Conjugation of fluorochromes to monoclonal antibodies

Detection of cell surface molecules labeled by monoclonal or polyclonal antibodies conjugated to a fluorochrome is probably the most widely used application of flow cytometry. This unit contains protocols for tagging monoclonal antibodies with fluorescein, biotin, Texas Red, and phycobiliproteins. In addition, it provides a procedure for preparing a PE-Texas Red tandem conjugate dye that can then be used for antibody conjugation. These protocols enable investigators to label antibodies of their choice with multiple fluorochromes and permit more combinations of antibodies for multicolor flow applications.

KEYWORDS

flow cytometry; monoclonal antibodies; fluorochromes; antibody labeling.

Fluorescence resonance energy transfer analysis of cell surface receptor interactions and signaling using spectral variants of the green fluorescent protein

BACKGROUND

Fluorescence resonance energy transfer (FRET) is a powerful technique for measuring molecular interactions at Angstrom distances. We present a new method for FRET that utilizes the unique spectral properties of variants of the green fluorescent protein (GFP) for large-scale analysis by flow cytometry.

METHODS

The proteins of interest are fused in frame separately to the cyan fluorescent protein (CFP) or the yellow fluorescent protein (YFP). FRET between these differentially tagged fusion proteins is analyzed using a dual-laser FACSVantage cytometer.

RESULTS

We show that homotypic interactions between individual receptor chains of tumor necrosis factor receptor (TNFR) family members can be detected as FRET from CFP-tagged receptor chains to YFP-tagged receptor chains. Noncovalent molecular complexation can be detected as FRET between fusions of CFP and YFP to either the intracellular or extracellular regions of the receptor chains. The specificity of the assay is demonstrated by the absence of FRET between heterologous receptor pairs that do not biochemically associate with each other. Interaction between a TNFR-like receptor (Fas/CD95/Apo-1) and a downstream cytoplasmic signaling component (FADD) can also be demonstrated by flow cytometric FRET analysis.

CONCLUSIONS

The utility of spectral variants of GFP in flow cytometric FRET analysis of membrane receptors is demonstrated. This method of analyzing FRET allows probing of noncovalent molecular interactions that involve both the intracellular and extracellular regions of membrane proteins as well as proteins within the cells. Unlike biochemical methods, FRET allows the quantitative determination of noncovalent molecular associations at Angstrom level in living cells. Moreover, flow cytometry allows quantitative analyses to be carried out on a cell-by-cell basis on large number of cells. Published 2001 Wiley-Liss, Inc.

A regulatory role for ADP-ribosylation factor 6 (ARF6) in activation of the phagocyte NADPH oxidase

In activated neutrophils NADPH oxidase is regulated through various signaling intermediates, including heterotrimeric G proteins, kinases, GTPases, and phospholipases. ADP-ribosylation factor (ARF) describes a family of GTPases associated with phospholipase D (PLD) activation. PLD is implicated in NADPH oxidase activation, although it is unclear whether activation of PLD by ARF is linked to receptor-mediated oxidase activation. We explored whether ARF participates in NADPH oxidase activation by formyl-methionine-leucine-phenylalanine (fMLP) and whether this involves PLD. Using multicolor forward angle light scattering analyses to measure superoxide production in differentiated neutrophil-like PLB-985 cells, we tested enhanced green fluorescent fusion proteins of wild-type ARF1 or ARF6, or their mutant counterparts. The ARF6(Q67L) mutant defective in GTP hydrolysis caused increased superoxide production, whereas the ARF6(T27N) mutant defective in GTP binding caused diminished responses to fMLP. The ARF1 mutants had no effect on fMLP responses, and none of the ARF proteins affected phorbol 12-myristate 13-acetate-elicited oxidase activity. PLD inhibitors 1-butanol and 2, 3-diphosphoglycerate, or the ARF6(N48R) mutant assumed to be defective in PLD activation, blocked fMLP-elicited oxidase activity in transfected cells. The data suggest that ARF6 but not ARF1 modulates receptor-mediated NADPH oxidase activation in a PLD-dependent mechanism. Because PMA-elicited NADPH oxidase activation also appears to be PLD-dependent, but ARF-independent, ARF6 and protein kinase C may act through distinct pathways, both involving PLD.

Measurement of molecular interactions in living cells by fluorescence resonance energy transfer between variants of the green fluorescent protein

Many signal transduction pathways operate through oligomerization of proteins into multi-subunit complexes. Although biochemical assays can identify potential protein-protein interactions, studying these interactions in living cells is more challenging. Fluorescence resonance energy transfer (FRET) has been used as a "spectroscopic ruler" to measure molecular proximity, but these methods have been limited by the need for chemical labeling of target proteins or labeled antibodies. We present methods for examining interactions between target proteins molecularly fused to cyan and yellow variants of the green fluorescent protein (GFP) by FRET in living cells. Flow cytometric and microscope-based methods are described that have been applied to a variety of interacting proteins.

Vitamin A deficiency in mice causes a systemic expansion of myeloid cells

To examine the role of retinoids in hematopoietic cell growth in vivo, we studied female SENCAR mice made vitamin A deficient by dietary restriction. Deficient mice exhibited a dramatic increase in myeloid cells in bone marrow, spleen, and peripheral blood. The abnormal expansion of myeloid cells was detected from an early stage of vitamin A deficiency and contrasted with essentially normal profiles of T and B lymphocytes. This abnormality was reversed on addition of retinoic acid to the vitamin A-deficient diet, indicating that the myeloid cell expansion is a direct result of retinoic acid deficiency. TUNEL analysis indicated that spontaneous apoptosis, a normal process in the life cycle of myeloid cells, was impaired in vitamin A-deficient mice, which may play a role in the increased myeloid cell population. Quantitative reverse transcriptase-polymerase chain reaction analysis of purified granulocytes showed that expression of not only RAR, but RXRs, 2 nuclear receptors that mediate biologic activities of retinoids, was significantly reduced in cells of deficient mice. This work shows that retinoids critically control the homeostasis of myeloid cell population in vivo and suggests that deficiency in this signaling pathway may contribute to various myeloproliferative disorders.

Peripheral blood-derived CD34+ progenitor cells: CXC chemokine receptor 4 and CC chemokine receptor 5 expression and infection by HIV

The present study demonstrates cell surface expression of both CXC chemokine receptor 4 (CXCR4) and CC chemokine receptor 5 (CCR5), major coreceptors for T cell-tropic and macrophage-tropic strains of HIV, respectively, on CD34+ progenitor cells derived from the peripheral blood. CD34+ progenitor cells were susceptible to infection by diverse strains of HIV, and infection could be sustained for prolonged periods in vitro. HIV entry into CD34+ progenitor cells could be modulated by soluble CD4, HIV gp120 third variable loop neutralizing mAb and the cognate ligands for the CXCR4 and CCR5 HIV coreceptors. This study suggests that a significant proportion of the circulating progenitor cell pool may serve as a reservoir for HIV that is capable of trafficking the virus to diverse anatomic compartments. Furthermore, the infection and ultimate destruction of these progenitor cells may explain in part the defective lymphopoiesis in certain HIV-infected individuals despite effective control of virus replication during highly active antiretroviral therapy.

Impaired generation of bone marrow B lymphocytes in mice deficient in C/EBPbeta

CAAT/enhancer binding proteins (C/EBP) are a family of transcription factors that mediates adipocyte differentiation and the regulation of genes expressed in immune responses and inflammation, such as interleukin-6 (IL-6), IL-8, and granulocyte colony-stimulating factor (G-CSF). We investigated the role of C/EBPbeta (NF-IL6) in the generation of bone marrow B lymphocytes by taking advantage of C/EBPbeta-/- mice. We found that the expansion of bone marrow (BM) B lymphocytes was impaired in long-term lymphoid cultures from C/EBPbeta-/- mice. Consistent with this finding, the number of BM B cells was decreased in C/EBPbeta-/- mice. Both the levels of IL-7 gene expression and bioactive IL-7 from BM stromal cells were decreased in C/EBPbeta-/- mice. Furthermore, the proliferative responsiveness of BM B-cell precursors to IL-7 was also reduced as compared to wild-type mice, indicating that C/EBPbeta is required for the generation of BM B cells induced by IL-7. Accordingly, IL-7 stimulates the C/EBPbeta DNA-binding activity of normal BM pre-B lymphocytes as well as of 70Z/3 pre-B cells. These results point to C/EBPbeta as a critical signaling molecule in BM B lymphopoiesis.

Characteristics of a murine gammaherpesvirus infection immunocompromised mice

BACKGROUND-MATERIALS: Mice with normal or impaired immune function were studied for responses to intranasal infection with MHV68, a gammaherpesvirus that acutely infects lung epithelial cells and establishes latency in B cells. Infection of normal mice induced a vigorous pulmonary inflammatory response composed of T, B, and NK cells and macrophages and stimulated activation and proliferation of T and B cells in spleen. METHODS-RESULTS-CONCLUSIONS: Resolution of the infection was associated with induction of MHV68-specific antibodies, but virus-specific cytotoxic T cells were not detected. Mice inoculated with retroviruses that induce severe immunodeficiency unexpectedly cleared MHV68 from lung in the same time-frame as controls and failed to develop latency as determined by infectious center tests of spleen cells. In contrast, control of MHV68 infection in spleen and/or lung was impaired in mice deficient in CD4+ or CD8+ T cells or both T cell subsets, B cells, IFN-gamma, or inducible nitric oxide synthase (iNOS). Infection was uniformly lethal in nude and iNOS-deficient mice and killed one-third of IFN-gamma-deficient mice. These results indicate that resistance to MHV68 is markedly influenced by expression of IFN-gamma from T cells leading to induction of iNOS and generation of nitric oxide.

Perceived self-care information needs and information--seeking behaviors before and after elective spinal procedures

Patients undergoing elective lumbar spinal surgical procedures pose a challenge to nurses who provide discharge instruction, because the decreased length of stay (LOS) severely limits time for comprehensive discharge instruction. The perspectives of 15 adult patients on their perceived self-care information needs and information seeking behaviors following elective spinal surgical procedures were examined. Content analytic techniques were used to categorize responses. Preoperatively, a majority of the subjects (93.3%) indicated that the neurosurgeon rather than the nurse, was anticipated to be the sole source of information related to self-care needs. Postdischarge, more than half of the subjects reported that they had difficulty describing the teaching session because they were either too sedated due to the analgesia, or were experiencing extreme pain at the time the discharge instruction was being delivered. Results substantiate the importance of supplementing oral discharge instruction with comprehensive written discharge instruction and of increasing public awareness of the teaching expertise of nurses.

Characterization of the expression and gene promoter of CD22 in murine B cells

CD22 is a B cell-restricted surface molecule which may play an important role in interactions between B cells and other cells and in regulating signals through the B cell receptor (BCR) complex. Here we have examined whether the mouse is a suitable in vivo model for studying CD22 functions. In primary and secondary lymphoid organs of adult mice CD22 is on all mature B cells, including resting IgM+IgD+ B cells, IgG+ HSA(lo) memory B cells, syndecan+ plasma cells and CD5+ B cells, but it is not on immature IgM+IgD- B cells. Biochemical analysis revealed that murine CD22 is associated with the IgM receptor in some, but not all, CD22+ B leukemic and lymphoma cell lines; as with human CD22, murine CD22 is rapidly phosphorylated on tyrosine after ligation of the BCR. In the CD22- murine pro-B cell line, FEMCL, CD22 expression was inducible by treatment with phorbol 12-myristate 13-acetate. A genomic fragment of the cd22b allele containing 1.3 kb 5' of exon 1 was sequenced in order to identify potential DNA regulatory elements in the CD22 promoter region. Consensus sequences for transcription factor binding sites including PU.1, AP-1, AP-2, C/EBP and SP-1 were present, but no classical TATA elements or initiator motifs were evident at relevant positions. The 1.3-kb promoter fragment 5' of exon 1 was sufficient for directing basal promoter activity in B and T cells. There was no significant sequence similarity between the murine and human cd22 gene promoters, although both contain repetitive elements and Sp-1 and AP1 binding sites. Thus, murine CD22 shares a number of features with human CD22 and the mouse provides a suitable model system for elucidating the function of CD22 in vivo.

Characterization of a new antigen expressed by B and myeloid lineage cells identified by the monoclonal antibody LIP-6

The LIP-6 MAb was produced against the undifferentiated cell line bh2-1 and recognizes an antigen expressed on all pre-B and B cell lines tested and some myeloid lineage lines. FACS analysis of normal tissues showed that LIP-6 is expressed on B lineage cells at all stages of differentiation, from bone marrow pre-B to plasma cells. T cells and thymocytes are LIP-6-, and splenic CD11b+ cells are heterogeneous for LIP-6 expression. The LIP-6 MAb was shown to precipitate a major 75-kDa and a minor 85-kDa protein under reducing conditions and a large protein of > 240 kDa under nonreducing conditions. Removal of N-linked sugars from the reduced lysates resulted in a single 65-kDa protein, suggesting that there is differential glycosylation of a single 65-kDa protein that forms disulfide-linked multimers. Finally, the LIP-6 antigen was shown not to be linked to the cell surface via a GPI linkage.

Contribution of B cell subsets to delayed development of MAIDS in xid mice

C57BL/6 (B6) mice develop a syndrome of progressive lymphoproliferation and immunodeficiency, murine AIDS (MAIDS), when infected with an etiologic replication-defective virus termed BM5def. Induction of MAIDS requires the presence of CD4+ T cells and B cells. B6 mice with altered conventional B cell function and a deficit in CD5+ B cells due to the xid mutation develop disease with a greatly prolonged latency. The association of this mutation with resistance to MAIDS was confirmed in studies of P.xid mice. To test the hypothesis that conventional B cells are required for rapid induction of disease, B6.xid mice were injected with spleen cells from nude mice or were given bone marrow from aged donors. Both sets of recipients developed advanced disease by 10 weeks post infection, suggesting that resistance to MAIDS in xid mutants may be due to effects of B cells other than the CD5+ subset.

Outcomes analysis in cranial base surgery - preliminary results

A system of analysis addressing predictors of management outcomes in Cranial Base Surgery has yet to be published. We therefore report data on seventy-nine consecutive patients undergoing surgery for tumors involving the cranial base, excluding patients with the diagnosis of pituitary microadenoma. Outcomes were defined prospectively in terms of completeness of tumor resection, complications of treatment with emphasis on neurological morbidity, and return to work or independent living. Also, preoperative features are analyzed as influencing cost of treatment, estimated in terms of the number of surgical procedures required, duration of hospital and Intensive Care Unit stay, and time taken to return to work. Preliminary analysis of data reveals that severe brainstem compression, large tumor size (average diameter > 3 cm), high cavernous sinus grade, and tumor encasement of major cerebral arteries are associated with incomplete tumor resection (p < 0.05). Patient age greater than 65, preoperative Karnofsky Performance Score (KPS) less than 80, and severe brainstem compression are associated with increased risk of stroke (p < 0.05). Age greater than 65 and preoperative KPS less than 80 are associated with an increased length of stay (p < 0.05). Other untoward events did not occur with sufficient frequency to reach statistical significance. A model of outcomes analysis in Cranial Base Surgery is proposed utilizing a database to incorporate a group of non-operated patients and include quality of life measurements in long-term patient follow-up.

Effects of exogenous, nonleukemogenic, ecotropic murine leukemia virus infections on the immune systems of adult C57BL/6 mice

Mouse AIDS (MAIDS) develops in mice infected with a mixture of replication-competent ecotropic and mink lung cell focus-inducing murine leukemia viruses and an etiologic replication-defective virus. Helper viruses are not required for induction of MAIDS, but the time course of disease is accelerated in their presence. To understand the possible contributions of ectropic murine leukemia viruses to MAIDS pathogenesis, we biologically cloned a series of viruses from the MAIDS-inducing LP-BM5 virus mixture. These viruses were examined for replication in tissues of infected mice and for effects on the immune system. All virus stocks replicated efficiently in mice. Infected animals showed slight lymphadenopathy and splenomegaly due primarily to B-cell proliferation associated with differentiation to immunoglobulin secretion resulting in twofold increases in serum immunoglobulin M levels; however, B-cell responses to helper T-cell-independent antigens were increased rather than decreased as in MAIDS. Analyses of CD8+ T-cell function showed that cytotoxic T-lymphocyte responses to alloantigens were comparable in control and infected mice. Finally, we showed that infection resulted in enhanced expression of transcripts for interleukin-10, interleukin-4, and gamma interferon. These cytokines can all contribute to B-cell activation and may promote the expansion of a target cell population for the MAIDS defective virus.

Long-term lymphoid reconstitution of SCID mice suggests self-renewing B and T cell populations in peripheral and mucosal tissues

Peyer's patch, peripheral lymph node, and mesenteric lymph node cells were transferred to immunodeficient SCID mice to assess the long-term (150-300 days) potential of these cells to repopulate the host's immune system. Results demonstrate that, irrespective of donor population, total serum Ig and isotype distribution appear normal within 4 weeks of reconstitution and remain at normal levels for up to one year following cell transfer. At the cellular level, each donor population reconstitutes splenic T and B cell compartments in a progressive and quantitatively indistinguishable manner. Immunohistological analyses of reconstituted mice indicate that, although some qualitative differences are evident, normal splenic composition and architecture are observed. In contrast, gut reconstitution varies significantly with donor population. Peyer's patch cells yield normal-appearing gut tissue with extensive infiltration of the lamina propria and intraepithelial compartments by T cells and IgA-secreting plasma cells. Peripheral lymph node cells give rise to T cells found almost exclusively in the lamina propria, while IgA secreting plasma cells are rarely detected. The course and extent of reconstitution further suggest that all donor populations contain long-lived T and B cells as well as self-renewing lymphocytes capable of extensive expansion. This latter observation has potentially important implications for both transplantation biology and gene therapy applications.

Changes in the subsets of CD4+ T cells in Trypanosoma musculi infection: delay of immunological cure in young mice and the weak ability of aged mice to control the infection

After a 3 week course (approximately), during which there is marked lymphoid hyperplasia, Trypanosoma musculi infections in young-adult mice are cured by an immune mechanism involving antibodies of the IgG2a isotype. Both the lymphoid hyperplasia and IgG2a antibody response are T-cell-dependent events and both processes appear to be defective in aged mice. The purpose of the studies reported here was to elucidate the effects of T. musculi infection on subsets of T cells for two reasons: (i) to gain insight into the probable roles of selected cytokines (IL-2, IL-4 and IFN-gamma) in facilitating the production of curative, IgG2a antibodies, and (ii) to examine the hypothesis that aging affects the competence of CD4+ T cells to participate in immunological control of infections. The major conclusions from these studies are that: (i) T. musculi infection of mice induces rapid change in the CD4+ T cell population toward predominance of the activated or memory (CD45RBloCD44hi) phenotype, cells which produce IFN-gamma, II-3, IL-4 and IL-5, accompanied by profound inhibition of IL-2 production, and (ii) in the old mice these changes are superimposed on the natural age-associated changes in the same direction (i.e. toward predominance of CD45RBloCD44hi T cells). Thus, in the old animals, the combined changes of aging and infection, moving in the same direction, are devastating, resulting in the aged animals being unable, or barely able, to control infection.

Long-term thymic reconstitution by peripheral CD4 and CD8 single-positive lymphocytes

Significant immigration of peripheral T cells into SCID thymus was observed following reconstitution with normal Peyer's patch, mesenteric lymph node or peripheral lymph node cells. Immunohistologic and flow cytometric analyses reveal that T cells from these tissues are found in the thymus for as long as 177 days and can account for up to 67% of intrathymic cells. The returning cells express the CD3/T cell receptor alpha/beta complex, indicative of mature cells, and are equally divided among helper (CD4+CD8-) and cytotoxic (CD4-/CD8+) phenotypes. The immigration of peripheral T cells is not accompanied by the appearance of immature, double-positive (CD4+CD8+) thymocytes as seen in similar reconstitutions using bone marrow. Taken together, these results suggest that peripheral T cells from a variety of lymphoid organs may regularly re-enter the thymus and, thus, possibly play a role in normal thymic development.

High expression of NK-1.1 antigen is induced by infection with murine AIDS virus

Spleen cells from mice infected with LP-BM5 MuLV, a causative agent of murine acquired immunodeficiency syndrome (MAIDS), were tested for frequency of NK-1.1+ cells and natural killer (NK) activity. During the first 3 weeks following infection, NK activity was well conserved, but by 9-12 weeks post-infection (p.i.), killer activity was depressed; however, the frequency of NK-1.1+ cells increased within 4 weeks of infection and remained elevated thereafter, even following the decline in functional killing activity. Since the absolute number of NK-1.1+ cells increased after infection, the ability of each NK-1.1+ cell to kill the targets seems drastically impaired. Extraordinary expansion of NK-1.1-positive cells was induced by infection with LP-BM5-defective virus (BM5def), a crucial element for MAIDS induction, but not with a helper non-pathogenic virus. With advance of MAIDS the NK-1.1 antigen (Ag) was preferentially expressed on B220+ and Thy-1+ cells, in contrast to CD4+ and CD8+ cells, and among activated large cells a higher proportion was NK-1.1+ than NK-1.1-. Mice with graft-versus-host disease (GVHD) due to class II major histocompatibility complex (MHC) Ag disparity showed a high frequency of NK-1.1 expression in association with other phenotypic alterations, very similar to those seen in mice with MAIDS. In contrast, B6-lpr/lpr mice developed similar activation of B cells but did not exhibit enhanced expression of the NK-1.1 marker. Thus, enhanced expression of the NK-1.1 Ag might be associated with chronic activation of lymphocytes through a common but not universal pathway.

B-1a and conventional B cells from autoimmune NZB.H-2bm12 mice exhibit similar functional characteristics in vivo

NZB.H-2bm12 mice develop an autoimmune syndrome characterized by the overproduction of anti-DNA antibodies and the expansion of B-1 B cells. Thus, these animals provide a useful model to examine the antigenic specificity, cross-reactivity and functional capability of B-1 versus conventional lymphocytes. Neither the repertoire expressed by in vivo activated Ly-1+ splenic lymphocytes, nor their cross-reactivity, differed significantly from that of conventional splenic B cells. When Ly-1+ cells were cultured in vitro in the presence of lipopolysaccharide plus interleukin-4 or interferon gamma, they underwent isotype switching at the same frequency as conventional B cells. Of interest, B-1 cells from the peritoneal cavity were significantly less likely to undergo isotype switching than those from the spleen. These findings indicate that in vivo activated B-1a and conventional B cells from mice with lupus manifest similar functional characteristics.

Importance of interferons in recovery from mousepox

Gamma interferon is shown to be critical in recovery of C57BL/6 mice from mousepox. Anti-gamma interferon treatment of mice infected in the footpad with ectromelia virus resulted in enhanced spread to and efficient virus replication in the spleen, lungs, ovaries, and, especially, liver. All treated, infected mice died within a mean of 7 days, 2.5 days earlier than mice with severe combined immunodeficiency that were given a comparable infection. On the other hand, alpha interferon appeared not to have a major role in controlling virus replication in tissues examined, and beta interferon was important for virus clearance in the liver and ovaries but not the spleen. Either anti-alpha, beta interferon or anti-beta interferon antibody therapy resulted in only 25% mortality. Infected control mice survived but showed persistence of ectromelia virus at the site of infection (the footpad) and transient presence of the virus in the spleen, liver, lungs, and ovaries and in the fibroreticular but not lymphoid cells of the draining popliteal lymph node. Depletion of gamma interferon but not alpha and/or beta interferon resulted in a significant reduction in the numbers of splenic T (especially gamma delta-TCR+), B, and Mac-1+ cells, although the proportion of Mac-1+ cells in the spleen increased compared with control values. Depletion of alpha, beta, or gamma interferons did not severely affect the generation of virus-specific cytotoxic T-lymphocyte responses or natural killer cell cytolytic activity. This study, in which a natural virus disease model was used, underscores the crucial importance of gamma interferon in virus clearance at all stages of infection and in all tissues tested except the primary site of infection, where virus clearance appears to be delayed.

Pulmonary histopathology induced by respiratory syncytial virus (RSV) challenge of formalin-inactivated RSV-immunized BALB/c mice is abrogated by depletion of CD4+ T cells

In previous studies, it was observed that children immunized with a formalin-inactivated respiratory syncytial virus vaccine (FI-RSV) developed severe pulmonary disease with greater frequency during subsequent natural RSV infection than did controls. During earlier efforts to develop an animal model of this phenomenon, enhanced pulmonary histopathology was observed after intranasal RSV challenge of FI-RSV-immunized cotton rats. Progress in understanding the immunologic basis for these observations has been hampered by the lack of reagents useful in manipulating the immune response of the cotton rat. This problem prompted us to reinvestigate the characteristics of immunity to RSV in the mouse. In the present studies, extensive pulmonary histopathology was observed in FI-RSV-immunized or RSV-infected BALB/c mice upon RSV challenge, and studies to determine the relative contributions of CD4+ or CD8+ T cells to this process were undertaken. Mice previously immunized with FI-RSV or infected with RSV were depleted of CD4+, CD8+, or both T-cell subsets immediately prior to RSV challenge, and the magnitude of inflammatory cell infiltration around bronchioles and pulmonary blood vessels and into alveolar spaces was quantified. The magnitude of infiltration at each anatomic site in previously FI-RSV-immunized or RSV-infected, nondepleted animals was similar, indicating that this is not a relevant model for enhanced disease. However, the effect of T-cell subset depletion on pulmonary histopathology following RSV challenge was very different between the two groups. Depletion of CD4+ T cells completely abrogated pulmonary histopathology in FI-RSV-immunized mice, whereas it had a much smaller effect on mice previously infected with RSV. FI-RSV-immunized or RSV-infected animals depleted of CD8+ T cells had only a modest reduction of pulmonary histopathology. In addition, RSV infection induced high levels of major histocompatibility complex class I-restricted cytotoxic T-cell activity, whereas FI-RSV immunization induced a low level. These data indicate that immunization with FI-RSV induces a cellular immune response different from that induced by RSV infection, which likely played a role in enhanced disease observed in infants and children.

Resistance to respiratory syncytial virus (RSV) challenge induced by infection with a vaccinia virus recombinant expressing the RSV M2 protein (Vac-M2) is mediated by CD8+ T cells, while that induced by Vac-F or Vac-G recombinants is mediated by antibodies

It was previously demonstrated that the vaccinia virus recombinants expressing the respiratory syncytial virus (RSV) F, G, or M2 (also designated as 22K) protein (Vac-F, Vac-G, or Vac-M2, respectively) induced almost complete resistance to RSV challenge in BALB/c mice. In the present study, we sought to identify the humoral and/or cellular mediators of this resistance. Mice were immunized by infection with a single recombinant vaccinia virus and were subsequently given a monoclonal antibody directed against CD4+ or CD8+ T cells or gamma interferon (IFN-gamma) to cause depletion of effector T cells or IFN-gamma, respectively, at the time of RSV challenge (10 days after immunization). Mice immunized with Vac-F or Vac-G were completely or almost completely resistant to RSV challenge after depletion of both CD4+ and CD8+ T cells prior to challenge, indicating that these cells were not required at the time of virus challenge for expression of resistance to RSV infection induced by the recombinants. In contrast, the high level of protection of mice immunized with Vac-M2 was completely abrogated by depletion of CD8+ T cells, whereas depletion of CD4+ T cells or IFN-gamma resulted in intermediate levels of resistance. These results demonstrate that antibodies are sufficient to mediate the resistance to RSV induced by the F and G proteins, whereas the resistance induced by the M2 protein is mediated primarily by CD8+ T cells, with CD4+ T cells and IFN-gamma also contributing to resistance.

Cytokine secretion by C3H-lpr and -gld T cells. Hypersecretion of IFN-gamma and tumor necrosis factor-alpha by stimulated CD4+ T cells

Mice homozygous for lpr and gld develop profound lymphadenopathy characterized by the expansion of two unusual T cell subsets, a predominant Ly-5(B220)+ CD4- CD8- double negative (DN) population and a minor CD4 dull+ Ly-5(B220)+ population. The mechanisms promoting lymphoproliferation are unknown, but one possibility is a abnormality in the production of cytokines that regulate T cell growth. In the present report, unfractionated LN cells and sorted T cell subsets from C3H-lpr, -gld, and -+/+ mice were compared for spontaneous and induced secretion of a spectrum of lymphokines. In addition, CD4+, CD4 dull+ Ly-5(B220)+, and DN T cells were examined for expression of CD3 epsilon, TCR-alpha/beta heterodimers, Ly-6C, and CD44 and for proliferative responses to immobilized anti-TCR mAb and cofactors. These studies revealed that sorted DN T cells did not secrete IL-3, IL-4, IL-5, IL-6, GM-CSF, TNF-alpha, or IFN-gamma spontaneously or after TCR-alpha/beta cross-linking. In contrast, stimulated unfractionated lpr and gld LN cells proliferated strongly and secreted high levels of IFN-gamma and TNF-alpha and low levels of IL-3, IL-4, and IL-6. Despite a 5- to 10-fold deficit in the frequency of CD4+ and CD8+ T cells, cytokine secretion by lpr and gld LN generally exceeded that of +/+ LN. Comparisons of cytokine secretion by stimulated CD4+ T cells revealed that +/+, lpr, and gld CD4+ Ly-5(B220)- T cells proliferated strongly, but only lpr and gld cells produced significant levels of IFN-gamma. The lpr and gld CD4+ T cells also produced higher levels of TNF-alpha and IL-2 than +/+ cells. In contrast to normal CD4+ T cells, lpr and gld CD4+ Ly-5(B220)+ T cells proliferated weakly and did not secrete TNF-alpha, IL-2, or, in most experiments, IFN-gamma after stimulation. Phenotypic studies of T cell subsets revealed that unstimulated lpr and gld CD4+ Ly-5(B220)- T cells express significantly higher levels of CD44 than +/+ CD4+ T cells. In addition, CD4 dull+ Ly-5(B220)+ cells closely resembled DN T cells in size and expression of TCR-alpha/beta, CD3epsilon, CD44, and Ly-6C. Since elevated CD44 expression is generally associated with T cell activation and only previously activated normal CD4+ T cells produce high levels of IFN-gamma in vitro, our data suggest that lpr and gld CD4+ Ly-5(B220)- T cells contain a higher than normal proportion of primed or memory T cells and thus may be polyclonally activated in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine secretion by C3H-lpr and -gld T cells. Hypersecretion of IFN-gamma and tumor necrosis factor-alpha by stimulated CD4+ T cells

Mice homozygous for lpr and gld develop profound lymphadenopathy characterized by the expansion of two unusual T cell subsets, a predominant Ly-5(B220)+ CD4- CD8- double negative (DN) population and a minor CD4 dull+ Ly-5(B220)+ population. The mechanisms promoting lymphoproliferation are unknown, but one possibility is a abnormality in the production of cytokines that regulate T cell growth. In the present report, unfractionated LN cells and sorted T cell subsets from C3H-lpr, -gld, and -+/+ mice were compared for spontaneous and induced secretion of a spectrum of lymphokines. In addition, CD4+, CD4 dull+ Ly-5(B220)+, and DN T cells were examined for expression of CD3 epsilon, TCR-alpha/beta heterodimers, Ly-6C, and CD44 and for proliferative responses to immobilized anti-TCR mAb and cofactors. These studies revealed that sorted DN T cells did not secrete IL-3, IL-4, IL-5, IL-6, GM-CSF, TNF-alpha, or IFN-gamma spontaneously or after TCR-alpha/beta cross-linking. In contrast, stimulated unfractionated lpr and gld LN cells proliferated strongly and secreted high levels of IFN-gamma and TNF-alpha and low levels of IL-3, IL-4, and IL-6. Despite a 5- to 10-fold deficit in the frequency of CD4+ and CD8+ T cells, cytokine secretion by lpr and gld LN generally exceeded that of +/+ LN. Comparisons of cytokine secretion by stimulated CD4+ T cells revealed that +/+, lpr, and gld CD4+ Ly-5(B220)- T cells proliferated strongly, but only lpr and gld cells produced significant levels of IFN-gamma. The lpr and gld CD4+ T cells also produced higher levels of TNF-alpha and IL-2 than +/+ cells. In contrast to normal CD4+ T cells, lpr and gld CD4+ Ly-5(B220)+ T cells proliferated weakly and did not secrete TNF-alpha, IL-2, or, in most experiments, IFN-gamma after stimulation. Phenotypic studies of T cell subsets revealed that unstimulated lpr and gld CD4+ Ly-5(B220)- T cells express significantly higher levels of CD44 than +/+ CD4+ T cells. In addition, CD4 dull+ Ly-5(B220)+ cells closely resembled DN T cells in size and expression of TCR-alpha/beta, CD3epsilon, CD44, and Ly-6C. Since elevated CD44 expression is generally associated with T cell activation and only previously activated normal CD4+ T cells produce high levels of IFN-gamma in vitro, our data suggest that lpr and gld CD4+ Ly-5(B220)- T cells contain a higher than normal proportion of primed or memory T cells and thus may be polyclonally activated in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

CD5+ peritoneal B cells express high levels of membrane, but not secretory, C mu mRNA

We used in situ hybridization to study Ig mRNA levels in murine peritoneal and splenic B cells. Ig mRNA production fell into three distinct groups: low, intermediate, and high. Splenic B cells primarily exhibited low levels characteristic of resting B cells or high Ig mRNA levels characteristic of plasma cells. In contrast, a significant fraction of peritoneal B cells exhibited intermediate Ig mRNA levels. Intermediate Ig mRNA was T cell dependent in that congenic nu/nu mice had far fewer peritoneal cells expressing the intermediate Ig message than their wild type counterparts. CD5+ CD11b+ IgMbright+ peritoneal B cells were found to be mainly responsible for the production of intermediate Ig mRNA levels. The peritoneal CD5- CD11b+ IgMbright+ "sister" B cell subpopulation contained a lower percentage of intermediate Ig mRNA-producing B cells. CD5-CD11b-IgMdull+ "conventional" B cells produced negligible levels of Ig mRNA, comparable to those of unfractionated splenic B cells. Northern analysis showed that the majority of Ig mRNA expressed in the peritoneum is of the membrane rather than the secreted form. Consistent with that result, in short-term culture, peritoneal cells showed markedly less Ig secretion than did spleen cells. These studies describe novel Ig mRNA expression by peritoneal B cells and emphasize that within the peritoneal cavity, B cells do not tend to become antibody-secreting cells.

CD5+ peritoneal B cells express high levels of membrane, but not secretory, C mu mRNA

We used in situ hybridization to study Ig mRNA levels in murine peritoneal and splenic B cells. Ig mRNA production fell into three distinct groups: low, intermediate, and high. Splenic B cells primarily exhibited low levels characteristic of resting B cells or high Ig mRNA levels characteristic of plasma cells. In contrast, a significant fraction of peritoneal B cells exhibited intermediate Ig mRNA levels. Intermediate Ig mRNA was T cell dependent in that congenic nu/nu mice had far fewer peritoneal cells expressing the intermediate Ig message than their wild type counterparts. CD5+ CD11b+ IgMbright+ peritoneal B cells were found to be mainly responsible for the production of intermediate Ig mRNA levels. The peritoneal CD5- CD11b+ IgMbright+ "sister" B cell subpopulation contained a lower percentage of intermediate Ig mRNA-producing B cells. CD5-CD11b-IgMdull+ "conventional" B cells produced negligible levels of Ig mRNA, comparable to those of unfractionated splenic B cells. Northern analysis showed that the majority of Ig mRNA expressed in the peritoneum is of the membrane rather than the secreted form. Consistent with that result, in short-term culture, peritoneal cells showed markedly less Ig secretion than did spleen cells. These studies describe novel Ig mRNA expression by peritoneal B cells and emphasize that within the peritoneal cavity, B cells do not tend to become antibody-secreting cells.

A unique subset of normal murine CD4+ T cells lacking Thy-1 is expanded in a murine retrovirus-induced immunodeficiency syndrome, MAIDS

Some strains of mice inoculated with LP-BM5 murine leukemia virus (MuLV) develop a syndrome, termed mouse acquired immunodeficiency syndrome (MAIDS), characterized by progressive lymphoproliferation and profound immunodeficiency. LP-BM5 MuLV is a virus mixture that contains ecotropic (eco) and mink cell focus-induced MuLV and a defective genome that is the proximal cause of disease. Flow cytometry analyses of spleen and lymph nodes from susceptible C57BL/6 mice infected with this virus mixture revealed the presence in spleen and peripheral lymph nodes of a previously unrecognized subset of CD4+CD3+ T cells that are Thy-1-. The frequency of these cells increased with progression of disease, eventually comprising between 30% and 50% of all CD4+ cells. Infection of A/J mice, a strain which is genetically resistant to development of MAIDS, did not induce an increase of this T cell population, indicating that infection with the virus mixture was insufficient to induce its proliferation. A central role for the defective virus in this process was suggested by the finding that C57BL/6 mice infected with LP-BM5 eco alone did not have increased frequencies of Thy-1-CD4+ cells in spleen. Studies of spleen and peripheral lymph node cells from normal mice demonstrated the presence of Thy-1-CD4+ cells at frequencies of 1%-2%. Studies using two anti-T cell monoclonal antibodies, SM6C10 and SM3G11, that define four CD4+ subsets showed that Thy-1-CD4+ T cells from normal and infected mice were present only in the 6C10- subsets.

CD4+ T cells in murine acquired immunodeficiency syndrome: evidence for an intrinsic defect in the proliferative response to soluble antigen

C57BL/6 mice inoculated with LP-BM5 murine leukemia viruses develop an immunodeficiency syndrome, termed murine acquired immunodeficiency syndrome (MAIDS), characterized by a variety of functional abnormalities of T and B cells. In the present study, we have analyzed the ability of lymph node cells from infected mice to generate secondary in vitro proliferative responses to soluble antigens. Our data demonstrate that the ability of lymph node cells to proliferate in response to soluble antigen or T cell mitogens declines progressively during the course of MAIDS. Impaired proliferative responses were shown to be characteristic of purified CD4+ but not CD8+ cells from infected mice when stimulated in the presence of normal accessory cells. In addition, the impaired responses of unseparated lymph node cells from infected mice could be reconstituted by the addition of purified CD4+ T cells from nodes of primed normal animals. These results strongly suggest that an intrinsic CD4+ T cell defect developing during the course of MAIDS contributes significantly to impaired responses to mitogens and to impaired secondary in vitro proliferative responses to soluble antigen.

Transformation of murine bone marrow cells with combined v-raf-v-myc oncogenes yields clonally related mature B cells and macrophages

Murine bone marrow cells infected with replication-defective retroviruses containing v-raf alone or v-myc alone yielded transformed pre-B cell lines, while a retroviral construct containing both v-raf and v-myc oncogenes produced clonally related populations of mature B cells and mature macrophages. The genealogy of these transformants demonstrates that mature myeloid cells were derived from cells with apparent B-lineage commitment and functional immunoglobulin rearrangements. This system should facilitate studies of developmental relationships in hematopoietic differentiation and analysis of lineage determination.

Differences in the repertoire expressed by peritoneal and splenic Ly-1 (CD5)+ B cells

Purified populations of B cells expressing the Ly-1 and/or Mac-1 surface Ag were isolated from normal unmanipulated mice by cell sorting. The number of lymphocytes in each population secreting antibodies reactive with DNA, bromelain-treated mouse RBC, phosphorylcholine and TNP-keyhole limpet hemocyanin was quantitated by ELISA spot assay. The proportion of B cells secreting Ig in vivo and the repertoire of antibodies they produced varied as a function of B cell phenotype and location. Among peritoneal lymphocytes, those that were Ly-1+ or Ly-1- Mac-1+ secreted Ig 10 times more frequently that Mac-1- Ly-1- B cells from the same location. In addition, the former populations expressed repertoires that were significantly skewed toward the production of antibodies reactive with bromelain-treated mouse RBC (p less than 0.001). In contrast, splenic B cells expressing the Ly-1 surface Ag did not differ significantly from splenic Ly-1- B cells in their expressed repertoire or frequency of Ig production. B cells isolated from the spleen and peritoneum tended to differ in antibody specificity from bone marrow and lymph node-derived lymphocytes. For example, B cells from the spleen secreted anti-DNA antibodies two to four times more frequently than B cells from other organs. These results demonstrate that phenotype and microenvironment influence the repertoire of antibodies expressed by B cells in vivo.

Differences in the repertoire expressed by peritoneal and splenic Ly-1 (CD5)+ B cells

Purified populations of B cells expressing the Ly-1 and/or Mac-1 surface Ag were isolated from normal unmanipulated mice by cell sorting. The number of lymphocytes in each population secreting antibodies reactive with DNA, bromelain-treated mouse RBC, phosphorylcholine and TNP-keyhole limpet hemocyanin was quantitated by ELISA spot assay. The proportion of B cells secreting Ig in vivo and the repertoire of antibodies they produced varied as a function of B cell phenotype and location. Among peritoneal lymphocytes, those that were Ly-1+ or Ly-1- Mac-1+ secreted Ig 10 times more frequently that Mac-1- Ly-1- B cells from the same location. In addition, the former populations expressed repertoires that were significantly skewed toward the production of antibodies reactive with bromelain-treated mouse RBC (p less than 0.001). In contrast, splenic B cells expressing the Ly-1 surface Ag did not differ significantly from splenic Ly-1- B cells in their expressed repertoire or frequency of Ig production. B cells isolated from the spleen and peritoneum tended to differ in antibody specificity from bone marrow and lymph node-derived lymphocytes. For example, B cells from the spleen secreted anti-DNA antibodies two to four times more frequently than B cells from other organs. These results demonstrate that phenotype and microenvironment influence the repertoire of antibodies expressed by B cells in vivo.

Fluctuations in subsets of splenocytes and isotypes of Ig in young adult and aged mice resulting from Trypanosoma musculi infections

A prominent feature of parasitic infections is the marked hyperplasia of lymphoid tissues. The resultant disruption of those tissues may be a major cause of the immunodepression that typifies parasitic infections. Trypanosoma musculi infections in mice evoke lymphoid hyperplasia and depressed immune responses. T. musculi infections are more severe in C3H than in C57BL/6 (B6) mice; and more severe in aged mice of either strain, compared with young adults. This report concerns a flow cytometric analysis of splenic leukocytes, identified by various surface Ag, in young and aged, trypanosome-infected mice of C3H and B6 strains. Companion studies included quantification of serum Ig isotypes at intervals during infection. The results support the following conclusions: a) all major types of splenic leukocytes were activated by trypanosome infection resulting in enlargement of the cells and proliferation ("blastogenic response"); b) in all young-adult mice and in aged B6 mice (but not aged C3H mice) Thy-1+, Ly-1+, and Ly-4+ cells increased moderately during infection whereas the number of Ly-2+ cells remained constant; c) all cells of the B lineage increased during the course of infection (except in aged C3H mice) with disproportionate increases in the most mature stage (IgG+); d) the responses of young adult C3H and B6 mice to infection differed as illustrated by the ability of B6, but not C3H, mice to limit hyperplasia and reverse the effect; e) aging of B6 mice was reflected by relative inability to regulate generation of mature Ig-producing cells; f) aging of C3H mice was severe as reflected by the relative inability of most subsets of leukocytes to react to the infection, possibly because of abnormalities that were intrinsic in aged, normal C3H mice. It is likely that: a) disruption of lymphoid tissue, probably mediated by alterations in the production of and responsiveness to cytokines, is responsible for the depressed ability of the immune system to defend against parasites; and b) such disruptive effects, being more pronounced in aged animals and less easily brought under control, account for the greater vulnerability of aged animals to parasitic infection.

Fluctuations in subsets of splenocytes and isotypes of Ig in young adult and aged mice resulting from Trypanosoma musculi infections

A prominent feature of parasitic infections is the marked hyperplasia of lymphoid tissues. The resultant disruption of those tissues may be a major cause of the immunodepression that typifies parasitic infections. Trypanosoma musculi infections in mice evoke lymphoid hyperplasia and depressed immune responses. T. musculi infections are more severe in C3H than in C57BL/6 (B6) mice; and more severe in aged mice of either strain, compared with young adults. This report concerns a flow cytometric analysis of splenic leukocytes, identified by various surface Ag, in young and aged, trypanosome-infected mice of C3H and B6 strains. Companion studies included quantification of serum Ig isotypes at intervals during infection. The results support the following conclusions: a) all major types of splenic leukocytes were activated by trypanosome infection resulting in enlargement of the cells and proliferation ("blastogenic response"); b) in all young-adult mice and in aged B6 mice (but not aged C3H mice) Thy-1+, Ly-1+, and Ly-4+ cells increased moderately during infection whereas the number of Ly-2+ cells remained constant; c) all cells of the B lineage increased during the course of infection (except in aged C3H mice) with disproportionate increases in the most mature stage (IgG+); d) the responses of young adult C3H and B6 mice to infection differed as illustrated by the ability of B6, but not C3H, mice to limit hyperplasia and reverse the effect; e) aging of B6 mice was reflected by relative inability to regulate generation of mature Ig-producing cells; f) aging of C3H mice was severe as reflected by the relative inability of most subsets of leukocytes to react to the infection, possibly because of abnormalities that were intrinsic in aged, normal C3H mice. It is likely that: a) disruption of lymphoid tissue, probably mediated by alterations in the production of and responsiveness to cytokines, is responsible for the depressed ability of the immune system to defend against parasites; and b) such disruptive effects, being more pronounced in aged animals and less easily brought under control, account for the greater vulnerability of aged animals to parasitic infection.

Functional and phenotypic alterations in T cell subsets during the course of MAIDS, a murine retrovirus-induced immunodeficiency syndrome

The functional and phenotypic characteristics of Ly-4(CD4)+ and Ly-2(CD8)+ T cells were studied after induction of murine AIDS with LP-BM5 murine leukemia virus. Assays of spleen cells for their ability to generate in vitro CTL responses to TNP-modified autologous cells (self + x CTL) and to alloantigens (allo CTL) showed that self + x CTL responses were greatly impaired at 3 to 4 wk postinfection and were undetectable thereafter. Allo CTL responses were normal at 3 to 4 wk, but were reduced at 8 to 9 wk and absent at 14 wk postinfection. This sequential loss of self + x and allo CTL responses was related to a selective defect in Ly-4(CD4)+ Th cell function associated with impaired production of IL-2 and deficient proliferative responses to Con A or to soluble Ag. Changes in the functional characteristics of Ly-4(CD4)+ T cells were unrelated to changes in their frequency in spleen, but did correlate with marked alterations in their distribution among four subsets defined by mAb SM3C11 and SM6C10. Assays of CTL responses generated by mixtures of spleen cells from normal and infected mice suggested that active suppression of Ly-4(CD4)+ Th function may contribute to this defect. Studies of Ly-2(CD8)+ T cells showed that infection with LP-BM5 murine leukemia virus also induced a major phenotypic shift in subpopulations defined by their reactivity with mAb 6C10. However, this phenotypic change did not appear to correlate with major functional defects.

Functional and phenotypic alterations in T cell subsets during the course of MAIDS, a murine retrovirus-induced immunodeficiency syndrome

The functional and phenotypic characteristics of Ly-4(CD4)+ and Ly-2(CD8)+ T cells were studied after induction of murine AIDS with LP-BM5 murine leukemia virus. Assays of spleen cells for their ability to generate in vitro CTL responses to TNP-modified autologous cells (self + x CTL) and to alloantigens (allo CTL) showed that self + x CTL responses were greatly impaired at 3 to 4 wk postinfection and were undetectable thereafter. Allo CTL responses were normal at 3 to 4 wk, but were reduced at 8 to 9 wk and absent at 14 wk postinfection. This sequential loss of self + x and allo CTL responses was related to a selective defect in Ly-4(CD4)+ Th cell function associated with impaired production of IL-2 and deficient proliferative responses to Con A or to soluble Ag. Changes in the functional characteristics of Ly-4(CD4)+ T cells were unrelated to changes in their frequency in spleen, but did correlate with marked alterations in their distribution among four subsets defined by mAb SM3C11 and SM6C10. Assays of CTL responses generated by mixtures of spleen cells from normal and infected mice suggested that active suppression of Ly-4(CD4)+ Th function may contribute to this defect. Studies of Ly-2(CD8)+ T cells showed that infection with LP-BM5 murine leukemia virus also induced a major phenotypic shift in subpopulations defined by their reactivity with mAb 6C10. However, this phenotypic change did not appear to correlate with major functional defects.

Characterization of the immunodeficiency of RIIS/J [corrected] mice. I. Association with the CD5 (LY-1) [corrected] B cell lineage

RIIIS/J mice produce low antibody responses to several polysaccharide Ag of bacterial origin. They have low levels of serum IgM and IgG3 and high levels of serum IgG2a and IgG2b. Low serum IgM and IgG3 have been attributed to a low frequency of CD5 (Ly-1) B cells, which play an important role in the production of natural antibodies. Indeed, RIIIS/J mice have a low frequency of CD5 (Ly-1)+, IgM bright+, Ly-5 (B220)dull+ (i.e., CD5 (Ly-1) B) cells in their peritoneum. RIIIS/J mice treated with LPS produce a low anti-bromelain-treated mouse RBC splenic plaque-forming cell response and a normal anti-mouse transferrin splenic PFC response. Those data are compatible with the fact that CD5 (Ly-1) B cells contain the precursors of B lymphocytes secreting anti-bromelain-treated mouse RBC antibody. However, they have a higher frequency of IgM bright+, Mac-1+ cells in their peritoneum. These cells represent the CD5 (Ly-1) "sister population" of CD5 (Ly-1) B cells described by others. This suggests that characteristics usually associated with the CD5 (Ly-1) lineage are applicable only to the CD5 (Ly-1)+ Mac-1+ IgM+ population, but not the related CD5 (Ly-1)- Mac-1+ IgM+ population. RIIIS/J mice should thus prove a valuable model to study the CD5 (Ly-1) B cell lineage.

Characterization of the immunodeficiency of RIIS/J [corrected] mice. I. Association with the CD5 (LY-1) [corrected] B cell lineage

RIIIS/J mice produce low antibody responses to several polysaccharide Ag of bacterial origin. They have low levels of serum IgM and IgG3 and high levels of serum IgG2a and IgG2b. Low serum IgM and IgG3 have been attributed to a low frequency of CD5 (Ly-1) B cells, which play an important role in the production of natural antibodies. Indeed, RIIIS/J mice have a low frequency of CD5 (Ly-1)+, IgM bright+, Ly-5 (B220)dull+ (i.e., CD5 (Ly-1) B) cells in their peritoneum. RIIIS/J mice treated with LPS produce a low anti-bromelain-treated mouse RBC splenic plaque-forming cell response and a normal anti-mouse transferrin splenic PFC response. Those data are compatible with the fact that CD5 (Ly-1) B cells contain the precursors of B lymphocytes secreting anti-bromelain-treated mouse RBC antibody. However, they have a higher frequency of IgM bright+, Mac-1+ cells in their peritoneum. These cells represent the CD5 (Ly-1) "sister population" of CD5 (Ly-1) B cells described by others. This suggests that characteristics usually associated with the CD5 (Ly-1) lineage are applicable only to the CD5 (Ly-1)+ Mac-1+ IgM+ population, but not the related CD5 (Ly-1)- Mac-1+ IgM+ population. RIIIS/J mice should thus prove a valuable model to study the CD5 (Ly-1) B cell lineage.

Biologic and molecular genetic characteristics of a unique MCF virus that is highly leukemogenic in ecotropic virus-negative mice

California wild mouse-derived ecotropic virus Cas-Br-M induces a spongiform encephalopathy and a wide variety of hematopoietic neoplasms on inoculation of neonatal mice. We isolated a MCF virus [Ns-6(186) MCF] from a thymic T-cell lymphoma developing in a NFS mouse inoculated with Cas-Br-M virus. Biologically cloned NS-6(186) MCF virus, in contrast to previously studied MCF viruses, was found to induce thymic or nonthymic T-cell lymphomas with high efficiency in the absence of ecotropic helper virus. Comparison of the restriction endonuclease maps derived from Cas-Br-M and NS-6(186) MCF revealed differences only in the env region, between 5.8 and 7.8 kb from the 5' end. Two biologically active molecular clones of the NS-6(186) MCF (clone 15 with two LTRs and clone 19 with 1 LTR) were studied. Although both clones exhibited similar in vitro activities, clone 15-derived virus induced only T-cell lymphomas with short latency whereas clone 19-derived virus induced a wide variety of neoplasms with a significantly longer latency. Nucleotide sequence analysis established that the U3 region of each of the two LTRs of clone 15 has a 53-bp duplication which includes "enhancer elements," but that the single LTR of clone 19 has no such duplication.

Transcriptional and post-transcriptional regulation of c-myc, c-myb, and p53 during proliferation and differentiation of murine erythroleukemia cells treated with DFMO and DMSO

The proto-oncogenes myc, myb, and p53 produce nuclear proteins which have been implicated in the regulation of proliferation or differentiation in a number of systems. The expression of these proto-oncogenes was studied in murine erythroleukemia (MEL) cells during (i) normal replication, (ii) DMSO-induced differentiation and (iii), alpha-difluoromethylornithine (DFMO)-restricted cell division and differentiation. The RNA levels of c-myc, c-myb, and p53 were all elevated during normal cellular proliferation; only c-myc expression declined when the cells stopped dividing although the rate of transcription for the gene was unaltered. In contrast, treatment of the cells with DFMO resulted in gradual cessation of cell replication and a decrease in transcription of c-myc, c-myb and p53. When the MEL cells were induced to differentiate with dimethyl sulfoxide (DMSO), a transient reduction in c-myc and c-myb RNA levels occurred immediately prior to the G1 arrest with a concomitant decrease in transcriptional activity, while p53 mRNA production was elevated without an increase in transcription. Similar changes of the proto-oncogene levels were observed when the MEL cells were incubated with DFMO and then later induced with DMSO, a protocol which restricts differentiation of the MEL cells. From these experiments we conclude that (i) c-myc, c-myb, and p53 are regulated independently at both the transcriptional and post-transcriptional levels, (ii) DFMO inhibits MEL cell proliferation and expression of several genes, including c-myc, c-myb and p53, and (iii) DFMO suppresses terminal differentiation but is unable to alter proto-oncogene changes associated with the early stages of differentiation.

Phenylhydrazine stimulates lymphopoiesis and accelerates Abelson murine leukemia virus-induced pre-B cell lymphomas

Infection of bone marrow or fetal liver cells with Abelson murine leukemia virus (A-MuLV) results in the transformation of pre-B cells and the development of erythroid colonies, indicating that the abl oncogene can affect the growth characteristics of immature cells in both the B cell and erythroid lineages. By comparison, infection of mice with A-MuLV results primarily in the development of pre-B cell lymphomas. To determine whether A-MuLV could induce erythroid disease in vivo, NFS/N mice were pretreated with phenylhydrazine (PHZ) to stimulate erythropoiesis and increase the frequency of potential target cells for A-MuLV. No erythroleukemias developed in mice treated with PHZ. Instead, the latency for pre-B cell lymphomas was reduced by half. This acceleration of disease could be attributed to a marked increase in pre-B cells as targets for transformation by A-MuLV in the bone marrows but not the spleens of treated mice. Increases in the frequencies of T cells in bone marrow and spleen also followed treatment with PHZ. These results show that although PHZ-induced anemia stimulates the production of T and B cells as well as erythroid progenitors, PHZ-treated mice do not develop erythroleukemia or T cell lymphomas. It was also found that the genetically determined resistance of adult C57BL/6 mice to lymphoma induction by A-MuLV could not be overcome by pretreatment with PHZ even though the frequency of pre-B cells in bone marrow was greatly increased by this treatment.

Phenylhydrazine stimulates lymphopoiesis and accelerates Abelson murine leukemia virus-induced pre-B cell lymphomas

Infection of bone marrow or fetal liver cells with Abelson murine leukemia virus (A-MuLV) results in the transformation of pre-B cells and the development of erythroid colonies, indicating that the abl oncogene can affect the growth characteristics of immature cells in both the B cell and erythroid lineages. By comparison, infection of mice with A-MuLV results primarily in the development of pre-B cell lymphomas. To determine whether A-MuLV could induce erythroid disease in vivo, NFS/N mice were pretreated with phenylhydrazine (PHZ) to stimulate erythropoiesis and increase the frequency of potential target cells for A-MuLV. No erythroleukemias developed in mice treated with PHZ. Instead, the latency for pre-B cell lymphomas was reduced by half. This acceleration of disease could be attributed to a marked increase in pre-B cells as targets for transformation by A-MuLV in the bone marrows but not the spleens of treated mice. Increases in the frequencies of T cells in bone marrow and spleen also followed treatment with PHZ. These results show that although PHZ-induced anemia stimulates the production of T and B cells as well as erythroid progenitors, PHZ-treated mice do not develop erythroleukemia or T cell lymphomas. It was also found that the genetically determined resistance of adult C57BL/6 mice to lymphoma induction by A-MuLV could not be overcome by pretreatment with PHZ even though the frequency of pre-B cells in bone marrow was greatly increased by this treatment.