Drug-induced thrombocytopenia is associated with increased binding of IgG to platelets both in vivo and in vitro

Thrombocytopenia is a common serious adverse effect of drug treatment. A variety of in vitro diagnostic techniques to confirm the diagnosis are available, but the majority lack sufficient sensitivity to detect all cases of drug-induced thrombocytopenia. We studied 19 patients with suspected drug-induced thrombocytopenia and demonstrated that platelet- associated IgG (PAIgG) was elevated in all at the time of thrombocytopenia, and PAIgG returned to normal levels as the thrombocytopenia resolved. In the majority of patients, the platelet count rapidly returned to normal after the drug was discontinued; however, in six patients, the thrombocytopenia persisted well beyond the period of time that the offending drug would be expected to be cleared from the blood. In 13 patients, serum obtained after recovery was used to identify the drug responsible for the thrombocytopenia in an in vitro assay. In all cases, the addition of the drug historically associated with the thrombocytopenic episode was associated with an increased binding of IgG to control platelets. For uncertain reasons, the concentration of drug required to increase the in vitro binding of IgG to test platelets was often more than the concentration usually achieved in vivo. Wider application of these techniques may provide better understanding of the clinical characteristics and mechanisms responsible for drug-induce thrombocytopenia.     

Immune hemolytic anemia associated with tolmetin and suprofen

This article reports the first case of immune hemolytic anemia possibly associated with the ingestion of suprofen. The patient suffered from massive hemoglobinuria and acute renal failure. Serologic studies of the patient's serum revealed suprofen-dependent red cell antibodies. However, tolmetin-dependent antibodies were also found in the serum, showing the same properties as the suprofen antibodies and an even higher titer. The patient not only had drug-dependent antibodies in the serum, but also had developed autoantibodies, a phenomenon that has been described for several other drugs. The working mechanism by which suprofen and tolmetin caused immune hemolysis had properties of both the immune complex model and the induction of autoimmunity. Although it was unclear whether the immune hemolytic anemia was the result of suprofen, tolmetin, or cross-reacting antibodies, we feel that suprofen should be added to the list of nonsteroidal anti-inflammatory drugs associated with a positive direct antiglobulin test.     

The role of oncogenes, tumour suppressor genes and growth factors in oral squamous cell carcinoma: a case of apoptosis versus proliferation

Mutation, deactivation and disregulated expression of oncogenes and tumour-suppressor genes may be involved in the pathogenesis of oral squamous cell carcinoma (SCC). Deactivation of the p53 tumour-suppressor gene allows cell proliferation and blocks apoptosis of malignant oral keratinocytes. Mutation in the ras oncog-ene results in persistent mitogenic signalling. Upregul-ated c-Myc expression, in the presence of growth factors, provides an additional proliferative signal. Loss of retino-blastoma tumour-suppressor gene (Rb) function may contribute to oral keratinocyte hyperproliferation and recent evidence suggests that simultaneous deactivation of both p53 and Rb is required for tumourigenesis. Enhanced Bcl-2 and reduced Fas expression inhibit tumour cell apoptosis and may convey resistance to cyto-toxic drugs and T cell-mediated cytotoxicity, respectively. Exogenous mutagens such as tobacco, alcohol and viral oncogenes may cause altered expression of oncogenes and tumour-suppressor genes in some cases of oral SCC. The impact of these mechanisms on future therapies for oral SCC is highlighted.     

FcgammaRIIa is a target for modulation by TNFalpha in human neutrophils

Activation of neutrophils by the interaction of immune complexes with Fc gamma receptors (FcgammaR) is amplified in tumor necrosis factor-alpha (TNFalpha)-primed cells, whereas interleukin-10 (IL-10) has been reported to suppress cytokine-mediated neutrophil activation. We examined whether the expression and function of FcgammaR in human neutrophils is modulated by TNFalpha and IL-10 in vitro, and whether FcgammaRIIa expression is altered following treatment with the TNFalpha inhibitor infliximab in rheumatoid arthritis (RA) patients in vivo. TNFalpha treatment induced upregulation of expression and function of the major activating Fc receptor, FcgammaRIIa, in neutrophils from healthy donors. Unexpectedly, treatment with IL-10 led to gain of FcgammaRIIa function in TNFalpha-primed neutrophils. In neutrophils from RA patients initiating infliximab therapy and followed longitudinally through consecutive treatments, FcgammaRIIa protein decreased during the course of TNFalpha blockade, indicating that FcgammaRIIa is a target of TNFalpha modulation in human neutrophils in vivo.     

Systemic lupus erythematosus monocytes are less responsive to interleukin‐10 in the presence of immune complexes

Objective

Systemic lupus erythematosus (SLE) is a systemic inflammatory disease characterized by autoantibody production and immune complex deposition. The level of interleukin‐10 (IL‐10), predominantly an antiinflammatory cytokine, is paradoxically elevated in patients with SLE. The aim of this study was to examine the hypothesis that the antiinflammatory function of IL‐10 is impaired in monocytes from patients with SLE with long‐term exposure to immune complexes.

Methods

CD14+ monocytes were isolated from healthy donors and patients with SLE. Cultured CD14+ cells were treated with heat‐aggregated human IgG (325 μg/ml) in the presence or absence of IL‐10 (20 ng/ml). To study gene expression, RNA was extracted 3 hours after treatment. To study cytokine production, supernatants were harvested after 8 hours. To study IL‐10 signaling, cell lysates were obtained from CD14+ cells treated with human IgG (325 μg/ml) for 1 hour followed by IL‐10 (20 ng/ml) treatment for 10 minutes. Western blot analysis was used to assess STAT‐3 phosphorylation. All experiments were performed in pairs.

Results

When stimulated with human IgG, SLE monocytes produced more tumor necrosis factor α (TNFα) and IL‐6 than did control cells. The suppressive effect of IL‐10 on human IgG–induced TNFα and IL‐6 production was lower in SLE monocytes compared with control monocytes, although IL‐10 receptor expression was similar in SLE and control monocytes. Human IgG suppressed IL‐10 receptor expression and altered IL‐10 signaling in control monocytes. Like SLE monocytes, interferon‐α (IFNα)–primed control monocytes stimulated with human IgG were also less responsive to IL‐10.

Conclusion

Human IgG and IFNα modulate IL‐10 function. In SLE monocytes, which are considered to be IFNα primed and persistently exposed to immune complexes, responses to IL‐10 are abnormal, limiting the antiinflammatory effect of this cytokine.