Quantitation of cytokine mRNA expression as an endpoint for prediction and diagnosis of xenobiotic-induced hypersensitivity reactions

Monitoring the acute phase response in non-immediate allergic drug reactions

PURPOSE OF REVIEW

The aim of this article is to evaluate the advantages of monitoring the immunological response of non-immediate allergic drug reactions in parallel with the affected tissues, skin and peripheral blood, in order to improve our understanding of the immunological response.

RECENT FINDINGS

Several studies have shown that in the skin and peripheral blood, the agents that take part in the development of the immunological reaction express a number of markers that parallel the evolution of the disease process. These markers include cytokines, chemokines, and cytotoxic factors, as well as many other markers involved in such mechanisms as drug metabolism and signal transduction.

SUMMARY

Monitoring the acute phase response to a drug in the skin with parallel studies in the blood provides clues that increase our understanding of the underlying pathological mechanisms in adverse reactions to drugs with an immunological basis. This approach, together with molecular biology techniques such as microarrays and genomic studies may be useful in future, in better characterizing the clinical subtype and prognosis of nonimmediate allergic drug reactions and generating targeted treatment regimens.

Genetic aspects of immune-mediated adverse drug effects

Adverse drug effects (ADEs) are of great importance in medicine and account for up to 5% of all hospital admissions. ADEs can arise from several mechanisms and a wide range of drugs can cause immune-mediated ADEs (IMADEs). For a drug to elicit an IMADE, it must be both immunogenic (that is, able to sensitize the immune system) and antigenic (that is, able to evoke a response from a sensitized immune system). Unlike protein therapeutics, small-molecule drugs (or xenobiotics) are usually neither immunogenic nor antigenic. IMADEs are therefore the result of complex interactions between drug-metabolizing enzymes, immune sensitization and immune effectors. The genetic aspects of this interplay are discussed in this review.

Positive responses to imipramine in the popliteal lymph node assay are due to primary irritation

The popliteal lymph node (PLN) assay has long been proposed as a tool to detect immunotoxicants with the potential to induce systemic autoimmunity. A major problem hampering the further validation of this assay is the need to rule out irritants that cause false-positive PLN responses. The anti-depressant, imipramine, has not been reported to induce systemic autoimmune reactions in treated patients, but has been repeatedly found positive in the PLN assay, suggesting that this is a false-positive response. To test this hypothesis, the effects of imipramine were compared to those of 50% ethanol in C57B1/6 mice. Footpad edema was evidenced in the few days after injection of both ethanol and imipramine. T-cell depletion using monoclonal antibodies against either CD4+ or CD8+ T-lymphocytes prior to the PLN assay did not influence the responses to either ethanol or imipramine. Cytokine (TNFalpha, IL-1alpha, IL-1beta, IL-2R, IL-6, IL-12 and IFN-gamma) fingerprinting of the PLNs after injection of ethanol and imipramine evidenced the same pattern of responses. These results indicate a closely similar pattern of responses following the footpad injection of either imipramine or ethanol. The conclusion can be drawn that imipramine induces positive responses in the PLN assay via primary (nonspecific) irritation.

Cytokine measurement techniques for assessing hypersensitivity

One of the most potentially useful tools in immunotoxicology is the assessment of cytokines, the molecules responsible for regulating a variety of processes including immunity, inflammation, apoptosis, and hematopoiesis. The particular profile of cytokine production may provide important information regarding the nature of an immunotoxic response such as hypersensitivity (i.e. TH(1) vs. TH(2) response). Proper evaluation of the role of cytokines in understanding hypersensitivity reactions requires attention to a multitude of technical details. Some of the details discussed in this review include the source of the sample to be tested (circulating, local, or ex vivo isolated cells), the potential effects of collection, processing, and storage on the results of the assays, potential variables associated with the source material (matrix effects, relevance, inhibitory substances), and factors influencing the choice of assay used (bioassay, immunoassay, molecular biology technique, flow cytometry). Other often-overlooked issues are discussed, including species considerations and quality control issues such as the use of reference standards and the expression of results.

Advances in molecular toxicology-towards understanding idiosyncratic drug toxicity

Idiosyncratic drug toxicity is a major complication of drug therapy and drug development. Such adverse drug reactions (ADRs) include anaphylaxis, blood dyscrasias, hepatotoxicity and severe cutaneous reactions. They are usually serious and can be fatal. At present, prediction of idiosyncratic ADRs at the preclinical stage of drug development is not possible because there are no suitable animal models and we do not understand the basic mechanisms involved in the toxicity when it does occur in man. Many idiosyncratic reactions appear to have an immunological aetiology. For example, there is increasing evidence for the role of T lymphocytes in severe skin reactions. Nevertheless, the sequence of events by which a simple chemical can elicit severe tissue damage remains poorly understood and alternative novel mechanisms of toxicity must also be explored. The purpose of this article will be to review the currently accepted mechanisms of idiosyncratic drug toxicity at the chemical and the molecular levels. In particular, we will consider how recent advances in cellular immunology and molecular biology can improve our understanding of both the chemical and clinical aspects of drug hypersensitivity. Recent advances in the role of both inter- and intra-cellular signalling in the regulation of the immune response to drugs and their metabolites will be discussed. The long-term aim of such research is to provide test systems for the evaluation of drug safety and patient susceptibility to idiosyncratic drug toxicity.