Strategies for COVID-19 vaccination under a shortage scenario: a geo-stochastic modelling approach.

In a world being hit by waves of COVID-19, vaccination is a light on the horizon. However, the roll-out of vaccination strategies and their influence on the pandemic are still open questions. In order to compare the effect of various strategies proposed by the World Health Organization and other authorities, a previously developed SEIRS stochastic model of geographical spreading of the virus is extended by adding a compartment for vaccinated people. The parameters of the model were fitted to describe the pandemic evolution in Argentina, Mexico and Spain to analyze the effect of the proposed vaccination strategies. The mobility parameters allow to simulate different social behaviors (e.g. lock-down interventions). Schemes in which vaccines are applied homogeneously in all the country, or limited to the most densely-populated areas, are simulated and compared. The second strategy is found to be more effective. Moreover, under the current global shortage of vaccines, it should be remarked that immunization is enhanced when mobility is reduced. Additionally, repetition of vaccination campaigns should be timed considering the immunity lapse of the vaccinated (and recovered) people. Finally, the model is extended to include the effect of isolation of detected positive cases, shown to be important to reduce infections.

Modelling the interplay of SARS-CoV-2 variants in the United Kingdom.

Many COVID-19 vaccines are proving to be highly effective to prevent severe disease and to diminish infections. Their uneven geographical distribution favors the appearance of new variants of concern, as the highly transmissible Delta variant, affecting particularly non-vaccinated people. It is important to device reliable models to analyze the spread of the different variants. A key factor is to consider the effects of vaccination as well as other measures used to contain the pandemic like social behaviour. The stochastic geographical model presented here, fulfills these requirements. It is based on an extended compartmental model that includes various strains and vaccination strategies, allowing to study the emergence and dynamics of the new COVID-19 variants. The model conveniently separates the parameters related to the disease from the ones related to social behavior and mobility restrictions. We applied the model to the United Kingdom by using available data to fit the recurrence of the currently prevalent variants. Our computer simulations allow to describe the appearance of periodic waves and the features that determine the prevalence of certain variants. They also provide useful predictions to help planning future vaccination boosters. We stress that the model could be applied to any other country of interest.

Detecting infected asymptomatic cases in a stochastic model for spread of Covid-19: the case of Argentina.

We have studied the dynamic evolution of the Covid-19 pandemic in Argentina. The marked heterogeneity in population density and the very extensive geography of the country becomes a challenge itself. Standard compartment models fail when they are implemented in the Argentina case. We extended a previous successful model to describe the geographical spread of the AH1N1 influenza epidemic of 2009 in two essential ways: we added a stochastic local mobility mechanism, and we introduced a new compartment in order to take into account the isolation of infected asymptomatic detected people. Two fundamental parameters drive the dynamics: the time elapsed between contagious and isolation of infected individuals ([Formula: see text]) and the ratio of people isolated over the total infected ones (p). The evolution is more sensitive to the [Formula: see text]parameter. The model not only reproduces the real data but also predicts the second wave before the former vanishes. This effect is intrinsic of extensive countries with heterogeneous population density and interconnection.The model presented has proven to be a reliable predictor of the effects of public policies as, for instance, the unavoidable vaccination campaigns starting at present in the world an particularly in Argentina.

Reduction in CYP1A1 and 2B2 activity at low oxygen tension.

The Cytochrome P450 (CYP) enzyme family comprises a wide array of monooxygenases involved in the oxidation of endobiotic and xenobiotic molecules. The active site of a CYP enzyme contains an iron protoporphyrin center coordinated to a cysteine thiolate, and then, molecular oxygen is associated with the iron to be converted into dioxygen complex plus substrate. Reduction by CYP reductase expedites hydroxylation of the compound. In this oxidation reaction, insufficient oxygen molecules would affect enzyme catalysis. Nevertheless, biochemical data about CYP kinetics at low oxygen concentrations are not available. In this work, we present the results on the variation in rat liver microsomal CYP Vmax app and Km app under normal and hypoxic conditions. Using alkoxyresorufin molecules as substrates, the Vmax/Km ratios for resorufin production decreased from 426 to 393 for CYP1A1 and from 343 to 202 for CYP2B1 at a low oxygen concentration (4.1 ppm) compared to the ratios observed at a normal oxygen concentration (6.5 ppm). Additionally, the bacterial mutagenicity of 2-aminoanthracene and cyclophosphamide, decreased by 32% and 42%, respectively, at low oxygen concentrations. These results support the hypothesis that low oxygen availability is implicated in the low efficiency of substrate oxidation by CYP.

Epitope mapping and neuroprotective properties of a human single chain FV antibody that binds an internal epitope of amyloid-beta 1-42.

Active and passive immunotherapy targeted at the amyloid-beta (Abeta) peptide has been proposed as therapeutic approach against Alzheimer's disease (AD), and efforts towards the generation and application of antibody-based reagents that are capable of preventing and clearing amyloid aggregates are currently under active investigation. Previously, we selected and characterized a new anti-Abeta1-42 phage-displayed scFv antibody, designated clone b4.4, using a non-immune human scFv antibody library and demonstrated that a peptide based on the sequence of the Ig heavy chain (VH) complementarity-determining region (HCDR3) of this antibody fragment bound to Abeta1-42)and had neuroprotective potential against Abeta1-42 mediated neurotoxicity in rat hippocampal cultured neurons. In the present study, using novel computational methods and in vitro experiments we demonstrated that b4.4 binds to the central region of Abeta1-42. We also demonstrated that this scFv antibody binds to Abeta-derived diffusible ligands (ADDLs) and neutralizes the toxicity of both fibrillar and oligomeric forms of Abeta1-42 tested in vitro in SH-SY5Y cell cultures.

Immunodiagnosis of neurocysticercosis. Disappointing performance of serology (enzyme-linked immunosorbent assay) in an unbiased sample of neurological patients.

To ascertain the reliability of serological diagnosis of neurocysticercosis in the everyday a priori situation of neurological consultation, the enzyme-linked immunosorbent assay test was used to predict the eventual diagnosis of neurocysticercosis in an unselected sample of 1064 consecutive neurological cases. Results showed 69% sensitivity and 71% specificity of the enzyme-linked immunosorbent assay test for the diagnosis of neurocysticercosis. In sharp contrast with publications that have proclaimed the excellent diagnostic performance of immunodiagnostic tests, our results suggest that identification of serum antibodies with standard enzyme-linked immunosorbent assay techniques is of little value when applied to a large and heterogeneous group of neurological patients in an endemic area of cysticercosis, and our results urge a reevaluation of currently used immunodiagnostic tests that are practiced in the serum of suspected cases.

Amyloid-beta peptide-specific single chain Fv antibodies isolated from an immune phage display library.

A single-chain fragment variable (scFv) antibody library displayed on phage was constructed using spleen cells from mice immunized with human amyloid-beta peptide (Abeta42). This first anti-Abeta42 scFv immune antibody library was selected against human Abeta42. A number of positive clones were obtained, and sequences of VH and Vkappa genes were analyzed using ExPASy and BLAST computer tools. This analysis revealed that only two unique clones with identical VH and Vkappa complementarity determining region (CDR) (except HCDR2) and identical germline genes were selected, indicating that oligoclonal immune response was occurring in Abeta42-immunized mice. Abeta42-specific scFv antibodies selected from this first immune anti-Abeta42 phage antibody library may be an important tool for the development of therapeutic molecules for Alzheimer's disease (AD).

Protection against murine cysticercosis using cDNA expression library immunization.

Genetic or DNA-based immunization, including genomic immunization, has shown to be a viable alternative approach to induce protective immunity against a number of pathogens in several disease models. Here we describe a new method, cDNA expression library immunization (cDELI), based on the use of a large number of cDNA clones. This immunization strategy was tested in experimental murine Taenia crassiceps cysticercosis model. A partial cDNA expression library of 2 x 10(4) members was constructed in eukaryotic expression vector pcDNA3 and used to immunize BALB/c female mice subcutaneously (s.c.) and intramuscularly (i.m.). In both cases significant reduction of parasite load (up to 65%) was obtained. We were unable to directly measure T. crassiceps-specific humoral immune response in any of the immunized mice, although the expression of pathogen proteins in vitro in macrophages transfected with cDNA expressing plasmids was demonstrated. Also, in three out of five randomly selected immunized mice detectable levels of interferon-gamma (IFN-gamma) were obtained. cDELI has additional advantages compared with recently developed single gene or genomic immunization approaches because a cDNA population represents only those genes that are being expressed in the pathogen cells and the selection of stage-specific antigens is possible. The use of cDELI could be particularly attractive for the pathogens with complicated life cycles and large genomes.

Sex hormone changes induced by the parasite lead to feminization of the male host in murine Taenia crassiceps cysticercosis.

Female mice are more susceptible to Taenia crassiceps (TC) infection than males. However, after a month parasite load increases massively in both genders reaching thousands of parasites per host. The possibility of hormonal changes in the infected mice was envisaged. Sex hormones levels were assayed after different periods of infection, the parasites present in the peritoneal cavity were collected and gonads, uterus and seminal vesicles were weighed. In male mice, serum estradiol increased to levels 200 times their normal values whilst those of testosterone decreased 90% relative to controls. The weight of seminal vesicles was significantly diminished. Infected female mice also showed a slight increase in estrogen blood levels after 8 weeks of infection and the weight of the uterus was significantly increased relative to controls. Serum estradiol and testosterone were almost undetectable after gonadectomy. Cytokines such as IL-6 are capable of stimulating aromatase activity and we found that splenocytes from infected mice produced amounts of IL-6 higher than control as measured by ELISA. In conclusion T. crassiceps infection triggers a feminization process in the infected hosts. The gonads are required for the parasite to induce higher estrogen synthesis. IL-6 could be involved in the immunoendocrine mechanism used by the parasite to maintain a highly permissive environment for its rapid growth.

Intraspleen DNA inoculation elicits protective cellular immune responses.

DNA immunization or inoculation is a recent vaccination method that induces both humoral and cellular immune responses in a range of hosts. Independent of the route or site of vaccination, the transfer of antigen-presenting cells (APC) or antigens into lymphoid organs is necessary. The aim of this investigation was to test whether intraspleen (i.s.) DNA inoculation is capable of inducing a protective immune response. We immunized mice by a single i.s. injection of a DNA construct expressing the immunoglobulin (Ig) heavy-chain variable domain (VH) in which the complementarity-determining regions (CDR) had been replaced by a Taenia crassiceps T-cell epitope. In these mice, immune responses and protective effects elicited by the vaccine were measured. We have shown here for the first time that i.s. DNA inoculation can induce protective cellular immune responses and activate CD8(+) T cells. Also, Ig V(H) appeared to be the minimal delivery unit of "antigenized" Ig capable of inducing T-cell activation in a lymphoid organ. The strategy of introducing T-cell epitopes into the molecular context of the V(H) domain in combination with i.s. DNA immunization could have important implications and applications for human immunotherapy.

Deciphering western blots of tapeworm antigens (Taenia solium, Echinococcus granulosus, and Taenia crassiceps) reacting with sera from neurocysticercosis and hydatid disease patients.

Complex antigen mixtures displayed in Western blots may be immediately and quantitatively categorized with respect to specificity and immunogenicity by immunoplotting. This involves plotting the frequency with which each antigen band reacts with a set of immune sera against the frequency of the same band when reacted with another set of immune sera. Immunoplotting has proven to be a powerful method of analyzing Western blots of reactions between vesicular fluids from the metacestodes of Taenia solium, E. granulosus, and T. crassiceps, and sera from human cases of neurocysticercosis and hydatid disease. Immunoplotting readily sorts out those antigens useful for discriminative immunodiagnosis from the multitude of bands in the sera of sick and healthy people. It aids in assessing the antigenic similarity between the human parasites and the murine parasite T. crassiceps, validating the latter as an alternative source of antigens for immunodiagnosis of cysticercosis and hydatid disease.

Immunodiagnosis of human cysticercosis in cerebrospinal fluid. Antigens from murine Taenia crassiceps cysticerci effectively substitute those from porcine Taenia solium.

Tapeworm antigens from Taenia crassiceps performed as well as those antigens from Taenia solium in an enzyme-linked immunosorbent assay for the detection of Cysticercus antibodies in 96 cerebrospinal fluid samples from patients with neurocysticercosis and in 96 CSF samples from patients with other varied neurological ailments. Thus, this manageable murine model of experimental cysticercosis solved the problem of antigen supply for clinical and epidemiological applications, and it provided an immediate means of abundant production of antigens for the wide distribution and standardization of immunodiagnostic tests for cysticercosis.

Depressed immunity to a Salmonella typhimurium vaccine in mice experimentally parasitized by Taenia crassiceps.

To assess the immunological status of mice parasitized with Taenia crassiceps metacestodes, 6-month old female BALB/c mice experimentally parasitized with T. crassiceps and immunized with Salmonella typhimurium antigens were infected with S. typhimurium virulent bacilli (1.6 x LD50). Both T. crassiceps-parasitized and immunized and parasitized mice showed a very high susceptibility to infection (**P < 0.01) with higher bacteremia than control and immunized-control animals and produced a reduced IgG response to S. typhimurium, antigens (* P < 0.05). This indicates that T. crassiceps is able to preclude development of immunity to S. typhimurium, because appropriate antibody production to a heterologous antigenic stimulus did not take place, and the bacteremia results suggest the parasitosis altered the mononuclear phagocyte system. It has been demonstrated that Taenia solium metacestodes produce a small RNA molecule in culture which suppresses humoral and cellular responses against homologous antigens in mice. We propose that T. crassiceps may be actively synthesizing such a factor, apart from other simultaneously acting immunomodulatory mechanisms, to induce an immunosuppressed state favorable to its development in the host.

Immunization of pigs against Taenia solium cysticercosis: factors related to effective protection.

Fifty-six (56) pigs were immunized against Taenia solium cysticercosis with antigens from Taenia crassiceps metacestodes, in a variety of protocols, and then challenged orally with Taenia solium proglottids or eggs. Results of immunization (expressed as individual parasite loads) ranged from significant reduction of parasite loads (host protection) to clear increase (parasite facilitation) in apparent relation to the immunogen dose, adjuvant employed and genetic background of the pigs. In all trials, however, immunized pigs harboured more damaged cysticerci than controls, indicating that immunization does induce some restrictions to parasite these are eventually overwhelmed by other parasite-promoting factors. Western blots in immunized-protected pigs indicated antigens of 242, 234, 118, 77, 55 and 45 kDa as possibly being involved in immunological protection.

Immunization against Taenia crassiceps cysticercosis: identification of the most promising antigens in the induction of protective immunity.

Cross immunity between Taenia solium and Taenia crassiceps parasites points to T. crassiceps cysticercosis as a convenient model to test promising antigens aimed at the development of a vaccine against T. solium cysticercosis. Since total antigens from T. crassiceps metacestodes induce significant levels of protection in pigs against T. solium cysticercosis, we initiated this work to identify the most interesting antigens involved in protection. Twelve different antigen fractions isolated from T. crassiceps cysticerci were evaluated with respect to their capacity to induce resistance against a challenge with 10 T. crassiceps cysticerci in male BALB/cAnN mice. Mice were intraperitoneally immunized with 2 doses of each antigen, 5 or 15 micrograms per mouse. The 12 antigen fractions were classified as protecting (200, 123, 74, 66, 56, 40-50, 27 and 8-14 kDa), facilitating (220-205 kDa), or irrelevant (150-160, 93, 108 kDa), according to their effect on the parasite load. The 3 most promising antigen fractions were reevaluated via subcutaneous immunization with Freund's complete adjuvant. A high level of protection was obtained when antigen fractions of 56, 66, and 74 kDa were used together. Interestingly, antigens with similar molecular weights were also detected in early steps of differentiation in T. solium cysticercosis. These observations may be helpful in the development of a synthetic or a recombinant vaccine against cysticercosis.

A role for 17-beta-estradiol in immunoendocrine regulation of murine cysticercosis (Taenia crassiceps).

In experimental murine cysticercosis caused by Taenia crassiceps, parasite reproduction is favored by thymectomy or by orchidectomy, and restricted by ovariectomy. Hormonal reconstitution experiments showed that 17-beta-estradiol increases parasite numbers whereas 5-alpha-dihydrotestosterone was ineffective. Parasite numbers decreased with increments in cellular immunity but were insensitive to antibody levels. A possible immunoendocrinological interaction involving estrogen as a depressor of cellular immunity is envisaged in the control of cysticercosis.

Shift from an early protective Th1-type immune response to a late permissive Th2-type response in murine cysticercosis (Taenia crassiceps).

In early stages of experimental murine cysticercosis caused by Taenia crassiceps, there is a clear but transient Th1-type immune response (characterized by high levels of interleukin [IL]-2, interferon-gamma, concanavalin A, and antigen specific response, delayed-type hypersensitivity, and immunoglobulin [Ig]G2a antibodies) that associates with a low rate of parasite reproduction. As time of infection progresses an energic and more permanent Th2-type response follows (characterized by high levels of IL-4, IL-6, IL-10, IgG2b, and IgG1 antibodies) that in turn associates with an increment in the rate of parasite reproduction. The sequential activation of Th1-type and Th2-type responses in murine cysticercosis would appear to favor progressively parasite reproduction, explaining the long time residence and the massive parasite intensity reached in chronic infections.

Thymus-related cellular immune mechanisms in sex-associated resistance to experimental murine cysticercosis (Taenia crassiceps).

The role of sex, thymus, and cellular immune mechanisms in mouse resistance to experimental cysticercosis with Taenia crassiceps was studied in male and female susceptible mice treated with cyclophosphamide, as well as in mice neonatally thymectomized and passively transferred with T-enriched lymphoid cells. High doses of cyclophosphamide increased delayed hypersensitivity and resistance of mice of both sexes without affecting antibody production. Neonatal thymectomy diminished resistance in both sexes but depressed delayed hypersensitivity in females only, without significantly affecting antibody response in either sex. Passive transfer of T-enriched lymphoid cells to thymectomized mice restored resistance to control levels without greatly affecting delayed hypersensitivity. Thus, our results indicate that cell-associated immune mechanisms are implicated in resistance to murine cysticercosis with T. crassiceps. Because neonatal thymectomy nearly equalized the intensity of infection of female and male mice, it is argued that the thymus is importantly involved in the interaction between gonads and the immune system in the control of this cysticercosis.

Inhibition of sexual behavior in male mice infected with Taenia crassiceps cysticerci.

Prominent estrogenization and deandrogenization ensue in male mice as a consequence of experimental intraperitoneal infection with Taenia crassiceps cysticerci. The impact of these endocrine changes upon sexual behavior was explored in a group of infected Balb/c male mice at weekly intervals for 15 wk and compared with the behavior of otherwise paired, nonparasitized male mice. Mounting, intromission, and ejaculation responses markedly declined as infection progressed. Six weeks after infection, none of the infected mice displayed ejaculation, the number of mounts and intromissions gradually decreased, and their latencies increased, until, by the 13th wk, none of the parasitized mice showed any sexual response toward female mice. Fifteen weeks after infection, the number of metacestodes per host increased to a couple of thousand, the mean serum estradiol level was approximately 50 times higher than the normal value, and testosterone fell to 5% of its normal level. To fully assess that the inhibition of sexual behavior resulted from the decrease in testosterone levels, a group of 8-wk-infected mice received testosterone, and complete restoration of their sexual behavior was observed. Inhibition of masculine sexual behavior during the infection period is the result of hormonal changes, estradiol being ineffective in maintaining copulation.

Kinetics and characterization of cellular responses in the peritoneal cavity of mice infected with Taenia crassiceps.

Changes in the leukocyte population of the peritoneal cavity ensue immediately after infection with Taenia crassiceps metacestodes. Basophils and neutrophils decrease, whereas macrophages, monocytes, and lymphocytes increase to reach only modest levels by 6 wk and then diminish to nearly disappear by 15 wk when the parasite begins rapid reproduction. Eosinophils also appear early in infection, but then abate to lower levels that persist. In late infections, when the mass of cysticerci equals that of the mouse, the cysticerci grow among surprisingly few inflammatory cells. Mingling with the peritoneal inflammatory cells is a number of odd-looking cells that could correspond to the metaplasic mesothelial cells of the host or be of parasite origin. These cells are multinucleated, they aggregate in varigerated clusters, and form cystic structures in vitro; they also bind specific anti-T. crassiceps antibodies and specific T. crassiceps DNA probes in their nuclei. When the peritoneal cell exudate is reinjected intraperitoneally into naive mice, the odd-looking cells subsist for months, inducing in the host the synthesis of specific anti-T. crassiceps antibodies and immune resistance to challenge but do not reassemble into cysticerci even after 6 mo of inoculation. The early appearance and the immunogenic and antigenic properties of these odd-looking cells suggest they are important protagonists in the early host-parasite confrontation when the outcome of infection is set.