Background/Purpose: Cell-bound complement activation products (CB-CAPs) have been validated as biomarkers for systemic lupus erythematosus (SLE) diagnosis, monitoring and stratification, and for identification of patients with pre-lupus. However, CB-CAP assays currently require live cells, are time and temperature sensitive, and must be performed by a dedicated technician with a flow cytometer. We have developed a CB-CAP assay that eliminates the need for live cells and a flow cytometer and can yield results in minutes.

Methods: Four different methods have been developed to measure CB-CAPs without the need for a flow cytometer. One method, described here, utilizes a CB-CAPillary^TM Test Kit (patent pending), analogous to a urine dipstick, to rapidly measure levels of CB-CAPs in body fluids. Erythrocyte C4d (EC4d) levels determined by a traditional flow-cytometric assay were compared with those determined using the novel CB-CAPillary^TM assay device. Assays were performed using fresh erythrocytes, freeze-thawed erythrocytes, and erythrocyte lysates. Blood samples were obtained from patients with SLE and from non-lupus subjects. Correlations between results obtained by flow cytometry and those generated by the CB-CAPillary^TM assay device were analyzed by Pearson correlation.

Results: EC4d levels determined by FACS ranged from 2.93-70.42. The correlation between EC4d in erythrocyte lysates determined using a FACs cytometer and EC4d determined using a CB-CAPillary^TM test kit was R²=0.89. The correlation between EC4d in erythrocyte freeze-thawed samples determined using a FACs cytometer and EC4d determined using a CB-CAPillary^TM test kit was R²=0.99. TC4d/BC4d were also successfully detected in buffy coat lysates.

Conclusion: This proof-of-concept study demonstrates that CB-CAP assays can be performed within minutes, and without the need for flow cytometry, live cells, or a dedicated technician. The CB-CAPillary^TM test kit enables a rapid and inexpensive method for determining cell-bound complement activation levels for lupus diagnosis, monitoring and stratification and for identification of patients with pre-lupus. As a point-of-care test kit, it could be available to patients and physicians globally. CB-CAPillary^TM test kits for measurement of BC4d, TC4d, PC4d and RC4d are also being developed with the methods described here.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-cb-capillarytm-test-kit-a-tool-for-point-of-care-assays-to-measure-cell-bound-complement-activation-products/