Identification of a synaptic vesicle-specific membrane protein with a wide distribution in neuronal and neurosecretory tissue

Two different monoclonal antibodies, characterized initially as binding synaptic terminal regions of rat brain, bind a 65,000-dalton protein, which is exposed on the outer surface of brain synaptic vesicles. Immunocytochemical experiments at the electron microscope level demonstrate that these antibodies bind the vesicles in many different types of nerve terminals. The antibodies have been used successfully to purify synaptic vesicles from crude brain homogenates by immunoprecipitation onto the surface of polyacrylamide beads. The profiles of the structures precipitated by these beads are almost exclusively vesicular, confirming the vesicle-specificity of the antibodies. In SDS gels, the antibodies bind a single protein of 65,000 daltons. The two antibodies are not identical, but compete for binding sites on this protein. Immune competition experiments also demonstrate that the antigenic components on the 65,000-dalton protein are widely distributed in neuronal and neural secretory tissues. Detectable antigen is not found in uninnervated tissue--blood cells and extrajunctional muscle. Low levels are found in nonneural secretory tissues; it is not certain whether this reflects the presence of low amounts of the antigen on all the exocytotic vesicles in these tissues or whether the antigen is found only in neuronal fibers within these tissues. The molecular weight and at least two antigenic determinants of the 65,000-dalton protein are highly conserved throughout vertebrate phylogeny. The two antibodies recognize a 65,000-dalton protein present in shark, amphibia, birds, and mammals. The highly conserved nature of the determinants on this protein and their specific localization on secretory vesicles of many different types suggest that this protein may be essential for the normal function of neuronal secretory vesicles.     

Monoclonal antibodies specific for glial fibrillary acidic (GFA) protein and for each of the neurofilament triplet polypeptides

Abstract. A panel of 10 mouse monoclonal antibodies specific for glial fibrillary acidic protein (GFA) has been isolated using porcine GFA as antigen. Although all antibodies recognize GFA purified from porcine spinal cord in the western blot technique, they can be subdivided into at least three groups on the basis of their reactivity against defined fragments of the molecule. Immunofluorescence staining patterns with the monoclonal antibodies performed on tissues and cell lines resemble those reported with conventional polyclonal antibodies directed against GFA. In particular astrocytes and Bergmann glia are strongly stained. In addition mouse monoclonal antibodies specific for either the 200 kd, or the 160 kd, or the 68 kd neurofilament triplet protein have been isolated and characterized. These antibodies are specific for neuronal cells and support conclusions made with similar antigen affinity-purified polyclonal antibodies. The combined set of monoclonal antibodies seems a valuable tool to characterize the different cell types of the nervous system.     

Monoclonal antibodies specific for glial fibrillary acidic (GFA) protein and for each of the neurofilament triplet polypeptides

A panel of 10 mouse monoclonal antibodies specific for glial fibrillary acidic protein (GFA) has been isolated using porcine GFA as antigen. Although all antibodies recognize GFA purified from porcine spinal cord in the western blot technique, they can be subdivided into at least three groups on the basis of their reactivity against defined fragments of the molecule. Immunofluorescence staining patterns with the monoclonal antibodies performed on tissues and cell lines resemble those reported with conventional polyclonal antibodies directed against GFA. In particular astrocytes and Bergmann glia are strongly stained. In addition mouse monoclonal antibodies specific for either the 200 kd, or the 160 kd, or the 68 kd neurofilament triplet protein have been isolated and characterized. These antibodies are specific for neuronal cells and support conclusions made with similar antigen affinity-purified polyclonal antibodies. The combined set of monoclonal antibodies seems a valuable tool to characterize the different cell types of the nervous system.     

Immunohistochemical study of carcinoembryonic antigen (CEA) in normal and embryonic human tissues using a CEA-specific oncoprecipitin, krustacin

Using immunoperoxidase technique, antibodies to CEA (Ab) were compared to a glycoprotein krustacin (Kr) extracted from Pagurus prideauxii, which has an ability to precipitate specifically CEA. It was found that Kr and Ab reacted in a similar manner with embryonic and normal gastrointestinal tissues, revealing practically identical localization of the antigen in the tissues and cells. It was possible, however, to note some quantitative and qualitative differences in the distribution of antigen, which showed that Kr and Ab reacted with different determinants of the CEA molecule.     

Tumor radioimmunolocation: differential antibody retention by antigenic normal tissue and tumor

On the assumption that a high specificity would be required for in vivo tumor location and drug targeting, much labor has been expended to produce monoclonal antibodies directed to antigens found primarily on tumors. However, for at least one tumor-associated antigen, stage-specific embryonic antigen 1 (SSEA-1), the concentration of the target antigen need not be higher in the tumor than that found in normal tissues for successful use of the corresponding monoclonal antibody in in vivo tumor location; rather, accessibility and antibody metabolism are more important.     

Xenopus gamma-crystallin gene expression: evidence that the gamma-crystallin gene family is transcribed in lens and nonlens tissues.

Crystallins, the major gene products of the lens, accumulate to high levels during the differentiation of the vertebrate lens. Although crystallins were traditionally thought to be lens specific, it has recently been shown that some are also expressed at very low levels in nonlens tissues. We have examined the embryonic expression pattern of gamma-crystallins, the most abundant crystallins of the embryonic lens in Xenopus laevis. The expression profile of five Xenopus gamma-crystallin genes mirrors the pattern of lens differentiation in X. laevis, exhibiting on average a 100-fold increase between tailbud and tadpole stages. Four of these genes are also ubiquitously expressed outside the lens at a very low level, the first demonstration of nonlens expression of any gamma-crystallin gene; expression of the remaining gene was not detected outside the head region, thus suggesting that there may be two classes of gamma-crystallin genes in X. laevis. Predictions regarding control mechanisms responsible for this dual mode of expression are discussed. This study raises the question of whether any crystallin, on stringent examination, will be found exclusively in the lens.     

A simple method for the immunocytochemical detection of proteins inside nuclear structures that are inaccessible to specific antibodies

It has been demonstrated elsewhere that a high concentration of an antigen within the nucleolus may prevent its proper recognition by specific antibodies. In this study, the authors found that a short proteinase treatment allowed for the detection of antigens in the nucleoli. The described approach is compatible with the simultaneous observation of proteins fused to fluorescent tags and with preembedding electron microscopy. It appears that the described method can be useful in situations when the proper recognition of antigens by specific antibodies is disturbed by a high density of cellular structures or a high concentration of antigens inside these structures.     

Antigen retrieval in cells and tissues: enhancement with sodium dodecyl sulfate

Immunocytochemistry provides important information on the localization of antigens in cells and tissues. However, the procedures used to prepare cells and tissues for immunocytochemical labeling may have deleterious effects on the results achieved. That is, the antigen of interest may be difficult or impossible to detect following labeling. These sorts of observations have led to the concept of antigen masking in which the antigen (or specific epitope) is hidden from antibodies specific for that antigen (or epitope). Various procedures to circumvent this problem have been developed. These different procedures generally fit under the term "antigen retrieval" (or epitope retrieval). The practice of antigen retrieval is widely employed with paraffin-embedded material. Antigen retrieval is less often applied to cells and tissues that are not embedded in paraffin. However, in the latter preparations there are situations in which the observed immunolabeling achieved falls short of expectations. This poor level of immunolabeling may, in some situations, be improved upon with antigen retrieval procedures. In this review, we describe experimental situations in which immunolabeling fell short of expectations. We also describe a procedure that has been useful in enhancing immunolabeling efficiency in these cases. The major feature of this procedure is the incorporation of a permeabilization/denaturation step using sodium dodecyl sulfate. This postfixation and prelabeling step dramatically improves immunolabeling for a number of antigens in both cells and cryosections of tissue.     

Basement membrane proteoglycan in various tissues: characterization using monoclonal antibodies to the Engelbreth-Holm-Swarm mouse tumor low density heparan sulfate proteoglycan

The Engelbreth-Holm-Swarm mouse tumor has been found to produce at least two molecular species of heparan sulfate proteoglycan, a low density one (LD) and a high density one, which differ not only in core proteins but also in glycosaminoglycan structures (Kato, M., Y. Koike, Y. Ito, S. Suzuki, and K. Kimata. 1987. J. Biol. Chem. 262:7180-7188). With aim at investigating their distribution and possible functions in tissues, monoclonal antibodies were produced. Hybridomas obtained by fusion of NS-1 mouse myeloma cells with spleen cells from the rat immunized with a mixture of these proteoglycans were selected by their ability to react with the antigen. Two of them secreted monoclonal antibodies (IgG2a), designated HK-84 and HK-102, that recognize specifically the core protein moiety of LD. Immunofluorescent staining of various tissues (skeletal muscle, cardiac muscle, lung, brain, and kidney) with these monoclonal antibodies has demonstrated that the antigen molecules were present in all basement membranes of these tissues. SDS-PAGE of heparitinase-treated proteoglycan fractions prepared from these tissues and subsequent immunoblotting using these monoclonal antibodies have confirmed that the antigen molecule was LD, and further suggested that there was a tissue-specific variation in the core molecular size. Based on these results, we propose that LD may be an essential component in all basement membranes.     

Rheumatoid arthritis specific anti-Sa antibodies target citrullinated vimentin

Antibodies directed to the Sa antigen are highly specific for rheumatoid arthritis (RA) and can be detected in approximately 40% of RA sera. The antigen, a doublet of protein bands of about 50 kDa, is present in placenta and in RA synovial tissue. Although it has been stated that the Sa antigen is citrullinated vimentin, experimental proof for this claim has never been published. In this study, we investigated the precise nature of the antigen. Peptide sequences that were obtained from highly purified Sa antigen were unique to vimentin. Recombinant vimentin, however, was not recognized by anti-Sa reference sera. In vivo, vimentin is subjected to various post-translational modifications, including citrullination. Since antibodies to citrullinated proteins are known to be highly specific for RA, we investigated whether Sa is citrullinated and found that Sa indeed is citrullinated vimentin. Anti-Sa antibodies thus belong to the family of anticitrullinated protein/peptide antibodies. The presence of the Sa antigen in RA synovial tissue, and the recent observation that vimentin is citrullinated in dying human macrophages, make citrullinated vimentin an interesting candidate autoantigen in RA and may provide new insights into the potential role of citrullinated synovial antigens and the antibodies directed to them in the pathophysiology of RA.     

H-Y antigens

H-Y antigen is defined as a male histocompatibility antigen that causes rejection of male skin grafts by female recipients of the same inbred strain of rodents. Male-specific, or H-Y antigen(s), are also detected by cytotoxic T cells and antibodies. H-Y antigen appears to be an integral part of the membrane of most male cells. In addition, H-Y antibodies detect a soluble form of H-Y that is secreted by the testis. The gene (Smcy/SMCY) coding for H-Y antigen detected by T cells has been cloned. It is expressed ubiquitously in male mice and humans, and encodes an epitope that triggers a specific T -cell response in vitro. Additional epitopes coded for by different Y-chromosomal genes are probably required in vivo for the rejection of male grafts by female hosts. The molecular nature of H-Y antigen detected by antibodies on most male cells is not yet known. Testis-secreted, soluble H-Y antigen, however, was found to be identical to Müllerian-inhibiting substance (MIS). MIS cross-reacts with H-Y antibodies and identical findings were obtained for soluble H-Y antigen and MIS, i.e., secretion by testicular Sertoli and, to a lesser degree, ovarian cells, binding to a gonad-specific receptor, induction of gonadal sex reversal in vitro and, in cattle, in vivo. H-Y antisera also detect a molecule or molecules associated with the heterogametic sex in nonmammalian vertebrates. Molecular data on this antigen or antigens are not yet available.     

Identification of a colon-specific antigen (CSA) in normal and neoplastic tissues.

An antigen has been isolated from a human signet-ring cell carcinoma serially growing in hamsters, GW-39, by saline, PCA, or phenol extraction, and has been found immunologically identical to a similarly extracted substance in normal human or hamster colon. No other hamster or human tissues or cells were found to contain this antigen, for which reason we have termed it colon-specific antigen, or CSA. CSA has been found to be distinct from the major blood group-specific antigens and from othercolon tumor-associated antigens, such as CEA, CCA-II, and CCA-III. It thus seems that a colon organ-specific antigen can be synthesized by this particular human tumor system. Hamsters immunized with CSA could reject cheek pouch grafts of GW-39 tumors, and tumor rejection by these animals correlated with their anti-CSA antibody titers. Preliminary characterization of CSA suggested that it is a glycoprotein on the cell surface having a molecular size of 30,000 to 50,000 daltons. It is proposed that CSA may play a role in the diagnosis of mucin-producing adenocarcinoma of the colon and in ulcerative colitis.     

The erythroblast antigen: a membrane protein bound to the erythroid form of the transferrin receptor?]

An interspecific marker of mammalian erythroid cells, which was called the erythroblast antigen, was identified in 1974, using polyclonal monospecific antibodies. Further studies have demonstrated the expression of this antigen in a variety of nonhemopoietic organs and tissues, which have the following common feature: they have a barrier location; that is, they are located at the boundary. It has been proposed that the erythroblast antigen participates directly or indirectly in the transport of various substances and specifically transport of iron. The present review deals with this topic.     

Use of Ultrasound for Creation of Highly Targeted Immune Response

A simple method for creating a highly targeted immune response has been proposed. It has been shown that under the impact of low- and moderate-intensity ultrasound it is possible to strip antigens off the cell surface (surface antigens). It has been found that the immunogenicity of these surface antigens is no lower than the immunogenicity of intact cells. These results imply that it may be possible to create a specific highly targeted immune response against tissues and cells from whose surface the antigens were stripped, in particular, a targeted immune response against malignant tumors.     

Isolation and characterization of calmodulin genes from Xenopus laevis.

Two cDNAs derived from Xenopus laevis calmodulin mRNA have been cloned. Both cDNAs contain the complete protein-coding region and various lengths of untranslated segments. The two cDNAs encode an identical protein but differ from each other by 5% nucleotide substitutions. The 5' and 3' untranslated regions, to the extent available, are highly homologous between the two cDNAs. The predicted sequence of X. laevis calmodulin is identical to that of vertebrate calmodulins from mammals and chickens and shows one substitution compared with electric eel calmodulin. Genomic DNA sequences homologous to each of the two cDNA clones have been isolated and were shown to account for the major calmodulin-coding DNA sequences in X. laevis. These data suggest that X. laevis carries two active, nonallelic calmodulin genes. Although no complete analysis has been carried out, it appears that the X. laevis calmodulin genes are interrupted by at least four introns. The relative concentrations of calmodulin mRNA have been estimated in different embryonic stages and adult tissues and found to vary by up to a factor of 10. The highest levels of calmodulin mRNA were found in ovaries, testes, and brains. In these three tissues, the two calmodulin genes appear to be expressed at approximately equal levels.     

An enzyme-linked immunoassay for the detection of antibodies to endoplasmic reticulum

A simple, sensitive solid-phase assay for the detection of antibodies to endoplasmic reticulum is described. The assay is dependent upon the amount of antigen bound to the solid support and upon the amount of antibody bound to the support via the relevant antigen. The assay can be used to measure both polyclonal and monoclonal antibody to endoplasmic reticulum. It has been used to isolate several monoclonal antibodies which can recognize and precipitate specific proteins of the endoplasmic reticulum. In addition, it has been used to probe the membrane orientation of endoplasmic reticulum antigens.