Evidence for a preferential iodination site within the thyroglobulin molecule

Mouse 330 kDa thyroglobulin labeled in vivo was analyzed using a tryptic peptide mapping technique and high performance liquid chromatography (HPLC). 30 min after Na125I injection, one peptide spot (spot 7) on a silica gel plate was the only prominent labeled peptide, followed by other labeled peptide spots after 1 h. HPLC showed that spot 7 was rich in monoiodotyrosine. The ratios between the iodoamino acids were strictly maintained from 1 to 6 h after Na125I injection. Spot 7 was again the first spot that appeared from the samples of iodine-deficient mice. These data indicate that there is some preferential iodination site(s) within the thyroglobulin molecule and also that their iodoamino acid composition is predetermined.

Antigen localization in immunoperoxidase-stained plastic-embedded soft tissues

Immunoperoxidase stains were performed on normal and neoplastic tissue from prostate, colon, thyroid, lung, nerve, uterus, and placenta embedded in both plastic (glycolmethacrylate [GMA]) and paraffin. Positive results in plastic section were obtained for carcinoembryonic antigen (CEA), keratin, epithelial membrane antigen (EMA), thyroglobulins, S-100, prostate-specific antigen, human chorionic gonadotrophin (HCG), and beta-HCG. More delicate staining with more precise localization of antigens is noted. Superior (paraformaldehyde) fixation and cold processing followed by GMA polymerization (4 degrees C) allow for optimum antigen survival. After fixation, tissue processing involves a series of 0.1 mol/L phosphate buffer rinses with sucrose and ammonium chloride in a conventional dip-and-dunk processor placed in a 4 degrees C cold room. Acetone dehydrations are used before GMA infiltration, cold polymerization, and sectioning. Before immunoperoxidase staining, the plastic section is digested in .25% bovine trypsin for ten minutes. The immunoperoxidase methods described can be useful when small biopsies are routinely embedded in plastic to obtain improved histologic (hematoxylin-eosin) sections. There may also be research applications in quantifying antigen expression in benign, dysplastic, and neoplastic tissues by examining the stains under high power.

Thyroglobulin immunostaining in follicular thyroid carcinoma: relationship to the degree of differentiation and cell type

A series of 47 primary and seven metastatic thyroid follicular carcinomas, including well, moderately and poorly differentiated, were tested for thyroglobulin (Tg) using immunohistology. In addition, three combined follicular undifferentiated carcinomas, 17 undifferentiated carcinomas and five renal cell carcinomas metastatic to the thyroid were examined. Only two follicular carcinomas did not stain for thyroglobulin. Some inter-tumour differences in Tg staining were found but there was no absolute correlation between this and the degree of tumour differentiation. The two tumours that failed to stain for Tg were poorly differentiated; thyroglobulin positive poorly differentiated tumours demonstrated a clearly weaker staining pattern for Tg. All but one of 15 oxyphilic follicular carcinomas stained positively for Tg but the staining intensity was often weak. Five of six clear cell follicular carcinomas were positive for Tg but the staining reaction was generally faint and there were often large areas devoid of positive cells. Positive staining was demonstrated in the differentiated areas of combined follicular undifferentiated carcinomas. Undifferentiated carcinomas and metastatic renal cell carcinomas gave negative results. Thyroglobulin is a reliable marker for thyroid follicular carcinoma but the patchy staining pattern, particularly in the less well-differentiated tumours may produce less reliable results in small biopsies.

[Characterization of thyroglobulin and thyroid peroxidase activity in patients with functioning thyroid benign tumors]

The content and chemical and immunological properties of thyroglobulin (Tg) and the activity of thyroid peroxidase (TPO) were studied in nodular and extranodular (periphery) thyroid tissue from patients with functioning thyroid tumors (hot nodules). From the present observations, the tumor extracts contained fairly large amounts of Tg, similar to that in the periphery tissue, while the content of Tg was markedly decreased in non-functioning thyroid tumors (cold nodules). The iodine content of Tg was significantly higher in nodular tissue compared with periphery tissue. These observations were in contrast to the results seen in the cold nodules in which hormone synthesis was defective. On the nature of carbohydrate moiety as compared with normal tissue, oligosaccharides of Tg from the periphery tissues changed in a manner similar to that of tumor oligosaccharides. That is, high-mannose type oligosaccharides were markedly decreased whereas multiantennary and unidentified oligosaccharides were increased. These observations were similar to those of non-functioning tumors. The content of sialic acid decreased markedly both in the tumor and periphery tissues. Immunologically, Tg preparations of the tumor and periphery tissue did not show the same affinity to the antibodies, depending on the content of iodine. Therefore, it seems that the contribution of the iodine content and iodo-amino acid has little or no significance in the heterogeneous nature of Tg-immunogenecity. Benign tumors and the periphery tissue were subjected to assay for thyroid peroxidase activity by the method employing guaiacol as the second substrate. The specific activities of the tumors were generally higher than those of periphery tissues, both in functioning and non-functioning benign tumors. In non-functioning carcinoma, on the other hand, TPO activities were lower in tumor portions than in periphery portions. This indicates that non-functioning thyroid carcinomas have a different characteristic.

Colorimetry of dehydroalanine residues preserved as 'lost side chains' in thyroglobulin

We developed a new assay method for dehydroalanine residues in thyroglobulin, which had been proposed to be the 'lost side chains' during thyroid hormonogenesis. Thyroglobulin preparations were labeled with 4-aminothiophenol at 30 degrees C for 10 days. Under the conditions, the reagent reacted only with dehydroalanine and cysteine residues. The 4-aminothiophenol bound to cysteine was eliminated by reductive cleavage. The 4-aminothiophenol-labeled dehydroalanine (4-aminophenylcysteine) residues were liberated by acidic hydrolysis, converted to a colored derivative by the Bratton-Marshall reaction and quantified colorimetrically. The number of dehydroalanine residues was the same as that of hormone residues in each thyroglobulin preparation. The results indicate that when one hormone residue is produced by the coupling of two iodotyrosine residues, the 'lost side chain' is preserved as one dehydroalanine residue in the thyroglobulin molecule.

Sulfation of thyroglobulin: a ubiquitous modification in vertebrates

Mammalian thyroglobulin is released by thyroid follicle cells as a sulfated glycoprotein; the sulfate residues are mostly linked to tyrosine, but they are also attached to the high-mannose carbohydrate side-chains. To decide whether sulfation of thyroglobulin is confined to mammals, representatives of other vertebrate classes were analyzed for the presence of sulfated thyroglobulin: fish (trout), amphibians (clawed toad) and birds (chicken). Mini-organs were prepared from thyroid tissue and suspended in a 35SO4-(-)-containing culture medium. Light- and electron-microscope autoradiographs prepared from the mini-organs showed that thyroid follicle cells from all species examined incorporate 35SO4-(-) and synthesize a sulfated secretory product which accumulates in the follicle lumen. The Golgi complex was detected as the primary intracellular site of sulfate organification. The 35SO4-(-)-radiolabeled secretory product of all species was shown by polyacrylamide-gel-electrophoretic analyses to consist of thyroglobulin, identified by comparison with biosynthetically 125I-labeled thyroglobulin. The results indicate that the sulfation of thyroglobulin is a ubiquitous post-translational modification observed already in the thyroglobulin of lower vertebrates. Our observations suggest that sulfation of thyroglobulin was acquired in the early stages of thyroid evolution.

A comparison of 30-kDa and 10-kDa hormone-containing fragments of bovine thyroglobulin

Studies have been carried out on reduced and alkylated 19 S bovine thyroglobulin to characterize naturally occurring, iodine-rich fragments. In this report, the purification and properties of a 30-kDa, hormone-enriched polypeptide (TgE) are described and compared to that of a previously reported 10-kDa fragment (TgF). The amino acid sequence of TgF was found to overlap with that of TgE. In spite of its larger size, TgE contains only a single hormone bearing site. Both the 10- and 30-kDa fragments are derived from the NH2-terminal end of the bovine thyroglobulin. These fragments contain the principal hormone-forming site at residue 5 of the thyroglobulin sequence and appear to be formed by cleavage of the parent polypeptide chain. The mechanism which generates these cleavages is not clear since the sequences surrounding the cleavage points which give rise to these peptides are quite different. These two fragments may be precursor and product in such a process. The amino acid sequence contained within TgE includes two putative sites for N-linked glycosylation. Since no glucosamine was observed and only small amounts of neutral sugar were detected, it appears that this part of the molecule is not extensively glycosylated.

Seronegative Hashimoto thyroiditis with thyroid autoantibody production localized to the thyroid

A patient without serologic evidence of an autoimmune disorder had a thyroidectomy for neck compression caused by her goiter. Histologic examination of the gland revealed pathologic changes compatible with Hashimoto disease, and lymphocytes isolated from her thyroid gland were transformed into lymphoblastoid cells in vitro by Epstein-Barr virus in the presence of cyclosporine. These cells produced antibodies against thyroglobulin, thyroid microsome, thyrocyte membrane, and thyrotropin, whereas lymphoblastoid cells produced from the patient's peripheral blood lymphocytes showed no antithyroid activity. Several human monoclonal antibodies were produced from the intrathyroidal lymphocytes by fusion with the SHM-D33 heteromyeloma, and the resulting cell lines produced antibodies with high-affinity binding specific for thyroid antigens. These studies show that lymphocytes capable of producing antithyroid antibodies can be present in the thyroid glands of patients with Hashimoto disease without evidence of a peripheral immune response, thus indicating that Hashimoto disease can exist as an organ-restricted autoimmune disorder.

Immunohistochemical hormone content in medullary and undifferentiated thyroid carcinoma and prognosis after surgery

Immunohistochemical determinations in tissue specimens of medullary and "undifferentiated" thyroid carcinomas were carried out with antisera against calcitonin, calcitonin-gene related peptide (CGRP), somatostatin, and also thyroglobulin, using the PAP method. All 8 samples of medullary carcinoma stained positive with antisera against calcitonin and CGRP, 7 samples were also positive for somatostatin. Out of 22 cases initially diagnosed as "undifferentiated thyroid carcinoma" 3 revealed positivity for calcitonin, 2 for CGRP, and 1 for somatostatin. Congo red stain for amyloid, performed several years ago in 2 of these 3 cases, had been negative. The patients with medullary carcinoma survived longer than those with "undifferentiated" carcinoma. One patient of the latter group, but with calcitonin, CGRP, and somatostatin immunoreactivity in the tumour tissue, is now alive and well, more than 4 a after initial treatment.

Thyroid hormonogenesis. Identification of a sequence containing iodophenyl donor site(s) in calf thyroglobulin

The formation of dehydroalanine in thyroglobulin is the result of the side chain elimination of an iodophenyl group during the thyroid hormone formation from two iodotyrosyl residues. This amino acid is easily converted to labeled alanine (upon reduction with [3H] borohydride) or changed to labeled aspartic acid (upon addition of Na14CN and subsequent acid hydrolysis). The cleavage of the protein by CNBr produced many stainable electrophoretic bands, but the autoradiography indicated the presence of a much smaller number of radioactive species. Although three major species raised attention, because they could be all jointly labeled and were present in all preparations, only a species of 15,900 Da was fully studied. It was isolated and its sequence partially determined by Edman degradation. It was established that this species corresponded to the thyroglobulin fragment between methionines 2,432 and 2,578. This peptide contains two hormonogenic sites (positions 2,555 and 2,569) which are either tyrosyl residues or hormone residues arising from them, and five additional tyrosines all potentially involved as donor sites in the hormonogenesis. Upon treatment with N-chlorosuccinimide, the fragment was split into three smaller peptides of about 2,900, 8,500, and 4,600 Da containing 1, 2, and 2 tyrosyl residues, respectively. Only the 8,500-Da subfragment contained [3H]Ala. This finding strongly suggests that at least some of the tyrosines involved as donor sites in thyroid hormonogenesis are within this peptide and possibly map at positions 2,469 and/or 2,522. Moreover, at minimum levels of iodination, when thyroglobulin contains the lowest number of hormone molecules, dehydroalanine is mostly found in the 15,900-Da peptide.

Variability in production and immunoreactivity of in-vitro secreted human thyroglobulin

We examined basal and bTSH-stimulated human thyroglobulin (hTg) secretion by autologous normal and abnormal (benign and malignant) human thyroid cell monolayers. Basal and bTSH-stimulated hTg secretion was highly variable and ranged from 50-700 ng/ml/10(5) cells over a 6 day period. All normal and benign 'non-functioning' adenoma cells demonstrated a dose and time related stimulation of hTg secretion in response to bTSH. Comparison of hTG secretion by autologous normal and abnormal cells showed that in six of eight pairs, the normal thyroid cells had a greater output of hTg than the benign adenoma cells in contrast to our previous studies using non-autologous cells. Malignant thyroid cell hTg production was less predictable than that obtained with normal and benign thyroid cells varying from absent to normal responses to bTSH. Characterization studies of the secreted hTg showed no difference between normal, benign and malignant thyroid cell hTg with reference to molecular weight. However, hTg secreted in vitro was non-iodinated and had a marked reduction (up to 200-fold) in immunoreactivity assessed by both polyclonal and monoclonal antibodies to hTg when compared to hTg standard prepared from intact thyroid tissue (which had 4.58 micrograms iodine/mg). This reduction in hTg immunoreactivity was greatest for hTg secreted by malignant thyroid cells. These data demonstrate the wide variability in the hTg secretory capacity of human thyroid cell monolayers and indicate, when compared to autologous normal cells, that abnormal human thyroid epithelial cells may be relatively deficient in their ability to secrete hTg in vitro. There were also qualitative differences in the immunoreactivity, and iodine content, of in-vitro secreted hTg. These observations suggest that there may be much greater heterogeneity in hTg secreted in vitro than previously realized, perhaps secondary to differences in iodine content and/or degree of glycosylation. Human thyroglobulin (hTg) is the major secretory protein of the thyroid cell (Van Herle et al., 1979). Intracellular hTg is the site of thyroid hormone iodination yet its extrathyroidal role, if any, remains unclear. While hTg is usually present in the peripheral circulation of normal individuals, in species of differing molecular weight (Feldt-Rasmussen et al., 1978), there have been few studies of in-vitro production of hTg by isolated human thyroid cells. Our interest in hTg is in its role as an antigen in thyroid autoimmune disease (De Bernardo et al., 1983; 1986).(ABSTRACT TRUNCATED AT 400 WORDS)

The potential value of the demonstration of thyroglobulin by immunoperoxidase techniques in fine needle aspiration cytology

The peroxidase-antiperoxidase method for the demonstration of thyroglobulin was performed on 30 fine needle aspiration smears. All of the benign thyroid lesions plus the papillary and follicular carcinomas of the thyroid were positive for thyroglobulin. Two cases of metastatic thyroid carcinoma in lymph nodes were also positive. Medullary carcinoma of the thyroid and ten control smears from various other tissues were negative. This proves the sensitivity and the specificity of the method, which may be used in routine cytology and may add to the accuracy of diagnosing metastatic tumors suspected of being of thyroid origin. The intranuclear cytoplasmic vacuoles in papillary carcinoma of the thyroid were negative for thyroglobulin. This unexpected finding is demonstrated, and a possible explanation is offered.

Immunoelectron microscopic demonstration of thyroglobulin and thyroid hormones in rat thyroid gland

We have developed a post-embedding immunogold technique for electron microscopic localization and quantitation of thyroglobulin (TG), thyroxine (T4), and triiodothyronine (T3) in rat thyroid. Labeling for TG was located on rough endoplasmic reticulum, Golgi apparatus, exocytotic vesicles, luminal colloid, colloid droplets, and lysosomes, whereas labeling for thyroid hormones was located on luminal colloid, colloid droplets, and lysosomes. We tested different procedures of fixation, dehydration, embedding, polymerization, and immunoincubation to optimize ultrastructural preservation and immunolabeling. Fixation with glutaraldehyde and osmium was possible with retained antigenicity. Dehydration temperature and the choice of embedding resin were the two crucial factors for good immunolabeling. Low-temperature dehydration greatly improved immunolabeling and could be combined with embedding in the methacrylate LR White or the epoxide Agar 100 (equivalent of Epon 812) polymerized at 40-60 degrees C, as the temperature during subsequent embedding and polymerization was of little importance for the immunoreactivity. Labeling on LR White sections was always higher than on Agar 100 sections. Various etching procedures were tested without improved specific labeling. Etching with hydrochloric acid gave nonspecific labeling of certain cell compartments.

Resistance to experimental autoimmune thyroiditis induced by physiologic manipulation of thyroglobulin level

The role of circulatory mouse thyroglobulin (MTg) level in activating mechanisms suppressive to induction of experimental autoimmune thyroiditis (EAT) was studied by two regimens to strengthen normal maintenance of self-tolerance in genetically susceptible mice. One was to administer graded doses of exogenous MTg either 7 days apart or daily for 10 days and then challenge the animals with MTg + LPS. The other was to infuse TSH via an osmotic pump for 7 days. The steady TSH infusion for 7 days resulted in an increase in MTg level peaking on Day 3. Such kinetics of MTg concentration in response to TSH coincided with enhanced resistance to EAT induction. After an initial rapid clearance rate of t1/2 of 3 hr, tolerogenic doses of exogenous MTg sustained similar levels for 2-3 days. In contrast, subtolerogenic doses declined to baseline levels in 2 days or less. Clearance can be best explained by a two-compartment model for distribution with an initial alpha phase (t1/2 about 3 hr), followed by a beta phase (t1/2 about 10 hr). We conclude that, for the prevention of EAT induction in the presence of potent adjuvants (CFA or LPS), a threshold, but above baseline, level of either exogenous or endogenous MTg, represented by the beta phase, is required for a critical period (greater than 2-3 days) to activate suppressor mechanisms over and above homeostatic regulation. Whether MTg concentration raised by TSH (TRH) administration activates suppressor T cells as observed after the injection of a tolerogenic dose of MTg remains to be determined.

Immunohistochemical demonstration of keratins in the cysts of thyroid glands, parathyroid glands, and C-cell complexes of the dog

Cyst structures were often detected in and around thyroid glands of the dog. The present study revealed the frequency of occurrence, the light microscopic features, and the immunoperoxidase reactions to anti-keratin and anti-19S-thyroglobulin antisera of each cyst located in parathyroid III, parathyroid IV, thymus IV, C-cell complexes, and thyroid parenchyma from 112 dogs. In each location, cysts showed characteristic features. In parathyroid III, the cysts were covered with single or pseudostratified epithelium composed of ciliated cells; whereas in parathyroid IV they were covered with keratinizing stratified squamous epithelium. In C-cell complexes, small cysts lined with small packed cells were predominant, and large cysts lined with single cuboidal cells or stratified squamous cells were also present. In thymus IV located in the close vicinity of parathyroid IV, cyst epithelium consisted of several types of cells showing variable features. In thyroid parenchyma, there were several types of cysts: some were covered with ciliated columnar cells, and others were covered with two or multilayers of small packed cells or cuboidal cells. In spite of these differences in appearance of the cysts located in different tissues, all their epithelia were immunoreactive to the keratin antisera, except for small cysts in C-cell complexes, which were regarded as immature structures. Thus, the presence of keratin filaments in epithelial cells seems to be a characteristic feature of all cysts. The lumens of each cyst contained variable amounts of amorphous materials, which showed colloid-like, flocculent, foamy, and granular features and were periodic acid-Schiff-positive in variable degrees, from weak to intense. Although the lumenal contents of the cysts in parathyroid III revealed no immunoreactivity for 19S-thyroglobulin, those in thyroid parenchyma, C-cell complexes, parathyroid IV, and thymus IV reacted strongly with the 19S-thyroglobulin antiserum.

Medullary thyroid carcinoma with thyroglobulin immunoreactivity. A special entity?

Fourteen medullary carcinomas of the thyroid (MCT) immunoreactive for both thyroglobulin and calcitonin were studied by light microscopy and immunohistochemistry. Thyroglobulin immunoreactivity was seen in neoplastic follicles and/or in solid foci in the lymph node metastases of two cases. Colocalization of thyroglobulin and calcitonin was found in the same neoplastic cells of eight cases using a double immunostaining method; in three of these (including one with metastases), thyroglobulin was found to be colocalized with calcitonin gene related peptide as well. Our histological and immunohistochemical results support the assumption that MCT with thyroglobulin immunoreactivity is an unusual variant of the multihormone producing MCT and strengthen the hypothesis that a common stem cell is the origin of these tumors. The available clinical data suggest that thyroglobulin-positive MCT carry a better prognosis than thyroglobulin-negative MCT.

Extrathyroidal synthesis and biologic action of thyroid receptor antibody (TRAb) in Graves' disease

In a patient with Graves' disease who underwent thyroidectomy with subsequent radioiodine therapy thyroid receptor antibody could be detected by radioligand assay. No thyroid tissue could be detected by 131I-scintiscanning. Thyroglobulin was repeatedly negative. Biologic activity of this patients serum could be demonstrated in the nude mice bio assay. 131I-incorporation and secretion of human thyroglobulin could be stimulated by injecting thymusdysplastic nude mice with transplants of thyroid tissue from a patient with Graves' disease with the athyroid patients serum. These results demonstrate evidence for extrathyroidal production and biological activity of TRAb in vivo.

Characterization of phosphate residues on thyroglobulin

Follicular 19 S thyroglobulin (molecular weight 660,000) from rat, human, and bovine thyroid tissues contains approximately 10-12 mol of phosphate/mol of protein. These phosphate residues can be radiolabeled when rat thyroid hemilobes, FRTL-5 rat thyroid cells, or bovine thyroid slices are incubated in vitro with [32P]phosphate. Thus labeled, the [32P]phosphate residues comigrate with unlabeled 19 S follicular thyroglobulin on sucrose gradients and gel filtration columns; are specifically immunoprecipitated by an antibody preparation to rat or bovine thyroglobulin as appropriate; and co-migrate with authentic 19 S thyroglobulin when subjected to analytic or preparative gel electrophoresis. Tunicamycin prevents approximately 50% of the phosphate from being incorporated into FRTL-5 cell thyroglobulin. Approximately one-half of the phosphate in FRTL-5 cell or bovine thyroglobulin can also be released by enzymatic deglycosylation and can be located in Pronase-digested peptides which contain mannose, are endo-beta-N-acetylglucosaminidase H but not neuraminidase-sensitive, and release a dually labeled oligosaccharide containing mannose and phosphate after endo-beta-N-acetylglucosaminidase H digestion. The remainder of the phosphate is in alkali-sensitive phosphoserine residues (3-4/mol of protein) and phosphotyrosine residues (approximately 2/mol of protein). This is evidenced by electrophoresis of acid hydrolysates of 32P-labeled thyroglobulin and by reactivity with antibodies directed against phosphotyrosine residues. The phosphoserine and phosphotyrosine residues do not appear to be randomly located through the thyroglobulin molecule since approximately 75-85% of the phosphotyrosine and phosphoserine residues were recovered in a approximately 15-kDa tryptic peptide or a approximately 24-kDa cyanogen bromide peptide, each almost devoid of carbohydrate. 31P nuclear magnetic resonance studies of bovine thyroglobulin confirm the presence and heterogeneity of the phosphate residues on thyroglobulin preparations.

Follicle structure-dependency of thyroglobulin and thyroxin staining in the thyroid glands of Graves' disease

H.E. morphology of the thyroid glands from 170 patients with Graves' disease was studied, and the thyroid follicles were classified into two main groups: (1) F pattern, in which the follicles show circle/ellipse on cut sections; (2) P pattern, in which the follicular epithelium protrudes into the lumen or a follicle, is accompanied by proliferation of tubular or microfollicular structures. Studies on three serial sections of 88 thyroid glands stained with hematoxylin and eosin, thyroglobulin (TG), and thyroxin (T4), respectively, revealed the followings: (i) TG/T4 staining is dependent on the follicle structure (i.e., F or P); while the epithelium and colloid including scalloped vesicles in F follicles generally exhibited a direct relationship between TG and T4 staining, those in P follicles often showed an intense TG, but negative T4 staining. (ii) The results of morphological and immunohistochemical studies of P follicles among the cases are consistent with the view that P follicles are in the process of proliferation of immature daughter follicles from a main follicle and of their maturation. (iii) P follicles of Graves' thyroid glands were evaluated as possible non-neoplastic counterparts of well-differentiated follicular and papillary tumors.

Direct evidence for a primary immune response of murine B-lymphocytes after in vitro immunization of dissociated splenocytes

Monoclonal antibodies against human thyroglobulin were generated using splenocytes cultured in vitro with the antigen. When splenocytes from non-immunized mice were used, about 90% of the hybridomas obtained produced immunoglobulins of the IgM class. In contrast, when splenocytes from mice previously immunized in vivo with human thyroglobulin were cultured in vitro with the antigen about 85% of the hybridomas obtained produced immunoglobulins of the IgG class. The properties of the monoclonal antibody produced by hybridoma 3D12, obtained after culturing splenocytes from non-immunized mice with human thyroglobulin, were examined in detail. Monoclonal antibody 3D12 reacted only with human thyroglobulin and not with the murine homologue in an enzyme-linked immunosorbent assay, in immunoblotting experiments and in an immunohistochemical test. These results provide direct evidence that a primary response to an antigen can be elicited by adding the antigen to cultures of splenocytes from non-immunized mice.