Human Immunoglobulin ELISA Kit

The screening for IgG subclass donor-specific antibodies (DSAs) in allograft recipients uses IgG1-4 subclass-specific monoclonal antibodies (mAbs) that should be mono-specific. The cross-reactivity discrepancies reported for IgG subclass-specific mAbs warranted a critical cross-reactivity pattern analysis of the IgG subclass-specific mAbs most commonly used to detect DSAs. We tested the reactivity of 2 anti-IgG1-, 3 anti-IgG2-, 1 anti-IgG3-, and 2 anti-IgG4-specific PE-conjugated mAbs against microbeads coated with IgG1-4 proteins separately. Each IgG subclass protein was coated at three densities on the beads (0.5, 1, and 2 pg of protein per 10(6) beads), and the PE-conjugated mAbs were titrated from 0.04 mu g/mL to 5 mu g/mL. The IgG subclass reactivity of the sample was acquired on the Luminex multiplex platform. Among the IgG subclass-specific mAbs, only the anti-IgG3 (clone: HP6050) mAb was mono-specific. All other mAbs tested were binding to IgG subclass proteins other than their respective immunogen, thereby being cross-reactive. IgG subclass cross-reactivity patterns were dependent on the concentration of both IgG subclass-specific mAbs and IgG1-4 protein targets coated onto the beads. With the current IgG subclass mAbs available, 3 of the 15 possible combinations of IgG1-4 subclass protein could be identified. While the remaining 12 unique combinations cannot be distinguished clearly, 6 groups that corresponded to two different unique combinations of IgG1-4 subclass protein could be identified. The dilution of serum samples and IgG subclass-specific mAbs, other than the anti-IgG3 (clone: HP6050), must be further optimized before their implementation in IgG subclass DSA screening in allograft recipients.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been redetected after discharge in some coronavirus disease 2019 (COVID-19) patients. The reason for the recurrent positivity of the test and the potential public health concern due to this occurrence are still unknown. Here, we analyzed the viral data and clinical manifestations of 289 domestic Chinese COVID-19 patients and found that 21 individuals (7.3%) were readmitted for hospitalization after detection of SARS-CoV-2 after discharge. First, we experimentally confirmed that the virus was involved in the initial infection and was not a secondary infection. In positive retests, the virus was usually found in anal samples (15 of 21, 71.4%). Through analysis of the intracellular viral subgenomic messenger RNA (sgmRNA), we verified that positive retest patients had active viral replication in their gastrointestinal tracts (3 of 16 patients, 18.7%) but not in their respiratory tracts. Then, we found that viral persistence was not associated with high viral titers, delayed viral clearance, old age, or more severe clinical symptoms during the first hospitalization. In contrast, viral rebound was associated with significantly lower levels of and slower generation of viral receptor-binding domain (RBD)-specific IgA and IgG antibodies. Our study demonstrated that the positive retest patients failed to create a robust protective humoral immune response, which might result in SARS-CoV-2 persistence in the gastrointestinal tract and possibly in active viral shedding. Further exploration of the mechanism underlying the rebound in SARS-CoV-2 in this population will be crucial for preventing virus spread and developing effective vaccines.