Biofilm formation, antibiotic resistance and genotyping of Shiga toxin-producing Escherichia coli isolated from retail chicken meats

1. The Shiga toxin-producing Escherichia coli (STEC) is a hazardous zoonotic agent for chicken meat consumers. This study determined the serogroups and evaluated the virulence genes, antibiotic resistance, biofilm-forming profiles and genetic relationships of STEC isolates in chicken meat.2. A total of 100 samples belonging to dressed-whole chicken and different parts of the chicken (wing, breast, thigh, drumstick) were collected between September and November 2019 from different retail markets in Kayseri, Türkiye.3. Phenotypic (identification, disc diffusion test, Congo red agar and microtitre plate tests) and molecular tests (identification, serogrouping, virulence factors, biofilm, antibiotic susceptibility, 16S rRNA sequencing and enterobacterial repetitive intergenic consensus-PCR for typing of the isolates) were carried out.4. E. coli was isolated from 35% of the samples and 35% of the samples harboured at least one STEC. Among 35 STEC isolates, 3 (8.5%), 6 (17.1%), 2 (5.7%) and 3 (8.5%) were found to be positive for fliCH2, fliCH8, fliCH11, fliCH19 genes, respectively. Out of 35 STEC positive isolates, 4 (11.4%) were identified as E. coli O157, from which 2 (5.7%) were E. coli O157:H7. E. coli O157 was detected in two (10%), one (5%), one (5%) of the thigh, drumstick and whole chicken samples, respectively.5. Biofilm-forming ability was reported in 33 (94.2%) of 35 E. coli isolates, whilst the biofilm-associated genes detected among 35 STEC isolates included csgA (88.5%), fimH (88.5%), bcsA (85.7%), agn43 (14.2%) and papC (8.5%). The STEC strains showed resistance against ampicillin (88.5%) and erythromycin (88.5%), followed by tetracycline (74.2%) and gentamicin (25.7%). However, the distribution of isolates harbouring bla_CMY, ere(A), tet(A) and aac(3)-IV antibiotic resistance genes was found to be 17.1%, 11.4%, 85.7% and 5.7%, respectively.6. ERIC-PCR showed that E. coli strains obtained from different parts and whole of chicken samples had genetic diversities. ERIC-PCR patterns grouped strains of 35 STEC into eight clusters designated A-H, with 73% similarity. Proper hygiene measures and staff training are essential for public health during poultry processing and in retail stores to control STEC.

Aerobic training prevents dexamethasone-induced peripheral insulin resistance

This study investigated how proteins of the insulin signaling cascade could modulate insulin resistance after dexamethasone (Dexa) treatment and aerobic training. Rats were distributed into 4 groups: sedentary control (SC), sedentary+Dexa (SD), trained control (TC), and trained+Dexa (TD), and underwent aerobic training for 70 days or remained sedentary. Dexa was administered during the last 10 days (1 mg · kg(-1) per day i. p.). After 70 days, an intraperitoneal glucose tolerance test (ipGTT) was performed. Protein levels of IRS-1, AKT, and PKC-α in the tibialis anterior (TA) muscle were identified using Western blots. Dexa treatment increased blood glucose and the area under the curve (AUC) of ipGTT. Training attenuated the hyperglycemia and the AUC induced by Dexa. Dexa reduced IRS-1 (- 16%) and AKT (- 43%) protein level with no changes in PKC-α levels. Moreover, these effects on IRS-1 and AKT protein level were prevented in trained animals. These results show for the first time that aerobic exercise prevented reductions of IRS-1 and AKT level induced by Dexa in the TA muscle, suggesting that aerobic exercise is a good strategy to prevent Dexa-induced peripheral insulin resistance.

Ubiquitination is essential for human cytomegalovirus US11-mediated dislocation of MHC class I molecules from the endoplasmic reticulum to the cytosol

Human cytomegalovirus encodes two glycoproteins, US2 and US11, which cause rapid degradation of MHC class I molecules, thus preventing recognition of virus-infected cells by the immune system. This degradation process involves retrograde transport or 'dislocation' of MHC class I molecules from the endoplasmic reticulum (ER) to the cytosol, where they are deglycosylated by an N-glycanase and degraded by the proteasome. At present it is unknown whether ubiquitination is required for US2- and US11-mediated dislocation and degradation of MHC class I molecules. Here, we show that in E36ts20 hamster cells, which contain a temperature-sensitive mutation in the E1 ubiquitin-activating enzyme, US11-mediated degradation of MHC class I molecules is strongly impaired at the non-permissive temperature, indicating the necessity for ubiquitination in this process. We next addressed the question of whether ubiquitination is a condition for the retrograde movement of MHC class I molecules from the ER to the cytosol, or whether ubiquitination is merely required for recognition of dislocated MHC class I molecules by the proteasome. In the absence of a functional ubiquitin system, complexes of US11 and MHC class I molecules accumulate in the ER. In this state the membrane topology of MHC class I molecules does not significantly change, as judged from proteinase K digestions. Thus the results indicate that a functional ubiquitin system is essential for dislocation of MHC class I molecules from the ER to the cytosol.

Activation of the EBV/C3d receptor (CR2, CD21) on human B lymphocyte surface triggers tyrosine phosphorylation of the 95-kDa nucleolin and its interaction with phosphatidylinositol 3 kinase

We previously demonstrated that CR2 activation on human B lymphocyte surface triggered tyrosine phosphorylation of a p95 component and its interaction with p85 subunit of phosphatidylinositol 3' (PI 3) kinase. Despite identical molecular mass of 95 kDa, this tyrosine phosphorylated p95 molecule was not CD19, the proto-oncogene Vav, or the adaptator Gab1. To identify this tyrosine phosphorylated p95 component, we first purified it by affinity chromatography on anti-phosphotyrosine mAb covalently linked to Sepharose 4B, followed by polyacrylamide gel electrophoresis. Then, the isolated 95-kDa tyrosine phosphorylated band was submitted to amino acid analysis by mass spectrometry; the two different isolated peptides were characterized by amino acid sequences 100% identical with two different domains of nucleolin, localized between aa 411--420 and 611--624. Anti-nucleolin mAb was used to confirm the antigenic properties of this p95 component. Functional studies demonstrated that CR2 activation induced, within a brief span of 2 min, tyrosine phosphorylation of nucleolin and its interaction with Src homology 2 domains of the p85 subunit of PI 3 kinase and of 3BP2 and Grb2, but not with Src homology 2 domains of Fyn and Gap. These properties of nucleolin were identical with those of the p95 previously described and induced by CR2 activation. Furthermore, tyrosine phosphorylation of nucleolin was also induced in normal B lymphocytes by CR2 activation but neither by CD19 nor BCR activation. These data support that tyrosine phosphorylation of nucleolin and its interaction with PI 3 kinase p85 subunit constitute one of the earlier steps in the specific intracellular signaling pathway of CR2.

RB18A, whose gene is localized on chromosome 17q12-q21.1, regulates in vivo p53 transactivating activity

Among the different cellular factors that regulated p53 functions, we previously identified (P. Drane et al., Oncogene, 15: 3013-3024, 1997) RB18A, a new gene whose encoded Mr 205,000 protein interacted in vitro, through its COOH-terminal domain, with p53. Therefore, we analyzed the in vivo role of RB18A by measuring its effect on the transactivating activity of p53 on physiological promoters. We herein demonstrated that RB18A, which interacted also in vivo with p53, activated Bax promoter and inhibited p21Waf1 or IGF-BP3 promoters. In addition, fluorescence in situ hybridization mapping led to localizing the RB18A gene on chromosome 17q12-q21.1, loci associated with human cancers. This is the first demonstration that in vivo RB18A, in a protein-protein interaction, regulates p53 transactivating activity.

Signaling through the EBV/C3d receptor (CR2, CD21) in human B lymphocytes: activation of phosphatidylinositol 3-kinase via a CD19-independent pathway

We herein analyzed the regulation of phosphatidylinositol 3-kinase (PI 3-kinase) activity by CR2 activated on B lymphocyte cell surface. We demonstrated that CR2 activation triggered in vivo PI 3-kinase activity and interaction of PI 3-kinase p85 subunit with a tyrosine-phosphorylated p95 component. The specificity of PI 3-kinase activity was controlled using wortmannin and LY294002. CR2 activation did not trigger tyrosine phosphorylation of PI 3-kinase p85 subunit, but induced direct interaction of tyrosine phosphorylated p95 with the Src homology 2 domain of p85 subunit, as shown using glutathione-S-transferase fusion proteins. Despite identical molecular masses, immunoblotting analysis demonstrated that tyrosine-phosphorylated p95 that interacted in vivo and in vitro with p85 was neither CD19, the 95-kDa proto-oncogene vav, nor Gab1 (a 95-kDa adaptor molecule). Furthermore, p95 tyrosine phosphoprotein also expressed in K562A cells (CR2+ CD19- cells) interacted with Src homology 2 domain of PI 3-kinase p85 subunit after CR2 activation. Activated CR2 did not interact directly with p85 subunit or tyrosine-phosphorylated p95. This suggests the presence of an intermediate molecule between activated CR2 and tyrosine-phosphorylated p95, which may be 3BP2. In addition, in contrast to CD19 activation, CR2 activation did not trigger interaction of CD19 or Vav with PI 3-kinase p85 subunit or coprecipitation of PI 3-kinase activity with CD19. Together, these data clearly demonstrated that CR2 activation triggered in vivo PI 3-kinase activation through a pathway distinct from that triggered through CD19 activation.

Evidence for a new transcript of the Epstein-Barr virus/C3d receptor (CR2, CD21) which is due to alternative exon usage

CR2 extracellular domain is constituted of 15 or 16 Short Consensus Repeats (SCR), with additional SCR 11 localized between SCRs 10 and 12. We amplified Raji cDNA library, with specific primers where SCR 11 is localized. This generated a new fragment of 643 bp (16b SCR), in addition to the two expected transcripts of 489 (15 SCR) and 667 (16a SCR) bp. Sequencing these three fragments and the corresponding genomic DNA, demonstrated the presence of a 24 bp deletion in 16b SCR, without change of open reading frame and that this 24 bp region was flanked by two splicing acceptor sites. This supported a new alternative splicing of CR2, with generation of a third distinct mRNA. This third transcript was expressed in human CR2 positive T cells, normal or transformed B cells and EBV negative B cell lines. The 24 bp deletion corresponds to a proline-rich region, which may influence CR2 conformation and more likely have consequences on CR2 extra and intracellular interactions.

Identification of RB18A, a 205 kDa new p53 regulatory protein which shares antigenic and functional properties with p53

Immunological screening with the anti-p53 moAb, PAb1801 of a cDNA expression library, prepared from human B lymphoma cells, led us to identify a new human 205 kDa protein called RB18A for 'Recognized By PAb1801 moAntibody'. Immunoblotting or immunoprecipitation of fusion protein or in vitro translated protein, respectively, demonstrated that RB18A protein was recognized by several anti-p53 moAb reacting with the N or C-terminal domains of p53. Full length sequence of RB18A cDNA and computer analysis demonstrated that despite common antigenic determinants between RB18A and p53 proteins, nucleotide and deduced protein sequences did not reveal any significant homologies. RB18A mRNA was detected in all tissues tested except in kidney. In addition, RB18A protein shared identical functions with p53 protein: binding to DNA or to p53 and self-oligomerization. Furthermore, RB18A regulated p53 specific binding on his DNA consensus binding site. These functions were associated to the C-terminal domain of RB18A protein and more specifically to the PAb421 binding site present in this domain. The activation by RB18A of p53 binding on DNA was induced through an unstable interaction between both proteins. Altogether, our data demonstrated that RB18A protein shares antigenic and functional properties with p53 and regulated p53 functions.

Tyrosine phosphorylation in peripheral lymphocytes from patients with systemic lupus erythematosus

A comparative study of tyrosine phosphorylation was performed on peripheral blood lymphocytes from systemic lupus erythematosus (SLE) patients and from healthy donors. Freshly isolated SLE lymphocytes presented an elevated tyrosine phosphorylation level when compared to healthy donors lymphocytes (p = 0.005). Among all phosphorylated proteins, those called p120, p110, p80 and p55-p60 were more phosphorylated. The level of tyrosine phosphorylation of p120 and p110 proteins discriminated significantly (p = 0.0048, respectively, p = 0.02) between SLE patients and healthy donors. Lymphocytes form SLE patients and healthy donors were then stimulated by cross-linking T cell antigens (CD3, CD4, CD8) to further distinguish the signal transduction between normal and pathologic lymphocytes. No statistical differences in the tyrosine phosphorylation pattern, following CD4 or CD8 cross-linking, were observed between SLE patients and healthy donors lymphocytes. CD3 cross-linking induced an effect on tyrosine phosphorylation different in SLE patients versus healthy donors lymphocytes. Thus, the lymphocytes of SLE patients were refractile in anti-CD3 stimulation in comparison with the healthy donors lymphocytes. Chi-square analysis demonstrated that a significantly larger number of healthy donors responded to anti-CD3 stimulation compared to SLE patients (p = 0.03). The high frequency of tyrosine phosphorylation of p110 and p80 proteins, following CD3 stimulation, in normal versus SLE lymphocytes, suggested that these proteins could be involved in abnormal signal transduction in SLE cells.

Identification on melanoma cells of p39, a cysteine proteinase that cleaves C3, the third component of complement: amino-acid-sequence identities with procathepsin L

We previously identified, on normal or tumour cells, two membrane proteinases, p57 and p65, that cleave human C3, the third component of complement, thus regulating C3's biological properties. Whereas p57 was purified from human erythrocytes, p65 was identified using polyclonal anti-p57 antibodies on a human melanoma cell line resistant to complement lysis. Analysis of cell distribution of C3-cleaving proteinases established that DSm, a murine melanoma cell line, expressed a C3-cleaving proteinase distinct from p57 and p65 proteinases. Thus we purified the C3-cleaving proteinase solubilized from membranes of DSm cells. The purified proteinase, termed 'p39' on the basis of its molecular mass of 39 kDa, was identified, using specific proteinase inhibitors, as a cysteine proteinase. Anti-p39 antibodies, prepared against highly purified p39, localized the p39 C3-cleaving proteinase mainly at the cell surface and demonstrated that p39 is also secreted. Anti-p39 antibodies inhibited solubilized C3-cleaving activity. Preincubation of DSm cells with anti-p39 F(ab')2 fragments increased up to 60% complement cell susceptibility. Amino acid analysis of N-terminal and three other regions of p39 demonstrated that this C3-cleaving proteinase carries 100% identity within four regions of procathepsin L. This is the first demonstration that a melanoma cell line expresses on its surface and secretes a p39 C3-cleaving cysteine proteinase that shares sequence identities with procathepsin L. Thus the p39 cysteine proteinase represents a new member of the C3-cleaving proteinase family associated with, and/or expressed on, the cell surface.

Pep34, a synthetic peptide whose sequence corresponds to the intracytoplasmic domain of the Epstein-Barr virus receptor (CR2, CD21), regulates human B lymphocyte proliferation triggered through CR2

CR2 is involved in regulation of human B lymphocyte proliferation by interacting, through distinct domains, with extracellular, cell surface or intracellular components. Contribution of CR2 intracytoplasmic domain in CR2 regulatory functions remains unclear. Thus, we used pep34, a 34 amino acid synthetic peptide whose sequence corresponds to CR2 intracytoplasmic domain. Pep34 was incorporated into B lymphocytes which were then activated by EBV or C3d through CR2. Our data demonstrate that pep34 inhibits 100% B lymphocyte proliferation triggered by EBV or C3d. Irrelevant peptide had no effect. When B lymphocyte proliferation was triggered by a multipotent B cell activator as SAC, pep34 did not exert any inhibitory effect. Our data demonstrate that pep34 inhibits B lymphocyte proliferation only when lymphocytes are triggered through CR2. Thus, this strongly supports that despite its short length. CR2 intracytoplasmic domain participates to regulatory functions of this receptor.

Epstein-Barr virus/C3d receptor (CR2, CD21) activated by its extracellular ligands regulates pp105 phosphorylation through two distinct pathways

We previously demonstrated that human C3d or pep16, a 16-amino acid synthetic peptide derived from human C3d, induced in vivo and in vitro tyrosine phosphorylation of pp105, an intracellular component found only in human cells that express CR2 at their surface. To determine the contribution of CR2 molecules to this enzymatic regulation, we first analyzed whether activation of CR2 by other extracellular CR2 ligands could trigger such regulation in cell extracts. Subsequently, we used cell extracts of either CR2-positive cells depleted in CR2 molecules by absorption with anti-CR2 antibodies or CR2-negative cells transfected with CR2 cDNA. We demonstrate here that pp105 phosphorylation was induced when CR2 was activated by C3d and pep16 as well as by gp350, the Epstein-Barr virus capsid protein or OKB7, an anti-CR2 monoclonal antibody (mAb). HB5, another anti-CR2 mAb, which did not activate B lymphocytes through CR2, did not induce pp105 phosphorylation. Thus, C3d, pep16, gp350, and OKB7 presented similar properties in activating CR2 to trigger pp105 phosphorylation and in regulating B lymphocyte proliferation, while HB-5 had no effect on either assays. Furthermore, our data demonstrate that the presence of CR2 activated by its extracellular ligands regulates pp105 phosphorylation through two distinct pathways: one which also requires the presence of non-activated CD19, and one which is independent of CD19. The involvement of CD19 in the first pathway was not due to the formation of putative CR2-CD19 complexes. Both pathways were TAPA-1 independent. This is the first demonstration that activated CR2 molecules can play a regulatory role in enzymatic function, such as phosphorylation, despite the absence of CD19 and TAPA-1.

Binding sites of the Epstein-Barr virus and C3d receptor (CR2, CD21) for its three intracellular ligands, the p53 anti-oncoprotein, the p68 calcium binding protein and the nuclear p120 ribonucleoprotein

Epstein-Barr virus/C3d receptor (CR2, CD21) interacts with three intracellular proteins: the p53 anti-oncoprotein expressed in human B lymphoma cells, the p68 calcium binding protein expressed in normal B lymphocytes and the nuclear p120 ribonucleoprotein (RNP). We previously demonstrated that p53 and p68 interacted with the intracytoplasmic carboxy-terminal domain of CR2. To analyse the amino acid sequence of CR2 binding sites for p53 and p68, we synthesized different peptides whose sequences were derived from this carboxy-terminal domain. Thus, CR2 bound to p53 and p68 through two distinct binding sites localized on the N-terminal and on the central part of its carboxy-terminal domain, characterized by the amino acid sequences of KHRERNYYTD and KEAFHLEARE, respectively. CR2 site reacting with the nuclear p120RNP was determined using either anti-CR2 mAb directed against its extracellular domain or pep34, pep14/SCR3 and pep14/SCR4, synthetic peptides whose sequences corresponded to the intracellular 34 amino acid domain or to sites of the extracellular domain of CR2, respectively. Data support that CR2 interacts with p120RNP through the DEGYRLQGPPSSRC amino acid sequence of its extracellular SCR4 domain. Furthermore, phosphorylation of CR2 inhibits its interaction with the nuclear p120RNP. Binding of CR2, through its intracellular and extracellular domains, with the p53 oncoprotein and p120RNP, respectively, and the co-localization of these three proteins on nuclear interchromatin fibrils, suggest that CR2 could act as a crosslinker between these two nuclear proteins to regulate their functions.

Human erythrocyte ankyrin, a cytoskeleton component, generates the p57 membrane proteinase which cleaves C3, the third component of complement

Human erythrocytes express a p57 membrane serine proteinase which cleaves C3, the third component of complement. Amino acid analysis of the first 20 N-terminal residues of the purified p57 proteinase demonstrated 100% homology with residues 910-929 of erythrocyte ankyrin, a sequence localized in its Mr = 62 kDa fragment. Thus, we analyzed whether ankyrin could generate the p57 C3-cleaving activity. We demonstrate herein that: 1) anti-ankyrin antibodies react with purified p57 proteinase; 2) anti-p57 proteinase antibodies react with purified ankyrin but not with spectrin, another cytoskeleton component; 3) while purified ankyrin did not carry any detectable proteinase activity, limited proteolysis of ankyrin by immobilized chymotrypsin generated this C3-cleaving serine proteinase. Spectrin did not generate any C3-cleaving activity. This is the first demonstration that erythrocyte ankyrin could generate a proteinase activity, which in addition, cleaves specifically human C3.

Expression of complement receptors (CR1 and CR3) and Fc gamma RIII on polymorphonuclears from patients with spondylarthropathies

We assessed the expression of complement receptors (CR1 and CR3) and Fc gamma RIII on unstimulated and FMLP activated polymorphonuclears (PMNs) by indirect immunofluorescence and flow cytometry using CD35 (CR1), CD11b (CR3) and CD16 (Fc gamma RIII) monoclonal antibodies in 24 patients with spondylarthropathies (SpA) and in 18 healthy subjects. SpA patients were classified into 3 groups according to the severity of the disease (severe = asymmetrical peripheral joint involvement and permanent limitation of spine motion; moderate = one of the two items, mild = none of the items). CR1 and Fc gamma RIII expression were significantly decreased in patients with mild SpA, whereas CR1 and CR3 expression were significantly increased in patients with severe disease as compared to control subjects. In patients with mild disease, CR1 expression increased after FMLP activation, but remained significantly lower than in control subjects. The results were confirmed by immunoelectroblotting. These findings suggest that membrane and intracellular pools of CR1 and CR3 may contribute to the clinical modulation of the spondylarthropathies.

EBV/C3d receptor (CR2) interacts by its intracytoplasmic carboxy-terminal domain and two distinct binding sites with the p53 anti-oncoprotein and the p68 calcium-binding protein

EBV/C3d receptor (CR2) interacts with the p53 anti-oncoprotein expressed in the human B lymphoma cells, Raji but not in normal B cells, and with the p68 calcium-binding protein, expressed in normal B lymphocytes but not in transformed B lymphocytes. To characterize the CR2 domain interacting with these two intracellular proteins, we synthesized a 34-amino acid peptide, pep34, corresponding to its intracytoplasmic carboxy-terminal domain and analyzed its binding and antigenic properties. Binding of 125I-labeled p53 or 125I-labeled p68 on immobilized pep34 was specific, additive, and totally inhibited by unlabeled p53 or p68, respectively, but not by unlabeled p68 or p53, respectively. Antigenic properties of pep34 were analyzed by immunizing rabbits with particle-bound pep34. Polyclonal anti-pep34 Ab carried anti-CR2 specificities that recognized only the intracellular domain of CR2. In addition, anti-pep34 Ab also carried anti-p53 or anti-p68 specificities. Anti-p53 or anti-p68 specificities were not due to putative common structural or conformational antigenic determinants between the pep34 synthetic peptide and the p68 or p53 proteins. These anti-p53 and anti-p68 specificities were identified as anti-idiotypic anti-CR2 Ab mimicking either p53 or p68 binding sites of CR2. These data clearly establish that despite its short length, the intracytoplasmic C-terminal tail of CR2 is involved in direct protein-protein interactions with the two intracellular regulatory proteins, p53 and p68. An additional feature of these data is the demonstration that particle-bound pep34 triggered "in vivo" anti-Id Ab restricted to either p53 or p68 specificities.

EBV/C3d receptor (CR2) interacts by its intracytoplasmic carboxy-terminal domain and two distinct binding sites with the p53 anti-oncoprotein and the p68 calcium-binding protein

EBV/C3d receptor (CR2) interacts with the p53 anti-oncoprotein expressed in the human B lymphoma cells, Raji but not in normal B cells, and with the p68 calcium-binding protein, expressed in normal B lymphocytes but not in transformed B lymphocytes. To characterize the CR2 domain interacting with these two intracellular proteins, we synthesized a 34-amino acid peptide, pep34, corresponding to its intracytoplasmic carboxy-terminal domain and analyzed its binding and antigenic properties. Binding of 125I-labeled p53 or 125I-labeled p68 on immobilized pep34 was specific, additive, and totally inhibited by unlabeled p53 or p68, respectively, but not by unlabeled p68 or p53, respectively. Antigenic properties of pep34 were analyzed by immunizing rabbits with particle-bound pep34. Polyclonal anti-pep34 Ab carried anti-CR2 specificities that recognized only the intracellular domain of CR2. In addition, anti-pep34 Ab also carried anti-p53 or anti-p68 specificities. Anti-p53 or anti-p68 specificities were not due to putative common structural or conformational antigenic determinants between the pep34 synthetic peptide and the p68 or p53 proteins. These anti-p53 and anti-p68 specificities were identified as anti-idiotypic anti-CR2 Ab mimicking either p53 or p68 binding sites of CR2. These data clearly establish that despite its short length, the intracytoplasmic C-terminal tail of CR2 is involved in direct protein-protein interactions with the two intracellular regulatory proteins, p53 and p68. An additional feature of these data is the demonstration that particle-bound pep34 triggered "in vivo" anti-Id Ab restricted to either p53 or p68 specificities.

A 16 amino acid synthetic peptide derived from human C3d triggers proliferation and specific tyrosine phosphorylation of transformed CR2-positive human lymphocytes and of normal resting B lymphocytes

We demonstrate herein that p16, a 16 amino acid synthetic peptide derived from human C3d, which carried LYNVEA sequence of C3d reacting with CR2 and C3d present in trypsin-cleaved C3, triggered "in vitro" and "in vivo" phosphorylations and "in vitro" proliferation of human B lymphocytes, depending on the stage of cell differentiation. Indeed, p16 and C3dT induced "in vivo" tyrosine phosphorylation of pp105 and "in vitro" proliferation only of CR2-positive and not of CR2-negative cell lines. In addition, p16 and C3dT also induced "in vivo" tyrosine phosphorylation of pp100 and "in vitro" proliferation of only small dense resting B lymphocytes and not other B lymphocyte subpopulations nor T lymphocytes. These data suggest that induction of pp100 and pp105 phosphorylation by p16 and C3dT could represent an early event associated with expression of CR2 in the regulation of human B lymphocyte proliferation.

Nuclear localization of the Epstein-Barr virus/C3d receptor (CR2) in the human Burkitt B lymphoma cell, Raji

Epstein-Barr virus/C3d receptor (CR2) is a glycoprotein of mol. wt 140,000 expressed on the surface of Raji cells. We previously isolated phosphorylated CR2 from purified Raji cell nuclei. We have analyzed the nuclear localization of CR2 by electron microscope immunochemistry of thin sections of Raji cells and we have compared the binding properties of CR2 expressed on purified plasma membranes or nuclei. Anti-CR2 mAb immunogold labeling of thin sections of Raji cells identified CR2 at the nuclear surface and also within the nucleus. Nuclear envelope associated CR2 was localized mainly at nuclear pores. Within the nucleus, CR2 was associated with ribonucleoprotein (RNP) interchromatin fibrils. This labeling was preserved in nuclear matrix preparations. CR2 expressed on the surfaces of purified nuclei or on the cell surface interacted with soluble and particle-bound C3bi/C3d. Monoclonal anti-CR2 antibodies, which recognized extracellular domains of CR2, reacted differently with CR2 depending on its subcellular localization. The presence of CR2 in nuclei may be due to translocation of the cell surface CR2 and/or the presence of two distinct intracellular pathways for mature CR2.

Intracellular interaction of EBV/C3d receptor (CR2) with p68, a calcium-binding protein present in normal but not in transformed B lymphocytes

To analyze direct intracellular interactions of CR2 in normal human B lymphocytes, we used polyclonal anti-Id anti-CR2 antibodies (Ab2) prepared against the highly purified CR2 molecule (gp140) as original immunogen. We previously demonstrated that this Ab2 contained specificities that mimicked extracellular and intracellular domains of CR2 and was helpful for identifying CR2-specific ligands. Indeed, some Ab2 specificities recognized human C3d and EBV, two extracellular CR2 ligands. In addition, other Ab2 specificities interacted directly, as CR2, with the intracellular p53 antioncoprotein that is expressed in transformed cells and not in normal cells. We demonstrate herein that Ab2 detected in normal B lymphocytes a 68-kDa protein, p68, that was not expressed in transformed B cells. p68 was localized in purified plasma membranes and cytosol fractions. Direct interaction of purified CR2 with purified p68 was demonstrated. Competitive studies supported that CR2 and Ab2 interacted with identical sites on p68. These interactions were calcium dependent. p68 was identified as a calcium-binding protein by its ability to be solubilized from B lymphocyte membranes by EGTA, a calcium-chelating agent, to bind specifically on phenothiazine-Sepharose in a calcium-dependent interaction, and to be recognized by specific antibodies directed against human p68, a calcium-binding protein of the annexin VI family. Thus, demonstration of different intracellular interactions of CR2 with distinct regulatory proteins, such as p53, the antioncoprotein, and p68, a calcium-binding protein, supports involvement of two regulatory pathways of signal transduction through CR2, depending on the normal or transformed state of human B lymphocytes.

Intracellular interaction of EBV/C3d receptor (CR2) with p68, a calcium-binding protein present in normal but not in transformed B lymphocytes

To analyze direct intracellular interactions of CR2 in normal human B lymphocytes, we used polyclonal anti-Id anti-CR2 antibodies (Ab2) prepared against the highly purified CR2 molecule (gp140) as original immunogen. We previously demonstrated that this Ab2 contained specificities that mimicked extracellular and intracellular domains of CR2 and was helpful for identifying CR2-specific ligands. Indeed, some Ab2 specificities recognized human C3d and EBV, two extracellular CR2 ligands. In addition, other Ab2 specificities interacted directly, as CR2, with the intracellular p53 antioncoprotein that is expressed in transformed cells and not in normal cells. We demonstrate herein that Ab2 detected in normal B lymphocytes a 68-kDa protein, p68, that was not expressed in transformed B cells. p68 was localized in purified plasma membranes and cytosol fractions. Direct interaction of purified CR2 with purified p68 was demonstrated. Competitive studies supported that CR2 and Ab2 interacted with identical sites on p68. These interactions were calcium dependent. p68 was identified as a calcium-binding protein by its ability to be solubilized from B lymphocyte membranes by EGTA, a calcium-chelating agent, to bind specifically on phenothiazine-Sepharose in a calcium-dependent interaction, and to be recognized by specific antibodies directed against human p68, a calcium-binding protein of the annexin VI family. Thus, demonstration of different intracellular interactions of CR2 with distinct regulatory proteins, such as p53, the antioncoprotein, and p68, a calcium-binding protein, supports involvement of two regulatory pathways of signal transduction through CR2, depending on the normal or transformed state of human B lymphocytes.

Characterization of a monoclonal antibody against P57, the C3/C3b-cleaving proteinase expressed in human erythrocyte membranes

A monoclonal antibody was raised against p57, a serine proteinase, characterized by an apparent molecular weight of 57 kDa, and purified from human erythrocyte membranes. P57 proteinase cleaves the human third component of complement, C3. The antibody selected, MP1, of IgG2a isotype, precipitated specifically the p57 antigen which carried the C3/C3b-cleaving activity present in membrane crude extract of human erythrocytes. P57 proteinase eluted from MP1-sepharose was inhibited by 5 x 10(-4) M PMSF, enhanced by 0.5% SDS and generated C3 fragments identical to those generated by membrane crude extract of human erythrocytes. All these properties were identical to those of the p57 previously purified by biochemical procedures. In addition, 5000 binding sites were detected on cell surface. This MP1 monoclonal antibody will be helpful to analyse the role of p57 in human erythrocytes.

A 16 amino-acid synthetic peptide, derived from human C3d, carries regulatory activity on in vitro phosphorylation of a cellular component of the human B lymphoma cells, Raji

We present herein the first evidence that human C3 and, with a higher efficiency, trypsin-cleaved C3 enhanced in vitro phosphorylation of a cellular component, characterized by an apparent molecular weight of 105 kDa, pp105, present in the human B lymphoma cells, Raji. This regulatory activity was associated with C3d fragment generated in trypsin-cleaved C3. A 16 amino-acid peptide, carrying the LYNVEA sequence of C3d reacting with the C3d receptor (CR2), was synthetized. P16 enhanced, in a dose-dependent curve between 0.3 to 10 microM, in vitro phosphorylation of pp105, as well as C3d fragments present in trypsin-cleaved C3. A fibrinogen-related synthetic peptide of 15 amino acids, used as control, had no effect on pp105 phosphorylation. P16 and trypsin-cleaved C3 regulate pp105 phosphorylation through identical pathways. Thus, p16 represents the 16 amino-acid sequence of C3 which regulated in vitro phosphorylation of pp105.

C3-cleaving membrane proteinase. A new complement regulatory protein of human melanoma cells

Human melanoma cells resistant to killing by the R24 mAb and human complement rapidly degrade surface-deposited C3b (M. Panneerselvam, S. Welt, L. J. Old, C.-W. Vogel. 1986. J. Immunol. 136:2534). We report that C-resistant melanoma cells express a membrane proteinase that can cleave C3b, generating a cleavage product with a molecular mass of approximately 30 kDa. The C3-cleaving proteinase was identified on the melanoma cells by its cross-reaction with antiserum to p57, a C3-cleaving proteinase previously isolated from human E membranes (C. Charriaut-Marlangue, M. Barel, R. Frade. 1986. Biochem. Biophys. Res. Commun. 140:1113). Preincubation of the C-resistant melanoma cells with anti-p57 IgG or their F(ab')2 fragments increased their susceptibility to complement killing from 25% to approximately 50% and reduced the rate of C3b cleavage and the amount of the 30-kDa fragment generated on the cells. Anti-p57 IgG stained C-resistant melanoma cells by indirect immunofluorescence and precipitated a protein with an apparent molecular mass of 65 kDa. This membrane protein, termed p65, was not detectable on C-susceptible melanoma cells. Membrane extracts from C-resistant melanoma cells also showed C3-cleaving activity when incubated with purified C3 or C3b, similarly generating a C3 fragment of approximately 35 kDa. This fluid-phase C3 cleaving activity could be partially inhibited by anti-p57 IgG. These data suggest that p65 is a C3-cleaving proteinase, antigenically related to p57, that is expressed on C-resistant melanoma cells and responsible for the C resistance of these cells. We propose that the membrane-bound C3-cleaving proteinase represents another C regulatory protein protecting host cells against killing by C.

C3-cleaving membrane proteinase. A new complement regulatory protein of human melanoma cells

Human melanoma cells resistant to killing by the R24 mAb and human complement rapidly degrade surface-deposited C3b (M. Panneerselvam, S. Welt, L. J. Old, C.-W. Vogel. 1986. J. Immunol. 136:2534). We report that C-resistant melanoma cells express a membrane proteinase that can cleave C3b, generating a cleavage product with a molecular mass of approximately 30 kDa. The C3-cleaving proteinase was identified on the melanoma cells by its cross-reaction with antiserum to p57, a C3-cleaving proteinase previously isolated from human E membranes (C. Charriaut-Marlangue, M. Barel, R. Frade. 1986. Biochem. Biophys. Res. Commun. 140:1113). Preincubation of the C-resistant melanoma cells with anti-p57 IgG or their F(ab')2 fragments increased their susceptibility to complement killing from 25% to approximately 50% and reduced the rate of C3b cleavage and the amount of the 30-kDa fragment generated on the cells. Anti-p57 IgG stained C-resistant melanoma cells by indirect immunofluorescence and precipitated a protein with an apparent molecular mass of 65 kDa. This membrane protein, termed p65, was not detectable on C-susceptible melanoma cells. Membrane extracts from C-resistant melanoma cells also showed C3-cleaving activity when incubated with purified C3 or C3b, similarly generating a C3 fragment of approximately 35 kDa. This fluid-phase C3 cleaving activity could be partially inhibited by anti-p57 IgG. These data suggest that p65 is a C3-cleaving proteinase, antigenically related to p57, that is expressed on C-resistant melanoma cells and responsible for the C resistance of these cells. We propose that the membrane-bound C3-cleaving proteinase represents another C regulatory protein protecting host cells against killing by C.

Epstein-Barr virus/complement fragment C3d receptor (CR2) reacts with p53, a cellular antioncogene-encoded membrane phosphoprotein: detection by polyclonal anti-idiotypic anti-CR2 antibodies

Epstein-Barr virus and the C3d fragment of the third component of complement are specific extracellular ligands for complement receptor type 2 (CR2). However, intracellular proteins that react specifically with CR2 and are involved in post-membrane signals remain unknown. We recently prepared polyclonal anti-idiotypic anti-CR2 antibodies (Ab2) by using the highly purified CR2 molecule as original immunogen. We showed that Ab2 contained anti-idiotypic specificities that mimicked extracellular domains of CR2 and detected two distinct binding sites on CR2 for its specific extracellular ligands, Epstein-Barr virus and C3d. We postulated that Ab2 might also contain specificities that could mimic intracellular domains of CR2. Here we report that Ab2, which did not react with Raji B-lymphoma cell surface components, detected specifically, among all components solubilized from Raji cell membranes, a single intracellular membrane protein of apparent molecular mass of 53 kDa. This protein was identified as the p53 cellular antioncogene-encoded membrane phosphoprotein by analyzing its antigenic properties with Pab1801, a monoclonal anti-p53 antibody, and by comparing its biochemical properties with those of p53. Additionally, solubilized and purified CR2 bound to solubilized p53 immobilized on Pab1801-Sepharose. p53, like CR2, was localized only in purified plasma membranes and nuclei of Raji cells. These data suggest strongly that p53, a cellular antioncogene-encoded phosphoprotein, reacted specifically with CR2 in Raji membranes. This interaction may represent one of the important steps through which CR2 could be involved in human B-lymphocyte proliferation and transformation.

Enhancement of Epstein-Barr virus/C3d receptor (EBV/C3dR or CR2) and nuclear p120 ribonucleoprotein phosphorylation by specific EBV/C3dR ligands in subcellular fractions of the human B lymphoma cell line, Raji

We present herein the first evidence that interaction of specific EBV/C3dR ligands, as human C3bi/C3d and anti-EBV/C3dR MoAb, with EBV/C3dR enhanced significantly, in a dose dependent process, phosphorylation of EBV/C3dR and p120 RNP present in subcellular fractions, as purified plasma membranes and nuclei, of the human B lymphoma cell line, Raji. The use of kinase effectors allowed to detect some of the kinases involved in these phosphorylations. Pp60src-like phosphotyrosine kinase and protein kinase C were involved in the phosphorylation of plasma membrane or nuclear EBV/C3dR. An additional calcium/calmodulin-dependent kinase was also involved in nuclear EBV/C3dR phosphorylation. P120 RNP phosphorylation was under the control of protein kinase C and of CaCl2/Calmodulin-dependent kinase but also of casein kinase II.

Monoclonal and anti-idiotypic anti-EBV/C3d receptor antibodies detect two binding sites, one for EBV and one for C3d on glycoprotein 140, the EBV/C3dR, expressed on human B lymphocytes

Glycoprotein (gp) 140, the EBV/C3dR of B lymphocytes, is a membrane site involved in human cell regulation. To analyze the specificities of the binding sites for EBV and for C3d on the gp 140 molecule, two distinct approaches were used. First, anti-EBV/C3dR mAb were prepared against highly purified EBV/C3dR. Nine anti-EBV/C3dR mAb were obtained. Four of these anti-EBV/C3dR mAb inhibited C3d binding but not EBV binding on gp 140, whereas four others exerted an inverse effect. These differences could not be due to differences in isotype, antibody concentration, affinity constant, and number of molecules bound on cell surface, as these parameters were identical for the nine used mAb. Second, polyclonal anti-idiotypic antibodies (Ab2) were prepared against F(ab)'2 fragments of polyclonal anti-EBV/C3dR (Ab1). Ab2 recognized the variable portion of Ab1 as controlled by immunoblotting experiments. Ab2, which did not react with the cell surface, inhibited Ab1 binding on Raji cells. Ab2 mimicked the EBV/C3dR by its properties to bind to particle-bound C3d and EBV, preventing their binding on Raji cell surface. C3d binding specificities contained in Ab2 were isolated by affinity chromatography on C3b/C3bi-Sepharose. These specificities, being the internal image of C3d binding site of EBV/C3dR, reacted with Ab1 and inhibited particle-bound C3d binding on Raji cells but did not react with EBV. Taken together, these data support strongly that gp 140, the EBV/C3dR, carried two distinct binding sites, one for EBV and one for C3d.

Monoclonal and anti-idiotypic anti-EBV/C3d receptor antibodies detect two binding sites, one for EBV and one for C3d on glycoprotein 140, the EBV/C3dR, expressed on human B lymphocytes

Glycoprotein (gp) 140, the EBV/C3dR of B lymphocytes, is a membrane site involved in human cell regulation. To analyze the specificities of the binding sites for EBV and for C3d on the gp 140 molecule, two distinct approaches were used. First, anti-EBV/C3dR mAb were prepared against highly purified EBV/C3dR. Nine anti-EBV/C3dR mAb were obtained. Four of these anti-EBV/C3dR mAb inhibited C3d binding but not EBV binding on gp 140, whereas four others exerted an inverse effect. These differences could not be due to differences in isotype, antibody concentration, affinity constant, and number of molecules bound on cell surface, as these parameters were identical for the nine used mAb. Second, polyclonal anti-idiotypic antibodies (Ab2) were prepared against F(ab)'2 fragments of polyclonal anti-EBV/C3dR (Ab1). Ab2 recognized the variable portion of Ab1 as controlled by immunoblotting experiments. Ab2, which did not react with the cell surface, inhibited Ab1 binding on Raji cells. Ab2 mimicked the EBV/C3dR by its properties to bind to particle-bound C3d and EBV, preventing their binding on Raji cell surface. C3d binding specificities contained in Ab2 were isolated by affinity chromatography on C3b/C3bi-Sepharose. These specificities, being the internal image of C3d binding site of EBV/C3dR, reacted with Ab1 and inhibited particle-bound C3d binding on Raji cells but did not react with EBV. Taken together, these data support strongly that gp 140, the EBV/C3dR, carried two distinct binding sites, one for EBV and one for C3d.

gp140, the EBV/C3d receptor (CR2) of human B lymphocytes, is involved in cell-free phosphorylation of p120, a nuclear ribonucleoprotein

gp140, the EB/C3d receptor (EBV/C3dR; CR2), is a membrane site involved in human B cell regulation. Cross-linking of this receptor on the cell surface by its specific ligands led to the enhancement of B cell proliferation in synergy with T cell factors. In vitro activation of human peripheral B lymphocytes by cross-linking membrane immunoglobulins with anti-mu antibody induced EBV/C3dR phosphorylation. These studies were pursued by analyzing cell-free phosphorylation of EBV/C3dR isolated from Raji cell fractions, and immobilized on OKB7, a monoclonal anti-EBV/C3dR antibody. Three EBV/C3dR-related antigens which could be cell-free phosphorylated were detected: gp140, the EBV/C3dR, p130 and p120. gp140, the mature form of EBV/C3dR, was isolated from plasma membrane and from purified nuclei. p130 was identified as an intracellular intermediate of EBV/C3dR glycosylation, localized in low-density microsomes. Phosphoamino acid analysis of EBV/C3dR allowed the detection of phosphotyrosine and phosphoserine residues. These data suggest that EBV/C3dR could carry an autophosphorylation activity and could be associated to serine kinases. Using polyclonal anti-p120 antibody and anti-120 kDa nuclear ribonucleoprotein monoclonal antibody (mAb), p120 was identified as a nuclear ribonucleoprotein antigenically not related to EBV/C3dR. Detection of p120 on EBV/C3dR, immobilized on OKB7, was due to interactions between both antigens, instead of anti-EBV/C3dR mAb cross-reactivity with p120. Cell-free phosphorylation of p120 was under the control of EBV/C3dR. However, it is not yet established whether other nuclear or membrane components were involved in the control of p120 cell-free phosphorylation by EBV/C3dR. From the data presented herein, we propose that phosphorylation of a 120-kDa nuclear ribonucleoprotein by EBV/C3dR-associated kinases could represent a crucial step in in vivo regulation of human B cell activation.

[C3 stimulates the proliferation of human pre-B Raji cells]

In a defined medium in which transferrin (3 micrograms/ml) was the only source of exogenous proteins, Raji cells of the human pre-B lymphoblastoid cell line died within 48 h after forming polykaryons. The simple addition of purified C3 at a concentration equal to or higher than 3 micrograms/ml allowed Raji cells to divide. This preliminary report provides a defined system for studying the mitogenic effect of human C3 or C3 fragments upon proliferation of human B-cells lines.

Activation of human platelets through gp140, the C3d/EBV receptor (CR2)

gp140, the C3d/EBV receptor (CR2), previously isolated and characterized from human B lymphocytes, was identified on human platelets: by measuring the specific binding of either polyclonal anti-gp140 IgG and monoclonal anti-C3d/EBVR antibodies, as OKB-7 and HB-5, or human C3d; by isolating gp140 from solubilized platelet components with polyclonal anti-gp140 IgG or monoclonal OKB-7, using immunoprecipitation and electro-immunoblotting assays; by inducing specific activation of human platelets. Cross-linking of this receptor by polyclonal anti-gp140 IgG induced aggregation of human platelets and stimulated ATP release. Absence of lactate dehydrogenase release and inhibition by EDTA and prostacyclin of anti-gp140-induced aggregation, support strongly active aggregation and absence of lysis. Platelet aggregation by anti-gp140 required metabolic activities and was modulated by fibrinogen, paf-acether or thrombin. OKB-7 triggered human platelet aggregation when cross-linked by anti-mouse second-step antibodies. In the same way, platelet activation by C3d fragment was detected, in presence of fibrinogen, only when C3d was cross-linked on the cell surface by anti-C3d F(ab')2 fragments.

Identification of P-57, a serine proteinase, from human erythrocyte membranes, which cleaves both chains of human third component (C3) of complement

A proteinase, which cleaves human third component of complement, was solubilized from erythrocyte membranes then purified by gel filtration chromatography, fluid phase electrophoresis, and hydroxylapatite chromatography. Labeling of the purified material by 125I or 3H-DFP and measurement of proteolytic activity subsequently isolated by SDS-polyacrylamide gel electrophoresis allowed to identify a 57 kDa single band, in non reducing conditions. Inhibition of this activity by PMSF supports covalent modification of an active serine residue. This membrane serine proteinase cleaved alpha and beta chains of human third component of complement, suggesting that p-57 is distinct from plasma serine proteinases.

Autoantibodies against gp140, the Epstein-Barr virus and C3d receptor in sera from rheumatoid arthritis patients

gp140 is the Epstein-Barr virus receptor and the C3d receptor (EBVR/C3dR) of human B lymphocytes. Recently, we have shown that cross-linking of EBVR/C3dR on cell surface by polyclonal anti-gp140 induced B cell activation, in presence of T cell factors. Immunoregulatory abnormalities of EBV-induced B cell activation have been demonstrated in rheumatoid arthritis (RA) patients. These data prompted us to analyze the putative presence of anti-EBVR/C3dR autoantibodies in human sera. The IgG fractions from eleven RA and 10 normal sera were tested for their ability to: (a) bind to Raji cell surface; (b) inhibit the binding to cell surface of 3 anti-EBVR/C3dR monoclonal antibodies (mAb), which recognized different epitopes on gp140; (c) inhibit the binding of particle-bound C3d and (d) react with 1% Nonidet-P40-solubilized gp140 from Raji cell membranes, in immunoblotting assays. Three RA sera carry anti-EBVR/C3dR autoantibodies which react with gp140 expressed on Raji cell surface or its solubilized form. The purification of monomeric IgG fraction of selected RA sera ruled out involvement of immune complexes carrying C3 molecules, which could interfere in these assays. One of these 3 RA sera was able to inhibit the binding to cell surface of anti-EBVR/C3dR mAb and particle-bound C3d. However, the 2 other RA sera, found positive by immunoblotting, did not inhibit particle-bound C3d and presented differences in their inhibitory effect on anti-EBVR/C3dR mAb binding to Raji cell surface. These data allow us to demonstrate differences which exist in the properties of anti-EBVR/C3dR autoantibodies. These autoantibodies were not detected in all the normal and other RA sera. Anti-EBVR/C3dR autoantibodies could play a role "in vivo" in B lymphocyte activation of RA patients.

gp 140, the C3d/EBV receptor (CR2), is phosphorylated upon in vitro activation of human peripheral B lymphocytes

gp 140, the C3d/EBV receptor (CR2), is a specific marker of human B lymphocytes. Very recent data suggest that CR2 is a membrane site involved in early B cell activation. These properties of CR2 led us to analyze the molecular events associated with gp 140. We analyzed whether in some conditions of B lymphocyte activation, CR2 could be phosphorylated. We have found that when highly enriched peripheral B cells were cultured for 48 h with anti-mu Ab and/or SAC, in order to provide an optimal activating signal, phosphorylation of the CR2 was induced.

gp140, a C3b-binding membrane component of lymphocytes, is the B cell C3dg/C3d receptor (CR2) and is distinct from the neutrophil C3dg receptor (CR4)

gp140, previously identified as a 140-kDa C3b-binding membrane glycoprotein present on Raji cell surface, was shown to be the C3dg/C3d receptor of B lymphocytes (CR2). Specific polyclonal anti-gp140, prepared by immunizing rabbits with this highly purified C3 receptor, blocked Raji cell rosettes with EC3b, EC3bi, EC3dg and EC3d, and also blocked normal lymphocyte rosettes with EC3dg and EC3d without affecting CR1 or CR3 activity. Moreover, a monoclonal anti-C3 (C3b/#130), described by others as reacting with the d region highly expressed on EC3bi, EC3dg and EC3d and poorly exposed on EC3b, completely inhibited EC3bi, EC3dg and EC3d rosettes with Raji cells, but had no effect on EC3b rosettes. Treatment of Raji cells with rabbit anti-gp140 blocked the uptake of three 125I-labeled monoclonal antibodies anti-B2, HB-5 and OKB7 reported to react with C3d-binding proteins, indicating that each of these monoclonal antibodies recognizes epitopes present on gp140. The neutrophil C3dg receptor was examined to determine its relationship to lymphocyte CR2. While neutrophil rosettes with EC3d were undetectable, a specificity for C3d was suggested by the inhibition of EC3dg rosettes by fluid phase C3d-complexes bearing no detectable C3dg. However, such neutrophil EC3dg and EC3bi rosettes were not inhibited by rabbit anti-gp140 nor an excess of anti-CR1, anti-CR2, and anti-CR3. In addition, neutrophils did not bind 125I-labeled anti-gp140, anti-B2, or HB-5. Thus, the neutrophil C3dg receptor is distinct from gp140, the lymphocyte CR2, and should be designated CR4.

Enhancement of human B cell proliferation by an antibody to the C3d receptor, the gp 140 molecule

The C3d receptor is a specific marker of B lymphocytes. Recently we have shown that C3d receptor activity is carried by a gp 140 membrane antigen. A polyclonal antibody has been prepared by immunizing a rabbit with highly purified gp 140 molecule isolated from membranes of the human B lymphoblastoid cell line Raji and its high specificity was previously demonstrated. We tested the effect of this antibody to the C3d receptor on the B cell proliferative response. Purified B cells from human blood were induced to proliferate by a B cell growth factor (BCGF)-containing partially purified supernatant from activated T cells. The anti-C3d receptor F(ab')2 enhanced the BCGF-dependent B cell proliferation. This effect was dose dependent, was observed in the presence of different concentrations of BCGF and did not correspond to a change in the time course of the response. The anti-C3d receptor F(ab')2 had no mitogenic effect in the absence of T cell supernatant. In contrast the undigested anti-C3d receptor IgG suppressed the BCGF-dependent B cell proliferation. These results emphasize the potentialities of anti-gp 140 F(ab')2 to explore the involvement of the C3d receptor in the regulation of B cell response to T cell products.

Analysis of gp 140, a C3b-binding membrane component present on Raji cells: a comparison with factor H

In a previous report (M. Barel et al. FEBS Lett., 1981. 136: 111) using radiolabeling methods, we characterized from the membrane of the human B lymphoblastoid cell line Raji, a 140 000-Mr glycoprotein (gp140) carrying a C3b-binding activity with 125I-labeled C3b or Sepharose-bound C3b. The facts of absence on Raji cells of CR1, the C3b receptor purified from human erythrocytes, the observations made by others that H-like activity (the 150 000 Mr C3b binding serum protein) was present in Raji cells and the same molecular weight range of H and gp140, led us to investigate the relationship between both antigens. A rabbit antibody anti-5.4 was prepared against gp140, highly purified from Raji cells. However, anti-H specificities were detected in crude anti-5.4 IgG, while anti-serum H IgG did not react with gp140 antigen. The crude anti-5.4 IgG fraction, anti-gp 140 IgG or F(ab')2 and anti-H specificities present in anti-5.4 IgG, separated by absorption on Sepharose-bound H, and anti-serum H IgG were tested on Raji cells by immunofluorescence techniques, by measuring the inhibition of specific cytotoxic assays and the inhibition of specific binding of soluble or particle-bound C3b to the cell surface and on solubilized antigens by immunoblotting techniques. All the data obtained support that: (a) anti-H specificities are not shared by antibodies bearing anti-gp 140 specificities and their presence in crude anti-5.4 IgG is more likely due to a contamination by H antigen of gp 140 antigen used in the immunization process, and (b) gp 140 antigen is highly expressed on Raji cell surface, whereas H antigen can not be detected under the same conditions. Molecular analysis of gp140 and H antigens confirmed differences between both antigens in molecular weight, trypsin sensitivity and charge properties. All the results presented herein support the notion that gp140 is not identical with the H molecule and that C3b binding to gp140 is not mediated by H. The relationship between gp140 and C3 receptors described by others is discussed.

A simple solid phase radioimmunoassay specific for human C3b to detect C3b receptors on human lymphoblastoid cell surfaces

Our aim was to detect C3b receptors on human lymphoblastoid cells using a solid phase radioimmunoassay (RIA) specific for human C3b. RIA was performed by coupling rabbit antihuman C3b to acrylamide beads to make immunobeads. The specificity and sensitivity of binding of 125I-C3b to immunobeads allowed the detection of as little as 6 X 10(-10) M unlabeled human C3b. The cells were incubated with a C3b concentration (10(-9) M) giving 25% inhibition in the RIA. The concentration of unbound C3b was then measured in the cell supernatants using RIA. Results showed that: (a) loss of C3b antigen in the cell supernatant was not due to degradation of C3b molecules, (b) C3b binding could be detected at 37 degrees C on the four B cell lines, but not on the two T cell lines or on the two non T-non B cell lines tested, (c) C3b bound on the B lymphoblastoid cells was not cleaved, neither into iC3b nor C3c and C3d fragments, supporting the presence of C3b receptors on the cells tested. This method allows screening of a variety of C3b receptor-positive cells.

Inhibition of in vitro natural killer activity by the third component of complement: role for the C3a fragment

Purified human native third component of complement, C3, was found to inhibit in vitro natural killer (NK) cell cytotoxicity in both mouse and human systems. The effect was dose and time dependent, a 50% inhibition being reached with 190 nM C3 (35 micrograms/ml) added during the NK assay or after a 30-min preincubation of the effector cells with this C3 concentration. C3 was shown to act at the effector-cell population level because pretreatment of the target cells did not modify the NK lysis. The inhibition was not due to general cytotoxicity nor to cell agglutination. Moreover, another in vitro cytotoxicity system (represented by alloreactive cytotoxic lymphocytes) was not affected by purified C3. Structural analysis of the active part of the C3 molecule shows that the C3-induced inhibition is supported by the C3a fragment. Release of carboxyl-terminal arginine residue by carboxypeptidase B, converting C3a into des-Arg77-C3a, did not alter the inhibitory effect displayed by this fragment. These results suggest that C3a may play an important role in the regulation of NK activity.

Behavior of soluble human 125I-labeled C3b, the third component of complement, after binding to human cells

The behavior of 125I-labeled C3b incubated with two C3b receptor-positive cells (human erythrocytes and the B lymphoblastoid Raji line), one C3b receptor-negative cell (T lymphoblastoid CEM line) and solubilized membranes from each cell was analyzed by sucrose density gradient (SDG) and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Whichever whole cell was tested, the unbound 125I-labeled C3b recovered in the cell supernatant was not cleaved. When 125I-labeled C3b was bound to whole cells or incubated with solubilized membranes, three different activities were detected: (a) nonspecific C3b polymerization, induced on the membrane of C3b receptor-positive or C3b receptor-negative cells; (b) specific C3b receptor activity solubilized only from the membrane of the two C3b receptor-positive cells and (c) C3b hydrolytic activity, inhibited by 5 X 10(-4)M phenyl methyl sulfonyl fluoride, only extracted from human erythrocyte membranes and carried by a molecule different from that of C3b receptor. C3b receptor activity solubilized from Raji and human erythrocyte membranes was detected by a 12S peak complex formation on a 10-30% SDG and characterized by an affinity constant of 2 X 10(7) to 4 X 10(7) mol-1. Hydrolysis of labeled C3b (Mr = 175000) by solubilized human erythrocyte membranes led to the formation of a split product of Mr = 35000 consisting of two disulfide-linked polypeptide chains of Mr = 17000. This is the first report of a breakdown of C3b on cell membranes different from the physiological breakdown described in the fluid phase.

Use of cell differentiation effectors to select a human B lymphoblastoid cell line enriched in C3b receptors

A study was undertaken to establish conditions of growth to increase C3b receptor synthesis on a human B lymphoblastoid cell line (Raji) by use of cell differentiation effectors. It appears that whereas two polar compounds HMBA (2mM) and Me2SO(2%) have no or little effect, 5 BrdU (30microM) and db cAMP (5 x10(-4) M) are able to increase in 48 h and 36 h respectively the synthesis of C3b receptor on Raji cell surface. These two compounds help to select a variant in which 100% of cells have C3b receptors with a high density of receptors per cell. The mechanism of BrdU action on the regulation of C3b receptor synthesis is discussed.

Detection of Fc gamma receptors on human lymphoblastoid cell surfaces using a simple solid phase radioimmunoassay specific for human IgG

The aim of this work was to detect Fc gamma receptors on human lymphoblastoid cells using a solid phase radioimmunoassay (RIA), specific to human IgG. RIA was performed by coupling rabbit anti-human IgG (AHIgG) to acrylamide beads to make immunobeads. The specificity and sensitivity of binding of human [125I]IgG to immunobeads permitted detection of as little as 10(-10) M unlabeled human IgG or aggregated human IgG (AHIgG) in competitive assay. The cells were incubated with an AHIgG concentration (3 x 10(-10) M) giving 25% inhibition in the RIA; unbound AHIgG concentration was then measured in the cell supernatants using RIA. Results show that Fc gamma receptors could be detected at 20 degrees C or at 37 degrees C (but not at 4 degrees C) on the four B cell lines tested. At whatever temperature of incubation, Fc gamma receptors were not detected on three T cell lines nor on two 'non T-non B' cell lines. This method allows screening of a large number of Fc gamma receptor positive cells. It is also useful for detecting Fc gamma receptors in membrane preparations or in detergent extracts of human B cell membranes.