To evaluate the development of coronavirus disease 2019 (COVID-19), the roles of interleukin 6 (IL-6) and procalcitonin (PCT) were assessed to diagnose severe COVID-19. Between January and February 2020, 100 consecutive patients with confirmed COVID-19 were included and divided into common (n = 56), severe (n = 28), and critical (n = 16) groups. IL-6 and PCT levels were assayed and compared among groups. IL-6 levels were significantly different among groups (common, 23.93±9.64 pg/mL; severe, 69.22 ± 22.98 pg/mL; critical, 160.34 ± 26.15 pg/mL; P < .05), and there was also a significant difference in the levels of PCT among groups (common, 0.23 ± 0.13 ng/mL; severe, 0.38 ± 0.16 ng/mL; critical, 0.73 ± 0.36 ng/mL; P < .05). Further analysis showed that patients in the critical group had the highest levels of IL-6 and PCT, and those in the common group had the lowest levels (all P < .05). IL-6 and PCT are associated with the severity of COVID-19, and thus have potential value in the diagnosis of COVID-19.

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Background Interleukin‐6 (IL‐6) is an inflammatory factor that increases rapidly in response to infectious diseases including sepsis. The aim of this study is to develop a quantum dot (QD)‐based fluorescence lateral flow immunoassay (LFIA) strip that can rapidly and accurately detect IL‐6 levels. Methods QD‐based LFIA strips were fabricated by conjugating CdSe/ZnS QDs to the IL‐6 antibody. Performance verification and clinical sample analysis were carried out to evaluate the newly developed strip. Results QD‐based LFIA strips were successfully fabricated. The test strip's linear range was 10–4000 pg/ml, with a linear correlation coefficient of R2 ≥ .959. The sensitivity of the test strip was 1.995 pg/ml. The recovery rate was 95.72%–102.63%, indicating satisfying accuracy. The coefficient of variation (CV) of the intra‐assay was 2.148%–3.903%, while the inter‐assay was 2.412%–5.293%, verifying the strip's high precision. The cross‐reaction rates with various interleukins (IL‐1α, IL‐1β, IL‐2, IL‐4, and IL‐8) and interferon‐γ (IFN‐γ) were all <0.1%. When the strip was placed in a 50°C oven for 1, 2, 3, and 4 weeks, the test results were not significantly altered compared to storage at room temperature. Furthermore, 200 clinical serum samples were analyzed to compare the strip with the Beckman chemiluminescence immunoassay (CLIA) kit, which revealed a high correlation (n = 200, R2 = .9971) for the detection of IL‐6. Conclusions The QD‐based test strip can rapidly and quantitatively detect IL‐6 levels, thus meeting the requirement of point‐of‐care test (POCT) and showing excellent clinical prospects.

We have established a highly efficient 96-well format based strategy to characterize nanobody (Nb) from an expressed alpaca Nb repertoire by combining heavy-chain antibody variable region gene cloning with Nb expression and reactivity profiling at the single cell level. Individual alpaca B lymphocytes were isolated based on B cell surface marker and membrane type antigen specific antibodies expression by fluorescence activated cell sorting (FACS). Single cell reverse transcription and polymerase chain reaction (PCR) amplification of CH1 and CH2 domain enable the identification and exclusion of B cell clones that express regular antibodies. The corresponding heavy-chain antibody variable region gene transcripts, which are CH1-CH2 domain negative, are then amplified from single B cell clones by nested PCR. Then Nbs were expressed in Escherichia coli cells and four Nbs showed high affinity against Pseudomonas aeruginosa Exotoxin A (PEA). Moreover, two PEA Nbs that recognize unique epitopes on PEA have been successfully applied to protect human cells from PEA induced apoptosis. In summary, our FACS and single cell reverse transcription polymerase chain reaction (RT-PCR) based strategy for identifying recombinant Nbs from single alpaca B cells allows highly efficient and unbiased characterization of the expressed Nb repertoires by sequence analysis, expression and parallel antibody reactivity testing.

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