Anti-Acidic Cytokeratins Antibody [AE1] (A86357)

Nasopharyngeal carcinoma (NPC) provides a unique opportunity to evaluate distinctive epidemiologic features and a possible etiologic relationship with Epstein-Barr virus (EBV) in human malignancy. The lack of a uniformly accepted pathologic classification for NPC has limited the application of this data, although the World Health Organization (WHO) developed a classification that may solve this problem. Monoclonal keratin antibodies were used for staining of NPC for evaluation of its assistance in diagnosis and classification. In the present immunohistochemical study, monoclonal keratin antibodies, designated AE1, AE2, and AE3, and a polyclonal keratin antibody (RAK) were used for study of the presence of keratin in 121 cases of NPC obtained from China and the United States. AE1 monoclonal antibody, which recognizes keratin protein classes 56.5K, 50K, and 40K, was shown to be the most sensitive and specific for NPC tumor cells among the keratin antibodies studied. In addition, some different keratin expression patterns could be identified between different kinds of epithelium and different tumor groups, with possible relevance to the histogenesis of the histologic subtypes of NPC.

The authors investigated the presence and distribution of keratin in germ cell tumors using a rabbit-anti-keratin antiserum and a monoclonal antikeratin antibody--which is specific for keratin classes of 40, 50, and 56.5 kdaltons--by various immunohistochemical methods on frozen sections, alcohol-fixed, and formalin-fixed paraffin-embedded tissues. Thirty-four germ cell tumors were studied. These were the following: 18 seminomas, 10 embryonal carcinomas, 2 teratocarcinomas, 3 yolk sac tumors and 1 choriocarcinoma. All seminomas, including four poorly differentiated (so-called anaplastic seminomas), gave negative results, regardless of the method employed. Embryonal carcinoma, the epithelial component of the teratocarcinoma, the yolk sac tumors, and choriocarcinoma were at least focally positive for keratin. The monoclonal antibody provided a cleaner background and stronger staining than the rabbit-anti-total-human-epidermal-keratin antibody. Best results were obtained from fresh-frozen sections or alcohol-fixed, paraffin-embedded materials. Formalin-fixed, nonseminomatous tumors, when predigested with trypsin and incubated overnight with primary antibody, gave no false-negative results but staining was often focal. The authors' results agree with the reported absence of detectable keratin in primordial germ cells of the normal testis, and with prevailing concepts of the histogenesis of germ cell tumors. These results indicate that the presence or absence of keratin by immunocytochemical methods can be helpful in distinguishing seminoma from embryonal carcinoma.

Human epidermal keratinocytes express under various growth conditions a total of at least nine keratins that can be divided into two subfamilies. Subfamily A comprises 40-, 46-, 48-, 50-/50'-, and 56.5-kilodalton (kd) keratins which are relatively acidic (pI less than 5.5) and, with the exception of 46-kd keratin, are recognized by AE1 monoclonal antibody. Subfamily B comprises 52-, 56-, 58-, and 65-67-kd keratins which are relatively basic (pI greater than 6) and are recognized by AE3 monoclonal antibody. Within each keratin subfamily, there is a constant member (50-/50'- and 58-kd keratins of the subfamilies A and B, respectively) that is always expressed. The other seven keratins of both subfamilies are variable members whose expression depends upon the cellular differentiated state, which is in turn modulated by the growth environment. The 56.5-kd keratin (subfamily A) and the 65-67-kd keratins (subfamily B) are coordinately expressed during keratinization. In contrast, the 40-, 46-, and 48-kd keratins (subfamily A) and the 52- and 56-kd keratins (subfamily B) are characteristic of cultured epidermal cells forming nonkeratinized colonies. These results demonstrate that human epidermal keratins can be classified according to their reactivity with monoclonal antikeratin antibodies, isoelectric point, and mode of expression. The classification of keratins into various subgroups may have important implications for the mechanisms of epidermal differentiation, the evolution of keratin heterogeneity, and the use of keratin markers for tumor diagnosis.

Keratins are a group of water-insoluble proteins (molecular weight range 40-70 K) that form 10-nm tonofilaments in a wide variety of epithelial cells. The subunit composition of the keratin filaments varies with cell type, period of embryonic development, stage of histologic differentiation, cellular growth environment, and disease state. To better understand the functional significance of individual keratin species, we have generated three monoclonal antikeratin antibodies to different subsets of keratins and used these antibodies to localize specific keratins in normal human epidermis by a combination of immunohistochemical and biochemical techniques. The results indicate that the 50 K and 58 K keratins are present in all cell layers including the relatively undifferentiated basal layer, whereas the 56.5 K and 65-67 K keratins are associated only with the more differentiated cells above the basal layer. In a separate series of experiments, we used the monoclonal antibodies to survey the keratins expressed by various nonepidermal epithelia. The data show that keratins can be divided into at least seven major classes according to their immunologic reactivity and size. Among the keratin classes, the 50 K and 58 K classes appear to be characteristic of all stratified squamous epithelia, whereas the 56.5 K and 65-67 K classes are unique to the keratinized epidermis. These findings suggest that specific keratin classes, as defined by monoclonal antibodies, may serve as useful markers for different types of epithelial differentiation (simple versus stratified, keratinized versus nonkeratinized).

Three monoclonal antibodies (AE1, AE2, and AE3) were prepared against human epidermal keratins and used to study keratin expression during normal epidermal differentiation. Immunofluorescence staining data suggested that the antibodies were specific for keratin-type intermediate filaments. The reactivity of these antibodies to individual human epidermal keratin polypeptides (65-67, 58, 56, and 50 kdaltons) was determined by the immunoblot technique. AE1 reacted with 56 and 50 kdalton keratins, AE2 with 65-67 and 56-kdalton keratins, and AE3 with 65-67 and 58 kdalton keratins. Thus all major epidermal keratins were recognized by at least one of the monoclonal antibodies. Moreover, common antigenic determinants were present in subsets of epidermal keratins. To correlate the expression of specific keratins with different stages of in vivo epidermal differentiation, the antibodies were used for immunohistochemical staining of frozen skin sections. AE1 reacted with epidermal basal cells, AE2 with cells above the basal layer, and AE3 with the entire epidermis. The observation that AE1 and AE2 antibodies (which recognized a common 56 kdalton keratin) stained mutually exclusive parts of the epidermis suggested that certain keratin antigens must be masked in situ. This was shown to be the case by direct analysis of keratins extracted from serial, horizontal skin sections using the immunoblot technique. The results from these immunohistochemical and biochemical approaches suggested that: (a) the 65- to 67-kdalton keratins were present only in cells above the basal layer, (b) the 58-kdalton keratin was detected throughout the entire epidermis including the basal layer, (c) the 56-kdalton keratin was absent in the basal layer and first appeared probably in the upper spinous layer, and (d) the 50-kdalton keratin was the only other major keratin detected in the basal layer and was normally eliminated during s. corneum formation. The 56 and 65-67-kdalton keratins, which are characteristic of epidermal cells undergoing terminal differentiation, may be regarded as molecular markers for keratinization.

We have prepared three monoclonal antibodies against human epidermal keratins. These antibodies were highly specific for keratins and, in combination, recognized all major epidermal keratins of several mammalian species. We have used these antibodies to study the tissue distribution of epidermis-related keratins. In various mammalian epithelia, the antibodies recognized seven classes of keratins defined by their immunological reactivity and size. The 40, 46 and 52 kilodalton (kd) keratin classes were present in almost all epithelia; the 50 kd and 58 kd keratin classes were detected in all stratified squamous epithelia, but not in any simple epithelia; and the 56 kd and 65-67 kd keratin classes were unique to keratinized epidermis. Thus the expression of specific keratin classes appeared to correlate with different types of epithelial differentiation (simple versus stratified; keratinized versus nonkeratinized).

A large number of human neoplasms were tested for their keratin expression in routinely processed tissues by a simple, three-stage immunoperoxidase method using a broadly reactive monoclonal anti-keratin antibody AE1, which recognizes a number of keratin polypeptides distributed in a wide variety of epithelia. All carcinomas, with the exception of hepatocellular, adrenocortical, and basal cell carcinomas and occasional renal cell, pulmonary small-cell, and pulmonary large-cell anaplastic carcinomas, reacted with this antibody irrespective of differentiation, in most instances displaying staining of strong or moderate intensity in the majority of tumor cells. Equivocal results were obtained in some seminomas and dysgerminomas. Malignant melanoma, large-cell lymphoma, Hodgkin's disease, malignant histiocytosis, and stromal mesenchymal elements in all tumors did not show any reactivity with AE1. Even after routine processing, the determinant detected by AE1 is conserved and restricted to epithelial neoplasms. This suggests that AE1 would be valuable in the diagnostic distinction of anaplastic carcinoma from lymphoma and melanoma in routinely processed tissues.