Rapid quasi-periodic oscillations in the relativistic jet of BL Lacertae.

Blazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales1-3. This variability seems mostly random, although some quasi-periodic oscillations (QPOs), implying systematic processes, have been reported in blazars and other AGN. QPOs with timescales of days or hours are especially rare4 in AGN and their nature is highly debated, explained by emitting plasma moving helically inside the jet5, plasma instabilities6,7 or orbital motion in an accretion disc7,8. Here we report results of intense optical and γ-ray flux monitoring of BL Lacertae (BL Lac) during a dramatic outburst in 2020 (ref. 9). BL Lac, the prototype of a subclass of blazars10, is powered by a 1.7 × 108 MSun (ref. 11) black hole in an elliptical galaxy (distance = 313 megaparsecs (ref. 12)). Our observations show QPOs of optical flux and linear polarization, and γ-ray flux, with cycles as short as approximately 13 h during the highest state of the outburst. The QPO properties match the expectations of current-driven kink instabilities6 near a recollimation shock about 5 parsecs (pc) from the black hole in the wake of an apparent superluminal feature moving down the jet. Such a kink is apparent in a microwave Very Long Baseline Array (VLBA) image.

Antigenically distinct conformations of CXCR4.

The major human immunodeficiency virus type 1 (HIV-1) coreceptors are the chemokine receptors CCR5 and CXCR4. The patterns of expression of the major coreceptors and their use by HIV-1 strains largely explain viral tropism at the level of entry. However, while virus infection is dependent upon the presence of CD4 and an appropriate coreceptor, it can be influenced by a number of factors, including receptor concentration, affinity between envelope gp120 and receptors, and potentially receptor conformation. Indeed, seven-transmembrane domain receptors, such as CCR5, can exhibit conformational heterogeneity, although the significance for virus infection is uncertain. Using a panel of monoclonal antibodies (MAbs) to CXCR4, we found that CXCR4 on both primary and transformed T cells as well as on primary B cells exhibited considerable conformational heterogeneity. The conformational heterogeneity of CXCR4 explains the cell-type-dependent ability of CXCR4 antibodies to block chemotaxis to stromal cell-derived factor 1 alpha and to inhibit HIV-1 infection. In addition, the MAb most commonly used to study CXCR4 expression, 12G5, recognizes only a subpopulation of CXCR4 molecules on all primary cell types analyzed. As a result, CXCR4 concentrations on these important cell types have been underestimated to date. Finally, while the factors responsible for altering CXCR4 conformation are not known, we found that they do not involve CXCR4 glycosylation, sulfation of the N-terminal domain of CXCR4, or pertussis toxin-sensitive G-protein coupling. The fact that this important HIV-1 coreceptor exists in multiple conformations could have implications for viral entry and for the development of receptor antagonists.

TH1 cytokine response of CD57+ T-cell subsets in healthy controls and patients with alcoholic liver disease.

Patients with chronic inflammatory diseases, including Crohn's disease and rheumatoid arthritis, as well as those with certain viral infections, and patients who are transplant recipients or who have certain hematologic malignancies have been observed to have CD57+ T cell expansion in both CD4+ and CD8+ subsets. We have reported previously that alcoholic patients also have CD57+ T cell expansion. Because many alcoholics become seriously deficient in cell-mediated immunity, it is of interest to determine whether the expanded CD57+ subsets can respond to stimulation with normal T helper cell subtype 1 (TH1) cytokine production. We report evaluation of the CD57 T-cell subsets of patients with alcoholic liver disease (ALD) with the use of cytoplasmic staining after stimulation through the T-cell receptor (TCR). The CD57+ subsets of the T cells of both healthy individuals and patients with ALD express significantly higher amounts of cytoplasmic tumor necrosis factor-alpha (TNF-) and interferon-gamma (IFN-) after 6 h of stimulation than do the CD57- subsets. This increased production can persist up to 46 h of continuous stimulation. Under these assay conditions, very little cytoplasmic interleukin (IL)-4 is observed in the T cells of either healthy control subjects or patients with ALD. Measurement of cytokine secretion by sort-purified CD57 T-cell subsets with the use of enzyme-linked immunosorbent assay (ELISA) shows that the CD57+ T-cell subset produces 18- to 30-fold more TNF- and IFN-, respectively, than does the CD57- subset in the first 12 h of stimulation. This response requires only stimulation through the TCR for the CD57+ subset, whereas significant secretion by the CD57- subset requires added IL-2 or anti-CD28 antibody. These results are consistent with the concept of the CD57+ T-cell subset as a differentiated effector cell and demonstrate that patients with ALD who are not drinking at the time of evaluation have normal or increased immediate TH1 T-cell responses.

Quantification of active caspase 3 in apoptotic cells.

We describe an enzyme-linked immunosorbent assay (ELISA) for quantifying relative amounts of active caspase 3 in apoptotic cells. Covalent modification of caspase 3 active sites with a biotinylated inhibitor differentiates active from latent caspases. Capture on an ELISA plate with an antibody specific for caspase 3 makes the assay specific for caspase 3. Detection is with horseradish peroxidase (HRP)-conjugated streptavidin that binds to the biotinylated inhibitor covalently bound to caspase 3. Using the assay we detected 6.6 ng active caspase 3 per 10(6) apoptotic staurosporine-treated Jurkat cells. Specificity of the assay for caspase 3 was demonstrated by lack of signal with purified caspases 2, 7, 8, and 10 that were modified by a biotinylated inhibitor. Specificity was also demonstrated by lack of signal with apoptotic MCF-7 cells which do not express caspase 3. The ability to discriminate between active and latent caspase 3 was shown by Western blotting with HRP-streptavidin and anti-caspase 3. Although latent caspase 3 was captured it was not covalently modified with the biotinylated inhibitor. The basic principle of using a covalent inhibitor to identify active enzymes and an antibody to differentiate between enzymes with similar activities has potential for quantifying active members of many classes of enzymes.

Factor(s) secreted by AFT024 fetal liver cells following stimulation with human cytokines are important for human LTC-IC growth.

Soluble factors produced by human marrow stroma or the murine marrow derived M2-10B4 cell line support ex vivo maintenance for 5-8 weeks of 50% of human long-term culture initiating cells (LTC-IC). As the AFT024 cell line supports LTC-IC cultured in contact conditions better than M2-10B4 feeders, we evaluated LTC-IC support in non-contact conditions above AFT024 feeders. We show that only 15% of LTC-IC were maintained for 5 weeks in AFT024 non-contact cultures (n=6, P<0.05). As AFT024-conditioned media added to M2-10B4 non-contact cultures did not inhibit LTC-IC maintenance, AFT024 cells do not secrete factors that inhibit LTC-IC growth. We next characterized heparan sulfate glycosaminoglycans (HS-GAGs) and cytokines produced by AFT024 cells, which are both required for LTC-IC maintenance in M2-10B4 non-contact cultures. The size and extent of O-sulfation of HS-GAGs in AFT024 and M2-10B4 conditioned medium were similar, indicating that absence of hematopoietic specific HS-GAGs is not responsible for the lack of hematopoietic in AFT024 non-contact cultures. Levels of 13 different cytokines secreted in AFT024- and M2-10B4-conditioned medium were similar. However, addition of human SCF, G-CSF, GM-CSF, LIF, MIP-1alpha and IL-6 in concentrations found in human marrow stroma-conditioned medium to AFT024 non-contact cultures increased LTC-IC-maintenance to 72% at 5 weeks. These cytokines improved LTC-IC maintenance in part through interaction with the progenitors and in part, through interaction with the AFT024 feeder. Thus, although LTC-IC maintenance is poor in AFT024 non-contact cultures, addition of human cytokines enhances LTC-IC maintenance in part through indirect effects on the AFT024 feeder. Characterization of known or novel growth factors secreted by AFT024 cells before and after cytokine stimulation may lead to the identification of cytokines that support growth of human hematopoietic stem cells.

IgM heavy chain complementarity-determining region 3 diversity is constrained by genetic and somatic mechanisms until two months after birth.

Due to the greater range of lengths available to the third complementarity determining region of the heavy chain (HCDR3), the Ab repertoire of normal adults includes larger Ag binding site structures than those seen in first and second trimester fetal tissues. Transition to a steady state range of HCDR3 lengths is not complete until the infant reaches 2 mo of age. Fetal constraints on length begin with a genetic predilection for use of short DH (D7-27 or DQ52) gene segments and against use of long DH (e.g., D3 or DXP) and JH (JH6) gene segments in both fetal liver and fetal bone marrow. Further control of length is achieved through DH-specific limitations in N addition, with D7-27 DJ joins including extensive N addition and D3-containing DJ joins showing a paucity of N addition. DH-specific constraints on N addition are no longer apparent in adult bone marrow. Superimposed upon these genetic mechanisms to control length is a process of somatic selection that appears to ensure expression of a restricted range of HCDR3 lengths in both fetus and adult. B cells that express Abs of an "inappropriate" length appear to be eliminated when they first display IgM on their cell surface. Control of N addition appears aberrant in X-linked agammaglobulinemia, which may exacerbate the block in B cell development seen in this disease. Restriction of the fetal repertoire appears to be an active process, forcing limits on the diversity, and hence range of Ab specificities, available to the young.

CD3 gamma, CD3 delta, and CD3 zeta mRNA in adult human marrow hematopoietic progenitors correlates with surface CD2 and CD7 expression.

Hematopoietic stem cells from adult marrow, cord blood, or fetal liver can differentiate into myeloid and lymphoid lineages. Early steps in this differentiation process are not yet fully understood. To correlate surface antigen expression with molecular events occurring during early lymphopoietic differentiation, we examined CD3 gamma, CD3 delta, and CD3 zeta gene expression in adult human CD34+ marrow progenitors and their subsets. Purification by fluorescence-activated cell sorter (FACS) was used to obtain 1) a CD34+ Lin-DR- population known to contain primitive, uncommitted progenitors; 2) CD34+/CD7+/CD2+ and 3) CD34+/CD7+/CD2+ cells expressing receptors associated with natural killer (NK) cell or T cell lineage commitment. We demonstrate that CD34+Lin-DR- cells do not contain CD3 gamma, CD3 delta, or CD3 zeta transcripts, consistent with the primitive uncommitted nature of progenitors in this cell population. Expression of the CD34+/CD7+/CD2- phenotype correlates with the transcription of CD3 zeta but not CD3 gamma or CD3 delta, a pattern of transcription observed in mature blood NK but not T cells. Expression of both CD7 and CD2 on CD34+ cells is associated with not only CD3 zeta gene transcription but also CD3 gamma and CD3 delta, a pattern found in T cells but not mature NK cells. We have identified unique patterns of mRNA transcription in phenotypically distinct lymphoid progenitors found in the marrow. These findings raise the possibility that although primitive NK and T cell progenitors share a common differentiation pathway, divergent NK and T lineage commitment steps may occur very early in lymphopoiesis. Our findings suggest that application of in vitro marrow and thymus culture techniques may be utilized to more fully describe commitment and differentiation of early lymphoid progenitors and define the role of the microenvironment in this process.

BCR/ABL-negative primitive progenitors suitable for transplantation can be selected from the marrow of most early-chronic phase but not accelerated-phase chronic myelogenous leukemia patients.

We have previously reported that selection of marrow cells on the basis of the CD34+HLA-DR- phenotype (34+DR-) may result in the recovery of Philadelphia chromosome (Ph)- and BCR/ABL-negative long-term culture-initiating cells (LTC-IC) in selected patients with chronic myelogenous leukemia (CML). We now present data on 27 early chronic-phase ([ECP] studied within 1 year after diagnosis) and 23 advanced-phase ([AP] late chronic phase, ie, studied >1 year from diagnosis, or accelerated phase) CML patients. Fluorescence-activated call-sorting (FACS)-selected 34+DR- and 34+DR+ cells were subjected to reverse transcriptase-polymerase chain reaction and fluorescence in situ hybridization. These cells were also cultured in long-term bone marrow culture for 1 to 5 weeks to examine the number of LTC-IC and the presence or absence of the BCR/ABL gene rearrangement in progeny of primitive LTC-IC. The number of 34+DR- cells and LTC-IC present in ECP CML marrow was similar to that in normal (NL) marrow, whereas the numbers were reduced in AP CML. Furthermore, 34+DR- cells from more than 80% of ECP CML patients were BCR/ABL mRNA- and Ph-negative and contained only BCR/ABL mRNA- and Ph-negative LTC-IC, whereas 34+DR- cells and LTC-IC from less than 40% of AP CML patients were BCR/ABL mRNA- and Ph-negative. In contrast to NL marrow, 34+DR+ cells from CML marrow, irrespective of clinical stage, contained large numbers of LTC-IC. CML 34+DR+ cells and LTC-IC were BCR/ABL mRNA- and Ph-positive. Since these studies suggested that a population of primitive progenitors that are Ph-negative can be selected from steady-state marrow in some ECP CML patients, we determined if similar results could be obtained when large quantities of marrow sufficient for transplantation are processed. We demonstrate that 1 to 3 x 10(5) BCR/ABL mRNA-negative 34+DR- cells/kg recipient body weight, containing only BCR/ABL mRNA-negative LTC-IC, can be obtained from a 2- to 2.5-L marrow collection by sequential COBE Spectra apheresis (COBE BCT, Lakewood, CO), CD34+ enrichment using the CEPRATE SC Cell-Concentrator (CellPro, Bothell, WA), and high-speed FACS. Thus, large-scale selection of a BCR/ABL mRNA- and Ph-negative 34+DR- cell population is possible in a fraction of chronic-phase CML patients, in whom these cells could be used to reconstitute the hematopoietic compartment following autologous transplantation.

Developmental regulation of the human antibody repertoire.

The ability to respond to antigen develops in a programmed fashion during ontogeny. In human, "fetal" immunoglobulin gene segment utilization appears biased towards a small set of evolutionarily conserved V gene segments. Many of these gene segments are also used in antibodies with antigen specificities that do not arise until after infancy. The human fetus primarily regulates the diversity of the antibody repertoire through control of the H (heavy) chain CDR 3, which is generated by VDJ joining and forms the center of the antigen-binding site. Molecular modeling suggests that limitations in the length and composition of fetal CDR 3 intervals result in antibodies that contain a relatively "flat" antigen-binding surface that could serve to maximize the number of different interactions possible between the antibody and potential antigens. We propose that these limitations in the sequence and structure of H chain CDR 3 contribute to the low affinity and multireactivity of fetal antibody repertoires. The specific mechanisms used to generate a restricted fetal repertoire appear to differ between human and mouse. Nevertheless, included in the final products of both human and mouse fetal B cells will be antibodies that are quite homologous in composition and structure. The precise role that these antibodies play in the development of immunocompetence remains to be elucidated.

The human immunoglobulin VH7 gene family consists of a small, polymorphic group of six to eight gene segments dispersed throughout the VH locus.

In this report we describe the analysis and mapping of members of the human immunoglobulin VH7 gene family. VH7 and VH1 gene segments are closely related, with individual gene segments sharing between 78% and 82% sequence identity. Divergence from VH1 gene sequence occurs as an abrupt event at the boundary between framework region (FR) 2 and complementarity-determining region (CDR) 2 and continues through a major portion of FR 3. We used polymerase chain reaction amplification to create a 162-base pair probe spanning the family-specific region of CDR 2 and FR 3 that proved suitable for standard Southern analysis of genomic DNA. The VH7 gene family was found to be a small but discrete VH gene family consisting of five to eight germ-line elements, of which at least three are polymorphic. Four different VH7 gene segments were cloned from the germ line of a single individual, and assigned to specific restriction fragments by sequence-specific hybridization. Two of the four VH7 elements were pseudogenes. The pattern of sequence variation in these and other known pseudogenes suggests that these nonfunctional elements may play a role in the evolution of novel VH families. A combination of one and two-dimensional pulsed field gel electrophoresis was employed to map the chromosomal location of all of these VH7 elements. Individual VH7 gene segments were found to be dispersed over a region of at least 940 kb of DNA, and interspersed with members from other VH gene families. The polymorphism of the VH7 gene segments and their scattered location throughout the VH locus makes them potentially useful markers for mapping and linkage studies.

Human cord blood antibody repertoire. Mixed population of VH gene segments and CDR3 distribution in the expressed C alpha and C gamma repertoires.

Developmental regulation of the diversity of the antibody repertoire is associated with the controlled stepwise acquisition of Ag responsiveness during ontogeny. The development of IgG and IgA serum levels in humans lags far behind the maturation of the rest of the immune response. We cloned cord blood mononuclear cell C gamma and C alpha transcripts and compared them with a large database of > 250 published and unpublished sequences, including C mu transcripts from this same cord blood cDNA library, to determine whether restrictions in the expressed antibody repertoire contributed to the limitations of the neonatal IgG and IgA response. We found a diverse antibody repertoire containing a high frequency of the same VH gene segments first identified in fetal liver, as well as VH elements homologous to those in the cord blood C mu transcripts. Although VH, DH, and JH utilization differed, the distribution of CDR3 lengths in the C gamma transcripts was similar to that found in fetal liver C mu transcripts, whereas the distribution of CDR3 lengths in the C alpha transcripts was similar to that found in cord blood C mu. This comprehensive analysis of the C mu, C gamma, and C alpha V domain repertoires provides new insights into our understanding of the timing of sequential B cell waves that seed peripheral lymphoid compartments during development.

Immunoglobulin VH clan and family identity predicts variable domain structure and may influence antigen binding.

Mammalian immunoglobulin VH families can be grouped into three distinct clans based upon sequence conservation in two of the three framework (FR) intervals. Through replacement/silent site substitution analysis, molecular modeling and mathematical evaluation of known immunoglobulin crystal structures, we demonstrate that this conservation reflects preservation of protein sequence and structure. Each clan contains a characteristic FR 1 interval that is solvent-exposed and structurally separated from the antigen binding site. Families within a clan contain their own unique FR 3 interval that is capable of either influencing the conformation of the antigen binding site or interacting directly with antigen. Our results provide a structural context for theories that address differential use of VH families in the immune response.

The human cord blood antibody repertoire. Frequent usage of the VH7 gene family.

We have previously demonstrated a consistent preferential usage of a small set of VH, DH and JH gene segments in second-trimester fetal liver. To examine the extent of heavy chain repertoire diversification in newborns, we generated an unrestricted cDNA library from cord blood mononuclear cells and sequenced the variable domains of randomly isolated Cmu+ transcripts. We found this set of transcripts to be enriched for JH4, 5 and 6, whereas previously reported fetal transcripts preferentially expressed JH3 and 4. The cord blood transcripts used a number of different DH gene segments, whereas fetal transcripts were enriched for DHQ52. Of the thirteen cord blood sequenced, three were members of the newly described VH7 family which to date has not been detected in fetal liver. Indeed, only one of the isolated VH gene segments had been previously observed in fetal transcripts. As a result of enhanced N-region addition and use of longer DH and JH gene segments, both the sequence diversity and range of potential antigen-binding structures of cord blood complementarity-determining region 3 domains was vastly expanded. Thus, the repertoire bias evident in fetal liver was no longer apparent in this more mature population of cord blood B cells.

Identification of a human bone marrow-derived immunoenhancing factor, BDEF.

In this report we describe the production and biological activity of human bone marrow-derived enhancing factor (BDEF). This factor is the constitutive product of cultured human BMC and could initially be recovered by ultrafiltration of cell-free BM supernatants to yield a crude fraction of Mr greater than 10,000 Da. This preparation can enhance the Ab response of human tonsillar cells, as well as murine spleen cells, to SRBC. HPLC fractionation of BM supernatants enriches for enhancing activity in a peak with an approximate Mr of 60 kDa. PAGE gel analysis reveals two protein bands which migrate to this area, one of 60 kDa, and a slightly smaller protein at 55 kDa. Antibodies generated against the above two proteins were shown to be specific by Western blotting and could recognize the native BM proteins as determined by ELISA. The antibodies were used to affinity purify the respective proteins, p60 and p55. The BM protein p60, but not p55, was able to enhance Ab synthesis in vitro and was also mitogenic for murine BMC and thymocytes. The addition of anti-p60 Ab to human tonsillar cells cultured with SRBC and human BDEF preparations resulted in abrogation of enhancement. These findings support the notion that the BM protein p60 is BDEF and that it may represent a novel enhancing molecule produced by normal human BM.

Production of human bone marrow-derived suppressor factor. Effect on antibody synthesis and lectin-activated cell proliferation.

Natural suppressor cells resident in normal human bone marrow (BM) exert potent suppressor activity on in vitro antibody responses and other immune functions. A suppressor-enriched population of BM cells can constitutively produce a soluble mediator with similar suppressor activity and kinetics as the suppressor cells. This novel BM-derived suppressor factor (BDSF) suppresses human in vitro primary antibody responses as well as lectin-activated proliferative responses. The mediator (BDSF) has a Mr of less than 1.5 kDa, contains a lipid component, and is insensitive to indomethacin treatment. The BM cells producing the factor bear the HNK-1 surface marker but not T, B, or macrophage markers. The ability of BDSF to suppress Ag-dependent IgM responses during the inductive phase makes it an ideal molecule with the potential to regulate early immune and hemopoietic events within the BM compartment.

Regulation of lymphoid colony growth by factors derived from human bone marrow.

We have previously demonstrated the ability of soluble factors derived from cultured murine and human bone marrow supernatants to modulate a variety of lymphoid functions, including DNA synthesis. In the present report, we show that human marrow supernatants contain a suppressor factor (BSF) that suppresses T-lymphoid colony formation, and an augmenting factor (BEF) that enhances T-colony growth. BSF suppression exhibits no tissue specificity, affecting marrow-derived and peripheral T colonies similarly. The suppressive activity occurs prior to mitogenic activation by TCGF. In contrast, a preferential augmentation of the size and number of marrow-derived T-cell colonies, as compared to peripheral T-cell colonies, was observed in the presence of BEF. BEF required prior mitogen activation of the colony inocula to effect colony enhancement. In addition, the response to BEF was greater for E- than for E+ colony-forming cells, indicating the target of BEF activity to be an early T cell. The active subfraction of BEF with colony-enhancing activity was found to be between 8000 and 30,000 daltons.

Immunoregulatory activity of human bone marrow. Identification of suppressor cells possessing OKM1, SSEA-1, and HNK-1 antigens.

Human bone marrow contains natural regulatory cells capable of suppressing the in vitro primary IgM response of normal tonsillar cells. The suppression is mediated by non-T cells possessing Fc receptors, OKM1, SSEA-1, and HNK-1 antigens on their surface. The suppression was abrogated by treatment of bone marrow cells (BMC) with anti-HNK-1 or anti-SSEA-1 antisera and complement. Furthermore, BMC depleted of HNK-1+ cells could respond in a primary in vitro antibody response when provided with accessory T cells and macrophages from tonsillar cells. Our findings support the idea that HNK-1+ and HNK-1- BMC populations act antagonistically in the regulation of antibody synthesis. Further, the finding of HNK-1+, SSEA-1+, and OKM1+ suppressor cells in human bone marrow may represent a precursor phenotype of mature natural killer cells with potent immunoregulatory activity.

Fractionation of human tumour-associated cells by centrifugal elutriation to establish lymphocyte, macrophage and tumor cell cultures from a single tumour biopsy.

The application of the Beckman centrifugal elutriator system for the simultaneous isolation of lymphocytes, macrophages and tumour cells from enzyme disaggregated tumour-associated cells or from peritoneal aspirates is described. Using this technique we have been able to prepare cultures of these cells from single human tumour biopsies. Overall cellular recovery was always in excess of 70% and the purity of cell fractions varied between 89 and 99%. Lymphocyte fractions were found to be free of tumour cell contamination and this allowed lymphocyte cultures in T-cell growth factor containing medium to be established. Using this approach it should prove possible to investigate the clonal effector functions of tumour infiltrating lymphocytes against autologous and allogeneic tumour cells.