectin, dendritic cell (DC)-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), present on the surface of the DCs, also binds to HIV-1 gp120 and facilitates viral transfer to the lymphoid tissues. DCs are also present at the site of HIV-1 entry, embedded in vaginal or rectal mucosa. In the present study, we report a direct protein-protein interaction between recombinant forms of SP-D (rfhSP-D) and DC-SIGN via their C-type lectin domains. Both SP-D and DC-SIGN competed for binding to immobilized HIV-1 gp120. Pre-incubation of human embryonic kidney cells expressing surface DC-SIGN with rfhSP-D significantly inhibited the HIV-1 transfer to activated peripheral blood mononuclear cells. In silico analysis revealed that SP-D and gp120 may occupy same sites on DC-SIGN, which may explain the reduced transfer of HIV-1. In summary, we demonstrate, for the first time, that DC-SIGN is a novel binding partner of SP-D, and this interaction can modulate HIV-1 capture and transfer to CD4⁺ T cells. In addition, the present study also reveals a novel and distinct mechanism of host defense by SP-D against HIV-1.