Loss of anti-AT1R reactivity in ELISA post-adsorption - False reactivity or interference in the assay?

Autoantibodies to Angiotensin II type 1 receptor (AT1R) are associated with detrimental outcomes in organ transplants. However, reports showed that adsorption with latex beads reduced positive anti-AT1R antibodies, suggesting possible false reactivity. To investigate this conundrum, we studied 11 samples positive for AT1R antibodies with an ELISA kit before and after adsorption. Adsorption significantly reduced the measurable level of AT1R antibodies (28.3 ± 9.8 vs. 6.3 ± 3.0 U/ml, p < 0.001). AT1R antibodies were lower when post-adsorption serum was added back at 1:1 ratio to the neat serum compared to the diluent control (8.6 ± 4.2 vs. 18.1 ± 10.3 U/ml, p = 0.02). Sham adsorption with the buffer from Adsorb Out™ kit without beads also suppressed the detection of anti-AT1R antibodies (32.7 ± 9.1 vs. 8.1 ± 3.9 U/ml, p < 0.001). Thus, rather than actively removing nonspecific antibodies by the beads, the adsorption process introduces soluble factors that interfere with the detection of anti-AT1R antibodies with the ELISA kit.