Immunological hyporesponsiveness in tuberculosis: The role of mycobacterial glycolipids

Glycolipids constitute a major part of the cell envelope of Mycobacterium tuberculosis (Mtb). They are potent immunomodulatory molecules recognized by several immune receptors like pattern recognition receptors such as TLR2, DC-SIGN and Dectin-2 on antigen-presenting cells and by T cell receptors on T lymphocytes. The Mtb glycolipids lipoarabinomannan (LAM) and its biosynthetic relatives, phosphatidylinositol mannosides (PIMs) and lipomannan (LM), as well as other Mtb glycolipids, such as phenolic glycolipids and sulfoglycolipids have the ability to modulate the immune response, stimulating or inhibiting a pro-inflammatory response. We explore here the downmodulating effect of Mtb glycolipids. A great proportion of the studies used in vitro approaches although in vivo infection with Mtb might also lead to a dampening of myeloid cell and T cell responses to Mtb glycolipids. This dampened response has been explored ex vivo with immune cells from peripheral blood from Mtb-infected individuals and in mouse models of infection. In addition to the dampening of the immune response caused by Mtb glycolipids, we discuss the hyporesponse to Mtb glycolipids caused by prolonged Mtb infection and/or exposure to Mtb antigens. Hyporesponse to LAM has been observed in myeloid cells from individuals with active and latent tuberculosis (TB). For some myeloid subsets, this effect is stronger in latent versus active TB. Since the immune response in individuals with latent TB represents a more protective profile compared to the one in patients with active TB, this suggests that downmodulation of myeloid cell functions by Mtb glycolipids may be beneficial for the host and protect against active TB disease. The mechanisms of this downmodulation, including tolerance through epigenetic modifications, are only partly explored

Soluble HIV-1 Env trimers in adjuvant elicit potent and diverse functional B cell responses in primates

Broadly neutralizing antibodies (bNAbs) against the HIV-1 envelope glycoproteins (Envs) have proven difficult to elicit by immunization. Therefore, to identify effective Env neutralization targets, efforts are underway to define the specificities of bNAbs in chronically infected individuals. For a prophylactic vaccine, it is equally important to define the immunogenic properties of the heavily glycosylated Env in healthy primates devoid of confounding HIV-induced pathogenic factors. We used rhesus macaques to investigate the magnitude and kinetics of B cell responses stimulated by Env trimers in adjuvant. Robust Env-specific memory B cell responses and high titers of circulating antibodies developed after trimer inoculation. Subsequent immunizations resulted in significant expansion of Env-specific IgG-producing plasma cell populations and circulating Abs that displayed increasing avidity and neutralization capacity. The neutralizing activity elicited with the regimen used was, in most aspects, superior to that elicited by a regimen based on monomeric Env immunization in humans. Despite the potency and breadth of the trimer-elicited response, protection against heterologous rectal simian-HIV (SHIV) challenge was modest, illustrating the challenge of eliciting sufficient titers of cross-reactive protective NAbs in mucosal sites. These data provide important information for the design and evaluation of vaccines aimed at stimulating protective HIV-1 immune responses in humans

Fine epitope signature of antibody neutralization breadth at the HIV-1 envelope CD4-binding site

Major advances in donor identification, antigen probe design, and experimental methods to clone pathogen-specific antibodies have led to an exponential growth in the number of newly characterized broadly neutralizing antibodies (bnAbs) that recognize the HIV-1 envelope glycoprotein. Characterization of these bnAbs has defined new epitopes and novel modes of recognition that can result in potent neutralization of HIV-1. However, the translation of envelope recognition profiles in biophysical assays into an understanding of in vivo activity has lagged behind, and identification of subjects and mAbs with potent antiviral activity has remained reliant on empirical evaluation of neutralization potency and breadth. To begin to address this discrepancy between recombinant protein recognition and virus neutralization, we studied the fine epitope specificity of a panel of CD4-binding site (CD4bs) antibodies to define the molecular recognition features of functionally potent humoral responses targeting the HIV-1 envelope site bound by CD4. Whereas previous studies have used neutralization data and machine-learning methods to provide epitope maps, here, this approach was reversed, demonstrating that simple binding assays of fine epitope specificity can prospectively identify broadly neutralizing CD4bs–specific mAbs. Building on this result, we show that epitope mapping and prediction of neutralization breadth can also be accomplished in the assessment of polyclonal serum responses. Thus, this study identifies a set of CD4bs bnAb signature amino acid residues and demonstrates that sensitivity to mutations at signature positions is sufficient to predict neutralization breadth of polyclonal sera with a high degree of accuracy across cohorts and across clades

Dissection of HIV-1 Env-specific B cell responses in non-human primates

It has been almost 30 years since the identification of HIV as the causative agent of AIDS. Despite considerable efforts to halt the spread of the virus, the epidemic continues in many parts of the world. The most efficient way to stop new infections is a prophylactic vaccine that blocks transmission at the viral portal of entry. To generate an efficacious vaccine, neutralizing antibodies directed against the envelope glycoproteins (Env), the only virally expressed proteins on the surface of the virion, likely need to be elicited. Early attempts to develop an HIV vaccine used soluble recombinant monomeric Env. This vaccine candidate generated high titers of Env binding antibodies in a large clinical trial; however, no protection against infection was observed. Since then attempts have been made to design Env immunogens that more closely mimic the native Env spike with the aim to improve the quality of vaccine-elicited humoral immune responses. Due to the lack of high resolution three dimensional structures of Env in its native conformation, these design efforts are still empirical. To guide future immunogen design efforts, it is important to understand what current Env vaccine candidates elicit in relevant pre-clinical models, both at the serological and cellular level. The focus of this thesis has been to investigate B cell responses in non-human primates following immunization with soluble HIV-1 Env trimers. We show that Env immunization in adjuvant elicits high levels of binding antibodies as well as robust peripheral memory B cell and plasma cell populations. The kinetics and magnitude of the responses at early time points after immunization are similar to those elicited by the successful human influenza and rabies vaccines. Despite these potent responses, we only observed a modest protective effect upon mucosal SHIV challenge of vaccinated animals. When quantifying the levels of Env-specific antibodies in the mucosa we found them to be 1000-10 000 fold lower than in serum, which may explain the lack of protection in this heterologous challenge model. From in vitro studies it has been proposed that interactions between Env and CD4-expressing T cells may detrimentally affect T cell function. To investigate if in vivo interactions between Env immunogens and CD4-expressing cells would negatively affect the elicitation of Envspecific immune responses, CD4 binding-competent and CD4 binding-defective trimers were constructed and inoculated into non-human primates. No difference was observed between the groups in regards to Env-specific antibody titers, memory B cell or T cell levels and functionality, indicating that Env binding to CD4 in vivo was not detrimental to vaccine elicited responses. Furthermore, using the CD4 binding-competent and CD4 binding-defective Env immunogens, we assessed if in vivo CD4 binding affected the outcome of an intravenous SHIV challenge. Antibodies directed against the conserved co-receptor binding site of Env were only observed following immunization with the CD4-binding competent trimers. However, the presence or absence of this class of antibodies did not influence the level of protection against SHIV infection. These results indicate that Env-CD4 in vivo interactions, and specifically co-receptor binding site-directed antibodies, did not contribute to the control of viremia observed in this challenge model

How to yield abnormal return by replicating insider trades - A study on the Swedish stock market

The objective of the study is to verify if it is possible to replicate insider trades in order to yield an abnormal return. The objective will be reached by investigating previous research within the field of insider trading in order to examine under which condition replication of insider trades can be profitable for outsiders. Further, to determine if previous researchers have identified a theory where replication of insider trades actually is possible. The theory will then be tested on current market data from the AFXG index. The course of action is within accordance to an event study presented by MacKinlay (1997), where assumptions and conditions are based upon the meta-analysis of previous research; hence the data has been calculated with the adjusted market model. But also examined within a 90 days event window, where both single insider- as well as cluster transactions has been analyzed. Further the research qualifies as a quantitative study where a deductive procedure has been used. All data has been gathered from the AFGX index, where 40 random firms have been selected; five from each of the eight sectors. Lastly, the data has been statistically tested with the student t-test in order to examine if the result is of statistical significance. The result of the study shows that one can yield an abnormal return between 1,96% to 2,45% by replicating single insider trades. This is with 99,95% significance. By replicating insider cluster transactions one can also yield an abnormal return, however, the return is lower than for single insider trades and no significance were found. As for the meta-analysis of previous research, it was found that a security is to be held for approximately 90 days in order to achieve the desired positive effect of the insider trade. Further, small firms seems to yield the highest abnormal return, clusters transactions increases the possible abnormal return and when higher executives in different positions trade, a stronger buying signal for the stock is given

A longitudinal study of plasma BAFF levels in mothers and their infants in Uganda, and correlations with subsets of B cells

Malaria is a potentially life-threatening disease with approximately half of the world’s population at risk. Young children and pregnant women are hit hardest by the disease. B cells and antibodies are part of an adaptive immune response protecting individuals continuously exposed to the parasite. An infection with Plasmodium falciparum can cause dysregulation of B cell homeostasis, while antibodies are known to be key in controlling symptoms and parasitemia. BAFF is an instrumental cytokine for the development and maintenance of B cells. Pregnancy alters the immune status and renders previously clinically immune women at risk of severe malaria, potentially due to altered B cell responses associated with changes in BAFF levels. In this prospective study, we investigated the levels of BAFF in a malaria-endemic area in mothers and their infants from birth up to 9 months. We found that BAFF-levels are significantly higher in infants than in mothers. BAFF is highest in cord blood and then drops rapidly, but remains significantly higher in infants compared to mothers even at 9 months of age. We further correlated BAFF levels to P. falciparum-specific antibody levels and B cell frequencies and found a negative correlation between BAFF and both P. falciparum-specific and total proportions of IgG+ memory B cells, as well as CD27− memory B cells, indicating that exposure to both malaria and other diseases affect the development of B-cell memory and that BAFF plays a part in this. In conclusion, we have provided new information on how natural immunity against malaria is formed

Antibody responses to merozoite antigens after natural Plasmodium falciparum infection: kinetics and longevity in absence of re-exposure

Abstract Background Antibodies against merozoite antigens are key components of malaria immunity. The naturally acquired antibody response to these antigens is generally considered short-lived; however, the underlying mechanisms remain unclear. Prospective studies of travellers with different levels of prior exposure, returning to malaria-free countries with Plasmodium infection, offer a unique opportunity to investigate the kinetics and composition of the antibody response after natural infection. Methods Adults diagnosed with P. falciparum malaria in Stockholm, Sweden (20 likely malaria naïve and 41 with repeated previous exposure during residency in sub-Saharan Africa) were sampled at diagnosis and 10 days and 1, 3, 6, and 12 months after treatment. Total and subclass-specific IgG responses to P. falciparum merozoite antigens (AMA-1, MSP-119, MSP-2, MSP-3, and RH5) and tetanus toxoid were measured by multiplex bead-based immunoassays and ELISA. Mathematical modelling was used to estimate the exposure-dependent longevity of antibodies and antibody-secreting cells (ASCs). Results A majority of individuals mounted detectable antibody responses towards P. falciparum merozoite antigens at diagnosis; however, the magnitude and breadth were greater in individuals with prior exposure. In both exposure groups, antibody levels increased rapidly for 2 weeks and decayed thereafter. Previously exposed individuals maintained two- to ninefold greater antibody levels throughout the 1-year follow-up. The half-lives of malaria-specific long-lived ASCs, responsible for maintaining circulating antibodies, ranged from 1.8 to 3.7 years for merozoite antigens and were considerably short compared to tetanus-specific ASCs. Primary infected individuals did acquire a long-lived component of the antibody response; however, the total proportion of long-lived ASCs generated in response to infection was estimated not to exceed 10%. In contrast, previously exposed individuals maintained substantially larger numbers of long-lived ASCs (10–56% of total ASCs). Conclusion The short-lived nature of the naturally acquired antibody response, to all tested merozoite antigens, following primary malaria infection can be attributed to a combination of a poor acquisition and short half-life of long-lived ASCs. Greater longevity is acquired with repeated infections and can be explained by the maintenance of larger numbers of long-lived ASCs. These insights advance our understanding of naturally acquired malaria immunity and will guide strategies for further development of both vaccines and serological tools to monitor exposure

Plasmodium falciparum-specific memory B-cell and antibody responses are associated with immunity in children living in an endemic area of Kenya

Identifying the mechanism of naturally acquired immunity against Plasmodium falciparum malaria could contribute to the design of effective malaria vaccines. Using a recently developed multiplexed FluoroSpot assay, we assessed cross-sectional pre-existing memory B-cells (MBCs) and antibody responses against six well known P. falciparum antigens (MSP-119, MSP-2 (3D7), MSP-2 (FC27), MSP-3, AMA-1 and CSP) and measured their associations with previous infections and time to clinical malaria in the ensuing malaria season in Kenyan children. These children were under active weekly surveillance for malaria as part of a long-term longitudinal malaria immunology cohort study, where they are recruited from birth. After performing Cox regression analysis, we found that children with a breadth of three or more antigen-specific MBC or antibody responses at the baseline had a reduced risk for malaria in the ensuing P. falciparum transmission season. Specifically, MBC responses against AMA-1, MSP-2 (3D7) and MSP-3, as well as antibody responses to MSP-2 (3D7) and MSP-3 were prospectively associated with a reduced risk for malaria. The magnitude or breadth of MBC responses were however not correlated with the cumulative number of malaria episodes since birth. We conclude that increased breadth for merozoite antigen-specific MBC and antibody responses is associated with protection against malaria