Insights into neutralizing antibody responses in individuals exposed to SARS-CoV-2 in Chile.

Chile has one of the worst numbers worldwide in terms of SARS-CoV-2 positive cases and COVID-19-related deaths per million inhabitants; thus, characterization of neutralizing antibody (NAb) responses in the general population is critical to understanding of immunity at the local level. Given our inability to perform massive classical neutralization assays due to the scarce availability of BSL-3 facilities in the country, we developed and fully characterized an HIV-based SARS-CoV-2 pseudotype, which was used in a 96-well plate format to investigate NAb responses in samples from individuals exposed to SARS-CoV-2 or treated with convalescent plasma. We also identified samples with decreased or enhanced neutralization activity against the D614G spike variant compared with the wild type, indicating the relevance of this variant in host immunity. The data presented here represent the first insights into NAb responses in individuals from Chile, serving as a guide for future studies in the country.

High density lipoproteins down-regulate transcriptional expression of pro-inflammatory factors and oxidative burst in head kidney leukocytes from rainbow trout, Oncorhynchus mykiss.

Teleosts are the first group of vertebrates possessing an acquired immune system; however, it is less developed than in mammals and is highly influenced by environmental changes. Therefore, innate immunity effectors play a more critical role in survival of pathogen-challenged fish. In a previous study we showed that trout high density lipoprotein (HDL), and its major apolipoprotein (ApoA-I) are widely expressed in primary defense barriers and other immune-relevant tissues, displaying important antibacterial activity in vitro. Here we show that trout HDL inhibits both basal and LPS-induced transcript expression of pro-inflammatory cytokines such as TNF-α and IL-1ß, and the acute phase protein serum amyloid A (A-SAA), in head kidney leukocytes (HLK) from rainbow trout. In addition, trout HDL was able to block the respiratory burst of PMA-stimulated HKL, at physiological concentrations and in a dose dependent manner. Moreover, this effect was only partially mimicked by supra-physiologic concentrations of the HDL-transported carotenoid, astaxanthin. These results constitute the first data suggesting that in addition to its antimicrobial activity, HDL would have a relevant immunomodulatory role in salmonid fish.

Vitamin C and oxidative stress in the seminiferous epithelium.

In this article, we focus on the fundamental role of vitamin C transporters for the normal delivery of vitamin C to germ cells in the adluminal compartment of seminiferous tubules. We argue that the redox status within spermatozoa or in semen is partly responsible for the etiology of infertility. In this context, antioxidant defence plays a critical role in male fertility. Vitamin C, a micronutrient required for a wide variety of metabolic functions, has long been associated with male reproduction. Two systems for vitamin C transport have been described in mammals. Facilitative hexose transporters (GLUTs), with 14 known isoforms to date, GLUT1-GLUT14, transport the oxidized form of vitamin C (dehydroascorbic acid) into the cells. Sodium ascorbic acid co-transporters (SVCTs), SVCT1 and SVCT2 transport the reduced form of vitamin C (ascorbic acid). Sertoli cells control germ cell proliferation and differentiation through cell-cell communication and form the blood-testis barrier. Because the blood-testis barrier limits direct access of molecules from the plasma into the adluminal compartment of the seminiferous tubule, one important question is the method by which germ cells obtain vitamin C. Some interesting results have thrown light on this matter. Expression of SVCT2 and some isoforms of GLUT transporters in the testis have previously been described. Our group has demonstrated that Sertoli cells express functionally active vitamin C transporters. Kinetic characteristics were described for both transport systems (SVCT and GLUT systems). Sertoli cells are able to transport both forms of vitamin C. These findings are extremely relevant, because Sertoli cells may control the amount of vitamin C in the adluminal compartment, as well as regulating the availability of this metabolite throughout spermatogenesis.

Vitamin C and oxidative stress in the seminiferous epithelium

In this article, we focus on the fundamental role of vitamin C transporters for the normal delivery of vitamin C to germ cells in the adluminal compartment of seminiferous tubules. We argue that the redox status within spermatozoa or in semen is partly responsible for the etiology of infertility. In this context, antioxidant defence plays a critical role in male fertility. Vitamin C, a micronutrient required for a wide variety of metabolic functions, has long been associated with male reproduction. Two systems for vitamin C transport have been described in mammals. Facilitative hexose transporters (GLUTs), with 14 known isoforms to date, GLUT1-GLUT14, transport the oxidized form of vitamin C (dehydroascorbic acid) into the cells. Sodium ascorbic acid co-transporters (SVCTs), SVCT1 and SVCT2 transport the reduced form of vitamin C (ascorbic acid). Sertoli cells control germ cell proliferation and differentiation through cell-cell communication and form the blood-testis barrier. Because the blood-testis barrier limits direct access of molecules from the plasma into the adluminal compartment of the seminiferous tubule, one important question is the method by which germ cells obtain vitamin C. Some interesting results have thrown light on this matter. Expression of SVCT2 and some isoforms of GLUT transporters in the testis have previously been described. Our group has demonstrated that Sertoli cells express functionally active vitamin C transporters. Kinetic characteristics were described for both transport systems (SVCT and GLUT systems). Sertoli cells are able to transport both forms of vitamin C. These findings are extremely relevant, because Sertoli cells may control the amount of vitamin C in the adluminal compartment, as well as regulating the availability of this metabolite throughout spermatogenesis.

Detection of up-regulated serum amyloid A transcript and of amyloid AA aggregates in skeletal muscle lesions of rainbow trout infected with Flavobacterium psychrophilum.

Serum amyloid A (SAA) is a family of acute-phase proteins, recognized as important effectors of innate immunity in higher vertebrates. Under pro-inflammatory conditions, up-regulation of saa transcripts occurs not only in the liver, but also in several extrahepatic tissues of a wide variety of vertebrates. SAA is also known as the precursor to amyloid A (AA), a major component of amyloid fibrils deposited in liver, kidney and spleen of humans suffering chronic inflammatory diseases. Here we show the up-regulation of saa transcription in lesions affecting skin, adipose tissue and skeletal muscle of rainbow trout naturally and experimentally infected with Flavobacterium psychrophilum, the causative agent of cold water disease (CWD). Using an antiserum against a trout acute SAA peptide that was previously shown to specifically recognize intact recombinant trout SAA and peptides derived from it, we showed by confocal microscopy analysis extensive colocalization of SAA and thioflavin T (ThT) staining in the skeletal muscle fibers of infected fish, suggesting for the first time the presence of AA-derived aggregates in the skeletal muscle of a lower vertebrate. These findings support the idea that SAA and/or its derivatives could constitute relevant markers for fish health and also for fish meat quality control.

Serum amyloid A: a typical acute-phase reactant in rainbow trout?

Acute serum amyloid A (A-SAA) has been considered a major acute-phase reactant and an effector of innate immunity in all vertebrates. The work presented here shows that the expression of A-SAA is strongly induced in a wide variety of immune-relevant tissues in rainbow trout, either naturally infected with Flavobacterium psychrophilum or challenged with lipopolysaccharide (LPS) or CpG oligonucleotides (CpG ODN). Nevertheless, A-SAA was undetectable by Western blot either in the plasma or in high-density lipoprotein (HDL) of infected or challenged fish, using either an anti-mouse SAA1 IgG or an anti-trout A-SAA peptide serum, which recognise both the intact recombinant trout A-SAA and fragments derived from it. However, the anti-peptide serum was the immunoreactive in all primary defence barriers and in mononuclear cells of head kidney, spleen and liver. These findings reveal that, unlike mammalian SAA, trout A-SAA does not increase significantly in the plasma of diseased fish, suggesting it is more likely to be involved in local defence.

Apolipoprotein A-I, an antimicrobial protein in Oncorhynchus mykiss: evaluation of its expression in primary defence barriers and plasma levels in sick and healthy fish.

Antimicrobial proteins and peptides play an important role in the primary defence barriers in vertebrates and invertebrates. In a previous study it was shown that high-density lipoprotein (HDL) and its major apolipoproteins, ApoA-I and ApoA-II display antimicrobial activity in the carp (Cyprinus carpio L.). The aim of this study was to evaluate if ApoA-I conserves this defensive function in a salmonid fish like the rainbow trout, in spite of the low level of primary sequence conservation between fish ApoA-I. Here it is shown that trout ApoA-I displays an antimicrobial activity in the micromolar range against Gram positive and Gram negative bacteria, including some fish pathogens. In addition, its expression was also demonstrated by immunohistochemistry and RT-PCR in epidermis, gills and intestinal mucosa, which constitute the main primary defence barriers in fish. Finally, no significant difference in the hepatic expression and plasma levels of this abundant apolipoprotein was found in groups of healthy and diseased fish, in clear contrast with mammals where ApoA-I have been considered a negative acute phase reactant. These findings suggest that ApoA-I could constitute an important innate immunity effector in trout and perhaps other teleost fish.