Effects of Phyto-Oestrogens on Veal Calf Prostate Histology

In veal calf production plant-based proteins are frequently included in milk replacer fed to the animals. Since soy products, which are mostly used, are known for their high levels of phyto-oestrogens, the effects of these feeds on the veal calf prostate were examined. Goal was to determine whether these compounds could interfere with histological screening for oestrogenic growth promoters. In a feeding experiment, four groups of veal calves fed plant-based protein-supplemented milk replacer (PBM), containing 5% soy concentrate, 5% soy isolate, 5% wheat gluten and 2% potato protein, for 4 weeks were compared to animals fed dairy-based control feed (DBM); animals treated with estradiol benzoate, diethylstilbestrol and ethinylestradiol served as positive controls. Daidzein and genistein levels measured in feed and urine showed high levels of genistein and daidzein in the soy isolate and soy concentrate supplemented feeds. Genistein and daidzein were also found in the urine of the animals that were fed these feeds. Haematoxylin–eosin-stained prostate sections of PBM-fed animals showed slight hyperplasia and some dilated tubules as compared to the DBM-fed group, but no metaplasia, which is used for screening for oestrogenic hormones. The positive controls showed extensive squamous metaplasia. Immunohistochemical staining for cytokeratin 5 (using RCK 103 monoclonal antibody) in basal cells showed a normal staining pattern of basal cells in the DBM-fed calves and extensive basal cell proliferation and squamous metaplasia in the oestrogen-treated positive control animals. PBM-fed calves showed no increase of basal cell staining but showed elongations of the basal cells in most animals, sometimes resulting in circular figures. It is concluded that the feeds examined in this study did not interfere with histological screening for oestrogens in male veal calves.     

Localization of Transforming Growth Factor Beta3 in Squamous Metaplasia of the Porcine Oviduct: a Case Report

Squamous metaplasia of the oviduct epithelium is a rare disorder of reproductive organs. We noted squamous metaplasia of the oviduct epithelium in a sow routinely slaughtered at day 2 of the oestrous cycle. Expression of transforming growth factor beta3 (TGF beta3) in the metaplastic epithelia was evaluated by immunohistochemistry, because TGF beta3 appears to play a key role as regulator of a variety of tissue remodelling events. Our results show that TGF beta3 immunostaining was specifically localized to foci of squamous metaplasia of the epithelial linings. Non‐metaplastic epithelial cells of the oviduct were not immunostained with anti‐TGF beta3 antibody. At the subcellular level, TGF beta3‐labelled cells occasionally showed signs of apoptotic cell death. It is concluded that signals produced by TGF beta3 in metaplastic lesions of the oviduct are potentially involved in pathophysiological processes.     

Intraepidermal adenocarcinoma in the perianal skin of two cats, a condition resembling human extramammary Paget's disease

In humans, mammary and extramammary Paget's disease is an uncommon to rare manifestation of intraepidermal adenocarcinoma arising from simple epithelium, usually glandular in origin. This report describes two cats with lesions in perianal skin consisting of atypical intraepidermal neoplastic cells. Differential diagnoses included intraepidermal adenocarcinoma, in situ squamous or basal cell carcinoma, junctional amelanotic melanoma, and epitheliotropic tumours of histiocytic or lymphocytic origin. The atypical intraepidermal cells in the cats were immunohistochemically positive for cytokeratin 8/18 (CK8/18), which stains simple (glandular) epithelium. The keratinocytes and basal cells were negative for CK8/18. In addition, the atypical intraepidermal cells were immunohistochemically negative for melanocytic, lymphocytic, and histiocytic markers. The staining results confirmed the atypical intraepidermal cells to be of simple glandular origin, and ruled out other causes of intraepidermal malignancy. In one cat the clinical lesions consisted of a pruritic erythematous eruption surrounding the anus. Another cat presented clinically for an area of irregular anal thickening; this cat had well-regulated diabetes mellitus. The cats were otherwise clinically healthy. The clinical features, histological appearance, and immunohistochemical staining of the skin lesions were consistent with those described for human perianal extramammary Paget's disease. To the authors' knowledge, this is the first report of an intraepidermal adenocarcinoma in a cat or other animal species.     

DNA measurement and immunohistochemical characterization of epithelial and mesenchymal cells in canine mixed mammary tumours: putative evidence for a common histogenesis.

DNA measurement by image cytometry, and a detailed immunohistochemical study using monoclonal antibodies directed against different human cytokeratin types, muscle-specific actin, vimentin and S100 protein were carried out on normal canine mammary tissue (n =4), benign canine mammary mixed tumours (n =20) and malignant canine mammary mixed tumours (n =13). The results showed that ductal and alveolar luminal cells in normal and neoplastic tissue were immunoreactive with CAM5.2 and AE1/AE3 antibodies recognizing human keratins.Basal/myoepithelial cells were clearly differentiated from ductal and alveolar epithelial cells, since the latter only expressed cytokeratins, whereas the former also expressed vimentin and muscle-specific actin. This immunohistochemical study showed that there is loss of expression of muscle-specific actin and cytokeratins in areas of myoepithelial proliferation, and enhanced expression of vimentin and S100 protein in proliferative areas with osseous and/or chondroid metaplasia. The ploidy studies revealed that 20% (4/20) of benign and 54% (7/13) of malignant mixed tumours of canine mammary gland were aneuploid and that the epithelial and myoepithelial components of the mixed tumours had identical DNA content.Our results reinforce the role of myoepithelial cells in mesenchymal metaplasia in mixed mammary tumours and suggest the possibility of a common origin of both components from a totipotential stem cell with capacity for divergent differentiation.     

Pathogenesis of sialodacryoadenitis in gnotobiotic rats.

The pathogenesis of sialodacryoadenitis was studied in gnotobiotic CD rats inoculated intranasally with the causal virus. Virus replication was detected sequentially in the nasopharynx, tracheobronchial tree, cervical lymph nodes, submaxillary and parotid salivary glands, exorbital gland, and Harderian gland. Acute rhinitis appeared within 2 days after inoculation, and salivary glands had lesions in 4 days. Early changes in salivary and exorbital glands were characterized by necrosis of ductal epithelium, which rapidly progressed to widespread acinar necrosis, marked inflammation, edema and total effacement of glandular architecture. Harderian glands also had massive necrosis of tubuloalveolar units. Repair in all glands was characterized by marked squamous metaplasia of tubuloalveolar units. Repair in all glands was characterized by marked squamous metaplasia of ducts. Neutralizing and complement-fixing antibodies were detected in 7 days, and there was a concomitant decrease in tissue-virus titers. There was no detectable evidence for hematogenous spread of virus or for retrograde infection by way of major salivary ducts.     

Expression of Prostate Glycoconjugates in the Stallion and Castrated Horse

This work was undertaken to determine the glycoconjugates secreted by the epithelium of the prostate in the intact stallion and castrated horse using lectin histochemical procedures in conjunction with enzymatic digestion and deglycosylation treatments. Additionally, anti‐5 and 13‐16‐cytokeratin antibodies were used to localize epithelial basal cells. In the stallion, lectin histochemistry showed the following sugar residues in the Golgi zone of the glandular cells: α‐Glu/Man, α‐Fuc and β‐Gal included in both O‐ and N‐linked oligosaccharides as well as β‐GalNAc, GlcNAc and α‐Gal, which belonged to O‐glycoproteins. β‐Gal and β‐GalNAc moieties were also noted subterminal to sialyl residues. Sialic acid specific lectins identified Neu‐5Ac(α2,3‐6)‐β‐Gal or Neu5Ac(α2,6)‐β‐GalNAc sequences in both N‐ and O‐bound glycoproteins. The prostatic glandular cells of the castrated horse expressed some of the same sugar moieties found in the stallions, such as α‐Glu/Man, α‐Gal and GlcNAc, but significant differences were also noted. In particular, β‐D‐GalNAc was only detected subterminal to sialic acid, β‐D‐Gal‐(1‐3)‐D‐GalNAc was found in N‐linked glycans, whereas β‐D‐Gal‐(1‐4)‐D‐GlcNAc and Neu5Acα2,6Gal/GalNAc were noted only in O‐glycoproteins. These results indicate that the lectin binding patterns in glandular cells may be modified by sex hormones. No specific lectin labelling of basal cells was found in either the stallion or the castrated horse even though they were immunostained with specific anti‐cytokeratin antibodies. These cells stained more strongly in the castrated horse than in the intact stallion suggesting that they are androgen responsive. The glycomolecules detected in the equine prostate secretions may contribute to the remodelling of the sperm surface, which occurs during sperm transit through the male genital tract and also after ejaculation in the seminal plasma. These changes may be important in the understanding of the stallion fertility.     

Immunohistochemistry with keratin,vimentin, desmin,and α‐smooth muscle actin monoclonal antibodies in canine mammary gland: Malignant mammary tumours

Summary

Ten malignant canine mammary gland tumours and five metastases from three of these tumours were studied immunohistochemically with monoclonal antibodies (MoAbs) directed against different human keratin types (K), α‐smooth muscle actin, vimentin, and desmin.

In all tumours the neoplastic epithelium was rather homogeneously labelled with the keratin MoAbs RCK 102 (K 5 and 8) and CAM 5.2 (K 8). The adenocarcinomas (n=5), the solid carcinomas (n=2), and the carcinosarcoma (n=1) showed heterogeneous labelling with the MoAbs specific for luminal cell antigens in the normal canine mammary gland, i.e., K 18, K 7 and K 19 MoAbs. These cells were also immunoreactive with K 4 and K 10 MoAbs. The spindle cell carcinomas (n=2), however, did not react with these MoAbs.

All tumours except one adenocarcinoma were characterized by the absence of immunoreactive labelling with the α‐smooth muscle actin MoAb. In the solid carcinomas this was associated with the absence of labelling with one or both basal cell specific keratin MoAbs, i.e., 8.7 (K 14 and 17) and RCK 107 (K 14), respectively. In contrast, the other malignant tumours showed marked labelling of neoplastic epithelium with these MoAbs. Another remarkable finding was the labelling of a limited to moderate number of neoplastic epithelial cells with the vimentin MoAb. The presence of such labelling patterns in canine mammary gland tumours may be indicative of malignancy. Metastatic tumour tissues had a labelling pattern largely similar to that of the primary tumour, although also loss of reactivity for some keratin MoAbs was seen.     

Prostatic squamous metaplasia in a cat with interstitial cell neoplasia in a retained testis

An 11-year-old cat with a retained testis was presented with a chronic history of dysuria and bladder atony. Medical therapy failed to alleviate the clinical signs. Contrast radiography demonstrated a diffusely narrowed urethra. During a celiotomy and prepubic urethrostomy, a retained testis, stenosed urethra, and irregularly enlarged prostate were observed. Histopathologic diagnosis was retained testis with a well-differentiated interstitial cell tumor, a poorly differentiated interstitial cell tumor, and marked squamous metaplasia of the prostatic epithelium with suppurative prostatitis. Neoplastic interstitial cells were immunoreactive for Melan A, consistent with reports of Melan A expression in steroid hormone-producing tissue. This is the first report of prostatic squamous metaplasia associated with testicular neoplasia in a felid.     

Effects of zeranol on reproduction in beef bulls: scrotal circumference, serving ability, semen characteristics, and pathologic changes of the reproductive organs

Effects of zeranol on scrotal circumference, serving ability, semen characteristics, and postmortem measurements of the genital organs were determined in beef bulls from 9 to 20 months of age. Group 1 (n = 5) served as a nonimplanted control group. Group 2A (n = 5) was implanted with 36 mg of zeranol at birth and at 3 and 6 months of age. Group 2B (n = 5) was implanted with 36 mg of zeranol every 3 months from birth through 18 months of age. Scrotal circumference was adversely affected by zeranol in groups 2A and 2B, but values approached those of group 1 with increasing age. Serving ability was also affected adversely but tended to recover with increasing age. Semen quality was low in groups 2A and 2B and did not improve with increasing age. There was no difference in testicular weight, vesicular gland weight, and penis length among groups when bulls were slaughtered at 20 months of age. Epididymal weight was greater in group-2B bulls and was most likely a consequence of epididymal lesions. Histologic examination of the genital organs revealed that zeranol induced adenomyosis and sperm granulomas in the caudae epididymidis and markedly altered the structure of the sexual accessory glands of bulls in groups 2A and 2B. Alterations in the vesicular glands were characterized by reduced alveolar development and an increase in connective tissue. Low epithelium associated with focal areas of squamous metaplasia were common in the prostate of groups 2A and 2B bulls. Lesions in the bulbourethral glands were characterized by low glandular epithelium, focal areas of squamous metaplasia, cystic collecting ducts, and an increase in connective tissue. Groups 2A and 2B had more abnormal seminiferous tubules than did group 1. Lesions in groups 2A and 2B may have been direct effects of zeranol or may have resulted from reduced testosterone secretion.     

Adenosquamous carcinoma of the oesophagus in a dog

A six‐year‐old mixed‐breed male dog weighing 7.0 kg was presented with chronic vomiting and regurgitation. Endoscopic examination revealed prominent oesophageal dilation in the thoracic region, multiple small greyish‐white nodules over the oesophageal lumen and cauliflower‐like masses in the caudal oesophagus. Histopathological studies revealed a characteristic pattern of coexisting elements of infiltrating adenocarcinoma and squamous cell carcinoma. Immunohistochemical staining with anti‐cytokeratin AE1 + AE3 was positive in both types of neoplastic cells. Neoplastic glandular cells stained positively for cytokeratin 8 while neoplastic squamous cells stained positively for cytokeratin 5/6. On the basis of these findings, the dog was diagnosed with oesophageal adenosquamous carcinoma. The case history and findings suggest that the malignancy might have developed from Barrett's oesophagus following irritation of the oesophageal mucosa due to chronic vomiting and regurgitation.     

p63: a novel myoepithelial cell marker in canine mammary tissues

Several immunohistochemical markers have been used to demonstrate the presence of myoepithelial cells in order to determine their role in the histogenesis of mammary tumors. p63, a recently characterized p53 homologue, is consistently expressed in myoepithelial cells of the human breast; however, no assessment of its immunoreactivity has been reported so far in canine mammary tissues. We investigated p63 immunohistochemical expression, as a novel myoepithelial cell nuclear marker, in 81 samples of normal (n = 2), hyperplastic (n = 11), and neoplastic (n = 68) canine mammary tissues. Myoepithelial phenotype was confirmed by using complementary monoclonal antibodies: alpha-smooth muscle actin, cytokeratin 14, cytokeratin AE1/AE3, and vimentin. p63 expression was observed in 91.4% (74/81) of the samples evaluated. Normal mammary glands, mammary hyperplasias, and benign tumors showed 100% immunoreactivity, with p63 expression restricted to myoepithelial cell nuclei. In general, benign mixed tumors showed a basal cell compartment immunoreactive to p63, with a gradual decrease of its expression during myoepithelial transformation. p63 expression was found in 72% of malignant tumors, allowing myoepithelial or basal cell identification in spindle-cell carcinomas (2/2), tubulopapillary carcinomas (8/9), solid carcinomas (7/10), and carcinosarcomas (1/3). The osteosarcoma analyzed was p63 negative. In our series, stromal components were consistently nonreactive to p63. In conclusion, the present study reveals p63 as a sensitive and highly specific marker of myoepithelial cells in canine mammary tissues, and the authors suggest p63 as an additional marker for defining myoepithelial histogenesis.     

Application of diethylstilbestrol dipropionate in bulls. I. Excretion of residues in urine and faeces and histological and immunohistochemical changes in the prostate

In this experiment 20 one year old bulls received a single intramuscular injection of the anabolic preparation diethylstilbestrol dipropionate (DES-DP) (an oil preparation or an emulsion). Four animals received a corresponding placebo. The application of DES-DP to bulls caused characteristic histological alterations in the peripheral glandular epithelium of the prostate, which could be observed until four weeks after treatment. The value of histological investigation as a screening method was, however, limited by the occurrence of only few metaplastic lesions and a rapid recovery. By contrast, immunohistochemistry using a polyclonal cytokeratin antiserum K40 appeared to be a specific and very sensitive method to detect oestrogen-induced lesions in the prostate. In only two animals, six weeks after injection with the DES-emulsion, false-negative results were obtained, demonstrating the potential value of this screening method. The excretion of DES in the urine and faeces was monitored using radioimmunoassay following chromatographic purification of the urine and faeces extracts. The excretion of DES in urine was faster for animals of the oil group. The DES content in urine decreased to the 1 microgram/l level after 42 days (emulsion group) or 70 days (oil group). The excretion in faeces was comparable to that in urine. After day 21 the excretion patterns of the two excreta were indistinguishable.     

Immunocytochemical study of tissues from clinically normal dogs and of neoplasms, using keratin monoclonal antibodies.

Three commonly used keratin monoclonal antibodies (MAB)--AE1:AE3, CAM 5.2, and MAK-6--were compared with routinely used cytokeratin antibody. The expression of these antibodies was analyzed in several tissues obtained from clinically normal dogs and in a variety of neoplasms from dogs. Using appropriate enzymatic digestion, paraffin-embedded tissues processed in routine manner retained their typical keratin expression. Differentiated and poorly differentiated epithelial neoplasms, lymphomas, and melanomas were studied by use of the avidin-biotin-peroxidase technique. All 4 of the aforementioned antibodies had similar staining profiles. Of 3 anaplastic carcinomas, 2 had positive reaction to all 4 antibodies. All lymphomas, plasma cell tumors, and amelanotic melanomas had negative reaction to MAK-6, CAM 5.2, AE1:AE3, and cytokeratin MAB. Three basal cell epitheliomas had positive reaction to all 4 antibodies, whereas 1 basal cell tumor with a solid pattern had negative staining reaction. Two carcinoids had negative reaction to all markers and 1 of 2 malignant chemodectomas and 1 transitional cell carcinoma had staining reaction to only AE1:AE3 MAB. Comparing the 4 antibodies, use of AE1:AE3 MAB produced the strongest staining intensity followed by cytokeratin, MAK-6, and CAM 5.2 MAB. All 4 antibodies had low background staining. In conclusion, AE1:AE3 and MAK-6 MAB are as useful as cytokeratin MAB for identification of poorly differentiated epithelial neoplasms in dogs and cats.     

Immunohistochemical analysis of cytokeratin expression in dog skin

The expression of cytokeratins and involucrin was analyzed to identify the skin cells which compose the epidermis of dogs. The distribution of cytokeratins and involucrin in normal dog skin was immunohistochemically examined with 27 commercial monoclonal antibodies for human use. Antibodies, No.4. OV-TL12/13, 35betaH11, 4.1.18, CAM5.2, NCL5D3, Ks.13.1, Ks.18.04, Ks.19.1, 170.2.]4 and Ks.20.8 stained hair follicles and/or the sweat gland duct, but not the epidermis. Antibodies, 34betaB4, AE3, 34betaE12. LP34, RCK102, MNF116, AE1, KLI, DE-K10 and DE-K13 reacted with every layer of the epidermis, hair follicles and the sweat gland duct. These results were similar to those reported in the human skin. No positive staining, however, could be detected in the epidermis, hair follicles and the sweat gland duct with commercial antibodies, 6B10, Ks.7.18, Mu146-uc, E3, RCK108 and involucrin. Therefore, immunohistochemical investigation with these commercial antibodies developed for human skin examination might be available for investigating the origin of skin tumors in dogs.     

The expression of p63 and cytokeratin 5 in mixed tumors of the canine mammary gland provides new insights into the histogenesis of these neoplasms

Cytokeratin 5 and p63 have been described as basal and myoepithelial cell markers in human breast. Mixed tumors of the canine mammary gland have been associated with a myoepithelial origin. Cytokeratin 5 expression has not been evaluated in these tumors. We investigated the relation between cytokeratin 5 and p63 double-immunohistochemical expression in 23 mixed tumors of the canine mammary gland (10 benign mixed tumors and 13 carcinomas arising from benign mixed tumors) and their origin. Cytokeratin 5 and p63 co-expression was observed in myoepithelial cells of benign mixed tumors, as well as in squamous differentiation of carcinoma arising from benign mixed tumors. Though a few interstitial spindle cells of the mesenchymal components expressed both p63 and cytokeratin 5, the basal epithelial cells were labeled only by cytokeratin 5. The co-expression of p63 and cytokeratin 5 in myoepithelial cells and squamous differentiation suggest that, like in human breast, cytokeratin 5 can also be considered a myoepithelial- and squamous-cell differentiating marker in canine tumors. The presence of some interstitial spindle cells stained for p63 and cytokeratin 5 might be associated with a myoepithelial origin of the mesenchymal component of mixed tumors of the canine mammary gland. Moreover, contrary to p63, basal epithelial cells were labeled by cytokeratin 5, indicating that cytokeratin 5 may not represent an exclusive myoepithelial cell marker but also a basal epithelial cell marker in canine mixed tumors. According to these data, basal epithelial cells may be related to the origin of the epithelial component of mixed tumors of the canine mammary gland.     

Estrogen-dependent induction of cyclooxygenase-2 in the canine prostate in vivo

Cyclooxygenase (COX)-2 is involved in several physiologic and pathologic processes. COX-2 is overexpressed in human and canine prostate cancer, but little is known about COX-2 inducers in the prostate. Our objective was to investigate the effect of sex steroid hormones on COX-2 expression in the canine prostate in vivo. COX-2 expression was evaluated by immunohistochemistry in intact and castrated dogs treated with exogenous androgen or estrogen. Results showed that no COX-2 staining was observed in prostates of untreated or androgen-treated castrated or intact dogs. However, treatment of intact and castrated dogs with estrogen resulted in squamous metaplasia with intense COX-2 expression observed in both squamous epithelial cells and in cells of acini without metaplasia. This is the first report to demonstrate the induction of COX-2 by estrogen in the prostate in vivo.     

Immunohistochemical demonstration of keratin in canine neuroepithelioma

Morphological features and immunoreactivity for cytokeratin (CK), glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) of three canine neuroepitheliomas and three canine ependymomas were investigated. Neuroepitheliomas were in three German shepherds as intradural-extramedullary solitary masses, with spinal cord displacement between T10 and L2. Histologically, they contained tubules and acini, lined by epithelial cells with focal squamous metaplasia, rosette-like structures, and polygonal to spindle-shaped cells between tubules. Acini were empty or filled with a homogeneous, eosinophilic periodic acid-Schiff (PAS)-positive material. Mitotic indices varied from low to moderate. Ependymomas occurred in the third (two cases) and fourth ventricle in adult boxers. Histologically, they were composed of cells with an ill-defined, scant amphophilic cytoplasm, with a central round euchromatic nucleus; cells formed pseudorosettes, with a central fibro-vascular stroma. Neuroepitheliomas stained for CK, but ependymomas did not. Both failed to stain for GFAP, NSE, or phosphotungstic acid hematoxylin (PTAH). Thus, antibodies to cytokeratin are useful to distinguish neuroepitheliomas from ependymomas.     

Monoclonal antibodies putatively identifying porcine B cells

Comparison was made of the binding of 38 test and three standard monoclonal antibodies (mAbs) to B cells from various pig lymphoid tissues by flow cytometry (FCM) and immunohistochemistry. Some mAbs were also tested on B cells from foetal pig tissues. Twenty of the new mAbs bound, though to variable degrees, to porcine B cells but only three were given cluster assignations: C35 (#147) and BB6-11C9 (#167) were assigned to wCD21 and 2F6/8 (#057) was assigned to SWC7.     

Bovine respiratory syncytial virus-specific monoclonal antibodies

Five hybridomas were produced which secreted monoclonal antibodies to bovine respiratory syncytial virus (BRSV). Two antibodies (8G12, 15C7) neutralized the virus and inhibited syncytia formation in vitro. These monoclonal antibodies also stained, by indirect fluorescent assay, an external envelope protein of living virus-infected cells, and recognized the 48k subunit of the viral fusion protein by Western blot analysis of bovine respiratory syncytial virus-infected cell lysates. Three other monoclonals (6A12, 14D3, 14E3) stained, by indirect fluorescent assay, acetone-fixed virus-infected cells but not living cells. Three hybridomas (6A12, 8G12, 15C7) secreted monoclonal antibody of isotype IgG1, k; two hybridomas secreted monoclonal antibody of isotype IgG2a, k. This apparently is the first report of monoclonal antibodies specific for BRSV glycoproteins.     

Distribution of cytokeratin polypeptides detected by monoclonal antibodies K8.13 and K8.12 in the fetal bovine ruminal epithelium.

Temporal and spatial distributions of cytokeratin (CK) polypeptides were detected by monoclonal antibodies (mAbs) K8.13 and K8.12 during the development of the bovine ruminal epithelium. By the Western blotting analysis after the sodium dodecyl sulfate-polyacrilamide gel electrophoresis, mAb K8.13 confirmed 60.8 and 63.0 kD CK polypeptides in the fetal ruminal epithelial extract, and mAb K8.12 also 48.0 and 54.0 kD CK polypeptides. Immunohistochemical reactivities against both mAbs were detected only in the epithelial cells throughout the fetal periods. Distributions of CK polypeptides detected only by mAb K8.13 were observed on the basal side of the epitherial layer, but not by mAb K8.12 in the 7 cm fetus in crown-rump length. MAb K8.13 reacted also intensely with columnar-shaped cells in the basal layer in the fetuses of the later developmental periods. These results suggest that CK polypeptides detected by mAb K8.13 might be involved in the differentiation and/or the maintenance of the basal layer in the ruminal epithelial development.