Murine leukemia cell hybrids: The quantity of TL antigens expressed by parental and hybrid cells fails to correlate with their sensitivity to TL antibody and complement

The quantity of thymus-leukemia (TL) antigens expressed by murine leukemia cells is significantly greater than that expressed by somatic hybrids of such cells. Based upon the results of ¹²⁵I-lactoperoxidase labeling and antibody absorption procedures, and corrected for size differences between the two cell types, the quantity of TL antigens expressed by RADA-1 cells, a radiation-induced murine leukemia cell line of strain A/J mice, is approximately 5.0 times greater than that of somatic hybrids of RADA-1 and LM(TK)^? cells. LM(TK)^? cells are a thymidine kinase-deficient TL(-) mouse fibroblast cell line. The quantity of TL antigens expressed is related only in part to their susceptibility to lysis by TL antibodies and guinea pig complement (GPC). RADA-1 cells resist lysis. The quantity of TL antigens expressed by RADA-1 cells is analogous to that formed by nonneoplastic thymocytes obtained from F₁ hybrids of two strains of TL(+) and TL(-) mice; cells from both strains are sensitive to TL antiserum and GPC. ASL-1 cells, a spontaneously occurring leukemia cell line of A/J mice, express TL antigens in significantly higher quantities than any of the cell types examined. Exposed to TL antisera, the quantity of TL antigens of ASL-1 cells, but not that of hybrid cells, gradually diminishes. ASL-1 cells convert over a 6-h period of exposure to antibody and guinea pig complement (GPC) resistance; hybrid cells remain sensitive. However, ASL-1 cells converted to TL antibody and GPC resistance continue for a time to express TL antigens in quantities similar to that of sensitive F₁ thymocytes and resistant RADA-1 cells. RADA-1 X LM(TK)^? hybrid cells, which are sensitive to TL antibodies and GPC, express the lowest quantities of TL antigens of any of the cell types examined. It is likely that differences in the quantities of TL antigens expressed by different cell lines reflect genetic mechanisms controlling TL antigen expression. The failure of TL antisera to affect the quantities of TL antigens expressed by hybrid cells is taken as an indication that genetic controls governing antigen expression may be distinguished from those involved in regulating responsiveness to specific antiserum.     

Combined flow cytometry and confocal laser scanning microscopy for evaluation of BR96 antibody cancer cell targeting and internalization.

BACKGROUND: Monoclonal antibodies (mAb) are important tools in the management of tumor disease, and the discovery of antibodies with both specific cancer cell targeting and capacity to enter the cells by internalization are critical to improve the therapeutic efficacy. METHOD: Antibody cancer cell targeting and internalization properties of fluoroscein-conjugated mAb made against Lewis Y (BR96) were evaluated quantitatively and qualitatively by means of flow cytometry (FCM) and confocal laser scanning microscopy (CLSM), respectively, on cells from a rat tumor cell line (BN7005-H1D2). RESULTS: The study demonstrated a specific binding of BR96 to LewisY (LeY) located in the cell membrane and as BR96/LeY immunocomplexes (BR96/LeY) internalized into the cytoplasm. BR96/LeY was internalized into about 15% of the cells, usually distributed throughout the cytoplasm, but also located close to the nuclei. Cytotoxic effects by BR96 were indicated, and CLSM visualized subpopulations containing cells with bound or internalized BR96/LeY that possessed morphologically pyknotic nuclei and disrupted DNA. CONCLUSION: The spatial-temporal pattern by BR96 cell targeting and internalization processes of BR96/LeY into the cancer cells expressing LeY was demonstrated by FCM and CLSM. Used together, the FCM and CLSM techniques provide a valuable tool for preclinical analyses of antibody targeting and their capacities as carriers of cytotoxic conjugates for the use in cancer therapy.     

Primary in vitro cytotoxic response of F1 T lymphocytes against parental antigens.

Spleen cells from adult female (AKR/J x BALB/(c)F1 mice can respond to mitomycin C-treated spleen from AKR/J mice and can generate effector CTL in a 5-day primary in vitro culture. The response is comparable in magnitude to the response to allogeneic H-2K or H-2D antigens. The response is T cell mediated and is directed to antigen(s) present only on the parental cells. The target cell must be homozygous at H-2Kk to be lysed and H-2Dk antigens do not serve as a target in this response. Spleen cells from (B10.BR x B10.D2) hybrids that have been stimulated with AKR/J lyse B10.Br as well as AKR/J target cells. Similar H-2k/d hybrid F1 anti-H-2k parent responses are seen in certain other strain combinations. A number of possible interpretations of these responses are discussed.     

A unique antigen on mature B cells defined by a monoclonal antibody

A novel 42,000 dalton antigen (MB-1) expressed by mature human B cells in blood and tonsil was identified and characterized by utilizing a hybridoma monoclonal antibody. A comparison of MB-1 with other known B cell antigens suggests that the MB-1 antigen has not been previously identified. From one-and two-color immunofluorescence studies, it appears that the MB-1 antigen is found on all normal immunoglobulin (Ig)-expressing cells, but not on T cells, thymocytes, granulocytes, or platelets. Studies of malignant B cell tumors reveal that the antigen is expressed by virtually all Ig-expressing B cell tumors but only 10% of SIg- B-lineage leukemias. Data from these studies suggest that the MB-1 antigen is expressed late in B cell ontogeny before the expression of SIg.     

Adenovirus 2 Ip+ locus codes for a 19 kd tumor antigen that plays an essential role in cell transformation

Adenovirus 2 large plaque (Ip) mutants produce large clear plaques on human KB cells. These mutants are shown to be defective in inducing transformation of the established rat embryo cell line 3Y1. The Ip mutation was localized within one of the two transforming early gene blocks, E1b (map position 4.5 to 11.2) which codes for two major T antigens of 53 kd and 19 kd by marker transfer. The mutational defects in mutants Ip3 and Ip5 were analyzed by DNA sequence analysis and by analysis of viral E1 proteins. These results reveal that Ip3 and Ip5 mutations map within the 19 kd tumor antigen coding region. Mutant Ip3 has a single base pair change at the N terminus of 19 kd polypeptide, resulting in the substitution of valine for alanine. Mutant Ip5 has two mutational changes, one of which results in the substitution of tyrosine for aspartic acid near the N-terminal region. The second mutation changes the termination codon into a leucine codon, increasing the size of the 19 kd tumor antigen. These results provide direct genetic evidence for an essential role of the 19 kd tumor antigen in cell transformation and indicate that the N-terminal region of the 19 kd tumor antigen is an essential function domain for the induction of cell transformation.     

Studies of in vitro activation and differentiation of human B lymphocytes. I. Phenotypic and functional characterization of the B cell population responding to anti-Ig antibody

Investigation of the activation of splenic B cells by anti-immunoglobulin (Ig) antibody has enabled us to characterize the anti-Ig-responsive B cell and to analyze the phenotypic changes which accompany proliferation and differentiation. The anti-Ig antibody-responsive B cell population was characterized by the expression of high levels of the B2 antigen and represented approximately 40% of splenic B cells. Brisk mitogenesis which peaked at 3 to 4 days was induced by anti-Ig antibody. The proliferative phase was characterized phenotypically by a dramatic decline in B2 antigen expression, with most cells showing no detectable B2 by 4 days post-activation. The other hallmark of this phase was de novo expression of a group of "activation antigens." These included the B cell-restricted antigens B-LAST 1, BB1, and B5, and the T cell-associated interleukin 2 receptor and T12 antigens. Concomitantly, B1, B4, and Ia expression increased, the increase being roughly proportional to the increase in cell size. After day 4, the mitogenic response progressively diminished, while Ig synthesis increased. During this differentiation phase, cell surface antigens again displayed a distinct sequence of changes. The five activation antigens and the B1, B4, and Ia antigens began to decrease. However, two markers, T10 and PCA-1, which are found on plasmacytomas, appeared and their level of expression steadily increased. These changes and the appearance of morphologically identifiable plasma cells required the presence of T cells in this system. T cell supernatants alone induced Ig secretion but did not induce expression of PCA-1 or the appearance of cells with plasma cell morphology. The culture system developed in this study has allowed us to analyze the antigenic changes following activation by anti-Ig antibody. This sequence of changes has not only permitted the identification of antigens which, by their appearance at distinct stages may have an important role in proliferation and differentiation of B cells, but also provides us with the means of studying the function of each antigen.     

IA mutant functional antigen-presenting cell lines

We describe a protocol for the selection of mutant cells with an altered pattern of Ia antigenic determinants and antigen-presenting properties from a homogeneous population of functional antigen-presenting cells (APC). The APC line used in this work was obtained by fusing lipopolysaccharide-stimulated B cells from (BALB/c x A/J)F1 donors with cells from the M12.4.1 BALB/c B lymphoma cell line. The resulting hybridomas, including TA3, retained the potent antigen-presenting activity of the parental B lymphoma line and expressed Ia antigens and immune response gene-determined antigen-presenting properties of the A/J type. Mutants of TA3 were obtained by subjecting the cells to negative immunoselection with one monoclonal anti-(alpha) 1-Ak antibody and complement followed by positive immunoselection via electronic cell sorting with a second monoclonal alpha I-Ak or alpha I-Ek antibody. Two types of mutants were obtained. One, A8, appeared to have undergone a fairly limited alteration, since it lost only some of the I-Ak antigenic determinants; the second type appeared to have lost the entire I-Ak molecule but to have retained the I-E molecule. Functional studies with the A8 mutant demonstrated that the loss of a limited number of I-Ak determinants correlated with the loss of a specific I-Ak-encoded restriction element, since A8 failed to present a specific antigen, hen egg lysozyme (HEL), to a HEL-specific I-Ak-restricted T cell hybridoma but retained some capacity to present a second antigen, poly(Glu60Ala30Tyr10) (GAT), to a GAT-specific I-Ak-restricted T cell hybridoma. These results indicate that Ia antigens are the products of immune response gene loci. The availability of such mutants should allow an examination of the relationship between the structure of an Ia molecule and the antigens with which it is co-recognized by T cells.     

hDlk-1: a cell surface marker common to normal hepatic stem/progenitor cells and carcinomas

Advances in stem cell biology have clarified that a tumour is a collection of heterogeneous cell populations, and that only a small fraction of tumour cells possesses the potential to self-renew. Delta-like 1 protein (Dlk-1) is a surface antigen present on foetal hepatic stem/progenitor cells but absent from mature hepatocytes in neonatal and adult rodent liver. Using a monoclonal antibody (mAb) against hDlk-1, Yanai et al. (Dlk-1, a cell surface antigen on foetal hepatic stem/progenitor cells, is expressed in hepatocellular, colon, pancreas and breast carcinomas at a high frequency. J. Biochem. 2010;148:85-92) have shown that human (h) Dlk-1 is expressed in human foetal, but not adult, liver and that 20% of all hepatocellular carcinomas (HCCs) are hDlk-1(+). Importantly, an even higher percentage of HCCs in younger patients are hDLK-1(+). These authors also found that hDlk-1 is present at high frequency in colon adenocarcinomas, pancreatic islet carcinomas and small cell lung carcinomas. Here, I discuss the implications of the expression of foetal hepatic stem/progenitor cell antigens on carcinoma cells.     

Modulation of lysosomal-associated membrane glycoproteins during retinoic acid-induced embryonal carcinoma cell differentiation

Differentiation of the murine embryonal carcinoma (EC) cell lines F-9 and PC-13, induced by beta-all transretinoic acid (RA) resulted in an increased level of two lysosomal-associated membrane glycoproteins (LAMP-1 and LAMP-2). After differentiation, the levels of both LAMPs in the EC cells were comparable to those found in visceral and parietal endoderm cell lines (PSA-5E and PYS-2, respectively). RA treatment of the EC cells also resulted in an increase in the apparent Mr of both LAMPs apparently due to increased glycosylation because the deglycosylated LAMP-1 from undifferentiated and from differentiated cells had a similar electrophoretic migration. Indeed, the binding of 125I-labeled L-phytohemagglutinin (L-PHA) to glycoproteins with Mr or 90,000-130,000 increased after differentiation and about 24 times more 125I-labeled L-PHA bound to LAMP-1 isolated by immunoprecipitation from extracts of RA-treated F-9 cells than to LAMP-1 from undifferentiated cells. The increased level of the LAMPs was detected in F-9 cells treated with greater than 10(-7) M RA and required greater than 48 h of treatment as did the increased expression of the B1 chain of laminin, an established marker for differentiation in this system. LAMP-1- and L-PHA-reactive glycoproteins were localized by fluorescence techniques to intracellular vesicles, presumably lysosomes, and to the cell surface and both increased after RA treatment. LAMP-2 was barely detectable intracellularly in undifferentiated cells but could be detected clearly after differentiation. In contrast, no LAMP-2 could be detected on the cell surface either before or after differentiation of F-9 cells. The increased level and glycosylation of both LAMP-1 and LAMP-2 was observed also in cells treated with a synthetic chalcone carboxylic acid analog of RA and by combination of either retinoid with dibutyryl cyclic AMP. These results demonstrate that differentiation of EC cells is accompanied by changes in the synthesis and glycosylation of LAMP glycoproteins and that these changes are specific for the cell type that results after differentiation.     

Gene dosage and antigenic expression on the cell surface of bovine erythrocytes.

Electron microscopic and serological techniques have been used to study the relationship between cell surface expression of bovine erythrocyte antigens and the genes coding for these antigens. Using cells which are genetically and serologically defined for their zygosity with respect to the Z allele, it was found that homozygous (Z/Z) cells have approximately twice as much surface Z antigen as heterozygous (Z/-) cells. Cells labeled for the J antigen, a soluble serum substance which secondarily adsorbs to the erythrocyte surface, display a quantity of antigen which is directly related to the J titer of the cells. A new antigen is described which is independent of the J antigen, and which is detectable by EM labeling and by indirect agglutination, but not by hemolysis.     

B cells

B cells are an important component of adaptive immunity. They produce and secrete millions of different antibody molecules, each of which recognizes a different (foreign) antigen. The fact that humans express a very large repertoire of antibodies is due to the complex mechanism of V(D)J recombination of immunoglobulin (Ig) genes as well as other processes including somatic hypermutation, gene conversion and class switching. The B cell receptor (BCR) is an integral membrane protein complex that is composed of two Ig heavy chains, two Ig light chains and two heterodimers of Igalpha and Igbeta. To eliminate foreign antigens, B cells cooperate with other cells of the immune system including macrophages, dendritic cells and T cells. B cell development is a tightly controlled process in which over 75% of the developing cells become apoptotic because of inappropriate immunoglobulin gene rearrangements or recognition of self antigens by Igs. Hence, the majority of B cell-associated disorders are caused by the incorrect function of genes/proteins involved in B cell development.     

Gene dosage and antigenic expression on the cell surface of bovine erythrocytes1

Electron microscopic and serological techniques have been used to study the relationship between cell surface expression of bovine erythrocyte antigens and the genes coding for these antigens. Using cells which are genetically and serologically defined for their zygosity with respect to the Z allele, it was found that homozygous (Z/Z) cells have approximately twice as much surface Z antigen as heterozygous (Z/-) cells. Cells labeled for the J antigen, a soluble serum substance which secondarily adsorbs to the erythrocyte surface, display a quantity of antigen which is directly related to the J titer of the cells. A new antigen is described which is independent of the J antigen, and which is detectable by EM labeling and by indirect agglutination, but not by hemolysis.     

A new mouse lymphoid alloantigen (Lgp100) recognized by a monoclonal rat antibody

A new genetically polymorphic cell surface antigen recognized by a monoclonal rat anti-mouse antibody is expressed on mouse lymphoid cells. Fluorescence analysis on the fluorescence-activated cell sorter (FACS) locates the antigen on thymocytes, lymph node cells, and both T and B cells in the spleen. It also appears on approximately 40% of cells in the bone marrow.Immune precipitations from surface iodinated spleen cells followed by 2-D gel electrophoresis demonstrate that the antigen is a glycoprotein of approximately 100,000 daltons. Since it is expressed in all lymphoid tissues and on both T and B cells, we designate it lymphoid glycoprotein 100 (Lgp100).Strains with Lgp100 include A/J, AKR/J, AKR/Cu, BALB/c, 129/J, CBA/N, C3H/HeJ, CBA/2J, and SJL/J. Strains with no detectable antigen include C57BL/6J, C57BL/10J, C57BR/cdJ, C57L/J, and C58/J. Intercrosses and backcrosses establish a pair of alleles, a positive and a negative one, at a single locus. Heterozygotes display about 50% as much antigen as homozygotes by quantitative membrane immunofluorescence on the FACS. Tests for Lgp100 in 35 recombinant inbred strains from three crosses (CXB, BXB, and BXH) locate this locus on chromosome 1, closely linked to theMls locus.     

Cutting edge: CD96 (tactile) promotes NK cell-target cell adhesion by interacting with the poliovirus receptor (CD155)

The poliovirus receptor (PVR) belongs to a large family of Ig molecules called nectins and nectin-like proteins, which mediate cell-cell adhesion, cell migration, and serve as entry receptors for viruses. It has been recently shown that human NK cells recognize PVR through the receptor DNAM-1, which triggers NK cell stimulation in association with beta(2) integrin. In this study, we show that NK cells recognize PVR through an additional receptor, CD96, or T cell-activated increased late expression (Tactile). CD96 promotes NK cell adhesion to target cells expressing PVR, stimulates cytotoxicity of activated NK cells, and mediates acquisition of PVR from target cells. Thus, NK cells have evolved a dual receptor system that recognizes nectins and nectin-like molecules on target cells and mediates NK cell adhesion and triggering of effector functions. As PVR is highly expressed in certain tumors, this receptor system may be critical for NK cell recognition of tumors.     

Fine specificities of autoantibodies directed against the Ro, La, Sm, RNP, and Jo-1 proteins defined by two-dimensional gel electrophoresis and immunoblotting

Although useful for specific purposes, immunofluorescence, precipitation in agarose gels, and the m.w. estimation of RNA or proteins immunoprecipitated from transformed cells often provide partial or ambiguous definition of autoantibody specificity. We have analyzed organ and cell extracts by one-and two-dimensional electrophoresis together with Western blotting to define the fine specificities of antibodies to the ribonucleoprotein (RNP) antigens Ro, La, Sm, RNP and Jo-1. One-dimensional analysis identified the Ro protein as a 57 kilodalton (kd) protein, although many anti-Ro sera also react with a 50 kd protein. La antisera react with 50 and 43 kd proteins. The 50 kd La protein readily breaks down into 43, 25, and smaller immunoreactive cleavage products. Partial proteolysis of Ro and La proteins in human spleen extracts produces similar immunoreactive products, providing evidence for a common structure. The major immunoreactive Sm antigens defined by human polyclonal antisera and a mouse monoclonal antiserum were doublets of 25/26 and 16/18 kd, whereas anti-RNP sera reacted with a protein of 68 kd. Most Sm-RNP antisera contained antibodies reactive with additional proteins, especially when whole cell extracts were used as a source of antigens. Two-dimensional analysis provided characteristic maps of the antigens. Ro and La were acidic, and La showed a unique set of acidic charge isomers at 50 and 43 kd. Anti-Sm antibodies reacted with discrete dots corresponding to both the acidic and basic regions of the first-dimension (charge) gels, whereas the RNP antigen showed a series of basic charge isomers of 68 kd. Many anti-Sm-RNP sera reacted with other closely spaced proteins of a similar charge and size to the Sm and RNP antigens, suggesting antibody cross-reactivity or reactivity with closely related functional proteins. Although Jo-1 had the same m.w. as the undegraded La antigen, the fingerprints were quite distinctive on two-dimensional electrophoresis. The results of this study indicate how the source and preparation of antigen extracts, as well as protein degradation, influence the m.w. determinations of soluble protein antigens. With these factors taken into account, two-dimensional fractionation with immunoblotting provides a highly discriminating, sensitive, and reproducible method of analysis of autoantibody specificity. This technique can be used to standardize reference antisera and to study protein antigens in normal and abnormal cell and tissue extracts, and could lead to new or more precise correlations with clinical disease.     

Adenovirus E1b-58kd tumor antigen and SV40 large tumor antigen are physically associated with the same 54 kd cellular protein in transformed cells

The adenovirus E1b-58kd tumor antigen has been detected in a physical association with a 54 kilodalton cellular protein in adenovirus-transformed mouse cells. Antibody specific for the E1b-58kd protein coimmunoprecipitates a 54 kd protein from transformed, but not from productively infected, cells. Monoclonal antibody specific for the cellular 54 kd protein coimmunoprecipitates the adenovirus E1b-58kd protein from transformed cell extracts. The same or closely related cellular 54 kd protein, associated with the adenovirus E1b-58kd protein, was present in the SV40 large T antigen-54 kd complex previously detected in SV40-transformed mouse cells. The identity of the 54 kd protein is based on the immunological specificities of the anti-54 kd monoclonal antibodies and partial peptide maps of the 54 kd protein associated with the adenovirus and SV40 tumor antigens. The adenovirus E1b-58kd-54 kd complex, like the SV40 large T antigen-54 kd complex, is heterogeneous in size or mass. While all of the cellular 54 kd protein in the adenovirus-transformed cell extract is found in a complex with the E1b-58kd protein, some of the viral 58 kd antigen is detected in a form not associated with the 54 kd protein. The fact that the adenovirus and Sv40 tumor antigens, both required for transformation, can be found in physical association with the same cellular protein in a transformed cell is a good indication that these two diverse viral proteins share some common mechanisms or functions.     

Characterization of human K cells by surface antigens and morphology at the single cell level

Human lymphocytes killing bovine erythrocytes in vitro in antibody-mediated reactions were characterized at the effector cell level in the ADCC plaque assay. Five to 10% of highly purified peripheral blood lymphocytes are active K cells in this system. Forty to 50% of these were T gamma cells expressing the T cell-associated surface antigens T3 and Leu-1. These cells also expressed the T8/Leu-2a antigens (approximately 20%) or the T4/Leu-3a antigens. Although approximately 30% of the K cells were T4+ when examined after completion of the ADCC assay (18 hr), only less than 10% were T4+ (and Leu-3a+) when examined before the assay. The results indicated that exposure to antigen/antibody complexes during the assay induced increased T4 expression, probably linked to Fc gamma R modulation on some initially T4-/T3+ lymphocytes. The expression of the other antigens (including Leu-3a) was not affected by exposure of the lymphocytes to antigen/antibody complexes. Two-color fluorescence experiments further demonstrated that a minor fraction (10 to 20%) of the K cells carrying T cell-associated antigens also expressed the monocyte/null cell-associated antigen M1 as detected with the monoclonal antibody OKM1. A second major category of effector cells, composed of at least 25% of the K cells, were large granular lymphocytes (LGL) that lacked detectable T cell-associated antigens but expressed the HNK-1 (Leu-7) as well as the M1 antigen. As seen from the size of the plaques formed by different effector cells, K cells of the LGL type had a greater recycling capacity and/or cytolytic efficiency than those of T gamma type.     

B lymphoblast antigen (BB-1) expressed on Epstein-Barr virus-activated B cell blasts, B lymphoblastoid cell lines, and Burkitt's lymphomas

Two new cell surface antigens expressed on B lymphoblastoid cell lines (B-LCL) were defined with cytotoxic mouse monoclonal antibodies. One marker, BB-1 (for B lymphoblast antigen-1), was detected on human and nonhuman primate B-LCL, Epstein-Barr virus (EBV)-activated B cell blasts, most Burkitt's lymphomas, and Ia+ B lymphoblast-like myelomas. Polyclonal B cell activators such as pokeweed mitogen (PWM) and lipopolysaccharide (LPS) also induced the expression of BB-1 on immunoglobulin (Ig)-positive cells. In contrast, BB-1 could not be detected on normal lymphoid tissues by complement-dependent cytotoxicity and immunofluorescence (IF) assays or by analysis with a fluorescence-activated cell sorter (FACS). T cell blasts, T cell leukemias, and pre-B cell or erythroblastic leukemia cell lines were also BB-1 negative. Of particular interest was the finding that BB-1 was expressed on the Jijoye lymphoma but only marginally on a subline of Jijoye, P3HR-1, that lacks receptors for EBV and produces a defective virus incapable of transforming lymphocytes. A second lymphoblast antigen (LB-1) unlike BB-1, was present on both T and B cell blasts and virus-transformed T- and B-LCL but not on normal lymphoid tissues.     

Specific Schistosoma mansoni rat T cell clones. I. Generation and functional analysis in vitro and in vivo

In an attempt to determine the role of schistosome-specific T cells in the immune mechanisms developed during schistosomiasis, Schistosoma mansoni-specific T cells and clones were generated in vitro and some of their functions analyzed in vitro and in vivo in the fischer rat model. The data presented here can be summarized as follows: a) Lymph node cells (LNC) from rats primed with the excretory/secretory antigens-incubation products (IPSm) of adult worms proliferate in vitro only in response to the homologous schistosome antigens and not to unrelated antigens (Ag) such as ovalbumin (OVA) or Dipetalonema viteae and Fasciola hepatica parasite extracts. b) After in vitro restimulation of the primed LNC population with IPSm in the presence of antigen-presenting cells (APC) and maintenance in IL 2-containing medium, the frequency of IPSm-specific T cells is increased and the T cells can be restimulated only in the presence of APC possessing the same major histocompatibility complex (MHC) antigens. c) Following appropriate limiting dilution assays (LDA) (1 cell/well), 10 IPSm-specific T cell clones were obtained, and two of four maintained in culture were tested for their helper activity because they expressed only the W3/13+ W3/25+ surface phenotypes. d) The two highly proliferating IPSm-specific T cell clones (G5 and E23) exhibit an IPSm-dependent helper activity, as shown by the increase in IgG production by IPSm-primed B cells. e) IPSm-T cell clone (G5) as well as IPSm-T cell lines when injected in S. mansoni-infested rats can exert an in vivo helper activity, which is characterized by an accelerated production of IgG antibodies specific for the previously identified 30 to 40 kilodaltons (kd) schistosomula surface antigens (Ag). As recent studies have demonstrated that rat monoclonal antibodies recognize some incubation products of adult S. mansoni as well as one of the 30 to 40 kd schistosomula surface antigens, and taking into account the fact that the T cell clones here studied were restimulated either with IPSm or with schistosomulum Ag, it appears that such IPSm-specific T cell clones could be involved in the concomitant immunity mechanisms.     

Cloning of murine and rat vascular cell adhesion molecule-1.

Vascular cell adhesion molecule-1 (VCAM1) is a member of the immunoglobulin (Ig) superfamily which interacts with the integrin very late antigen 4 (VLA4). We have cloned the cDNAs for both murine and rat VCAM1 from endotoxin-treated lung libraries. Both sequences encode proteins with seven extracellular Ig-like domains, which show 75.9% and 76.9% identity, respectively, with human VCAM1. Both murine and human cell lines show VLA4-dependent binding to COS cells transiently expressing murine and rat VCAM1. Two mAbs, M-K/1 and M-K/2, which recognize an antigen on murine bone marrow stromal cell lines, bind to murine VCAM1 expressed in COS cells and block VCAM1-dependent adhesion, confirming that these mAbs recognize murine VCAM1.