Isolation of a normal B cell subset with a Burkitt-like phenotype and transformation in vitro with Epstein-Barr virus

Epstein-Barr virus (EBV) is causally linked with endemic Burkitt's lymphoma (BL), a tumor whose homogeneous cell surface phenotype suggests derivation from a particular subset of activated germinal centre B cells in vivo. Endemic BL also shows an unusual form of EBV infection with down-regulation of certain of the virus latent proteins which are constitutively expressed when EBV infects and transforms normal resting B cells in vitro. Here we question whether this virus:cell interaction is unique to malignant BL cells or whether it might be reproduced by in vitro infection of those particular germinal centre cells displaying the BL-like phenotype. Firstly, we show by biochemical means that a subset of normal tonsillar B cells does indeed express the globotriaosylceramide glycolipid BLA and the common acute lymphoblastic leukaemia antigen CALLA, 2 important markers of the BL phenotype. Secondly, using 2-colour immunofluorescence labelling with anti-BLA and anti-CALLA monoclonal antibodies (MAbs), 4 subsets of low buoyant density tonsillar B cells (BLA+ CALLA+, BLA+ CALLA-, BLA- CALLA+, BLA- CALLA-) have been separated by means of a FACS and tested for their susceptibility to EBV-induced growth transformation in a limiting dilution assay. The BLA+ CALLA+ (i.e., BL-like) subset contained the highest proportion of cells already actively in cycle in vivo and gave the lowest yield of transformants, perhaps reflecting the greater efficiency with which EBV transforms resting target cells. Of the cell lines established from the BLA+ CALLA+ population, a significant number retained BLA expression but CALLA was always lost. In 2 further respects, these lines resembled conventional in vitro transformants rather than lines of BL type; thus the cells expressed cellular "activation" antigens (CD23, CD39, CD30, Ki-24) characteristic of the lymphoblastoid phenotype and contained the full spectrum of EBV latent proteins.

Characterization of the serological response in man to the latent membrane protein and the six nuclear antigens encoded by Epstein-Barr virus

A total of 116 sera from healthy individuals and from patients with Burkitt's lymphoma (BL), nasopharyngeal carcinoma (NPC) or rheumatoid arthritis (RA) were studied with respect to antibody responses to each of the seven known transformation-associated Epstein-Barr virus (EBV)-encoded antigens [latent membrane protein (LMP) and six nuclear proteins (EBNAs 1 to 6)]. The antibodies were detected using modified standard immunoblotting techniques. Antibodies to LMP were detected for the first time in sera from 6/27 (22%) healthy, EBV-immune individuals (seropositive for the viral capsid antigens). An increased incidence of anti-LMP antibodies was found in EBV-immune sera from patients with BL (17/24 positive; 71%), NPC (21/33; 64%), and RA (16/21; 76%). Antibodies to EBNA 1 were detected in all EBV-immune sera at a standard 1:20 dilution. Antibodies to the other EBNAs were detected in only a proportion of these sera (20 to 95%) at the same dilution. Only minor disease-associated differences in the incidence of these antibodies were observed, the most consistent being that RA sera had a higher incidence of antibodies to EBNAs 2 to 6 compared with healthy controls. Testing of the sera at a 1:100 dilution suggested that there were some disease-related differences in the titres of anti-EBNA antibodies. At this serum dilution, a reduced incidence of antibodies to EBNA 2 was seen in NPC (6/31) compared with RA (18/19) and healthy EBV-seropositives (16/26); antibodies to EBNA 3 were detected at an increased incidence in BL (8/15) and NPC (16/31) compared with control sera (7/26); antibodies to EBNA 4 were detected at increased incidence in BL (5/15) and RA (6/19) compared with control sera (1/26); and antibodies to EBNA 6 were detected at increased incidence in NPC (19/31) and RA (7/19) compared with control sera (3/26).

Different patterns of Epstein-Barr virus gene expression and of cytotoxic T-cell recognition in B-cell lines infected with transforming (B95.8) or nontransforming (P3HR1) virus strains

Epstein-Barr virus (EBV)-negative Burkitt's lymphoma (BL) cell lines have been converted to EBV genome positivity by in vitro infection with the transforming EBV strain B95.8 and with the nontransforming mutant strain P3HR1, which has a deletion in the gene encoding the nuclear antigen EBNA2. These B95.8- and P3HR1-converted lines have been compared for their patterns of expression of EBV latent genes (i.e., those viral genes constitutively expressed in all EBV-transformed lines of normal B-cell origin) and for their recognition by EBV-specific cytotoxic T lymphocytes (CTLs), in an effort to identify which latent gene products provide target antigens for the T-cell response. B95.8-converted lines on several different EBV-negative BL-cell backgrounds all showed detectable expression of the nuclear antigens EBNA1, EBNA2, and EBNA3 and of the latent membrane protein (LMP); such converts were also clearly recognized by EBV-specific CTL preparations with restriction through selected human leukocyte antigen (HLA) class I antigens on the target cell surface. The corresponding P3HR1-converted lines (lacking an EBNA2 gene) expressed EBNA1 and EBNA3 but, surprisingly, showed no detectable LMP; furthermore, these converts were not recognized by EBV-specific CTLs. Such differences in T-cell recognition were not due to any differences in expression of the relevant HLA-restricting determinants between the two types of convert, as shown by binding of specific monoclonal antibodies and by the susceptibility of both B95.8 and P3HR1 converts to allospecific CTLs directed against these same HLA molecules. The results suggest that in the normal infectious cycle, EBNA2 may be required for subsequent expression of LMP and that both EBNA2 and LMP (but not EBNA1 or EBNA3) may provide target antigens for the EBV-specific T-cell response.

The application of immunoassays and fluorometry to the detection of polycyclic hydrocarbon-macromolecular adducts and anti-adduct antibodies in humans

The metabolic activation of polycyclic aromatic hydrocarbons (PAH) to chemical species that form covalent adducts with cellular macromolecules (DNA and protein) is central to theories of carcinogenesis. Assays are currently being developed that will accurately reflect human macromolecular exposure to these carcinogens. Immunoassays are capable of detecting low levels of PAH-DNA adducts and antibodies directed against these adducts in humans and HPLC/spectrophotofluorimetry allows the detection of carcinogen-DNA or carcinogen-protein adducts in human peripheral blood. Both types of method have inherent advantages and disadvantages, and the use of more than one type of corroborative assay is a feature in our work. Simplified but highly specific synchronous fluorescence spectra have been obtained for BP-tetrols after mild acid hydrolysis and HPLC of sample materials. When using a wavelength difference of 34 nm to drive the excitation and emission monochromators simultaneously, the pyrene fluorophore, when present, has a signature peak at 345 nm (excitation). The results of immunoassays demonstrate human exposure to PAH as a class of carcinogen, since serological cross-reactivity of antibodies does not limit detection in this system to a single chemical compound. In addition the formation in humans of anti-PAH-DNA antibodies has been shown, presumably in response to both past and present exposure to the parent compounds. In summary the results of each assay can indicate human exposure to PAH and have the potential for molecular dosimetry of this exposure.

Monoclonal and polyclonal antibodies against Epstein-Barr virus nuclear antigen 5 (EBNA-5) detect multiple protein species in Burkitt's lymphoma and lymphoblastoid cell lines

The Epstein-Barr virus nuclear antigen 5 (EBNA-5) is encoded by highly spliced mRNA from the major IR1 (BamHI-W) repeat region of the virus genome. A mouse monoclonal antibody, JF186, has been raised against a synthetic 18-amino-acid peptide deduced from the EBNA-5 message of B95-8 and Raji cells. The antibody showed characteristic coarse nuclear granules by indirect immunofluorescence and revealed multiple EBNA-5 species by immunoblotting and immunoprecipitation. The B95-8 line itself and all B95-8 virus-carrying cells, whether lymphoblastoid cell lines or in vitro-converted sublines of Epstein-Barr virus (EBV)-negative Burkitt's lymphoma (BL) lines, were EBNA-5 positive. Among 36 cell lines carrying different EBV strains, only 10 expressed the B95-8-Raji-prototype EBNA-5 recognized by JF186; this was probably due to genetic variation in the epitope recognized by JF186, as shown for P3HR-1. Human antibodies, affinity purified against EBNA-5-JF186 immunoprecipitates, detected EBNA-5 in the majority of EBV-positive BL lines and in all lymphoblastoid cell lines containing the BL-derived viruses. Thus, EBNA-5 can be expressed by all virus isolates examined, but is down-regulated, together with other latent gene products, in a minority of BL lines which have a particular cellular phenotype. EBNA-5 was detected as a ladder of protein species of 20 to 130 kilodaltons (kDa), with a regular spacing of 6 to 8 kDa, consistent with the coding capacity of the combined BamHI-W 66- and 132-base-pair exons, together with shifts of 2 to 4 kDa, consistent with the size of the separate 66- and 132-base-pair exons. Multiple EBNA-5 proteins can be expressed by the single cell as shown by cloning of newly infected cells.

Differences in B cell growth phenotype reflect novel patterns of Epstein-Barr virus latent gene expression in Burkitt's lymphoma cells

Recently established Epstein-Barr virus (EBV)-positive Burkitt's lymphoma (BL) cell lines, carrying chromosomal translocations indicative of their malignant origin, have been monitored for their degree of in vitro progression towards a more 'lymphoblastoid' cell surface phenotype and growth pattern, and for their expression of three EBV latent gene products which are constitutively present in all virus-transformed normal lymphoblastoid cell lines (LCLs). BL cell lines which stably retained the original tumour biopsy phenotype on serial passage were all positive for the nuclear antigen EBNA 1 but did not express detectable amounts of two other 'transforming' proteins, EBNA 2 and the latent membrane protein (LMP). This novel pattern of EBV gene expression was also observed on direct analysis of BL biopsy tissue. All three viral proteins became detectable, however, in BL cell lines which had progressed towards a more LCL-like phenotype in vitro. This work establishes a link between B cell phenotype and the accompanying pattern of EBV latent gene expression, and identifies a novel type of EBV:cell interaction which may be unique to BL cells.

The level of expression of class-I MHC antigens in adenovirus-transformed human cell lines

The level of expression of the class-I major histocompatibility (MHC) antigen was determined in a series of human embryo cell lines transformed with either adenovirus 12 (Ad 12) early region I (EI) or adenovirus 5 (Ad 5) EI DNA or with combinations of Ad 12 early region IA (EIA) or Ad 2 EIA with activated N-ras DNA. MHC class-I antigen expression was greatly reduced in all Ad 12 transformants, compared to primary cells. Expression was also reduced in the Ad 5 cell lines transformed with EIA and EIB DNA, but levels were near normal in those lines with only EIA DNA present. Amounts of MHC class-I antigen on the cell surface, as determined by RIA and FACS analysis, generally reflected total cellular levels as determined by Western blotting. Expression of beta 2 microglobulin was also much reduced in those cell lines with low levels of MHC class-I antigen. The treatment of primary cells and all the transformants with human gamma-interferon resulted in increased expression of HLA on the cell surface. Infection of primary human cells with Ad 12 or with a series of Ad 12 mutants did not have any effect on the MHC class-I antigens present.

Epstein-Barr virus-transformed human precursor B cell lines: altered growth phenotype of lines with germ-line or rearranged but nonexpressed heavy chain genes

A series of lymphoblastoid cell lines (LCLs) have been established by in vitro infection of fetal bone marrow and fetal liver cells with Epstein-Barr virus (EBV). While most lines showed the usual mature B cell phenotype, a small proportion were cytoplasmic and surface immunoglobulin (Ig) heavy and light chain negative. Analysis of gene rearrangements indicated that the Ig- lines were either germ-line or nonproductively rearranged when probed for JH and were in germ-line configuration for C chi; no mu or chi mRNA could be detected in such cells. Precursor B cell lines were indistinguishable from their normal Ig+ counterparts in their expression of a wide variety of cell surface markers including "activation" antigens usually associated with the lymphoblastoid state; even the single LCL showing germ-line heavy and light chain genes expressed B lineage-specific cell surface antigens. However, the Ig- lines were distinct from their Ig+ counterparts in three important respects: (a) they grew much more slowly and achieved lower saturation densities, (b) they showed unusually high proportions (8-16%) of cells in EBV-productive cycle, and (c) they contained unusually high proportions (up to 40%) of cells expressing free joining (J) chain. These results suggest that precursor B cells differ in their response to the growth-transforming effects of EBV such that the virus-cell interaction in precursor B cell lines is inherently less stable than in conventional LCL. In particular there may be a greater movement of cells out of cycle and along the B cell maturation pathway. It is possible that such movement leads in individual cells either to virus replication or to a "sterile" plasmacytoid differentiation with J chain expression in the absence of Ig synthesis.

Monoclonal antibodies to the latent membrane protein of Epstein-Barr virus reveal heterogeneity of the protein and inducible expression in virus-transformed cells

Monoclonal antibodies specific for the 'latent membrane protein' (LMP) of Epstein-Barr virus (EBV), one of the effector proteins of EBV-induced B cell transformation, have been generated from mice immunized with a beta-galactosidase fusion protein containing the carboxyl half of the B95.8 strain LMP sequence. Four monoclonal IgG1 antibodies, designated CS.1, CS.2, CS.3 and CS.4, which together recognized at least three different epitopes on the molecule, were used to examine various aspects of LMP expression in B cell lines transformed in vitro. The pooled CS.1 to 4 reagent detected the LMPs encoded by each of 20 geographically distinct EBV isolates, despite a degree of inter-isolate heterogeneity in the size and antigenicity of the protein. In cell lines carrying the prototype B95.8 virus strain, particularly if these were virus producers, an additional lower molecular weight LMP was also detected; this appeared to correspond to the truncated form of the protein already predicted to exist from the analysis of B95.8 lytic cycle mRNAs. Attempts were made to identify an analogous truncated form of LMP in cell lines carrying other virus isolates after treatment with phorbol ester and/or sodium butyrate to induce virus production. Surprisingly these experiments showed that expression of the full length LMP molecule was itself strongly inducible by these agents; when monitored at the single cell level, this was a generalized response and was not restricted to cells entering a lytic cycle. Expression of LMP in EBV-transformed B cells therefore appears to be subject to a distinct type of regulation.

Influence of the Epstein-Barr virus nuclear antigen EBNA 2 on the growth phenotype of virus-transformed B cells

Epstein-Barr virus (EBV) isolates show sequence divergence in the BamHI YH region of the genome which encodes the nuclear antigen EBNA 2, a protein thought to be involved in the initiation of virus-induced B-cell transformation; type A isolates (such as B95-8 EBV) encode a 82- to 87-kilodalton EBNA 2A protein, whereas type B isolates (such as AG876 EBV) encode an antigenically distinct 75-kilodalton EBNA 2B protein. In the present work 12 type A isolates and 8 type B isolates have been compared for their ability to transform resting human B cells in vitro into permanent lymphoblastoid cell lines. Although the kinetics of initial focus formation was not markedly dependent upon the EBNA 2 type of the transforming virus, on subsequent passage type A virus-transformed cells (type A transformants) yielded cell lines much more readily than did type B transformants. Direct comparison between the two types of transformant revealed clear differences in several aspects of growth phenotype. Compared with type A transformants, cell lines established with type B virus isolates consistently displayed an unusual growth pattern with poor survival of individual cells shed from lymphoblastoid clumps, a lower growth rate and a greater sensitivity to seeding at limiting dilutions, and a significantly lower saturation density that could not be corrected by supplementation of the medium with culture supernatant containing B-cell growth factors. This is the first direct evidence that, in EBV-transformed B-cell lines, the EBNA 2 protein plays a continuing role in determining the cellular growth phenotype.

Epstein-Barr virus nuclear antigen 2 specifically induces expression of the B-cell activation antigen CD23

Epstein-Barr virus (EBV) infection of EBV-negative Burkitt lymphoma (BL) cells induces some changes similar to those seen in normal B lymphocytes that have been growth transformed by EBV. The role of individual EBV genes in this process was evaluated by introducing each of the viral genes that are normally expressed in EBV growth-transformed and latently infected lymphoblasts into an EBV-negative BL cell line, using recombinant retrovirus-mediated transfer. Clones of cells were derived that stably express the EBV nuclear antigen 1 (EBNA-1), EBNA-2, EBNA-3, EBNA-leader protein, or EBV latent membrane protein (LMP). These were compared with control clones infected with the retrovirus vector. All 10 clones converted to EBNA-2 expression differed from control clones or clones expressing other EBV proteins by growth in tight clumps and by markedly increased expression of one particular surface marker of B-cell activation, CD23. Other activation antigens were unaffected by EBNA-2 expression, as were markers already expressed on the parent BL cell line, including BL markers (cALLA and BLA), proliferation markers (transferrin receptor and BK19.9), and cell adhesion-related molecules (LFA-1 and LFA-3). Increased CD23 expression in cells expressing EBNA-2 was apparent from monoclonal anti-CD23 antibody binding to the cell surface, from immunoprecipitation of the 45-kDa and 90-kDa CD23 proteins with monoclonal antibody, and from RNA blots probed with labeled CD23 DNA. The results indicate that EBNA-2 is a specific direct or indirect trans-activator of CD23. This establishes a link between an EBV gene and cell gene expression. Since CD23 has been implicated in the transduction of B-cell growth signals, its specific induction by EBNA-2 could be important in EBV induction of B-lymphocyte transformation.

Epstein-Barr virus-specific T-cell recognition of B-cell transformants expressing different EBNA 2 antigens

Epstein-Barr (EB) virus isolates can be classified as type A or type B depending upon the identity of the virus-encoded nuclear antigen EBNA 2; the EBNA 2A and 2B proteins show limited amino-acid homology and induce largely non-cross-reactive antibody responses in humans. To examine whether EBNA 2 might also be a target for virus-specific cytotoxic T-cell responses (like "intracellular" antigens in other viral systems), normal B cells from non-immune donors of known HLA type were transformed in vitro with virus isolates either of type A (from the B95-8 and IARC-BL74 cell lines) or of type B (from the AG876 and IARC-BL16 cell lines) to provide a suitable panel of target cells. DNA hybridization with type-specific probes and immunoblotting with type-specific antisera confirmed the EBNA 2 type of the resident virus in the various in vitro transformants. These cells were then tested as targets for virus-specific cytotoxic T cells, the latter being prepared from type-A virus-infected donors by in vitro reactivation of memory cells from peripheral blood using autologous type-A virus-transformed cells as stimulators. Such effector cells lysed type-A virus-transformed and type-B virus-transformed target cells equally well, indicating that EBNA 2 (in particular that part of the protein which varies between virus types) seems not to be a dominant antigen for the induction of EB virus-specific cytotoxic responses.

Evidence for an association between CD23 and the receptor for a low molecular weight B cell growth factor

Low molecular weight B cell growth factor (BCGF) and a monoclonal antibody (MHM6) to the 45-kDa, B lineage-restricted, CD23 activation antigen (BLAST-2; EBVCS) were found to be indistinguishable in their biological effects. Individually, both augmented DNA synthesis in activated, but not resting, B lymphocytes while no additional enhancement resulted from using the two agonists in combination. Furthermore, by increasing the expression of Tac, both MHM6 and BCGF promoted activated B cells to respond more vigorously to the late addition of recombinant interleukin 2. The presence of BCGF during B cell activations was found to down-regulate the expression of the CD23 antigen while the coating of activated cells with MHM6 antibody diminished their capacity to absorb BCGF activity. The findings demonstrate that CD23 and a low molecular weight BCGF deliver a comparable growth-promoting signal to activated B cells. A possible relationship between CD23 and the receptor for the low molecular weight BCGF is discussed.

Restricted expression of EBV latent genes and T-lymphocyte-detected membrane antigen in Burkitt's lymphoma cells

Certain newly established Epstein-Barr virus-containing Burkitt's lymphoma cell lines do not express the cytotoxic T-lymphocyte-detected membrane antigen (LYDMA) through which EBV infection is normally controlled by the host. When the EB virus recovered from these BL lines was used to transform peripheral blood lymphocytes from seronegative donors, the lymphoblastoid cell lines (LCLs) that arose were all LYDMA positive. This indicates that the LYDMA-negative nature of the BLs is not the result of a mutation in the resident viral genome but is rather a specific adaptation in those cells, perhaps permitting evasion of the host immune surveillance in tumour development. A comparison of the EBV gene expression in six LYDMA-negative and two LYDMA-positive BL lines and in their corresponding LCLs revealed that several of the BL lines did not express all of the viral gene products classically associated with latent transformation by EBV. Four out of eight cell lines showed restricted expression of the latent membrane protein (LMP) and/or the EB nuclear antigen, EBNA 2. A new level of EBV gene regulation therefore appears to be operating in some of the BL cell lines. The patterns of expression of EBV genes in the cell lines did not show any correlation with the known susceptibility of the lines to T cell killing.

Endemic Burkitt's lymphoma: phenotypic analysis of tumor biopsy cells and of derived tumor cell lines

Tumor cells from 10 patients with Epstein-Barr virus-positive endemic Burkitt's lymphoma (BL) have been examined for cell surface phenotype, both at the biopsy stage and during BL cell line outgrowth in vitro, the cultures being followed for up to 150 passages. In all 10 cases, the biopsy cells showed coexpression of the common acute lymphoblastic leukemia antigen (CALLA) and of the BL-associated glycolipid antigen (BLA) with no accompanying expression of several "lymphoblastoid" cell surface markers defined by selected monoclonal antibodies. During cell line establishment and in vitro passage, the individual BL cell lines showed different degrees of progression toward a more "lymphoblastoid" cell surface phenotype, some even losing CALLA and BLA expression while retaining the chromosomal translocations indicative of their malignant origin. This differential capacity for phenotypic progression in vitro explains much, if not all, of the heterogeneity of the BL cell phenotype apparent from many previous studies with panels of long-established lines. Such heterogeneity in vitro belies the true homogeneity of the tumor cell phenotype in vivo.

Burkitt-like lymphoma in an English child: characterisation of tumour biopsy cells and of the derived tumour cell line

An eight year old English boy presented with an abdominal undifferentiated 'Burkitt-like' lymphoma. Lymphoma cells from ascitic fluid were cultured on a human embryo fibroblast feeder layer and, after a short lag period, a cell line (DH-BL) was established which, like the original tumour, was both negative for the Epstein-Barr nuclear antigen (EBNA) and expressed a monoclonal pattern of surface immunoglobulin (alpha lambda). DH-BL also possessed the Burkitt-related 8:14 chromosome translocation in all metaphases analysed; no other chromosomal abnormalities were present. The cell surface phenotype of the original biopsy cells and the cultured tumour cells in early passage were investigated using a panel of monoclonal antibodies to B lineage-associated antigens. These antibodies had recently been used to characterise African 'endemic' Burkitt's lymphoma (BL) biopsy cells and their derived cell lines. The cell surface phenotype of this English EBNA negative Burkitt-like lymphoma biopsy was indistinguishable from that previously shown by biopsies of EBNA positive endemic BLs. It therefore appears that both the endemic and sporadic forms of BL, as illustrated by this case, may be derived from the same subset of progenitor cells.

Ligation of the CD23,p45 (BLAST-2,EBVCS) antigen triggers the cell-cycle progression of activated B lymphocytes

CD23,p45 (BLAST-2,EBVCS) is a 45-kDa lineage-restricted antigen which appears on the surface of human B cells shortly after activation. A monoclonal antibody (MHM6) to CD23,p45, as well as a polyclonal rabbit antibody raised against the purified antigen were found to promote DNA synthesis in purified tonsillar B cells which had been activated with phorbol ester. Interleukin 1, which was not, by itself, stimulatory for either resting or activated B cells, significantly augmented the growth-promoting properties of MHM6. Kinetic studies indicated that while MHM6 exerted its influence in early G1, interleukin 1 acted later in the cycle just prior to the entry of cells into S phase. The findings demonstrate a role for CD23,p45 in triggering the progression of activated B lymphocytes through the G1 phase of the cell cycle. The possibility that this antigen serves as a receptor for a B cell stimulatory factor is discussed.

Control of human B-lymphocyte replication. I. Characterization of novel activation states that precede the entry of G0 B cells into cycle

Tonsillar B lymphocytes of a particularly high buoyant density were prepared essentially free of contaminating monocytes and T cells. When exposed to anti-immunoglobulin, such cells initiated the hydrolysis of inositol phospholipids. This provides a postulated 'dual signal' for growth through the liberation of intracellular calcium stores and the activation of protein kinase C. Nevertheless, neither anti-immunoglobulin nor direct agonists of this bifurcating pathway (respectively, calcium ionophore and the phorbol ester TPA) were capable, when used alone, of driving cells out of G0 and into RNA synthesis. All three agents did, however, induce two activation antigens at the surface of G0 B cells, which included CD23, p45 and a lineage-unrestricted antigen identified by the monoclonal antibody BK.19.9. Cells that had been exposed to calcium ionophore, but not those activated with either TPA or anti-immunoglobulin, revealed further change indicated by an increased accessibility of their native DNA for the intercalating dye acridine orange. Cells receiving full mitogenic signals in the form of Staphylococcus aureus Cowan Strain I (SAC) or a combination of TPA and calcium ionophore showed the same initial sequelae but continued to enter the cell cycle and progress through to DNA synthesis. The observations identify two phases in the early activation of human B cells, both in terms of various temporal events, and the signals required to promote each activation state. before entering the proliferative cycle. Thus, the exit of human B cells from G0 appears subject to multiple controls that precede those associated with G1 and later phases of the cell cycle.

Control of human B-lymphocyte replication. II. Transforming Epstein-Barr virus exploits three distinct viral signals to undermine three separate control points in B-cell growth

Highly purified resting (Go) B lymphocytes were monitored for their response to transforming Epstein-Barr virus (B95-8 strain), to a non-transforming mutant (P3HR-1) containing a deletion in the EBNA-2 coding region, and to inactivated virus of either type. All preparations induced an early appearance of two activation antigens, which included the CD23,p45 ("Blast-2') antigen. Thus, virus binding was sufficient for an initial activation step. Further change required an active viral genome. Infection with the P3HR-1 strain prompted the exit of cells out of Go but led to an arrest in the early G1 phase of the cycle. While initially showing sequels to activation indistinguishable from those observed with P3HR-1 virus, cells infected with B95-8 virus continued through G1 to express late activation antigens, enter S-phase and complete the replicative cycle. The addition of the phorbol ester TPA was found to compensate for the abortive cell cycle entry achieved with the P3HR-1 mutant, but could not supplement the minimal activation observed with inactivated virus. These findings demonstrate that the Epstein-Barr virus undermines three separate control points in the growth cycle of human B lymphocytes, and exploits three distinct viral signals to achieve this end.

Epstein-Barr virus status and tumour cell phenotype in sporadic Burkitt's lymphoma

Burkitt's lymphoma (BL) biopsy cells and derived cell lines can be grouped according to their patterns of reactivity with 6 selected monoclonal antibodies (MAbs) against B cell-associated surface antigens. Group I cells react only with MAbs J5 and 38.13, recognising the common acute lymphoblastic leukaemia antigen and a BL-associated antigen respectively; group II cells react with J5 and 38.13 and with one or more of a set of MAbs (Ki-24, MHM6, AC2, Ki-1) against "lymphoblastoid" antigens; group III cells react only with these anti-"lymphoblastoid" MAbs. Tumour biopsy cells from 17 cases of sporadic BL, 9 positive for the Epstein-Barr (EB) virus genome and 8 negative, have been analysed during the process of cell line establishment in vitro. In early passage the EB virus-negative BL cells showed either a group I phenotype or gave an additional reactivity with MAb Ki-24 which placed them in group II; these phenotypes remained essentially stable with continued growth of the cell lines for up to 50 passages. By contrast the EB virus-positive BL cells were much more susceptible to phenotypic change in vitro. Although such cells displayed a group I or group II phenotype in early passage, many of the lines soon moved into group III whilst retaining the karyotypic markers indicative of their malignant origin. These observations suggest that a resident EB virus genome can drive the in vitro progression of BL cells towards a more "lymphoblastoid" phenotype. This was confirmed in subsequent experiments where virus-negative BL cell lines were converted to EB virus positivity by in vitro infection. Clearly, therefore, phenotypic analysis of long-established lines can lead to false distinctions being drawn between the EB virus-positive and -negative forms of sporadic BL; both may derive from the same sub-population of target B cells in vivo.

Epstein-Barr virus-positive Burkitt's lymphoma cells not recognized by virus-specific T-cell surveillance

The pathogenesis of Epstein-Barr (EB) virus-positive Burkitt's lymphoma (BL) appears to involve the combined actions of virus-induced B-cell proliferation, and a rare chromosomal translocation juxtaposing c-myc and immunoglobulin gene loci in a single B cell; holoendemic malarial infection in some way facilitates the oncogenic process. Outgrowth of the EB virus-positive tumour suggests either breakdown or evasion of those immune controls, in particular cytotoxic T-cell responses against the virus-induced lymphocyte-detected membrane antigen LYDMA, which limit virus-infected B-cell numbers in healthy virus carriers. Immunosuppression, such as that which malarial infection may induce, cannot itself be a sufficient explanation in this regard since our studies have identified a number of BL patients who retain detectable LYDMA-specific T-cell surveillance. The present work shows that in many cases of virus-associated BL, the emerging malignant clone is insensitive to such surveillance. Several EB virus-positive BL cell lines, recently established in vitro and expressing the class I histocompatibility locus antigens (HLAs) which restrict cytotoxic T-cell function, were not killed by HLA-matched LYDMA-specific effector populations in assays where the EB virus-positive lymphoblastoid cell line (LCL), derived from normal B cells of the same patient, sustained high levels of lysis.

Benzo(a)pyrene diolepoxide-DNA adducts detected by synchronous fluorescence spectrophotometry

Using benzo(a)pyrene (BP) as a model carcinogen we are currently applying a fluorescence technique to detect the very low levels of carcinogen-DNA adducts in human populations due to environmental exposure. In synchronous fluorescence spectrophotometry for detection of BP-diol epoxide-DNA, excitation and emission wavelengths are scanned simultaneously with a fixed wavelength difference (delta lambda) of 34 nm. Compared to conventional fluorescence methods only one peak emerges because excitation and emission peaks have to match delta lambda to show. Because of the quenching effect of DNA, samples are hydrolyzed by acid. After this, BP-diol epoxide (BPDE)- -modified DNA gives a peak at the same wavelength and of the same fluorescence yield as BP-tetrols. When DNA from peripheral blood lymphocytes of 44 coke oven workers were analyzed, 10 had a sharp peak at 379. Among 36 coke oven workers from another factory, 4 had detectable levels of adducts. A much smaller percentage of samples was positive in a group of aluminum plant workers. We have also found BPDE-DNA adducts in DNA from pulmonary alveolar macrophages and peripheral blood lymphocytes from tobacco smokers and some of the nonsmokers.

Distinctions between endemic and sporadic forms of Epstein-Barr virus-positive Burkitt's lymphoma

Tumour cell lines were established in vitro from 16 cases of Epstein-Barr (EB) virus genome-positive Burkitt's lymphoma (BL), 7 of "endemic" origin (i.e. from holoendemic malarial areas of Africa and of New Guinea) and 9 of "sporadic" origin (i.e. from outside such high-incidence areas). All the BL cell lines thus established were monoclonal by immunoglobulin isotype expression and displayed a characteristic chromosomal translocation, t(8:14) or t(8:22), confirming their malignant origin. Clear differences observed between the individual BL cell lines appeared to be related to their endemic or sporadic status. All 7 endemic cell lines began growth as a carpet of single cells, often with small, loose clumps appearing in later passage. Whilst 3 lines of sporadic origin displayed a similar pattern to the above, the majority of sporadic lines grew as large, tight clumps of cells from the first passage onwards. These differences in growth pattern were reflected by differences in cell surface phenotype, as defined in indirect immunofluorescence tests using a panel of monoclonal antibodies (MAbs) specific for B-lineage-associated antigens. BL cell lines could be classified into 3 separate groups on the basis of their reactivity with 6 particular antibodies (MHM6, AC2, Ki-1, Ki-24, J5 and 38.13). All 7 endemic BL cell lines and 2 of the 3 sporadic BL cell lines which began growth as single cells showed a group-I cell-surface phenotype (MHM6, AC2, Ki-1, Ki-24 negative; J5, 38.13 positive) in early passage. In contrast, all 6 sporadic BL cell lines which began growth in large clumps displayed a distinct group-II phenotype (MHM6, AC2, Ki-1 positive/negative; Ki-24, J5, 38.13 positive); in later passage most of these sporadic lines progressed to a group-III phenotype (MHM6, AC2, Ki-1, Ki-24 positive; J5, 38.13 negative) without loss of those immunoglobulin and chromosomal markers identifying the cells' malignant origin. These clear differences between endemic BL cell lines on the one hand and the majority of sporadic BL cell lines on the other suggest that endemic BL arises from a more restricted range of progenitor B cells than does the sporadic form of the disease.

T-cell-mediated regression of "spontaneous" and of Epstein-Barr virus-induced B-cell transformation in vitro: studies with cyclosporin A

The regression of Epstein-Barr (EB) virus-transformed B-cell outgrowth which is seen in experimentally-infected cultures of blood mononuclear (UM) cells from healthy seropositive donors can be abolished in medium containing the T-cell-suppressive agent cyclosporin A (CSA) at concentrations of 0.05 microgram/ml and above. CSA mediates its effect within the first 4 days post-infection of the UM cells and this prevents subsequent in vitro generation of the EB virus-specific cytotoxic-T-cell response which normally brings about regression. Regression can be fully restored by supplementing the CSA-treated culture with interleukin 2 (IL-2)-containing culture supernatants or indeed with purified IL-2 itself, suggesting that CSA mediates its effect in this system through inhibiting the endogenous production of IL-2 which is required to amplify the virus-specific cytotoxic response. "Spontaneous transformation" to EB virus genome-positive lymphoblastoid cell lines in noninfected cultures of UM cells from healthy seropositive donors, though rare in normal medium, is enhanced to such a degree in the presence of CSA that, for many donors, the phenomenon becomes titratable against input cell dose across the 2.0 X 10(6)-2.5 X 10(5) cells/culture range. Cell mixing experiments suggest that the spontaneously transformed cell lines which arise with such efficiency under these conditions do so not by direct in vitro outgrowth of progenitor cells transformed by the virus in vivo, but by a two-step mechanism involving virus release and secondary infection in vitro.

Heparin prevents formation of the human C3 amplification convertase by inhibiting the binding site for B on C3b

Fluid-phase heparin prevents generation of the C3 amplification convertase of human complement, C3b, Bb most likely by inhibiting the formation of the bimolecular complex between cell-bound C3b and B. The effect of heparin on the binding of B to C3b was examined using 125I-labelled B and C3b-bearing sheep erythrocytes (EsC3b). In the absence of heparin, B bound to EsC3b with an affinity of 0.5-1 X 10(6) M-1 in the presence of 5 mM Mg2+. Incremental amounts of heparin (100-700 micrograms/10(7) EsC3b) inhibited the binding of 125I-B to C3b in a dose-dependent manner. Scatchard analysis of the binding data in the presence of four inhibitory concns of heparin revealed that heparin did not affect the binding affinity of B for C3b but decreased the number of C3b sites recognized by B on the cells. No inhibition of binding occurred in the presence of totally (N- and O-) desulfated heparin which has no anticomplementary activity. These results demonstrate that heparin prevents generation of the C3 amplification convertase by binding to cell-bound C3b and masking the binding site for B on C3b.

Selective reactivation of Epstein-Barr virus-specific cytotoxic T cells by stimulation in vitro with allogeneic virus-transformed HLA-homozygous typing cells

Epstein-Barr (EB) virus-specific cytotoxic T-cell preparations, produced by stimulation in vitro of peripheral blood lymphocytes with the autologous virus-transformed cell line, are HLA-A and B antigen-restricted and, with some donors, show preferential restriction through one or two of the four relevant antigens of the donor's HLA type. It has now been demonstrated that such EB virus-specific cytotoxic T cells may also be reactivated by stimulation with allogeneic virus-transformed cells provided that there is no mismatch of the HLA-A and B antigens between the responder and stimulator cell donors. In particular, virus-transformed cell lines from HLA-homozygous donors HLA-A and B antigen-matched to one of the haplotypes of an HLA-heterozygous responder were shown to reactivate selectively only those EB virus-specific cytotoxic T cells restricted through the HLA-A and B antigens present on the allogeneic stimulating cells. In addition to confirming the polyclonal nature of the HLA-restricted EB virus-specific cytotoxic T-cell response, this new experimental procedure has allowed the production, and subsequent expansion as cell lines dependent upon T-cell growth factor, of those effector cells restricted through the "nonpreferred" HLA antigens that are poorly represented in the response induced by stimulation with autologous virus-transformed cells.

Cytotoxic T cell recognition of Epstein-Barr virus-infected B cells. III. Establishment of HLA-restricted cytotoxic T cell lines using interleukin 2

Epstein-Barr virus (EBV)-specific cytotoxic T cell precursors, present in the circulation of previously infected (seropositive) individuals, have been reactivated in vitro by challenging with autologous EBV-transformed cells, and the reactivated populations subsequently expanded as interleukin 2 (IL2)-dependent cell lines. These lines were dominated by T cells possessing the cytotoxic/suppressor cell surface phenotype and, when tested for effector function in chromium-release assays, demonstrated potent EBV-specific, HLA-A and -B antigen-restricted cytotoxicity even when derived from seropositive donors whose initial cytotoxic response to in vitro reactivation was relatively weak. With all the lines tested from 10 seropositive donors, strong killing of autologous EBV-transformed cells was observed in the absence of any significant lysis of autologous mitogen-stimulated lymphoblasts or of a panel of EBV genome-negative cell lines sensitive to natural killing. Furthermore, the availability of IL2-expanded effectors cell populations allowed their being tested upon a wide panel of allogeneic EBV-transformed targets such that the dominant HLA-restricted reactivities within these populations could be identified. Monoclonal antibody blocking experiments confirmed that lysis of the autologous EBV-transformed cell line by IL2-expanded effectors could be specifically inhibited (a) by pretreatment of the target cells with antibodies binding to the HLA/beta 2-microglobulin complex, and (b) by pretreatment of the effector cells with the cytotoxic/suppressor T cell-specific antibody Leu 2a.

Monoclonal antibodies to Epstein-Barr virus-induced, transformation-associated cell surface antigens: binding patterns and effect upon virus-specific T-cell cytotoxicity

Spleen cells from mice immunized with Epstein-Barr virus-transformed lymphoblastoid cells (EB-LCL) were used to generate monoclonal antibodies to cell surface antigens associated with the EB virus-transformed state. Radioimmune and immunofluorescence binding assays identified two antibodies, MHM6 and AC2, which reacted consistently with all EB-LCL tested, with a subpopulation of cells in some but not all EB virus genome-positive Burkitt lymphoma lines, but with none of a range of EB virus genome-negative cell lines of lymphoma or leukaemia origin. While MHM6 appeared to bind an EB virus-related antigen, AC2 bound some other cell surface antigen which was also found on a small subpopulation of cells in lymphocyte cultures stimulated with phytohaemagglutinin or with pokeweed mitogen. MHM6 and AC2 recognized single polypeptides with apparent molecular weights of 45 kd and 80 kd respectively as shown by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 125I-labeled cell surface polypeptides immunoprecipitated with these antibodies. These polypeptides were induced on experimentally-infected B cells within 24 h of the expression of the EB virus nuclear antigen, EBNA, at a time known to coincide with the appearance of the lymphocyte-detected membrane antigen, LYDMA. However, saturating concentration of MHM6 and AC2 were unable to protect EB-LCL target cells from lysis by LYDMA-specific cytotoxic T cells in a chromium-release assay.

Reactivation of Epstein-Barr virus-specific cytotoxic T cells by in vitro stimulation with the autologous lymphoblastoid cell line

Unfractionated mononuclear (UM) cells and T cells freshly prepared from the blood of adult donors were co-cultivated in microtest plate wells with progressively lower numbers of cells from the autologous EB-virus-transformed B-cell line. The fresh cells present in co-cultures from EB virus antibody-negative (seronegative) donors regularly facilitated autologous cell line outgrowth, monitored after 4 weeks, whereas outgrowth was markedly inhibited in the corresponding co-cultures from seropositive donors. Larger-scale co-cultures, set up at a ratio of 80-100 fresh UM cells to one autologous virus-transformed B cell, were harvested after 8 to 12 days and the T-cell subpopulation was examined for cytotoxicity both by growth inhibition and by chromium release assays. Cytotoxic T cells were generated exclusively in seropositive donor co-cultures and were strongly active against the autologous virus-transformed cell line without affecting either autologous uninfected B cells or any of a range of EB virus genome-negative target cell lines chosen as sensitive indicators of non-specific cytotoxicity. Recognition of allogeneic EB-virus-transformed cells was restricted to those whose HLA-A and/or B and/or B and/or C antigen expression matched that of the effector cells themselves;; moreover target cell lysis was specifically inhibited in the presence of monoclonal antibodies binding to these HLA antigens. The results indicate that EB-virus-specific HLA-restricted memory T cells, present in the blood of previously-infected individuals, can be reactivated in vitro using the established autologous virus-transformed cell line as a stimulus. THe reactivated cytotoxic cells appear to recognize a virus-induced lymphocyte-detected membrane antigen, LYD-MA, analogous to that first invoked to explain the cytotoxic response to primary EB virus infection observed during infectious monoucleosis.

Bioavailability of 11 quinidine formulations adn pharmacokinetic variation in humans

The bioavailabilities of eight quinidine sulfate, two gluconate, and one polygalacturonate formulations were compared, with one of the sulfate formulations as a reference (R) in a panel of 24 volunteers, according to a design comprising duplicate 6 x 6 Latin squares in two subject groups. Only one gluconate formulation (H) gave a significantly lower (p less than 0.05) area under the curve from 0 to 30 hr (AUC30), 90% or R, which was not as significant as AUC infinity (94% of R). Formulation H also gave a significantly lower peak concentration (Cmax) and a longer time to peak concentration (tmax) and generally exhibited some characteristics of sustained-release product. In addition, one product (F) gave a significantly higher Cmax while another formulation (D) gave a longer tmax. The wide range of dissolution times obtained with these products with three test conditions was not reflected in the AUC, Cmax, or tmax values obtained, except the Formulation H was consistently the slowest to dissolve. The terminal rate constants, expressed as t 1/2, of the 24 subjects gave an overall mean of 7.49 +/- 0.77 hr and ranged from 6.24 +/- 0.28 to 0.49 +/- 0.90 hr in individuals. The estimated total body clearance, with the assumption that the oral bioavailability was 70%, gave an overall mean of 4.22 +/- 1.05 and ranged from 2.49 +/- 0.28 to 6.42 +/- 0.70 mg/min/kg in individuals, demonstrating the wide range of quinidine disposition even in healthy subjects; this finding is in agreement with recently published results.

The effect of sympathetic nerve stimulation on responses of cutaneous pacinian corpuscles in the cat

In the cat electrical stimulation of the distal segments of transected sympathetic nerves to the forelimb produces either an increase or a decrease in the responsiveness of the Pacinian corpuscles under the glabrous skin of th forepaw when the corpuscles are stimulated with high frequency mechanical vibration. The minimum latency of the change in Pacinian response is about 1-2 sec. As these effects could be stimulated by reduction in the forelimb blood supply it is probable that the changes in cutaneous corpuscle responsiveness following sympathetic stimulation are caused by local changes in blood flow.

Lymphocyte 5'-nucleotidase in primary hypogammaglobulinaemia and cord blood

The 5'-nucleotidase (5'-N) deficiency on circulating mononuclear cells of patients with 'common variable' hypogammaglobulinaemia (CV-H) was shown to be the result of one or more of three factors: reduced T cell 5'-N activity, a reduced percentage of circulating B cells, and a low B cell 5'-N activity. A lack of circulating B lymphocytes, together with a low T cell 5'-N activity in some cases, was found to be responsible for the deficiency of lymphocyte 5'-N in patients with X-linked hypogammaglobulinaemia (X-H). The low levels of 5'-N activity in CV-H and X-H patients were not due to abnormal compartmentalization of the enzyme, altered enzyme kinetics, or the presence of a regulatory factor. Cord Blood B and T cells have a lower 5'-N activity than adult lymphocytes. The patient and cord blood data are discussed in relation to the stage of cellular maturity.

Metabolism and disposition of trimethadione in pregnant rats

The metabolism and disposition of a suspected human teratogen, trimethadione (TMO), was studied in pregnant rats following administration of the drug at doses of 60 and 240 mg/kg/day during 6 to 15 days of gestion, with a view to understanding the fetotoxicity of the drug. Following the last dose, animals were sacrificed at 6, 12, and 24 hr, and the fetuses were removed by caesarean section. The concentrations of TMO and its N-demethylated metabolite, dimethadione (DMO), were determined by a specific GLC procedure in maternal plasma, urine, brain, and liver, as well as in placenta and whole fetus. The plasma and liver concentrations of TMO and DMO suggested that the parent drug is rapidly converted to DMO. Total 24 hr urinary recoveries of the unchanged drug and the metabolite were 61 and 82% following 240 and 60 mg/kg/day doses of TMO, respectively. The DMO concentrations in brain and all other tissues analyzed were far greater than those of TMO. The fetus to maternal plasma concentration ratios of TMO suggested that the placental transfer of the drug was greater than the clearance from the fetus over the periods examined, whereas the transfer of the metablite seemed to be independent of dose. Furthermore, the rate of decline of DMO in fetus was far slower than that of the placenta and maternal plasma, causing accumulation of DMO in the fetus. The results suggest that the fetotoxic effects produced by TMO when given to pregnant rats could be due to accumulation of DMO in fetus.

5'-nucleotidase of B and T lymphocytes isolated from human peripheral blood

The ecto-5'-nucleotidase activities of highly purified T and B lymphocytes from human peripheral blood have been investigated using biochemical and histochemical techniques. The enzyme activity of the purified B cells was about 3.5 times that of the T cells. Using a histochemical assay, 21--55% of the B cells stained positively for 5'-nucleotidase, but only 2--22% of the T cells were positive. These results are discussed in relation to the low 5'-nucleotidase activities found on peripheral blood lymphocytes from patients with chronic lymphatic leukaemia and some patients with primary hypogammaglobulinaemia.

Coding of information about tactile stimuli by neurones of the cuneate nucleus

1. The responses of cuneate neurones to controlled tactile stimulation of the foot pads were examined in unanaesthetized, decerebrate cats. The neurones were divided into three functional classes; one sensitive to steady tactile stimuli, and two dynamically sensitive classes which could be readily differentiated by their responsiveness to cutaneous vibration. Each class appeared to receive an exclusive input from only one of the three known groups of tactile receptors associated with the foot pads, namely the Pacinian corpuscles, the Merkel endings and the intradermal, encapsulated endings known as Krause or Meissner corpuscles. 2. Cuneate neurones responsive to steady indentation of the skin displayed approximately linear or sigmoidal stimulus-response relations over indentation ranges up to approximately 1.5--2 mm. Response variability at a fixed stimulus intensity was relatively low and showed little systematic change over the full range of the stimulus-response curves. 3. One class of dynamically sensitive cuneate neurones responded to cutaneous vibration over a range of approximately 5-80 Hz with maximal responsiveness around 30 Hz. The other class, the Pacinian neurones, responded over a range of approximately 80- greater than 600 Hz with maximal responsiveness at 200-400 Hz. The thresholds and combined band width of vibratory sensitivity of these populations were comparable with known subjective thresholds and range of cutaneous vibratory sensibility. 4. Responses of cuneate neurones were phase-locked to the vibratory stimulus suggesting that information about vibration frequency could be coded by the patterns of impulse activity. Quantitative measures indicated that maximal phase-locking occurred in responses to vibration frequencies of 10-50 Hz with a progressive decline at higher frequencies. Above 400 Hz, impulse activity occurred almost randomly throughout the vibratory stimulus cycle and therefore carried little further signal of vibratory frequency. The decline, with increasing frequency, in the ability of cuneate neurones to signal information about vibratory frequency parallels the known subjective capacities for frequency discrimination. 5. A switch-over occurred at approximately 80 Hz in the population of cuneate neurones able to provide the more reliable signal of vibratory frequency; above 80 Hz, the Pacinian neurones; below 80 Hz, the neurones receiving intradermal, rapidly adapting receptor input from the pads. 6. The observed properties of cuneate neurones are compatible with a role in signalling information which could contribute to subjective tactile abilities.

Human tactile detection thresholds: modification by inputs from specific tactile receptor classes

1. Human detection thresholds for a vibratory stimulus applied to the volar surface of the index finger were examined under conditions where afferents from specific tactile receptor classes were simultaneously activated from the thenar eminence. The experiments were designed to test whether stimuli which have been shown previously to induce afferent inhibition of ;tactile' neurones in the cuneate nucleus of the cat could modify human subjective performance in a tactile detection task. Conditioning stimuli to the thenar eminence were usually of three forms; steady indentation to engage slowly adapting tactile receptors; 300 Hz vibration to engage Pacinian corpuscles; and 30 Hz vibration to engage the intradermal, rapidly adapting tactile receptors which are thought to be Meissner's corpuscles.2. In ten subjects the mean detection threshold for a 30 Hz test stimulus in the absence of conditioning stimulation was 8.6 +/- 1.0 mum (S.E.). Detection thresholds were increased substantially in the presence of a 300 Hz, 100 mum conditioning stimulus (mean increase 11.1 +/- 2.0 mum), whereas minor or insignificant effects were seen with conditioning stimuli consisting of (a) 30 Hz, 100 mum (mean increase 1.4 +/- 0.8 mum), (b) steady indentation, 1.5 mm in amplitude (mean increase 1.3 +/- 0.7 mum) or (c) 300 Hz, 100 mum to the contralateral thenar eminence (mean increase 0.4 +/- 0.5 mum).3. The 300 Hz conditioning stimulus to the ipsilateral thenar eminence caused a marked increase in detection thresholds at all test stimulus frequencies over the range 10-450 Hz. The effects of the conditioning stimulation therefore operated on inputs from Pacinian corpuscles, which are responsible for vibration detection at 80-450 Hz, and on inputs from the intradermal, rapidly adapting receptors which are responsible for vibration detection at 10-80 Hz.4. The band width of conditioning vibratory frequencies which was effective at amplitudes of 100 mum in bringing about increases in detection threshold extended from 50-80 Hz to 300 Hz, the maximum tested.5. Whereas amplitudes of 1-2 mum produced clear increases in detection thresholds with conditioning stimuli of 300 Hz, amplitudes of > 200 mum were needed at 30 Hz.6. The observed elevations in detection threshold are consistent with an afferent-induced inhibitory action exerted at synaptic relays of the sensory pathway by tactile inputs arising exclusively or predominantly from Pacinian corpuscles.

Inhibition of cuneate neurones: its afferent source and influence on dynamically sensitive "tactile" neurones

1. Responses were recorded in decereberate, unanaesthetized cats from individual cuneate neurones in order to determine firstly, the afferent sources of inhibition on cuneate neurones and secondly, the influence of afferent-induced inhibition on those response features of dynamically sensitive tactile neurones which determine their capacity to code information about parameters of tactile stimuli.2. For all cuneate neurones which displayed afferent-induced inhibition from areas surrounding or within their excitatory receptive field (71% of the sample) it was consistently found that 300 Hz vibration at low amplitudes (< 25-50 mum) which selectively engages Pacinian corpuscles was an effective source of inhibition. In contrast, steady indentation which activates slowly adapting tactile afferents was quite ineffective, as was low frequency vibration (30 Hz) at amplitudes of < 50-100 mum. The latter stimulus can be used to engage rapidly adapting receptors either within glabrous skin (presumed to be Meissners corpuscles) or in association with hair follicles. It is concluded that afferents from Pacinian corpuscles are the dominant or exclusive source of afferent-induced inhibition of cuneate neurones.3. For dynamically sensitive neurones responsive to low frequency cutaneous vibration (30 Hz) there was a reduction in the slope of stimulus-response relations with afferent-induced inhibition, but no expansion of the range of stimulus amplitudes over which the neurone responded.4. The influence of afferent-induced inhibition on the phase-locking of impulse activity to a cutaneous vibratory wave form was examined by constructing post-stimulus time histograms and cycle histograms. Measures of dispersion of impulse activity around the preferred point of firing in the vibratory waveform indicated that the capacity of individual cuneate neurones to code information about the frequency of the cutaneous vibration was not systematically changed in the presence of afferent-induced inhibition.