Production of thyroid stimulation blocking antibody without TSH receptor binding activity in rabbits with...

When rabbits were immunized with porcine thyroid plasma membrane, some cases of produced antibodies showed the blocking activity for TSH stimulated cAMP production in cultured porcine thyroid cells in spite of negative TSH binding inhibitory immunoglobulin (TBII) activity. The inhibitory effect of these thyroid stimulation blocking antibodies (TSBAbs) on cAMP increase by forskolin and GTP gamma S in porcine thyroid cells was observed in 1 and 3 rabbits, respectively. When the blocking activity of these antibodies for stimulated cAMP production by forskolin, GTP gamma S and NaF was examined in the isolated porcine thyroid membrane, no blocking activity for these 3 stimulators except in 1 case was found. The blocking activity of these antibodies could be absorbed significantly by incubation with porcine thyroid plasma membrane as antigen. The blocking activity was not observed in rabbits immunized with porcine thyroglobulin. The present experiment demonstrated that the produced antibody in rabbits against porcine thyroid membrane had the blocking activity for TSH stimulation to thyroid cells without affecting TSH binding to its receptor. These facts suggest that this type of blocking antibody may be produced against any antigen of thyroid membrane origin except the TSH receptor.