Cultured human myeloid cells (K562) are known to bear Fc receptors that bind with aggregated human IgG (AHG). These cells were used to develop a radiometric assay for detection and quantitation of immune complexes (IC) in human sera. The binding of AHG or in vitro-formed IC between keyhole lympet hemocyanin (KLH) and human anti-KLH to the K562 cells did not require complement. When the K562 radiometric assay was compared to the complement-consumption assay, the K562 radiometric assay could detect IC over a wider range of antibodytantigen ratios. The incidence and mean IC values detected by the K562 radiometric assay in sera from cancer patients and patients with connective tissue diseases (498 ± 445 and 436 ± 209 μg AHG equ/ml, respectively) were significantly higher than in sera from healthy volunteers (107 ± 62 μg AHG equ/ml). The IC level among sera from cancer patients ranged from 1-3200 μg AHG equ/ml. Studies with a limited number of sera from melanoma and sarcoma patients revealed that the mean IC values were significantly higher in patients who had clinically detectable disease than in those with no evidence of disease. Since the K562 cells do not require complement to interact with AHG, the K562 radiometric assay may be potentially useful for detecting IC in pathologic sera which may or may not contain in vivo-bound complement components.
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