A chemically inert drug can stimulate T cells in vitro by their T cell receptor in non-sensitised individuals.

Drugs can interact with T cell receptors (TCR) after binding to peptide-MHC structures. This binding may involve the formation of a stable, covalent bond between a chemically reactive drug and MHC or the peptide embedded within. Alternatively, if the drug is chemically inert, the binding may be non-covalent and readily reversible. Both types of drug presentation account for a substantial number of adverse side effects to drugs. Presently no tests are available to predict the ability of chemically inert drugs to stimulate an immune response. Here we present data on the successful induction of a primary T cell immune response in vitro against a chemically inert drug using blood from healthy individuals, previously not exposed to the drug. Blood lymphocytes were stimulated by the chemically inert drug sulfamethoxazole and the protein-reactive drug-metabolite sulfamethoxazole-nitroso in the presence of IL-2. 9/10 individuals reacted in response to sulfamethoxazole-nitroso, but only three reacted to the chemically inert compound sulfamethoxazole. Drug reactive T cells could be detected after 14-35 days of cell culture by drug-specific proliferation or cytotoxicity, which was MHC-restricted. These cells were CD4, CD8 positive or CD4/CD8 double positive and T cell clones generated secreted Th0 type cytokines. Drug interaction lead to down-regulation of specific TCR. These data confirm the ability of chemically inert drugs to stimulate certain T cells by their TCR and may provide the opportunity to screen new drugs for their ability to interact with TCRs.

Cellular and molecular pathophysiology of cutaneous drug reactions.

Hypersensitivity reactions to drugs can cause a variety of skin diseases like maculopapular, bullous and pustular eruptions. In recent years increasing evidence indicates the important role of T cells in these drug-induced skin diseases. Analysis of such drug-specific T cell clones has revealed that drugs can be recognized by alpha beta-T cell receptors, not only if bound covalently to peptides, but also if the drug binds in a rather labile way to the presenting major histocompatibility complex (MHC)-peptide. This presentation is sufficient to stimulate T cells. In maculopapular exanthema (MPE), histopathological analysis typically shows a dominant T cell infiltration together with a vacuolar interface dermatitis. Immunohistochemical studies demonstrate the presence of cytotoxic CD4+ and to a lesser degree of CD8+ T cells, which contain perforin and granzyme B. They are close to keratinocytes that show signs of cell destruction. Expression of Fas ligand is barely detectable, suggesting that cytotoxic granule exocytosis may be the dominant pathway leading to keratinocyte cell damage. While in MPE, the killing of cells seems to be predominantly mediated by CD4+ T cells, patients with bullous skin disease show a strong CD8+ T cell migration to the epidermis. This is probably due to a preferential presentation of the drug by MHC class I molecules, and a more extensive killing of cells that present drugs on MHC class I molecules. This might lead to bullous skin diseases. In addition to the presence of cytotoxic T cells, drug-specific T cells also orchestrate the inflammatory skin reaction through the release and induction of various cytokines [i.e. interleukin (IL)-5, IL-6, tumor necrosis factor-alpha and interferon-gamma] and chemokines (RANTES, eotaxin or IL-8). The increased expression of these mediators seems to contribute to the generation of tissue and blood eosinophilia, a hallmark of many drug-induced allergic reactions. However, in acute generalized exanthematous pustulosis (a peculiar form of drug allergy), neutrophils represent the predominant cell type within pustules, probably due to their recruitment by IL-8 secreting drug specific T cells and keratinocytes.