Individual differences in lutropin immunoreactivity revealed by monoclonal antibodies

We screened 11 monoclonal anti-lutropin (LH) antibodies for use in two-site immunometric combinations, with time-resolved fluorescence as the detection principle. Seven immunofluorometric assays (IFMA), six detecting only the intact hormone and one detecting both the intact hormone and free beta subunit, were compared with each other and with a conventional radioimmunoassay involving a polyclonal antiserum. Two monoclonal antibodies that exclusively reacted with intact LH showed restricted reactivity with LH in 25% of the samples tested. The LH of one individual was not detected at all by one of the antibodies. The existence of two distinct populations suggests the existence of a genetic variant of LH. A comparison of the results obtained by IFMAS with those by radioimmunoassay showed marked discrepancies in the low range, with IFMAS measuring much lower values. The excellent correlation between the various monoclonal IFMA strongly suggests that the discrepancies seen are caused by the insufficient sensitivity and matrix effects of the radioimmunoassay.