T cells can recognize small molecular compounds like drugs. It is thought that covalent binding to MHC bound peptides is required for such a hapten stimulation. Sulfamethoxazole, like most drugs, is not chemically reactive per se, but is thought to gain the ability to covalently bind to proteins after intracellular drug metabolism. The purpose of this study was to investigate how sulfamethoxazole is presented in an immunogenic form to sulfamethoxazole-specific T cell clones. The stimulation of four CD4 ϩ and two CD8 ϩ sulfamethoxazole-specific T cell clones by different antigen-presenting cells (APC) was measured both by proliferation and cytolytic assays. The MHC restriction was evaluated, first, by inhibition using anti-class I and anti-class II mAb, and second, by the degree of sulfamethoxazole-induced stimulation by partially matched APC. Fixation of APC was performed with glutaraldehyde 0.05%. The clones were specific for sulfamethoxazole without cross-reaction to other sulfonamides. The continuous presence of sulfamethoxazole was required during the assay period since pulsing of the APC was not sufficient to induce proliferation or cytotoxicity. Stimulation of clones required the addition of MHC compatible APC. The APC could be fixed without impairing their ability to present sulfamethoxazole. Sulfamethoxazole can be presented in an unstable, but MHC-restricted fashion, which is independent of processing. These features are best explained by a direct, noncovalent binding of sulfamethoxazole to the MHC-peptide complex. ( J. Clin. Invest. 1997. 100:136-141.)

Perforin-mediated killing of autologous keratinocytes in the presence of soluble sulfamethoxazole by drug-specific CD4+ lymphocytes may be a pathway for generalized drug-induced delayed skin reactions. The requirement of interferon gamma pretreatment of keratinocytes for efficient specific killing might explain the increased frequency of drug allergies in generalized viral infections like HIV, when interferon gamma levels are elevated.

Penicillin G (Pen G) and other beta-lactam antibiotics frequently induce allergic reactions constituting typical examples of human immune responses to haptens. In fact, penicillins represent a unique set of haptens with outstanding structural variability on the basis of an identical protein-reactive beta-lactam containing backbone. Although both cellular and humoral responses are involved in drug-induced allergies, little is known about the T cell reactivity to penicillins. To understand which structural features determine antigenic specificity, we isolated a panel of MHC-restricted, Pen G-reactive T cell clones from different penicillin-allergic patients and tested them for their capacity to proliferate in the presence of other penicillin derivatives. We found that the antigenic epitope consists of both the amide-linked side chain, which is different in every member of the penicillin family, as well as the thiazolidine ring common to all penicillin derivatives. We also demonstrated the presence of two different types of penicillin-specific T cells, one dependent, and the other independent of antigen processing by autologous antigen-presenting cells. Our data strongly suggest that penicillins form part of the epitopes contacting the antigen receptors of T cells.

To analyze whether and how T cells are involved in drug allergies, we analyzed the drug-induced activation of T cell subsets, T cell receptor V-β usage and cytokine secretion of T cells from the peripheral blood of drug-allergic individuals. The specificity of the T cells was demonstrated by specific restimulation of drug specific clones. We found that drugs which do not need to be metabolized to become immunogenic (haptens like penicillin G) can stimulate CD4+ and CD8+ T cells in vitro. The T cell response to penicillin can be oligoclonal (use of a certain T cell receptor Vβ only) or polyclonal. Only polyclonal T cell lines were cross-reactive with other β-lactam antibiotics. Sulfamethoxazole and lidocaine are thought to gain their ability to bind to proteins by intracellular drug metabolism. They were found to stimulate CD4+ and CD8+ T cells in vitro, and some reactive T cell lines were oligoclonal. The majority of lidocaine-specific clones secreted rather high amounts of IL-5 and IL-4 after PMA/ionomycin stimulations (Th2-like), but some CD4+ and all CD8+ clones had a Th1-like phenotype (high INF-γ and TNF-α). The data clearly demonstrate the existence of drug-specific αβ+ T cells in the circulation of drug-allergic individuals and reveal a great heterogeneity of T-cell-mediated responses. Further studies are needed to correlate the type of T cell response to the clinical picture, which can be quite heterogeneous.

The B cell antigen B7 delivers a strong co-stimulatory signal for the activation of T cells by binding to its ligands CD28 and CTLA4. Here we demonstrate the surface expression of the B7 molecule on activated human T cells in vitro and under certain conditions in vivo and its functional importance in T-T cell interactions. B7 was detected by flow cytometry on antigen-specific CD4+ and allospecific CD8+ cloned T cells from different donors with anti-B7 monoclonal antibody (mAb) or a soluble CTLA4-C gamma 1 chimera molecule and by reverse transcription-polymerase chain reactions. The expression of B7 was up-regulated following restimulation of the T cell clones and peaked after 7-9 days. Moreover, we show that the B7 molecule on T cells is functionally involved in T-T cell interactions: mAb to CD28 and the CTLA4-Ig fusion protein could inhibit the proliferation of specific T cell clones in response to T cells as antigen-presenting cells (APC) or the proliferation of peripheral blood mononuclear cells in a primary allostimulation with activated T cells as stimulator cells. Finally, we found that B7 can be expressed on freshly isolated circulating T cells since in a preliminary study with a limited number of patients, B7 was present on a subset of CD3+ cells. B7 was expressed on activated T cells (CD4+ and CD8+) of certain human immunodeficiency virus (HIV)-infected individuals (0.5-20% B7+CD8+ cells) or some patients with autoimmune diseases whereas CD3+ cells of healthy individuals did not express B7. The coexpression of major histocompatibility complex class II molecules and B7 may be relevant for the capacity of activated T cells to function as APC. The expression of B7 on T cells in vivo in autoimmune diseases and in HIV infection may be important for a better understanding of these diseases.