Monoclonal Antibodies to Human Thyroglobulin: Evaluation of Immunoreactivity

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Abstract
We have earlier reported production and characterization of monoclonal antibodies (MAbs) to human thyroglobulin (h-tg).In the present study H10 I MAb was evaluated for its immunoreactivity towards different forms of tg and various human thyroid tumours. The specificity of H10 I MAb was validated by the absence of cross reaction with tri-iodothyronine (T3 ) Thyroxine (T4 ) and human gamma globulins. Sodium-dodicyl-sulphate polyacrylamide gel electrophoresed (SDS-PAGE) immunoblot of h-tg on the nitrocellulose membrane revealed multiple immunoreactive bands on reaction with polyclonal antibody (PAb) in comparison with total lack of reactivity with H10 I MAb. The absence of immunoreactivity of H10 I MAb was demonstrated with SDS treated, Dithiothreitol (DT) treated and heat denatured tg using dot immunobinding technique. However, the H10 I MAb was able to react with tg treated with unfolding agents such as urea and guanidine hydrochloride. All the treated forms of tg were equally recognized by PAb. The immunoreactivity of the oxidized/reduced tg towards H10 I MAb was markedly reduced (60.0%) as compared to that obtained with native tg. It appears that H10 I MAb is directed towards conformational epitope involving sulphydryl bonds. Immunohistochemically, a comparable immunoreactivity between PAb and MAb was observed with normal thyroid tissues, follicular thyroid tissues, Hurthle cell carcinoma tissues and poorly differentiated thyroid tumor tissues using immunoperoxidase staining. The sections from papillary carcinoma tissue (thyroid as well as metastatic lymph node) exhibited intense immunoreactivity with PAb. Thyroglobulin present on these sections was not recognized by H10 I MAb. Nonetheless, H10 I MAb was able to detect tg in follicular differentiation wherever present. The absence of immunoreactivity of H10 I MAb in papillary carcinoma strongly suggests that this neoplasm produces tg which is antigenically different from the protein present in the normal tissue. The reactivity of H10 I MAb with metastatic lymph node of an unknown primary origin suggests its usefulness in the identification of prevalent metastasis of differentiated thyroid carcinoma other than papillary type.