Signaling via interleukin-4, receptor alpha chain is required for successful vaccination against schistosomiasis in BALB/c mice

Radiation-attenuated (RA) schistosome larvae are potent stimulators of innate immune responses at the skin site of exposure (pinna) that are likely to be important factors in the development of Th1-mediated protective immunity. In addition to causing an influx of neutrophils, macrophages, and dendritic cells (DCs) into the dermis, RA larvae induced a cascade of chemokine and cytokine secretion following in vitro culture of pinna biopsy samples. While macrophage inflammatory protein 1 and interleukin-1 (IL-1) were produced transiently within the first few days, the Th1-promoting cytokines IL-12 and IL-18 were secreted at high levels until at least day 14. Assay of C3H/HeJ mice confirmed that IL-12 secretion was not due to lipopolysaccharide contaminants binding Toll-like receptor 4. Significantly, IL-12 p40 secretion was sustained in pinnae from vaccinated mice but not in those from nonprotected infected mice. In contrast, IL-10 was produced from both vaccinated and infected mice. This cytokine regulates IL-12-associated dermal inflammation, since in vaccinated IL-10/ mice, pinna thickness was greatly increased concurrent with elevated levels of IL-12 p40. A significant number of IL-12 p40 cells were detected as emigrants from in vitro-cultured pinnae, and most were within a population of rare large granular cells that were Ia, consistent with their being antigen-presenting cells. Labeling of IL-12 cells for CD11c, CD205, CD8, CD11b, and F4/80 indicated that the majority were myeloid DCs, although a proportion were CD11c F4/80, suggesting that macrophages were an additional source of IL-12 in the skin

Do schistosome vaccine trials in mice have an intrinsic flaw that generates spurious protection data?

The laboratory mouse has been widely used to test the efficacy of schistosome vaccines and a long list of candidates has emerged from this work, many of them abundant internal proteins. These antigens do not have an additive effect when co-administered, or delivered as SWAP homogenate, a quarter of which comprises multiple candidates; the observed protection has an apparent ceiling of 40–50 %. We contend that the low level of maturation of penetrating cercariae (~32 % for Schistosoma mansoni) is a major limitation of the model since 68/100 parasites fail to mature in naïve mice due to natural causes. The pulmonary capillary bed is the obstacle encountered by schistosomula en route to the portal system. The fragility of pulmonary capillaries and their susceptibility to a cytokine-induced vascular leak syndrome have been documented. During lung transit schistosomula burst into the alveolar spaces, and possess only a limited capacity to re-enter tissues. The acquired immunity elicited by the radiation attenuated (RA) cercarial vaccine relies on a pulmonary inflammatory response, involving cytokines such as IFNγ and TNFα, to deflect additional parasites into the alveoli. A principal difference between antigen vaccine protocols and the RA vaccine is the short interval between the last antigen boost and cercarial challenge of mice (often two weeks). Thus, after antigen vaccination, challenge parasites will reach the lungs when both activated T cells and cytokine levels are maximal in the circulation. We propose that “protection” in this situation is the result of physiological effects on the pulmonary blood vessels, increasing the proportion of parasites that enter the alveoli. This hypothesis will explain why internal antigens, which are unlikely to interact with the immune response in a living schistosomulum, plus a variety of heterologous proteins, can reduce the level of maturation in a non-antigen-specific way. These proteins are “successful” precisely because they have not been selected for immunological silence. The same arguments apply to vaccine experiments with S. japonicum in the mouse model; this schistosome species seems a more robust parasite, even harder to eliminate by acquired immune responses. We propose a number of ways in which our conclusions may be tested

Altered Patterns of Gene Expression Underlying the Enhanced Immunogenicity of Radiation-Attenuated Schistosomes

Schistosoma mansoni is a blood-dwelling parasitic worm that causes schistosomiasis in humans throughout Africa and parts of South America. A vaccine would enhance attempts to control and eradicate the disease that currently relies on treatment with a single drug. Although a manufactured vaccine has yet to generate high levels of protection, this can be achieved with infective parasite larvae that have been disabled by exposure to radiation. How these weakened parasites are able to induce protective immunity when normal parasites do not, is the question addressed by our experiments. We have used a technique of gene expression profiling to compare the patterns in normal and disabled parasites, over the period when they would trigger an immune response in the host. We found that only a handful of genes were differentially expressed, all of them diminished in the disabled parasite. However, a more sensitive technique to examine groups of genes revealed that those involved in nervous system and muscle function were depressed in the disabled parasites. We suggest that reduced mobility of these larvae permits them longer contact with the immune system, thus enabling a strong protective immune response to develop

Characterising the determinants of hypoxia inducible transcription factors binding to chromatin

Hypoxia regulates many hundreds of genes that play important roles in numerous physiological and pathophysiological processes. The hypoxia inducible transcription factors (HIFs) are central to the transcriptional activation of these hypoxia-regulated genes. However, to date, little is known about the determinants of HIF-1 and HIF-2 binding site selection. Both HIF-1 and HIF-2 appear to bind as HIF-α/HIF-1β heterodimers, and recognise the same core consensus DNA motif, the hypoxia response element (HRE). However, each has its own distinct but partially overlapping set of binding sites that accounts for only a subset of the total accessible HRE motifs. Here, I have utilised ChIP-seq to systematically compare pan-genomic HIF-1α, HIF-2α and HIF-1β DNA binding in multiple cell lines and have related this to RNA-seq analyses and other publically-accessible next-generation sequencing datasets. I show that endogenous HIF-α subunits exhibit a high-degree of binding site concordance with HIF-1β, consistent with largely canonical binding of intact heterodimers. Despite cell-type specific differences in HIF-1 and HIF-2 binding site occupancy, each isoform exhibits a remarkable rigidity in its preference to bind either promoter-proximal or promoter-distal sites, respectively. These specific distribution patterns are unaffected by the absence of the other HIF-α subunit, suggesting that they do not result from exclusion of one isoform by competition with the other, but rather are discrete properties of each. Furthermore, hypoxia regulated genes neighbouring sites that are shared by both HIF-1 and HIF-2 are more likely to be regulated by HIF-1 when the site is closer to the gene and by HIF-2 when further away, indicating that post-binding mechanisms of transcriptional regulation also follow a similar pattern. Comparison of sites preferentially bound by HIF-1 and HIF-2, respectively, revealed associations with distinct histone environments, distinct accessory transcription factor binding motifs and distinct patterns of transcription factor binding site occupancy, suggesting that each may be influencing specific HIF-1 and HIF-2 binding site selection. In particular, both the AP-1 motif and AP-1 binding site occupancy were enriched within HIF-2 binding sites compared to HIF-1 sites. Intervention on AP-1 DNA-binding using the dominant-negative protein, AFos, attenuated HIF binding, specifically at sites co-occupied by AP-1 and HIF. This indicates that a cooperative relationship exists between the two transcription factors. However, binding of both HIF-1α and HIF-2α were affected suggesting that while AP-1 binding may account for the ability of HIF to bind some HRE motifs but not others, it is not a determinant of differential binding between the two isoforms. Overall, this work reveals remarkably distinct and functionally relevant patterns of HIF-1 and HIF-2 binding across the genome, and provides insight into underlying mechanisms of binding.</p

Radiation-attenuated schistosome vaccination--a brief historical perspective.

The high level of protection which can be induced by vaccination of a range of hosts, from rodents to primates, with live radiation-attenuated schistosome larvae offers great promise for development of a human schistosome vaccine. Studies of the irradiated vaccine models benefitted from significant funding during the 1970-90s and much was learned concerning the inducers, targets and mechanisms of immunity. Less progress was made in definition of the protective antigens involved. The application of new techniques for identifying membrane and secreted antigens has recently provided new vaccine candidates and a new impetus for schistosome vaccine development. This article is intended as an overview of some of the main lessons learned from the studies of the irradiated vaccines as a backdrop to renewed interest in schistosome vaccine development