Studies on the level of natural antibodies reactive with various tumor cells during urethane carcinogenesis in BALB/c mice

Identification of target antigens of antiendothelial cell antibodies in healthy individuals: A proteomic approach

In order to identify target antigens of anti-endothelial cell (anti-EC) antibodies (AECA) in healthy individuals, we have used a proteomic approach combining 2-DE and immunoblotting. Whole cell protein extracts obtained from human umbilical vein EC (HUVEC) cultures were used as a source of antigens. Serum IgG from 12 healthy blood donors were tested at a concentration of 200 microg/mL. Targeted spots were identified by MS. The HUVEC proteome was composed of 884 protein spots. Among these, 61 +/- 25.8 (mean +/- SD) spots were recognized by serum IgG from healthy individuals, with marked differences from one individual to another. Among these spots, 11 were recognized by serum IgG from all healthy individuals tested. These spots corresponded to six different proteins with several spots corresponding to different isoforms of the same protein. Target antigens were: cytoskeletal proteins (beta-actin, alpha-tubulin, and vimentin); glycolytic enzymes (glucose-3-phosphate-deshydrogenase and alpha-enolase); and prolyl-4-hydroxylase beta subunit, a member of the disulfide isomerase family. This study shows that the repertoire of IgG AECA is heterogeneous among healthy individuals. IgG from all of the healthy individuals tested recognized a restricted set of highly conserved ubiquitous proteins playing key roles in cell biology and maintenance of homeostasis.

Self-reactive antibodies (natural autoantibodies) in healthy individuals

Antibodies that are present in the serum of healthy individuals in the absence of deliberate immunization with any antigen, are refered to as natural antibodies. A vast majority of natural antibodies react with one or more self antigens and are termed as natural autoantibodies. The importance of natural autoantibodies in immune regulation has long been neglected, since tolerance to self was thought to be primarily dependent on the deletion of autoreactive clones, rather than on peripheral suppressive mechanisms. Clonal deletion and energy cannot account, however, for the prevalence of natural autoreactivity among healthy individuals. It is now well established that autoreactive antibodies and B cells, and autoreactive T cells, are present in healthy individuals, and in virtually all vertebrate species. Autoreactive repertoires are predominantly selected early in ontogeny. Questions pertaining to the role of natural antibodies in the regulation of the immune response and maintenance of immune homeostasis and to the distinction between natural autoreactivity and pathological autoimmunity have not been adequately addressed. Here, we focus on the current knowledge on the physicochemical and functional properties of NAA in man, and the use of NAA for therapeutic intervention. reserved.

FcR may function as a progression factor of nonlymphoid tumors

Tumor progression is a multistep process involving genetic and epigenetic changes in a transformed clone. Some of these changes may be induced by host factors which may also select for transformed cellular variants with a high ability to survive and propagate. In this article we review studies showing that receptors for the Fc portion of IgG may be expressed on cells from human or animal tumors of nonlymphoid origin. We also review data demonstrating that at least with respect to cells transformed in vitro with Polyoma virus, transformation per se is not sufficient for the induction of Fc receptor expression. We also summarize preliminary data showing that Fc receptor expression is causally involved in conferring a high malignancy phenotype upon transformed cells. Possible mechanisms to explain these observations are discussed.

The immune system during the precancer period: naturally-occurring tumor reactive monoclonal antibodies and urethane carcinogenesis

Previous results obtained in our laboratory suggested that natural antibodies reactive with L5178Y lymphoma cells play a role in the induction of lung tumors by the chemical carcinogen urethane. In order to characterize some of the naturally-occurring L5178Y reactive antibodies we prepared hybridomas that secreted natural monoclonal IgM antibodies reactive with L5178Y lymphoma cells. In the present study we characterized some of these antibodies and provided further proof as to their role in urethane carcinogenesis. One hybridoma secreted a cytotoxic antibody that reacted only with mouse lymphoma cell lines. Other non-cytotoxic monoclonal L5178Y-reactive antibodies showed various degrees of cross-reactivity with syngeneic, allogeneic and xenogeneic cells of normal or malignant origin. One of these antibodies reacted much better with activated T cells than with resting ones. Four groups of mice were treated with urethane. Three groups were injected twice a week during 5 months with different IgM preparations of natural monoclonal antibodies. The mice in the fourth group were not treated with IgM and served as controls. Five months after the urethane treatment the mice were sacrificed and the number of tumor foci in the lungs of each mouse was determined. The results show that the group treated with the cytotoxic monoclonal antibody 1.80 had a significant decrease, while the group treated with the IgM myeloma protein 104E had a significant increase in the number of tumor foci compared to urethane-treated mice that did not receive any IgM treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on the determinant recognized by naturally-occurring murine autoantibodies reacting with bromelain-treated erythrocytes

Radioimmunoassays (RIA) have confirmed previous studies that trimethylammonium (TMA) or its derivatives constitute part of the determinant recognized by naturally-occurring antibodies (NOA) with the ability to interact with bromelain-treated mouse erythrocytes (BrMRBC). Further studies on this determinant revealed its presence on erythrocytes from several species in addition to mice. In most cases (except in chickens) the determinant was cryptic and could be exposed only after proteolytic treatment of the erythrocytes. The determinant was also found on certain murine lymphoma cells. We also found that bromelain was not the only enzyme that could be used to expose the determinant. Papain, but not trypsin, was able to unmask the determinant on mouse erythrocytes. Rabbit antibodies directed against the idiotypes of four different monoclonal BrMRBC-binding NOA were prepared. Direct RIA assays and inhibition assays showed that the different monoclonal BrMRBC-binding NOA shared a common idiotype specific to such antibodies. The common idiotype was detected in the serum from several mouse strains and in wild mice.

Naturally-occurring tumor-reactive autoantibodies: a monoclonal antibody from normal mice reacts with tumor cells and with DNA

A natural IgM monoclonal antibody, 1.67, was generated from apparently healthy unstimulated BALB/c mice. This antibody reacted with L5178Y murine T cell lymphoma, with human Raji cells, and with several normal cells. Further analysis of its ligand binding capacity disclosed strong binding to single-stranded DNA (ssDNA). However, this naturally-occurring monoclonal antibody binds to different epitopes on cell membranes and on DNA than another anti-DNA monoclonal antibody (18/103/1) from human origin. This conclusion was based on competition assays. Furthermore, NOA 1.67 lacks the 16/6 idiotype expressed on the 18/103/1 antibody. The 16/6 idiotype is shared by human and mouse lupus monoclonal autoantibodies that bind simultaneously to lymphoid cells and DNA. This is a first report on a natural autoantibody that binds to malignant and to normal cell membrane(s) as well as to ssDNA. It may have regulatory functions controlling malignancy and or autoimmunity.