Flow cytometric detection of β‑lactam induced T‑cell activation

Abstract According to the World Health Organization, antimicrobial resistance is one of the most serious threats to global health. Adverse reactions towards antibiotics are considered an indirect facilitator of resistance as it available treatment options, which thereby reduce therapeutic efficacy, and β-lactams are the most reported antibiotics to cause drug hypersensitivity events. However, only 1–10% of reported allergic hypersensitivity reactions are genuine, and confirming the diagnosis is challenging. We investigated whether β‑lactam-induced T‑cell activation can be detected by flow cytometry using an in vitro lymphocyte stimulation test in patients with confirmed β‑lactam allergy. Our prospective comparative pilot study included two clinically characterized patient groups recruited at the Regional Centre of Asthma, Allergy, and Hypersensitivity, at Haukeland University Hospital. We examined two methods for analysing T‑cell activation by flow cytometry. Both were normalized to CD69 MFI of unstimulated cells, while one method additionally incorporated CD69‑positive cell frequencies. Cut‑offs based on healthy controls were applied to reduce false positives. Our findings indicate that the method only adjusting for MFI performed more consistently in our cohort, whereas the method incorporating CD69‑positive frequencies, previously used in similar assays, showed less diagnostic value. Overall, a flow‑cytometry-based lymphocyte stimulation test for β‑lactam allergy appears feasible and merits further investigation to determine its clinical utility in diagnostically challenging cases.