Pharmacological interaction of drugs with immune receptors: the p-i concept

Drug-induced hypersensitivity reactions have been explained by the hapten concept, according to which a small chemical compound is too small to be recognized by the immune system. Only after covalently binding to an endogenous protein the immune system reacts to this so called hapten-carrier complex, as the larger molecule (protein) is modified, and thus immunogenic for B and T cells. Consequently, a B and T cell immune response might develop to the drug with very heterogeneous clinical manifestations. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the MHC-peptide complex in order to trigger an immune response. Rather, some drugs may bind directly and reversibly to immune receptors like the major histocompatibility complex (MHC) or the T cell receptor (TCR), thereby stimulating the cells similar to a pharmacological activation of other receptors. This concept has been termed pharmacological interaction with immune receptors the (p-i) concept. While the exact mechanism is still a matter of debate, non-covalent drug presentation clearly leads to the activation of drug-specific T cells as documented for various drugs (lidocaine, sulfamethoxazole (SMX), lamotrigine, carbamazepine, p-phenylendiamine, etc.). In some patients with drug hypersensitivity, such a response may occur within hours even upon the first exposure to the drug. Thus, the reaction to the drug may not be due to a classical, primary response, but rather be mediated by stimulating existing, pre-activated, peptide-specific T cells that are cross specific for the drug. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the peculiar nature of many drug hypersensitivity reactions.

Transfection of drug-specific T-cell receptors into hybridoma cells: tools to monitor drug interaction with T-cell receptors and evaluate cross-reactivity to related compounds

In the context of drug hypersensitivity, our group has recently proposed a new model based on the structural features of drugs (pharmacological interaction with immune receptors; p-i concept) to explain their recognition by T cells. According to this concept, even chemically inert drugs can stimulate T cells because certain drugs interact in a direct way with T-cell receptors (TCR) and possibly major histocompatibility complex molecules without the need for metabolism and covalent binding to a carrier. In this study, we investigated whether mouse T-cell hybridomas transfected with drug-specific human TCR can be used as an alternative to drug-specific T-cell clones (TCC). Indeed, they behaved like TCC and, in accordance with the p-i concept, the TCR recognize their specific drugs in a direct, processing-independent, and dose-dependent way. The presence of antigen-presenting cells was a prerequisite for interleukin-2 production by the TCR-transfected cells. The analysis of cross-reactivity confirmed the fine specificity of the TCR and also showed that TCR transfectants might provide a tool to evaluate the potential of new drugs to cause hypersensitivity due to cross-reactivity. Recombining the alpha- and beta-chains of sulfanilamide- and quinolone-specific TCR abrogated drug reactivity, suggesting that both original alpha- and beta-chains were involved in drug binding. The TCR-transfected hybridoma system showed that the recognition of two important classes of drugs (sulfanilamides and quinolones) by TCR occurred according to the p-i concept and provides an interesting tool to study drug-TCR interactions and their biological consequences and to evaluate the cross-reactivity potential of new drugs of the same class.

Adverse side-effects to biological agents

Biological agents-like cytokines, monoclonal antibodies and fusion proteins are widely used in anti-inflammatory and tumour therapy. They are highly efficient in certain diseases, but can cause a great variety of adverse side-effects. Based on the peculiar features of biological agents a new classification of these adverse side-effects of biological agents is proposed - related but clearly distinct from the classification of side-effects observed with chemicals and drugs. This classification differentiates five distinct types, namely clinical reactions because of high cytokine levels (type alpha), hypersensitivity because of an immune reaction against the biological agent (beta), immune or cytokine imbalance syndromes (gamma), symptoms because of cross-reactivity (delta) and symptoms not directly affecting the immune system (epsilon). This classification could help to better deal with the clinical features of these side-effects, to identify possible individual and general risk factors and to direct research in this novel area of medicine.

Immunocompetence of nestling great tits in relation to rearing environment and parentage

Theoretical models of host-parasite coevolution assume a partially genetic basis to the variability in susceptibility to parasites among hosts, for instance as a result of genetic variation in immune function. However, few empirical data exist for free-living vertebrate hosts to support this presumption. In a cross-fostering experiment with nestling great tits, by comparing nestlings of the same origin we investigated (i) the variance in host resistance against an ectoparasite due to a common genetic origin, (ii) the effect of ectoparasite infestation on cell-mediated immunity and (iii) the variance in cell-mediated immunity due to a common genetic origin. Ectoparasitic hen fleas can impair the growth of nestling great tits and nestling growth was therefore taken as a measure of host susceptibility. A common origin did not account for a significant part of the variation in host susceptibility to fleas. There was no significant overall effect of fleas on nestling growth or cell-mediated immunity, as assessed by a cutaneous hypersensitivity response. A common rearing environment explained a significant part of the variation in cell-mediated immunity among nestlings, mainly through its effect on nestling body mass. The variation in cell-mediated immunity was also related to a common origin. However, the origin-related variation in body mass did not account for the origin-related differences in cell-mediated immunity. The results of the present study thus suggest heritable variation in cell-mediated immunity among nestling great tits. [References: 49]

Activation of T cells by carbamazepine and carbamazepine metabolites

BACKGROUND: T-cell-mediated hypersensitivity is a rare but serious manifestation of drug therapy. OBJECTIVES: To explore the mechanisms of drug presentation to T cells and the possibility that generation of metabolite-specific T cells may provoke cross-sensitization between drugs. METHODS: A lymphocyte transformation test was performed on 13 hypersensitive patients with carbamazepine, oxcarbazepine, and carbamazepine metabolites. Serial dilution experiments were performed to generate drug (metabolite)-specific T-cell clones to explore the structural basis of the T-cell response and mechanisms of antigen presentation. 3-Dimensional energy-minimized structures were generated by using computer modeling. The role of drug metabolism was analyzed with 1-aminobenzotriazole. RESULTS: Lymphocytes and T-cell clones proliferated with carbamazepine, oxcarbazepine, and some (carbamazepine 10,11 epoxide, 10-hydroxy carbamazepine) but not all stable carbamazepine metabolites. Structure activity studies using 29 carbamazepine (metabolite)-specific T-cell clones revealed 4 patterns of drug recognition, which could be explained by generation of preferred 3-dimensional structural conformations. T cells were stimulated by carbamazepine (metabolites) bound directly to MHC in the absence of processing. The activation threshold for T-cell proliferation varied between 5 minutes and 4 hours. 1-Aminobenzotriazole, which inhibits cytochrome P450 activity, did not prevent carbamazepine-related T-cell proliferation. Substitution of the terminal amine residue of carbamazepine with a methyl group diminished T-cell proliferation. CONCLUSION: These data show that carbamazepine and certain stable carbamazepine metabolites stimulate T cells rapidly via a direct interaction with MHC and specific T-cell receptors. CLINICAL IMPLICATIONS: Some patients with a history of carbamazepine hypersensitivity possess T cells that cross-react with oxcarbazepine, providing a rationale for cross-sensitivity between the 2 drugs.

Modulation of allergy incidence in icelandic horses is associated with a change in IL-4-producing T cells

BACKGROUND: Equine insect bite hypersensitivity (IBH) is an immediate-type hypersensitivity reaction provoked by insect-derived allergens. Icelandic horses living in Iceland do not have IBH due to absence of relevant insects, but acquire it at high frequency after being imported to mainland Europe. In contrast, their offspring born in mainland Europe has reduced IBH incidence. T helper 1 (Th1) and Th2 cells and cytokines were determined in Icelandic horses born in Iceland and on the continent and which either have IBH or are healthy. METHODS: Peripheral blood mononuclear cells (PBMC) from these horses were stimulated for 18 h during summer and winter with polyclonal T cell stimuli, IBH allergen(s) or irrelevant allergen(s). Cells were analysed by flow cytometry for interferon-gamma (IFN-gamma) and interleukin-4 (IL-4); RNA was analysed for IFN-gamma, IL-4, IL-5 and IL-13 mRNA. RESULTS: During summer, but not during winter, IBH PBMC stimulated polyclonally showed reduced IFN-gamma mRNA and IFN-gamma-producing cells when compared with those of healthy horses, regardless of origin. PBMC stimulated polyclonally or with IBH allergen showed increased IL-4 mRNA levels and higher numbers of IL-4-producing cells when born in Iceland or showing IBH symptoms. IL-5 and IL-13 mRNA were modulated neither by disease nor by origin. Abrogation of IL-4 production in healthy horses born in mainland Europe may be due, at least in part, to IL-10. There was an increased level of IL-10 in supernatants from PBMC of healthy horses born in mainland Europe and stimulated polyclonally or with IBH allergen. CONCLUSIONS: Modulation of IBH incidence is governed by altered Th1/Th2 ratio, which might be influenced by IL-10.

IgE-bearing cells in bronchoalveolar lavage fluid and allergen-specific IgE levels in sera from RAO-affected horses

Recurrent airway obstruction (RAO) is a common condition in stabled horses characterized by small airway inflammation, airway neutrophilia and obstruction following exposure of susceptible horses to mouldy hay and straw and is thus regarded as a hypersensitivity reaction to mould spores. However, the role of immunoglobulin E antibodies (IgE) in the pathogenesis of RAO is unclear. We hypothesized that the number of cells with receptor-bound IgE in bronchoalveolar lavage fluid (BALF) and IgE levels in serum would be higher in RAO-affected than in healthy horses living in the same environment. Therefore, IgE-positive (+) cells were identified by immunocytochemistry on cytospins from BALF and counted. IgE levels against the mould extracts Aspergillus fumigatus (Asp. f.) and Alternaria alternata (Alt. a.) and the recombinant mould allergen Aspergillus fumigatus 8 (rAsp f 8) were measured by enzyme-linked immunosorbent assay (ELISA) in the sera of seven RAO-affected and 22 clinically healthy mature horses housed in the same conventional stable environment. After correcting for the number of neutrophils, there were no significant differences in IgE+ cells on cytospins from BALF between both groups of horses (5% versus 7%, P > 0.1). Serum IgE levels against the mould extracts were significantly higher in RAO-affected than in clinically healthy horses [median = 119 versus 66 relative ELISA units (REU), P < 0.05]. Furthermore, significantly more RAO-affected than healthy horses had detectable serum IgE against the recombinant allergen rAsp f 8 (4/7 and 3/22, respectively, P < 0.05). Age had no significant effect on BALF cell ratios or on specific serum IgE levels. These results show that high IgE levels against mould antigens are associated with RAO under controlled environmental conditions but ranges of mould-specific serum IgE levels overlapped too much between diseased and clinically healthy animals to be of any diagnostic value. Further studies are needed to assess whether IgE-mediated reactions contribute to the pathogenesis of RAO.

Maculopapular drug eruptions

Maculopapular (exanthematous) reactions are the most common adverse drug eruptions affecting the skin. Several studies indicate that immunological mechanisms including cytotoxic T cells (CD4+ > CD8+), both type 1 (e.g. IFN- γ ) and type 2 (e.g. IL-5) cytokines and various chemokines are critically involved in the pathogenesis of these eruptions. While maculopapular exanthems can virtually be elicited by any drug, antimicrobials (e.g. Β -lactam antibiotic, sulfonamides), anticonvulsants, allopurinol, and NSAIDs are most frequently involved. Clinical manifestations are variable and range from faint macules to widespread erythematous and maculopapular lesions, which usually begin on the trunk, neck and upper extremities and subsequently spread downwards in a symmetrical fashion. Although the clinical course is often relatively mild, these exanthems may sometimes progress to erythroderma or represent the beginning of even more severe drug reactions like Stevens-Johnson syndrome, toxic epidermal necrolysis or a drug rash with eosinophilia and systemic symptoms. In most cases, management includes early withdrawal of the offending drug and usually supportive treatment with emollients, topical corticosteroids and systemic antihistamines depending on the severity of the eruption. Allergological work-up is recommended to provide the patient with appropriate information about the causative drug and possible alternatives for future use.

Reduction of airspace after lung resection through controlled paralysis of the diaphragm

OBJECTIVES: Residual airspace following thoracic resections is a common clinical problem. Persistent air leak, prolonged drainage time, and reduced hemostasis extend hospital stay and morbidity. We report a trial of pharmacologic-induced diaphragmatic paralysis through continuous paraphrenic injection of lidocaine to reduced residual airspace. The objectives were confirmation of diaphragmatic paralysis and possible procedure related complications. METHODS: Six eligible patients undergoing resectional surgery (lobectomy or bilobectomy) were included. Inclusion criteria consisted of: postoperative predicted FEV1 greater than 1300 ml, right-sided resection, absence of parenchymal lung disease, no class III antiarrhythmic therapy, absence of hypersensitivity reactions to lidocaine, no signs of infection, and informed consent. Upon completion of resection an epidural catheter was attached in the periphrenic tissue on the proximal pericardial surface, externalized through a separate parasternal incision, and connected to a perfusing system injecting lidocaine 1% at a rate of 3 ml/h (30 mg/h). Postoperative ICU surveillance for 24h and daily measurement of vital signs, drainage output, and bedside spirometry were performed. Within 48 h fluoroscopic confirmation of diaphragmatic paralysis was obtained. The catheter removal coincided with the chest tube removal when no procedural related complications occurred. RESULTS: None of the patients reported respiratory impairment. Diaphragmatic paralysis was documented in all patients. Upon removal of catheter or discontinuation of lidocaine prompt return of diaphragmatic motility was noticed. Two patients showed postoperative hemodynamic irrelevant atrial fibrillation. CONCLUSION: Postoperative paraphrenic catheter administration of lidocaine to ensure reversible diaphragmatic paralysis is safe and reproducible. Further studies have to assess a benefit in terms of reduction in morbidity, drainage time, and hospital stay, and determine the patients who will profit.

Psychologic factors are related to some sensory pain thresholds but not nociceptive flexion reflex threshold in chronic whiplash

OBJECTIVES: Sensory hypersensitivity, central hyperexcitability [lowered nociceptive flexion reflex (NFR) thresholds], and psychologic distress are features of chronic whiplash. However, relationships between these substrates are not clear. This study tested the hypothesis that psychologic distress and catastrophization are correlated with sensory hypersensitivity and NFR responses in chronic whiplash. METHODS: Pressure and thermal pain thresholds (mean values across 3 body sites), NFR threshold, and pain at threshold Visual Analog Scale were measured in 30 participants with chronic whiplash and 30 asymptomatic controls. Pain and disability levels Neck Disability Index, psychologic distress (GHQ-28), and catastrophization (PCS) were also measured in the whiplash group. RESULTS: Whiplash injured participants demonstrated lowered pain thresholds to pressure and cold (P<0.05); lowered NFR thresholds (P=0.003), and demonstrated above threshold levels of psychologic distress (GHQ-28) and levels of catastrophization comparable with other musculoskeletal conditions. There were no group differences for heat pain thresholds or pain at NFR threshold. In the whiplash group, PCS scores correlated moderately with cold pain threshold (r=0.51, P=0.01). In contrast, there were no significant correlations between GHQ-28 scores and pain threshold measures or between psychologic factors and NFR responses in whiplash participants. There were no significant correlations between psychologic factors and pain thresholds or NFR responses in controls. DISCUSSION: We have demonstrated that psychologic factors have some association with sensory hypersensitivity (cold pain threshold measures) in chronic whiplash but do not seem to influence spinal cord excitability. This suggests that psychologic disorders are important, but not the only, determinants of central hypersensitivity in whiplash patients.

New method for quantification and statistical analysis of nociceptive reflex receptive fields in humans

A method for quantifying nociceptive withdrawal reflex receptive fields in human volunteers and patients is described. The reflex receptive field (RRF) for a specific muscle denotes the cutaneous area from which a muscle contraction can be evoked by a nociceptive stimulus. The method is based on random stimulations presented in a blinded sequence to 10 stimulation sites. The sensitivity map is derived by interpolating the reflex responses evoked from the 10 sites. A set of features describing the size and location of the RRF is presented based on statistical analysis of the sensitivity map within every subject. The features include RRF area, volume, peak location and center of gravity. The method was applied to 30 healthy volunteers. Electrical stimuli were applied to the sole of the foot evoking reflexes in the ankle flexor tibialis anterior. The RRF area covered a fraction of 0.57+/-0.06 (S.E.M.) of the foot and was located on the medial, distal part of the sole of the foot. An intramuscular injection into flexor digitorum brevis of capsaicin was performed in one spinal cord injured subject to attempt modulation of the reflex receptive field. The RRF area, RRF volume and location of the peak reflex response appear to be the most sensitive measures for detecting modulation of spinal nociceptive processing. This new method has important potential applications for exploring aspects of central plasticity in volunteers and patients. It may be utilized as a new diagnostic tool for central hypersensitivity and quantification of therapeutic interventions.

Statins induce regulatory T cell recruitment via a CCL1 dependent pathway

The statins, a group of inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, are reported to influence a variety of immune system activities through 3-hydroxy-3-methylglutaryl coenzyme A reductase-dependent and -independent mechanisms. How statin treatment regulates immune system function in vivo nonetheless remains to be fully defined. We analyzed the immunomodulatory effects of lovastatin in a Candida albicans-induced delayed-type hypersensitivity reaction in mice. In this model, lovastatin administration reduced the acute inflammatory response elicited by C. albicans challenge. This anti-inflammatory activity of lovastatin was associated with a shift from a Th1 to a Th2 immune response, as well as an increase in the percentage of regulatory T cells at the inflammation site and in the regional draining lymph node. The lovastatin-induced increase in regulatory T cells in the inflamed skin was dependent on expression of CCL1, a chemokine that is locally up-regulated by statin administration. The anti-inflammatory effect of lovastatin was abrogated in CCL1-deficient mice. These results suggest that local regulation of chemokine expression may be an important process in statin-induced modulation of the immune system.

Severe hepatotoxicity following ingestion of Herbalife nutritional supplements contaminated with Bacillus subtilis

BACKGROUND/AIMS: Nutritional supplements are widely used. Recently, liver injury after consumption of Herbalife preparations was reported but the underlying pathogenesis remained cryptic. METHODS: Two patients presented with cholestatic hepatitis and pruritus, and cirrhosis, respectively. Viral, alcoholic, metabolic, autoimmune, neoplastic, vascular liver diseases and synthetic drugs as the precipitating causes of liver injury were excluded. However, both patients reported long-term consumption of Herbalife products. All Herbalife products were tested for contamination with drugs, pesticides, heavy metals, and softeners, and examined for microbial contamination according to standard laboratory procedures. Bacteria isolated from the samples were identified as Bacillus subtilis by sequencing the 16S rRNA and gyrB genes. RESULTS: Causality between consumption of Herbalife products and disease according to CIOMS was scored "probable" in both cases. Histology showed cholestatic and lobular/portal hepatitis with cirrhosis in one patient, and biliary fibrosis with ductopenia in the other. No contamination with chemicals or heavy metals was detected, and immunological testing showed no drug hypersensitivity. However, samples of Herbalife products ingested by both patients showed growth of Bacillus subtilis of which culture supernatants showed dose- and time-dependent hepatotoxicity. CONCLUSIONS: Two novel incidents of severe hepatic injury following intake of Herbalife products contaminated with Bacillus subtilis emphasize its potential hepatotoxicity.

Intimal proliferation and restenosis in paclitaxel-eluting stents with aminoparylene as carrier substance in swines

BACKGROUND: Polymer as carrier substance for drugeluting stents (DES) has been accused of inducing inflammation and hypersensitivity reactions leading to restenosis and stent thrombosis. Thus, a new paclitaxel-eluting stent (PES) with aminoparylene as a carrier substance is tested in the present study. METHODS: In 10 pigs, stents were implanted in the epicardial coronary arteries: 1) bare-metal stents (BMS, control stent); 2) cobalt-chromium stents (CCS); and 3) PES. Stent length was 15 mm, and diameter was 3 mm. The animals were restudied after 6 weeks. Quantitative coronary angiography was performed at baseline and follow up. Minimum luminal diameter (MLD) and late loss were calculated in all animals. Histologic vessel lumen, intimal proliferation and restenosis were determined by morphometry. Disruption of the lamina elastica interna (LEI) and inflammatory reactions were assessed by histology. RESULTS: The MLD at baseline was 2.83 +/- 0.28 mm, and at follow up it was 2.29 +/- 0.44 (p < 0.05; n = 30). Late loss and angiographic restenosis were smallest in the CCS and largest in the PES (ns). Neointimal proliferation was similar for all 3 stents, ranging between 1.38 and 1.64 mm(2) (ns). There was a significant correlation between disruption of the LEI and inflammatory reactions. CONCLUSIONS: PTs with aminoparylene as a carrier substance show similar late loss and angiographic restenosis to that of BM and CCS. The incidence of inflammatory reactions (35% of all histologic sections) is similar in all stents, but highest in PES. The mechanism of this reaction is unclear, but may be either due to the drug itself, the disruption of the LEI or to a hypersensitivity reaction.

Correlation of intravascular ultrasound findings with histopathological analysis of thrombus aspirates in patients with very late drug-eluting stent thrombosis

BACKGROUND: Intravascular ultrasound of drug-eluting stent (DES) thrombosis (ST) reveals a high incidence of incomplete stent apposition (ISA) and vessel remodeling. Autopsy specimens of DES ST show delayed healing and hypersensitivity reactions. The present study sought to correlate histopathology of thrombus aspirates with intravascular ultrasound findings in patients with very late DES ST. METHODS AND RESULTS: The study population consisted of 54 patients (28 patients with very late DES ST and 26 controls). Of 28 patients with very late DES ST, 10 patients (1020+/-283 days after implantation) with 11 ST segments (5 sirolimus-eluting stents, 5 paclitaxel-eluting stents, 1 zotarolimus-eluting stent) underwent both thrombus aspiration and intravascular ultrasound investigation. ISA was present in 73% of cases with an ISA cross-sectional area of 6.2+/-2.4 mm(2) and evidence of vessel remodeling (index, 1.6+/-0.3). Histopathological analysis showed pieces of fresh thrombus with inflammatory cell infiltrates (DES, 263+/-149 white blood cells per high-power field) and eosinophils (DES, 20+/-24 eosinophils per high-power field; sirolimus-eluting stents, 34+/-28; paclitaxel-eluting stents, 6+/-6; P for sirolimus-eluting stents versus paclitaxel-eluting stents=0.09). The mean number of eosinophils per high-power field was higher in specimens from very late DES ST (20+/-24) than in those from spontaneous acute myocardial infarction (7+/-10), early bare-metal stent ST (1+/-1), early DES ST (1+/-2), and late bare-metal stent ST (2+/-3; P from ANOVA=0.038). Eosinophil count correlated with ISA cross-sectional area, with an average increase of 5.4 eosinophils per high-power field per 1-mm(2) increase in ISA cross-sectional area. CONCLUSIONS: Very late DES thrombosis is associated with histopathological signs of inflammation and intravascular ultrasound evidence of vessel remodeling. Compared with other causes of myocardial infarction, eosinophilic infiltrates are more common in thrombi harvested from very late DES thrombosis, particularly in sirolimus-eluting stents, and correlate with the extent of stent malapposition.