The effects on rabbits of immunization with bovine thyroid-stimulating hormone and its subunits

Rabbits were immunized with bovine thyroid-stimulating hormone (bTSH), bovine Inteinizing hormone (bLH), and their subunits. In two immunization experiments, thyroid-stimulating activity was found in the serum of 6 out of 12 rabbits immunized with bTSHbeta subunits. The thyroid-stimulating activity in the anti-bTSHbeta sera was greater at 2 h than at 8, was eluted with the globulin fraction from Sephadex G-100, was completely neutralized by both anti-bTSH and anti-rabbit gamma globulin, and was completely suppressed by administration of triiodothyronine (T(3)) to the immunized rabbit. These findings led to the conclusion that the thyroid-stimulating activity resided in soluble complexes of rabbit TSH bound to anti-bTSHbeta. Two of nine rabbits immunized with bTSH developed thyroid-stimulating activity in their serum, but it was nonsuppressible by T(3). None of the animals immunized with bTSHalpha, bLH, bLHbeta, or bLHalpha developed serum thyroid-stimulating activity.Hypopituitary hypothyroidism, evidenced by decreased serum thyroxine (T(4)) and thyroidal (131)I uptake and by the histologic appearance of large follicles with flat cells, was found in the bTSHbeta- and bTSH-immunized animals, despite the presence of thyroid-stimulating activity in the serum of many. The reasons for this paradox are unclear; possibly the complexes block the effect of TSH on the rabbit thyroid.

Neutralizing and non-neutralizing antibodies to bovine thyroid-stimulating hormone and its subunits

To test the possibility that the long-acting thyroid stimulator (LATS) might represent an immune complex either of thyroid-stimulating hormone (TSH) with anti-TSH or of a subunit of TSH with an appropriate antibody, we immunized rabbits with bovine TSH (bTSH), bLH (luteinizing hormone), and their alpha and beta subunits (bTSHalpha and bTSHbeta). Binding, neutralizing, and nonneutralizing antibodies were demonstrated in the antisera obtained. First, antisera to TSH, TSHbeta, and TSHalpha all bound [(125)I]TSH and [(125)I]TSHbeta. Anti-bTSHbeta antisera bound [(125)I]bTSHbeta better than did anti-TSH sera, while the binding of [(125)I]bTSH was similar with both types of antiserum. Second, the thyroid-stimulating activity (McKenzie bioassay) of TSH could be neutralized by incubation with various dilutions of anti-TSH or anti-TSHbeta. Finally, when incubation mixtures containing TSH and dilutions of anti-TSHbeta antisera that only partially neutralized TSH were treated with an antiserum against rabbit immunoglobulins to precipitate immune complexes, the bioassay response of the TSH was abolished. This phenomenon was not observed when antiserum to the intact hormone was substituted in the incubation mixture. The removal of TSH biological activity from a mixture of TSH and anti-bTSHbeta by addition of an anti-immunoglobulin indicated that biologically active immune complexes were formed between TSH and anti-TSHbeta but not between TSH and anti-TSH. The time-course of the bioactivity and several other characteristics of these complexes differentiate them from LATS.

Preparation and properties of subunits of human luteinizing hormone

Separation of the subunits of human pituitary luteinizing hormone (LH) has been accomplished by dissociation of the hormone with 8 m-urea followed by chromatography on CM-cellulose at pH 5·0 or by counter-current distribution. Each procedure resulted in isolation of one subunit, the other subunit being contaminated with reassociated LH. The isolated subunits (α and β) are each of low biological activity, but when recombined in a 1:1 ratio at pH 7, reassociation occurs with restoration of full activity. The amino acid compositions of the two subunits are significantly different from each other, but the composition of the α subunit is very similar to published data on the corresponding subunit of human chorionic gonadotrophin (HCG) and human thyroid-stimulating hormone. Significant differences were observed when comparing the compositions of the β subunits of the hormones. By immunoradiometric assay using antibodies to HCG, the α subunit was as active as native LH on a weight basis, but the β subunit was significantly lower in immunological activity.