Trans-generational Immune Priming in Invertebrates: Current Knowledge and Future Prospects

Trans-generational immune priming (TGIP) refers to the transfer of the parental immunological experience to its progeny. This may result in offspring protection from repeated encounters with pathogens that persist across generations. Although extensively studied in vertebrates for over a century, this phenomenon has only been identified 20 years ago in invertebrates. Since then, invertebrate TGIP has been the focus of an increasing interest, with half of studies published during the last few years. TGIP has now been tested in several invertebrate systems using various experimental approaches and measures to study it at both functional and evolutionary levels. However, drawing an overall picture of TGIP from available studies still appears to be a difficult task. Here, we provide a comprehensive review of TGIP in invertebrates with the objective of confronting all the data generated to date to highlight the main features and mechanisms identified in the context of its ecology and evolution. To this purpose, we describe all the articles reporting experimental investigation of TGIP in invertebrates and propose a critical analysis of the experimental procedures performed to study this phenomenon. We then investigate the outcome of TGIP in the offspring and its ecological and evolutionary relevance before reviewing the potential molecular mechanisms identified to date. In the light of this review, we build hypothetical scenarios of the mechanisms through which TGIP might be achieved and propose guidelines for future investigations.

Mendelian inheritance of endogenous viral elements (EVE) of white spot syndrome virus (WSSV) in shrimp

Previous work has shown that non-retroviral endogenous viral elements (EVE) are common in crustaceans, including penaeid shrimp. So far, they have been reported for infectious hypodermal and hematopoietic necrosis virus (IHHNV) and white spot syndrome virus (WSSV). For the latter, it was shown that shrimp sperm were positive for an EVE of WSSV called EVE₃₆₆, suggesting that it was heritable, since shrimp sperm (non-motile) do not contain mitochondria. However, to prove this hypothesis that EVE₃₆₆ was heritable and located in chromosomal DNA, it was necessary to carry out mating tests to show that EVE₃₆₆ could be detected in parental shrimp and distributed in their offspring in a Mendelian fashion. To do this, we analyzed two shrimp crosses using polyacrylamide gels with a multiple-allele, microsatellite marker Pmo11 as a quality control for single allele detection. In both crosses, all of the shrimp (parents and siblings) were positive for 2 Pmo11 alleles as expected. In Cross 1, the female was PCR-positive for EVE₃₆₆ while the male was negative, and in Cross 2, both the female and male were PCR-positive for EVE₃₆₆. Individual analysis of the offspring of Cross 1 revealed a distribution of 1:1 for EVE₃₆₆, indicating that the EVE₃₆₆-positive female parent was heterozygous for EVE₃₆₆. In the second cross, the distribution of EVE₃₆₆ in the offspring was 3:1, indicating that both PCR-positive parents were heterozygous for EVE₃₆₆. These results supported the hypothesis that EVE₃₆₆ was present in shrimp chromosomal DNA and was heritable in a Mendelian fashion. This work provides a model to screen for heritable EVE in shrimp and shows that selection of one parent heterozygous for an EVE and the other negative for it can result in approximately half of the siblings positive and half negative for that EVE as expected. Dividing the siblings of such a cross into an EVE positive group and an EVE negative group followed by challenge with the originating lethal virus should reveal whether or not possession of that specific EVE results in any significant protection against disease caused by the homologous virus.

A heritable antiviral RNAi response limits Orsay virus infection in Caenorhabditis elegans N2

Orsay virus (OrV) is the first virus known to be able to complete a full infection cycle in the model nematode species Caenorhabditis elegans. OrV is transmitted horizontally and its infection is limited by antiviral RNA interference (RNAi). However, we have no insight into the kinetics of OrV replication in C. elegans. We developed an assay that infects worms in liquid, allowing precise monitoring of the infection. The assay revealed a dual role for the RNAi response in limiting Orsay virus infection in C. elegans. Firstly, it limits the progression of the initial infection at the step of recognition of dsRNA. Secondly, it provides an inherited protection against infection in the offspring. This establishes the heritable RNAi response as anti-viral mechanism during OrV infections in C. elegans. Our results further illustrate that the inheritance of the anti-viral response is important in controlling the infection in the canonical wild type Bristol N2. The OrV replication kinetics were established throughout the worm life-cycle, setting a standard for further quantitative assays with the OrV-C. elegans infection model.

Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity

Bacterial pathogens can cause multiple plant diseases and plants rely on their innate immune system to recognize and actively respond to these microbes. The plant innate immune system comprises extracellular pattern recognition receptors that recognize conserved microbial patterns and intracellular nucleotide binding leucine-rich repeat (NLR) proteins that recognize specific bacterial effectors delivered into host cells. Plants lack the adaptive immune branch present in animals, but still afford flexibility to pathogen attack through systemic and transgenerational resistance. Here, we focus on current research in plant immune responses against bacterial pathogens. Recent studies shed light onto the activation and inactivation of pattern recognition receptors and systemic acquired resistance. New research has also uncovered additional layers of complexity surrounding NLR immune receptor activation, cooperation and sub-cellular localizations. Taken together, these recent advances bring us closer to understanding the web of molecular interactions responsible for coordinating defense responses and ultimately resistance.

Combined Immune Deficiencies in Children

Combined immune deficiencies are a heterogeneous group of congenital disorders usually attributable to a single gene defect. The hallmark of these disorders is recurrent infections resulting from defects in both T- and B-cell function. This article reviews the basic components of the immune system as well as the clinical presentation, laboratory findings, and treatment for 3 distinct combined immune deficiencies.

Tuberculosis in children and adults: two distinct genetic diseases

Disseminated disease in children and pulmonary disease in adults constitute two major epidemiological and clinical forms of tuberculosis. Paradoxically, only a small fraction of infected individuals develop clinical tuberculosis, typically one form of the disease or the other. Mendelian and complex genetic predispositions to tuberculosis were reported recently in children and adults, respectively. Here, we argue that tuberculosis and its clinical expression largely reflect the underlying human genetic background.