Processing-dependent and -independent pathways for recognition of iodinated contrast media by specific human T cells

BACKGROUND

One to three percent of patients exposed to intravenously injected iodinated contrast media (CM) develop delayed hypersensitivity reactions. Positive patch test reactions, immunohistological findings, and CM-specific proliferation of T cells in vitro suggest a pathogenetic role for T cells. We have previously demonstrated that CM-specific T cell clones (TCCs) show a broad range of cross-reactivity to different CM. However, the mechanism of specific CM recognition by T cell receptors (TCRs) has not been analysed so far.

OBJECTIVE

To determine how T cells specifically recognize CM.

METHODS

CM-specific TCCs were generated from human blood of three CM-allergic patients and a specific TCR was transfected into a mouse T cell hybridoma. Functional analysis such as proliferation assays, IL-2 secretion assays, and calcium influx experiments were performed using irradiated, glutaraldehyde-fixed, CM-pre-incubated, human leucocyte antigen (HLA)-DR-matched or -mismatched antigen-presenting cells (APCs), and HLA-blocking antibodies.

RESULTS

We identified two mechanisms of T cell stimulation: some TCCs and the transfectant reacted to CM independent of uptake by APCs because proliferation/IL-2 secretion occurred in the presence of glutaraldehyde-fixed APCs, and intracellular calcium increased within seconds after drug addition. Other TCCs required functional APCs, compatible with uptake and presentation of CM on MHC-class II molecules, as implied by three findings: (1) glutaraldehyde fixation of APCs abrogated presentation; (2) CM could not be washed away from CM-pre-incubated APCs; and (3) the optimal pulsing time was 10-20 h. Because allogeneic, MHC-matched, CM-pulsed APCs could induce proliferative responses as well, the ability of CM uptake and presentation is not unique to APCs from patients with CM-induced delayed hypersensitivity.

CONCLUSION

Our data suggest that CM may be stimulatory for T cells either by direct binding to the MHC-TCR complex or by binding after uptake and processing by APCs. This questions the assumed inert nature of CM.

Effects of iodinated contrast media on blood and endothelium

The aim of the study was to assess the effects of iodinated contrast media on blood components and endothelium based on experimental and clinical studies and to produce clinically relevant guidelines for reducing thrombotic and hematologic complications following the intravascular use of contrast media. A report was drafted after review of the literature and discussions among the members of the Contrast Media Safety Committee of the European Society of Urogenital Radiology. The final report was produced following discussion at the 12th European Symposium on Urogenital Radiology in Ljubljana, Slovenia (2005). Experimental data indicate that all iodinated contrast media produce an anticoagulant effect and that this effect is greater with ionic contrast media. Several of the in vitro and experimental in vivo studies on haematological effects of contrast media have not been confirmed by clinical studies. Low- or iso-osmolar contrast media should be used for diagnostic and interventional angiographic procedures, including phlebography. Meticulous angiographic technique is the most important factor for reducing the thrombotic complications associated with angiographic procedures. Drugs and interventional devices that decrease the risk of thromboembolic complications during interventional procedures minimize the importance of the effects of contrast media.