ELISAs for free light chains of human immunoglobulins using monoclonal antibodies: comparison of their specificity with available polyclonal antibodies

For the measurement of human immunoglobulin free light chains (LCs) in clinical samples, highly specific assays for free LCs are required to discriminate them from LC portions of intact immunoglobulins (bound LCs). To develop specific enzyme-linked immunosorbent assays (ELISAs) for free LCs, two anti-free LC kappa and lambda monoclonal antibodies (MAbs) were raised by a mouse/mouse hybridoma technique. We compared the specificities of these two MAbs with those of six commercially available anti-free LC antisera, which are widely used in free LC immunoassays. Comparative titrations against free LCs and intact IgGs showed the MAbs had less cross-reactivity to intact IgGs, while the four of six antisera had high reactivity to intact IgGs. Using these MAbs, we developed LC kappa and LC lambda ELISAs with ranges from 7.8 to 500 micro g/l of free LCs and less cross-reactivity to intact IgGs (less than 0.12%). On the other hand, ELISAs with anti-free LC antisera showed low specificity and/or sensitivity. Thus, the use of these MAbs may provide reliable methods for specific measurements of free LCs in clinical samples.