Thyroid-stimulating antibodies (TSAb) were found to inhibit the binding of labelled thyrotrophin (TSH) to thyroid membranes in a dose-dependent manner and this effect was localized in the Fab part of the TSAb molecule. Analysis of the binding data suggested that TSAb and TSH bound to the same receptor site. Production of cyclic AMP by the thyroid membranes was stimulated by TSAb and TSAb-Fab with a similar time course to that observed with TSH. Kinetic studies indicated that the binding of TSAb to the thyroid membranes was not rate-limiting in the process of stimulation of cyclic AMP production.
Triiodothyronine (T3) suppression and thyrotropin-releasing hormone (TRH) tests were used to study thyroid function in 50 patients with thyroid disease. The results of the thyroid function tests were compared with the levels of serum thyroid-stimulating immunoglobulins (TSI) measured by a radio-receptor assay. In euthyroid and hyperthyroid patients, the presence of TSI corresponded with the absence of TSH control of thyroid function. However, in two hypothyroid patients with serum TSI levels readily detectable in the receptor assay, T3 suppression and TRH tests indicated that thyroid function was under TSH control.
The abilities of antigen-presenting cells (APC) from nine independent major histocompatibility complex haplotypes and a number of intra-H-2 recombinant congenic strains of mice to present staphylococcal enterotoxin B (SEB) and induce proliferation in murine T-cell receptor Vi8' T-cell clones were compared. SEB presented by APC of all haplotypes tested induced significant responses in each of the T-cell clones. The magnitude of response was similar for most haplotypes, but there were limited quantitative differences between certain haplotypes. SEB presented by APC from H-2b mice as well as the intra-H-2 recombinant strains B1O.GD and B1O.A(4R), which do not express cell surface I-E (designated I-E-), induced the poorest T-cell responses. However, APC from AE-, A5E-, and AqE-mice were as potent in SEB presentation as APC expressing both I-A and I-E. Antibodies against I-E were more effective than anti-I-A antibodies at inhibiting responses to SEB presented by APC expressing both I-A and I-E, whereas responses induced by APC expressing I-A but not I-E were blocked by antibodies against I-A. Thus, our results show that I-A can present SEB efficiently but that expression of both I-A and I-E on the same APC results in presentation of SEB predominantly by I-E. In addition, experiments using four distinct I-E-strains of mice indicate that I-A alleles differ in their ability to present SEB.
The ability of splenic antigen-presenting cells (APC) from nine independent mouse major histocompatibility complex (MHC) haplotypes to present recombinant streptococcal exotoxin A (rSPEA) to heterogeneous T cells and mouse T cell clones were compared using proliferation assays. We report that there is marked variation between MHC haplotypes, which can be ranked as follows: H2z > H2s = H2f = H2p = H2r = H2k > H2d > H2b = H2q. In some haplotypes both A and E molecules bind rSPEA with low affinity. In addition, we show that presentation is preferentially by E molecules in haplotypes where A and E are coexpressed, but that A alleles also bind and present rSPEA, based on inhibition of responses by anti-E and anti-A mAbs. Furthermore, using strains of mice which fail to express E, we demonstrate that A(s) and Af present rSPEA with high efficiency, whereas Aq and Ab are the least efficient of all haplotypes. The results suggest that there is significant variation in the ability of different alleles of both E and A molecules to bind and present rSPEA.
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