The recent paper by Lara Belmar Vega and coworkers introduced the role of a CD123pos/HLADRneg basophil activation test (BAT) in a case report of interstitial nephritis, suggesting the occurrence of an interstitial nephropathy secondary to the use of omeprazole.1 Omeprazole is well known from past reports to cause interstitial nephritis.2 The renal oedematosus interstitium having a massive infiltration of leukocytes and eosinophils, suggested the author to assess an immune response, due to the omeprazole therapy. This case report should assess the optimal use of BAT in omeprazole hypersensitivity.3 Despite the fact that the authors were not endowed with further allergic tests, such as skin prick test (SPT) or serum IgEs to assess their evidence, they moved on the clinical suspicion of an allergy-driven nephropathy caused by an hypersensitivity response to omeprazole and found a CD63 stimulation index (SI) ≥4.1 and ≥10% respect the basal, non activated level.1 The analytical performance of a BAT based on the CD123pos/HLADRneg gating protocol allowed the authors to easily capture basophils in a flow cytometry (FC) approach and to assess cell activation by evaluating the CD63 membrane upregulation upon the activation from omeprazole-caused drug hypersensitivity. Yet, the activation is only slightly higher (i.e. 10.25%) than the indicated cut off, which is ≤5% and did not reach the much more encouraging level of an fMLP-mediated activation (34.9%).1 Causes underlying this moderate, poor activation may be further elucidated by introducing in the test a polyclonal anti-IgE agonist, to probe the level of releasability and activation of basophils in the IgE-mediated mechanism.4 Furthermore, a CD203c marker to assess also a possible involvement of non IgE-mediated reactions might be useful to better comprehend the observed reaction to omeprazole.1 Noteworthy, omeprazole targets H2-receptors, so hampering the counter-regulation of basophil activation by histamine, their costitutive activation and the subsequent down-regulation of the FcɛRI/IgEs complexes, causing therefore a desensitized cell and/or a CD63 exhausted pool.5–8 The apparently low level of activation can be also explained by the same gating strategy used by the authors. As already reported in our labs, capturing basophils as SSClow/CD123pos cells, results in the inclusion of further non basophilic CD123pos cells.9 These cells can be differentiated as CD45pos cells and/or CD203cneg leukocytes, while basophils are notoriously CD45dim/CD123bright cells.9 The inclusion of more CD123pos events in the gate, while basophils are only Cd123bright cells, underestimates the CD63%, because a possible apparet “cellular loss”, as previously reported, actually caused by a biased gating protocol.10,11

Therefore, the enthusiastic conclusion about the use of BAT in drug hypersensitivity, should be softened by introducing some bias-preventing warnings:

• a)

  basophils should be optimally captured in FC as CD45dim/CD123bright/HLA-DRneg cells, without starting in the FSC/SSC dot plot;

• b)

  the introduction of a CD203c activation marker may be particulaly useful to discern non IgE from IgE-mediated responses.

In the case report described by the authors one cannot exclude the hypothesis that the effect of omeprazole on basophils may be of immune, pharmacological origin, rather than allergic. The interaction with H2 and H4-receptors may block the histamine-mediated loop to deactivate basophils, causing the ongoing release of IL-4 from these leukocytes and the activation of a Th-mediated response, an effect that can increase the production of IgGs, with consequent nephritis onset.12,13

This paper is interesting because permits to focus onto the major effect exerted by a BAT in the clinics.