Generation of continuous large granular lymphocyte lines by interleukin 2 from the spleen cells of mice infected with Moloney leukemia virus. Involvement of interleukin 3

Strain-dependent inhibitory effect of mutant mi-MITF on cytotoxic activities of cultured mast cells and natural killer cells of mice

MITF is a transcription factor encoded by the mi locus. MITF encoded by mi and Mi(or) mutant alleles (mi-MITF and Mi(or)-MITF, respectively) possessed an inhibitory effect, whereas the tg, mi(ew) and mi(ce) were null mutants. We examined the cytotoxic activities of cultured mast cells (CMCs) and natural killer (NK) cells of various MITF mutants in C57BL/6 (B6) background. Cytotoxic activities of CMCs and NK cells of B6-mi/mi and B6-Mi(or)/Mi(or) mice were remarkably reduced. In B6-tg/tg, B6-mi(ew)/mi(ew) and B6-mi(ce)/mi(ce) mice, however, the cytotoxic activity of CMCs was reduced only slightly and the NK activity was normal. The cytotoxic activity of CMCs paralleled with the expression level of granzyme B (Gr B) mRNA, and the NK activity with that of perforin (Pfn) mRNA. In contrast to the case of B6-mi/mi mice, cytotoxic activities of CMCs and NK cells were not impaired in WB-mi/mi mice. The expression of Gr B mRNA was not reduced in CMCs of WB-mi/mi mice, and that of Pfn mRNA was not reduced in NK cells of WB-mi/mi mice. WB-mi/mi mice appeared to have factor(s) compensating for the inhibitory effect of mi-MITF on the expression of Gr B and Pfn genes.

Inhibitory effect on natural killer activity of microphthalmia transcription factor encoded by the mutant mi allele of mice

The mouse mi locus encodes a basic-helix-loop-helix-leucine zipper-type transcription factor, microphthalmia transcription factor (MITF). Mice of mi/mi genotype express a mutant form of MITF (mi-MITF), whereas mice of tg/tg genotype have a transgene in the 5' flanking region of the mi gene and do not express MITF. Although the mi/mi mouse is deficient in natural killer (NK) activity, it was found that the tg/tg mouse was normal in this respect. To know the cause, spleen cells of both genotypes were compared. Although the proportion of spleen cells expressing an NK cell marker, NK1.1, was comparable in both mice, the proportion of large granular lymphocytes decreased only in mi/mi mice. The difference between mi/mi and tg/tg mice was reproducible in the culture supplemented with interleukin-2. Moreover, the perforin gene expression was reduced in mi/mi-cultured spleen cells. Wild-type (+) MITF transactivated, but mi-MITF suppressed, the perforin gene promoter through the NF-P motif, a strong cis-acting element. However, neither +-MITF nor mi-MITF bound the NF-P motif. Instead, 2 nuclear factors that bound the NF-P motif were retained in the cytoplasm of mi/mi-cultured spleen cells. In addition, overexpression of mi-MITF resulted in cytoplasmic retention of the 2 NF-P motif-binding factors in cytotoxic T lymphocytes. The presence of mi-MITF rather than the absence of +-MITF appeared to lead to poor transactivation of the NF-P motif by intercepting NF-P motif-binding factors. This inhibitory effect of mi-MITF may cause the deficient cytotoxicity of NK cells in mi/mi mice. (Blood. 2001;97:2075-2083)

Inactivation and proteolytic degradation of perforin within lytic granules upon neutralization of acidic pH

In our recent studies, an inhibitor of vacuolar-type H(+)-ATPase, concanamycin A (CMA) has been shown to neutralize acidic pH in vacuolar organelles, including lytic granules, and to decrease the perforin content markedly. In the present paper, we have further investigated the role of acidification in perforin storage by using CMA. In CD8+ cytotoxic T-lymphocyte (CTL) clones, the amount of perforin decreased rapidly at 30-90 min but no more decrease occurred at 90-120 min after the addition of CMA. Since exposure to actinomycin D, cycloheximide, or brefeldin A failed to reduce the perforin content, the perforin decrease in CMA-treated cells seems to be largely due to a reduction in the perforin already stored in lytic granules, rather than to the inhibition of the de novo synthesis or the intracellular glycoprotein transport of perforin. Diisopropylfluorophosphoridate (DFP) markedly antagonized the decrease in the perforin content in CMA-treated cells, while other protease inhibitors, i.e. antipain, E-64, leupeptin, pepstatin A and phenylmethylsulphonyl fluoride, did not. Nevertheless, DFP hardly reversed the abrogation of the killing activity by CMA. Indeed, the lytic granules prepared from DFP plus CMA-treated cells showed only a marginal level of haemolytic activity. In cell-free experiments using perforin-enriched granule fractions, acidic pH completely blocked the perforin activity. Under the acidic conditions, perforin was more resistant to an inactivation by calcium when exposed to calcium prior to the haemolysis test. Thus, these data suggest that perforin is primarily inactivated, possibly in a calcium-dependent manner, and is subsequently hydrolysed by DFP-sensitive proteases in the lytic granules at neutral pH. We conclude that acidic pH plays an essential role to maintain the integrity of perforin within the lytic granules.

A nonstructural gag-encoded glycoprotein precursor is necessary for efficient spreading and pathogenesis of murine leukemia viruses

In addition to the Gag-Pol and Env precursors whose translation initiates at AUG codons, murine, feline, and simian type C oncoviruses also express glycosylated Gag-Pol precursors (glycoGag), glycoGag translation is initiated at CUG codons located upstream of the Gag AUG initiation codon. In contrast to Gag, glycoGag is translocated into the endoplasmic reticulum and is absent from virions. Since glycoGag has been described to be dispensable ex vivo, we investigated the in vivo effects of a glycoGag- mutation in the Friend murine leukemia virus (F-MuLV). F-MuLV induces severe early hemolytic anemia and subsequent erythroleukemia within 2 months after inoculation of newborn mice. We obtained a glycoGag- F-MuLV, strain H5, by inserting an octanucleotide linker downstream of the CUG codon leading to the reading of a stop codon in all reading frames upstream of the Gag AUG. F-MuLV H5 did not induce severe early hemolytic anemia, and latency of erythroleukemia was significantly increased most likely because of an approximately 1-week delay in the in vivo spreading. Accordingly, induction of recombinant polytropic viruses was also significantly delayed. Close examination of ex vivo spreading kinetics also showed a slower dissemination of F-MuLV H5. Western blot (immunoblot) performed after inoculation of newborn mice with this glycoGag- virus indicated the emergence of new glycoGag+ viruses. PCR analyses with F-MuLV-specific primers demonstrated in vivo pseudoreversions restoring the glycoGag reading frame. Our results demonstrated that glycoGag expression is positively selected and essential for full spreading and pathogenic abilities.

Transfection of the bcr/abl oncogene into factor-dependent cells by electroporation: acquisition of autonomous proliferation

In order to clarify the function of P210 bcr/abl oncogene in leukemogenesis, IL-3 dependent murine hematopietic cell line, FDC-P2, was transfected with the plasmid containing cDNA of P210 bcr/abl oncogene (pGD'210) or murine IL-3 (pcDmIL3) by electroporation. Four out of five pGDH210 transfected clones as well as FDC-P2 transfected with pcDmIL3, acquired autonomous proliferation (i.e. lost the requirement for IL-3 supplementation). The expression of bcr/abl oncogene was weak in one clone, which remained dependent on IL-3. Unlike pcDmIL3 transfectants, which secrete IL-3 into the supernatant, IL-3 was not demonstrated in the culture supernatant of pGD'210 transfected FDC-P2. These finding suggest that P210 bcr/abl oncogene is directly associated with autonomous proliferation, which is the first process of leukemogenesis.

IL-2-dependent generation of natural killer cells from bone marrow: role of MAC-1-, NK1-1- precursors

We have previously shown that interleukin-2 (IL-2) is able to induce the generation of natural killer (NK) activity in bone marrow (BM) cell cultures from mice pretreated with 5-fluorouracil (5-FU). Cell fractionation experiments to analyze the nature of BM precursors indicate that MAC-1-, NK1-1- noncytotoxic precursors are induced by IL-2 to proliferate and generate cytolytic NK cells. These data demonstrate that the phenotype and functional characteristics of the IL-2-responsive cells in the FUBM are different from those of mature NK cells in that they are MAC-1+, NK1.1+, CD3- and susceptible to boosting by IFN-alpha.

Effect of interleukin-4 on interleukin-2-dependent generation of natural killer cells

We have previously shown that interleukin-2 (IL-2) is able to induce the generation of natural killer (NK) activity in bone marrow (BM) cells from mice pretreated with 5-fluorouracil. IL-2 alone could dose-dependently induce NK activity in marrow cells and interleukin-4 (IL-4) has dual effect on the NK activity in that, depending on the concentration of IL-2, IL-4 inhibits or stimulates development of NK cells. The inhibitory effect was in part antagonized by interleukin-1 alpha. These effects were not obtained when NK-reactive spleen cells were cultured with the same concentrations of IL-2 or IL-2 plus IL-4 with or without irradiated BM cells as feeders. The effects of IL-4 were also obtained by preincubation for 6-24 hr before culturing with IL-2 alone and correlated with the expression of interleukin-2 receptor (IL-2/r), suggesting that IL-4 might play a regulatory role in the IL-2-dependent generation of NK cells in BM.

Isolation and expression of the full-length cDNA encoding CD59 antigen of human lymphocytes

To identify the primary structure of CD59 antigen and to elucidate its function, a full-length cDNA clone of CD59 was isolated. The cDNA sequence contained an open reading frame that encodes an 128-amino-acid peptide. The amino-terminal 25 amino acids represented a typical signal peptide sequence and the carboxy-terminal hydrophobic amino acids were characteristic for phosphatidylinositol-anchored proteins. The predicted mature protein sequence showed 35% homology with murine Ly-6C.1 and 31% with Ly-6A.2. The number and the distribution of cysteine residues were conserved, implying that the CD59 represented a human homologue of murine Ly-6. RNA blot hybridization analysis revealed the expression of CD59 mRNA in placental, lung, and pancreatic tissues. The mRNA was not only expressed in T-cell lines but in some of monocytic, myeloid, and B-cell lines. In all of these tissues and cell lines, at least four mRNA species were detected. DNA blot hybridization analysis revealed a rather simple genomic structure, which suggested a single gene as compared with the complex multigene family of murine Ly-6.

Individual NK cell clones lyse both tumor cell targets and herpes simplex virus-infected fibroblasts in the absence of interferon

The target specificity of natural killer (NK) cells for either tumor cells or virus-infected cells has been investigated. Lymphocyte clones with the surface phenotype of NK cells (CD3-, CD16+) were obtained by limiting dilution of peripheral blood mononuclear cells stimulated with PHA, Herpes simplex virus type 1 (HSV-1), or Varicella-Zoster antigens. Clones were maintained in media with recombinant interleukin 2 (IL-2). Both NK-sensitive (K562 cells) and NK-resistant (Raji cells) targets were lysed by three cloned lines of NK cells. The ability to lyse NK-resistant target cells was largely lost when the cloned lymphocytes were cultured overnight in the absence of IL-2. Effector cells from all three clones were also capable of specifically lysing HSV-1 infected human fibroblasts in comparison with uninfected fibroblasts. We also showed that lysis of HSV-1 infected targets by NK cloned cells was independent of interferons in the culture system.

Interleukin 3 enhanced interleukin 2-dependent maturation of NK progenitor cells in bone marrow from mice with severe combined immunodeficiency

Human recombinant interleukin 2 (IL 2) and highly purified murine interleukin 3 (IL 3) were tested for their ability to generate NK activity in bone marrow cells from mice with severe combined immunodeficiency. IL 2 alone could dose dependently induce NK activity in marrow cells as determined by cytotoxicity against YAC-1 target cells. It was demonstrated that IL 3 had dual effects on the generation of NK activity in this culture system. The addition of IL 3 resulted in inhibition of NK cell activity seen at high concentrations of IL 2. In contrast, when IL 3 was added together with low concentrations of IL 2, the generation of NK cells as judged by cytotoxicity assay as well as the appearance of cells with NK phenotypes was markedly augmented. In some experiments, mice were treated with 5-fluorouracil (5-FU) to eliminate relatively differentiated NK precursors from bone marrow cells. It was noted that the residual immature marrow cells from 5-FU-treated mice showed little NK activity even after the culture with high concentrations of IL 2. Importantly, IL 3 could induce the generation of NK activity from 5-FU-treated marrow cells in the presence of IL 2. Kinetic studies indicated that NK activity was appreciably generated from 5-FU-treated marrow cells when preincubated with IL 3 at least for 12 hr and subsequently cultured with IL 2. The cells bearing IL 2 receptors appeared in 5-FU-treated marrow cells, even though cultured only with IL 3, which implied that IL 3 could support the development of very primitive NK cells from IL 2-unresponsive to IL 2-responsive states. These results suggested that IL 3 might play a crucial role for the IL 2-induced generation of NK cells in bone marrow through promoting the expression of IL 2R on NK progenitor cells.

Homology of perforin to the ninth component of complement (C9)

Perforin is one of the cytolytic factors present in the cytoplasmic granules of mouse cytotoxic T lymphocytes and natural killer cells. We have determined the sequence of the N-terminal amino acids of perforin purified from a mouse natural killer cell line, and, by using oligonucleotide probes corresponding to the amino acid residues, we have identified a complementary DNA encoding perforin from the cDNA library of a mouse cytotoxic T lymphocyte clone. As predicted from the functional similarities between perforin and the ninth component of the serum cytolytic system, complement (C9) (refs 4-8), the deduced primary structure of perforin has homology with C9 at their respective functionally conserved regions. We find that perforin is only expressed in killer cell lines, and not in helper T lymphocytes or other tumour cells tested. Thus we have provided direct molecular evidence that a killer-cell-specific protein evolutionally linked to C9 is involved in cell-mediated cytolysis.

Differentiation in vitro of T3+ large granular lymphocytes with characteristic cytotoxic activity from an isolated hematopoietic progenitor colony

Blast colonies were developed by rIL-3 from the spleen cells of mice pretreated with 5-fluorouracil (5-FU) in the methylcellulose cultures. When such IL-3-induced blast colonies were individually lifted up and recultured in the presence of rIL-3 and recombinant erythropoietin (rEpo), a variety of hematopoietic colonies developed from every single colony, including neutrophils, macrophages, eosinophils, megakaryocytes, mast cells, and erythroblasts. The results indicated that IL-3-induced blast colonies consisted of multipotential hematopoietic progenitor cells. By culturing individual IL-3-induced blast colonies in the presence of rIL-2 and irradiated peritoneal macrophages, on the other hand, the proliferation of homogeneous lymphoid cells was observed in 5 of 24 wells, each of which received a single blast colony. Morphologically, they were typical large granular lymphocytes (LGL), and thus it was indicated that LGL could be differentiated directly from the hematopoietic progenitor cells utterly in vitro by rIL-2 and accessory macrophages. From one of these culture wells, a continuous LGL line, IL3B1, was successfully obtained. The proliferation of IL3B1 was dependent on IL-2 in the presence of accessory macrophages, but they no longer responded to IL-3, nor to another T cell growth factor, IL-4. Flow cytometric analysis indicated that the phenotype of IL3B1 was Thy-1+,T3+,L3T4-,Lyt-2-,T200+ Asialo GM1+, whereas that of original IL-3-induced blast cells was Thy-1+,T3-,L3T4-,Lyt-2-,B220-. The results suggested that the expression of T3 molecules was induced in the process of LGL differentiation from the hematopoietic progenitor cells in vitro. Conforming to this, it was revealed that both gamma and beta chain genes of the TCR were rearranged in IL3B1. Northern blot analysis indicated that IL3B1 had abundant mRNA for gamma chain, while mRNA for beta chain was rather faint. Functionally, IL3B1 exhibited typical NK-patterned cytotoxic activity against a panel of tumor cell targets. In addition, they showed significant cytotoxic activity against normal bone marrow cells, as well as various factor-dependent myelogenous progenitor cell lines, all of which were resistant to endogenous NK activity of the fresh spleen cells. These results indicated that at least a set of T3+ LGL with rearranged TCR genes could be directly differentiated from isolated hematopoietic progenitor cells in vitro. Results also suggested that such a prethymically differentiated subset of T-lineage lymphocytes, namely T3+ double-negative LGL, had particular cytotoxic activity in addition to conventional NK activity, which might well contribute to feedback regulation of hematopoiesis.

Resistance of mouse cytolytic cells to pore-forming protein-mediated cytolysis

Pore-forming protein (perforin, PFP) was isolated from a mouse large granular lymphocyte (LGL) [natural killer (NK-like)] cell line. Purified PFP lysed a variety of mouse tumor cell lines and helper T lymphocyte cell lines. However, LGL and cytotoxic T lymphocyte cell lines were resistant to PFP-mediated cell lysis. The presence of hemolytic activity in the granule was examined in these resistant cell lines. Four out of five of these resistant cell lines had hemolytically active granules. We determined whether NK cells freshly isolated from BALB/c nude mouse spleens were resistant to PFP-mediated cytolysis. Nylon column-passed spleen cells with an enriched content of NK cells exhibited more resistance than whole spleen cells. Moreover, when spleen cells were treated with PFP the remaining live cells showed enriched NK activity suggesting that normal peripheral cells with NK activity are resistant to PFP. These results indicate that cytolytic cells containing PFP have developed defense mechanisms to inhibit PEP-mediated cell lysis.