TRYPTIC PEPTIDES OF HUMAN THYROGLOBULIN .1. IMMUNOREACTIVITY WITH MURINE MONOCLONAL-ANTIBODIES

Human thyroglobulin (Tg) was treated with trypsin at different concent rations of trypsin/Tg for various incubation times at 37 degrees C usi ng non-reducing conditions. A ratio of trypsin to Tg of 1:100 (w/w) wa s optimal to release small peptides that were reactive to murine MoAbs to human Tg. Most peptides were released after only 1 h incubation wi th trypsin, but these peptides were further degraded at longer incubat ion times. However, a few small peptides, the largest of which with an apparent molecular weight (MW(ap)) of 40 kD, resisted tryptic digesti on up to at least 12 h of incubation. These resistant peptides were fu rther degraded by trypsin at 18-24 h of incubation. Tryptic peptides o f Tg, released at 1 h and 4 h of incubation, were analysed for their i mmunoreactivity to 16 well characterized anti-Tg MoAbs by Western immu noblot. Patterns of peptide recognition of these MoAbs were generally unique. Eight MoAbs reacted with peptides of MW(ap) of 10-25 kD and ab ove. Four other MoAbs reacted with peptides of MW(ap) of 25-43 kD and above, and the remaining four reacted with peptides of MW(ap) > 43 kD. Nine of these MoAbs failed to recognize peptides after reduction, sug gesting that the MoAbs bind conformation-dependent epitopes. The above information will promote the development of models relating the struc ture of Tg to the autoimmune process, and may provide an understanding of those regions of Tg responsible for the induction of autoimmune th yroiditis.