In this consensus document, we attempt to make recommendations that are based on bioanalytical best practices and statistical thinking for development and validation of LBAs.

The time of appearance of relaxin in peripheral blood was determined in conceptive and non-conceptive cycles using a sensitive and specific double-antibody enzyme-linked immunoassay for human relaxin. For study of relaxin in early pregnancy, daily plasma samples were collected from women receiving artificial insemination of donor semen. The day of ovulation was determined by daily LH monitoring and ultrasound observation. In three conceptive cycles, relaxin was significantly elevated over baseline 9-10 days following the LH peak. Relaxin concentrations quickly rose over the next 15 days of observation to over 800 pg/ml. Relaxin was observed to increase 1 to 2 days prior to the first detectable increase in plasma hCG as measured by enzyme-linked immunosorbent assay. To compare the relaxin profile in conceptive cycles with normal luteal phase concentrations, relaxin was also measured in daily plasma samples collected from women contracepting with barrier methods, bilateral tubal ligation, or abstinence. A small but consistent rise in relaxin in the late luteal phase was observed in nine of eleven women, which began 6-9 days after the LH peak, averaged approximately 50 pg/ml, and was declining by the next menses. It is concluded that a small but measurable rise in plasma relaxin is associated with the normal luteal phase and that relaxin secretion is accelerated around the time that hCG is first detected in conceptive cycles. This acceleration of relaxin secretion which is associated with the onset of hCG may provide additional evidence for identification of transient early pregnancy.

To determine if insulin-like growth factor I (IGF-I) inhibits pulsatile growth hormone (GH) secretion in man, recombinant human IGF-I (rhIGF-I) was infused for 6 h at 10 ,ug * kg-' * hduring a euglycemic clamp in 10 normal men who were fasted for 32 h to enhance GH secretion. Saline alone was infused during an otherwise identical second admission as a control. As a result of rhIGF-I infusion, total and free IGF-I concentrations increased three-and fourfold, respectively. Mean GH concentrations fell from 6.3±1.6 to 0.59±0.07 ,g/liter after 120 min.GH secretion rates, calculated by a deconvolution algorithm, decreased with a t1/2 of 16.6 min and remained suppressed thereafter. Suppression of GH secretion rates occurred within 60 min when total and free IGF-I concentrations were 1.6-fold and 2-fold above baseline levels, respectively, and while glucose infusion rates were < 1 ,umol -kg-' * min-'. During saline infusion, GH secretion rates remained elevated. Infusion of rhIGF-I decreased the mass of GH secreted per pulse by 84% (P < 0.01 ) and the number of detectable GH secretory pulses by 32% (P < 0.05). Plasma insulin and glucagon decreased to nearly undetectable levels after 60 min of rhIGF-I. Serum free fatty acids, jl-hydroxybutyrate, and acetoacetate were unaffected during the first 3 h of rhIGF-I but decreased thereafter to 52, 32, and 50% of levels observed during saline. We conclude that fasting-enhanced GH secretion is rapidly suppressed by a low-dose euglycemic infusion of rhIGF-I. This effect of rhIGF-I is likely mediated through IGF-I receptors independently of its insulin-like metabolic actions. (J. Clin. Invest.

CD80 and CD86 (also known as B7-1 and B7-2, respectively) are both ligands for the T cell costimulatory receptors CD28 and CD152. Both CD80 and CD86 mediate T cell costimulation, and as such, have been studied for their role in promoting allograft rejection. In this study we demonstrate that administering monoclonal antibodies specific for these B7 ligands can delay the onset of acute renal allograft rejection in rhesus monkeys. The most durable effect results from simultaneous administration of both anti-B7 antibodies. The mechanism of action does not involve global depletion of T or B cells. Despite in vitro and in vivo evidence demonstrating the effectiveness of the anti-B7 antibodies in suppressing T cell responsiveness to alloantigen, their use does not result in durable tolerance. Prolonged therapy with murine anti-B7 antibodies is limited by the development of neutralizing antibodies, but that problem was avoided when humanized anti-B7 reagents are used. Most animals develop rejection and an alloantibody response although still on antibody therapy and before the development of a neutralizing antibody response. Anti-B7 antibody therapy may have use as an adjunctive agent for clinical allotransplantation, but using the dosing regimens we used, is not a tolerizing therapy in this non-human primate model.

The quantitation of human GH in a serum sample is not consistent among various commercially available immunoassays. We measured serum GH concentrations with four RIAs [Cambridge, Kallestad, National Hormone and Pituitary Program, and Radioassay Systems Laboratories (RSL)] and two immunoradiometric assays (IRMAs; Hybritech and Nichols). Serum GH concentrations measured by the RIAs were between 1.9 and 2.8 times higher than those determined by the Hybritech IRMA, whereas the concentrations measured by the Nichols IRMA were approximately 3.0 times higher than the Hybritech values. We evaluated the effects of differences in standards, assay diluents, and antibody specificity on GH measurement in the various assays. When GH standards from each of the assays were measured in the Hybritech IRMA, only the RSL standard was less immunoreactive than the other assay standards. Different assay diluents also resulted in varying GH values. In the RIAs, GH diluted in serum was more immunoreactive than GH diluted in phosphate-buffered saline-0.5% BSA. This enhanced immunoreactivity appeared to be due to a nonspecific effect generated by serum. The Nichols and Hybritech IRMAs provide standards diluted in horse serum. In the Nichols assay, GH diluted in human serum was more immunoreactive than GH diluted in horse serum, whereas the immunoreactivity of GH diluted in either serum was equal in the Hybritech IRMA. These IRMAs also differ in that the Nichols assay detected the 20K variant of GH, whereas the Hybritech assay did not. Considering these discrepancies, comparison of data obtained using different assays should be made carefully.