“Omics” Technologies and the Immune System

Systematic Review of Multi-Omics Approaches to Investigate Toxicological Effects in Macrophages

Insights into the modes of action (MoAs) of xenobiotics are of utmost importance for the definition of adverse outcome pathways (AOPs), which are essential for a mechanism-based risk assessment. A well-established strategy to reveal MoAs of xenobiotics is the use of omics. However, often an even more comprehensive approach is needed, which can be achieved using multi-omics. Since the immune system plays a central role in the defense against foreign substances and pathogens, with the innate immune system building a first barrier, we systematically reviewed multi-omics studies investigating the effects of xenobiotics on macrophages. Surprisingly, only nine publications were identified, combining proteomics with transcriptomics or metabolomics. We summarized pathways and single proteins, transcripts, or metabolites, which were described to be affected upon treatment with xenobiotics in the reviewed studies, thus revealing a broad range of effects. In summary, we show that macrophages are a relevant model system to investigate the toxicological effects induced by xenobiotics. Furthermore, the multi-omics approaches led to a more comprehensive overview compared to only one omics layer with slight advantages for combinations that complement each other directly, e.g., proteome and metabolome.

In vitro testing for direct immunotoxicity: state of the art

Immunotoxicity is defined as the toxicological effects of xenobiotics including pharmaceuticals on the functioning of the immune system and can be induced in either direct or indirect ways. Direct immunotoxicity is caused by the effects of chemicals on the immune system, leading to immunosuppression and subsequently to reduced resistance to infectious diseases or certain forms of nongenotoxic carcinogenicity.In vitro testing has several advantages over in vivo testing, such as detailed mechanistic understanding, species extrapolation (parallelogram approach), and reduction, refinement, and replacement of animal experiments. In vitro testing for direct immunotoxicity can be done in a two-tiered approach, the first tier measuring myelotoxicity. If this type of toxicity is apparent, the compound can be designated immunotoxic. If not, the compound is tested for lymphotoxicity (second tier). Several in vitro assays for lymphotoxicity exist, each comprising specific functions of the immune system (cytokine production, cell proliferation, cytotoxic T-cell activity, natural killer cell activity, antibody production, and dendritic cell maturation). A brief description of each assay is provided. Only one assay, the human whole blood cytokine release assay, has undergone formal prevalidation, while another one, the lymphocyte proliferation assay, is progressing towards that phase.Progress in in vitro testing for direct immunotoxicity includes prevalidation of existing assays and selection of the assay (or combination of assays) that performs best. To avoid inter-species extrapolation, assays should preferably use human cells. Furthermore, the use of whole blood has the advantage of comprising multiple cell types in their natural proportion and environment. The so-called "omics" techniques provide additional mechanistic understanding and hold promise for the characterization of classes of compounds and prediction of specific toxic effects. Technical innovations such as high-content screening and high-throughput analysis will greatly expand the opportunities for in vitro testing.

What’s So Special about the Developing Immune System?

The evolution of the subdiscipline of developmental immunotoxicology (DIT) as it exists today has been shaped by significant regulatory pressures as well as key scientific advances. This review considers the role played by legislation to protect children’s health, and on the emergence of immunotoxcity and developmental immunotoxicity guidelines, as well as providing some context to the need for special attention on DIT by considering the evidence that the developing immune system may have unique susceptibilities when compared to the adult immune system. Understanding the full extent of this potential has been complicated by a paucity of data detailing the development of the immune system during critical life stages as well as by the complexities of comparisons across species. Notably, there are differences between humans and nonhuman species used in toxicity testing that include specific differences relative to the timing of the development of the immune system as well as more general anatomic differences, and these differences must be factored into the interpretation of DIT studies. Likewise, understanding how the timing of the immune development impacts on various immune parameters is critical to the design of DIT studies, parameters most extensively characterized to date in young adult animals. Other factors important to DIT, which are considered in this review, are the recognition that effects other than suppression (e.g., allergy and autoimmunity) are important; the need to improve our understanding of how to assess the potential for DIT in humans; and the role that pathology has played in DIT studies in test animals. The latter point receives special emphasis in this review because pathology evaluations have been a major component of standard nonclinical toxicology studies, and could serve an important role in studies to evaluate DIT. This possibility is very consistent with recommendations to incorporate a DIT evaluation into standard developmental and reproductive toxicology (DART) protocols. The overall objective of this review is to provide a ‘snapshot’ of the current state-of-the-science of DIT. Despite significant progress, DIT is still evolving and it is our hope that this review will advance the science.