Production and characterization of monoclonal antibodies against a novel 1alpha,25-dihydroxyvitamin D3-bovine serum albumin conjugate linked through the 11alpha-position

To obtain an antibody which is useful for developing a selective immunoaffinity chromatography (IAC) of 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], which is an effective pretreatment tool for determining this metabolite in biological fluids, a variety of monoclonal antibodies have been produced against a novel haptenic derivative, 11alpha-hemiglutaryloxy-1alpha,25-dihydroxyvitamin D3, linked to bovine serum albumin. BALB/c, A/J and C57BL/6 mice, as well as Wistar and SD rats, were immunized with the hapten-carrier conjugate and the titer of the anti-1,25(OH)2D3 antibody in serum was examined. Spleen cells from A/J mice or SD rats, which showed a high titer, were fused with P3/NS1/1-Ag4-1 myeloma cells. After serial screening by enzyme-linked immunosorbent assay and radioimmunoassay, sixteen kinds of hybridoma clones secreting different anti-1,25(OH)2D3 antibodies were established. Scatchard analysis revealed that 12 antibodies out of 16 have enough affinity to 1,25(OH)2D3 (Ka>10(9) M[-1]). By a cross-reaction study using various related compounds, two antibodies, M114 and M129, both derived from A/J mice, were found to have suitable specificity. Although they showed relatively high cross-reactivities with the 1,25(OH)2D3 derivatives having 24-hydroxylated (both 20%) or lactonized (30%, 8.9%) side chain, all the tested 1alpha-deoxy-type metabolites, some of which interfere with the 1,25(OH)2D3 assays, were successfully discriminated [25(OH)D3: 0.67%, 0.40%; 24,25(OH)2D3: 0.27%, 0.24%; 25(OH)D3 3-sulfate: 0.11%, 0.14%]. These monoclonal antibodies will be applicable for developing not only IAC but also various immunoassay procedures.

Specificity of polyclonal antibodies raised against a novel 24,25-dihydroxyvitamin D3-bovine serum albumin conjugant linked through the C-11alpha or C-3 position

Novel hapten-carrier conjugants were prepared by coupling 11 alpha-hemiglutaryloxy-(24R)-24,25-dihydroxyvitamin D3 or (24R)-24,25-dihydroxyvitamin D3 [24,25(OH)2D3] 3-hemiglutarate with bovine serum albumin (BSA), to obtain an antibody with high specificity and affinity for use in 24,25(OH)2D3 immunoassay. The polyclonal antibodies showing high titre were each elicited in three or four rabbits against these two conjugants; the antibodies obtained from the former and the latter conjugants were expressed as Ab11 and Ab3, respectively. These had a much higher affinity for 24,25(OH)2D3 than that of the vitamin D binding protein (DBP). Specificity of the antibodies was investigated by crossreactivities with 11 related compounds in a radioimmunoassay (RIA) system. The Abll well discriminated the 1 alpha-hydroxylated metabolites such as 1,24,25(OH)3D3 (< or = 0.69%) and 1,25(OH)2D3 (< or = 0.25%), but significantly crossreacted with some side chain modified compounds such as (24S)-24,25-dihydroxyvitamin D3 [24S,25(OH)2D3] (> or = 67%), 25(OH)D3 (> or = 14%) and 25,26(OH)2D3 (> or = 23%). On the other hand, the Ab3 showed only negligible crossreactivities with the compounds having a different side chain structure such as 24S,25(OH)2D3 (< or = 3.0%), 25(OH)D3 (< 0.3%) and 25,26(OH)2D3 (< or = 0.53%). A significant crossreaction was found only with 1,24,25(OH)3D3 (> or = 68%). These results demonstrated that the Ab3 are promising for developing an immunoassay system which is much more specific and sensitive than conventional competitive protein binding assays based on DBP.