Production of IL-5 and granulocyte-macrophage colony-stimulating factor by naive human mast cells activated by high-affinity IgE receptor ligation.

BACKGROUND: The late-phase allergic reaction is an eosinophilic inflammatory response that begins several hours after allergen exposure, may persist for 24 hours, and is an important pathogenic mechanism in allergic disease. OBJECTIVE: Cultured naive human mast cells were used to investigate whether mast cells are a direct source of the eosinophil-promoting cytokines IL-5, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). METHODS: Naive human mast cells were derived from bone marrow mononuclear cells cultured in the presence of stem-cell factor. Cytokine message and protein production in response to high-affinity IgE receptor ligation of cultured mast cells were measured by semiquantitative polymerase chain reaction and ELISA, respectively. RESULTS: IL-5, IL-3, and GM-CSF messenger RNA increased within 2 hours of mast cell activation, with IL-5 and GM-CSF message remaining elevated for 24 hours, whereas IL-3 mRNA rapidly declined. IL-5 and GM-CSF protein were measurable 4 to 6 hours after stimulation and peaked by 24 and 12 hours, respectively. IL-3 protein was not detectable. CONCLUSION: These findings demonstrate that naive mast cells do not constitutively produce IL-5 or GM-CSF protein but are a major source of these eosinophilotropic cytokines on high-affinity IgE receptor ligation.

Human B cells express IL-5 receptor messenger ribonucleic acid and respond to IL-5 with enhanced IgM production after mitogenic stimulation with Moraxella catarrhalis.

The potential for IL-5 to regulate human B cells is controversial despite its well established role as a regulatory factor for murine B cells. We hypothesized that the mechanism by which human B cells were stimulated would, as with murine B cells, determine their potential to respond to IL-5. Since Staphylococcus aureus Cowan strain I (SAC) and Moraxella catarrhalis (MCat) stimulate human B cells by distinct interactions with cell-surface Ig, we compared their potential to induce an IL-5-responsive state by human B cells purified to homogeneity. Neither SAC alone nor SAC plus IL-5 stimulated Ig production, although microgram quantities of IgM were produced with SAC plus IL-2. In contrast, MCat induced microgram quantities of IgM by B cells in the absence of exogenous cytokines, and IL-5 significantly increased IgM production over twofold in the majority of donors. Synergism of IL-5 and IL-2 was detected using suboptimal concentrations of IL-2 with MCat-, but not SAC-, stimulated B cells. Donor B cells unresponsive to IL-5 when stimulated with MCat, became IL-5 responsive in the presence of IL-2. Since message for the IL-5R alpha, IL-5R beta, and soluble IL-5R alpha chains was detected in freshly isolated B cells, we further investigated whether IL-5 responsiveness to MCat, but not SAC, was due to their differential regulation of IL-5R mRNA. Surprisingly, stimulation by either MCat or SAC, without or with IL-2, increased both IL-5R alpha and IL-5R beta mRNA and decreased soluble IL-5R alpha mRNA. These studies demonstrate that, as with murine B cells, human B cells express message for IL-5R but can respond to IL-5 only if appropriately stimulated to undergo terminal differentiation.

Delineation of IL-5 domains predicted to engage the IL-5 receptor complex.

IL-5 is an interdigitating homodimeric glycoprotein and a member of the helical bundle family of cytokines. IL-5 is a potent activator of eosinophils and a specific promoter of their differentiation. This activity has implicated IL-5 in the pathogenesis of asthma and allergic disease. A detailed understanding of IL-5 structure and function is required to develop immunomodulators of IL-5-mediated inflammatory responses. We generated a panel of neutralizing anti-IL-5 mAbs which were used to map functional domains on IL-5. In addition, the nucleotide sequences for human IL-5, murine IL-5, rat IL-5, and eight human/murine IL-5 chimeras were engineered and expressed in COS-7 cells. These recombinant cytokines and mAbs were used in TF-1 bioassays to identify five functional epitopes on the tertiary structure of IL-5. Residues responsible for the species-specific activity of human IL-5 were identified with the murine BCL1 bioassay. One set of epitopes cluster around the helix A-loop 2 region, which is predicted to engage the IL-5 receptor beta-chain. The second set of epitopes as well as the species specificity domain cluster around the loop 3-helix D region, which is predicted to engage the IL-5 receptor alpha-chain. Together, these analyses target the A/D helical face of IL-5 as the region involved in receptor engagement.

Enhanced detection of human IL-5 in biological fluids utilizing murine monoclonal antibodies which delineate distinct neutralizing epitopes.

Interleukin 5 (IL-5) is a homodimeric cytokine arranged in a head-to-tail configuration covalently linked by two disulfide bonds. IL-5 has pleiotropic effects on murine and human leukocytes and has been implicated in the pathogenesis of many inflammatory disorders. To facilitate the study of functionally relevant IL-5 domains involved in receptor binding and to develop a highly sensitive and specific ELISA capable of detecting IL-5 in biological fluids, a library of murine anti-human IL-5 (hIL-5) mAb was generated to baculovirus expressed recombinant hIL-5 (rhIL-5). Fifteen subclones of seven hybridomas were characterized. All mAb bound hIL-5, but not murine IL-5 (mIL-5), and neutralized hIL-5 biological activity in the BCl1 proliferation assay. By competitive ELISA, the mAb were divided into two binding groups. Utilizing comparative analysis with TRFK-5, a rat anti-mIL-5 mAb crossreactive with hIL-5, at least three hIL-5 neutralizing epitopes were defined. By ELISA and Western analysis, each epitope was shown to be present as a conformationally identical pair on the hIL-5 dimer. Various combinations of mAb in sandwich ELISA were used to predict the relative proximity of each epitope pair. Utilizing mAb binding characteristics, highly sensitive and specific sandwich ELISA were developed with a minimum detection limit of 6.25 pg hIL-5/ml (P < 0.05). Quantitation of hIL-5 in both serum and bronchoalveolar lavage (BAL) fluid demonstrated the utility of these anti-hIL-5 mAb for investigating the role of hIL-5 in inflammation. These mAb should also serve as useful reagents for epitope mapping of functional hIL-5 domains.

Abnormal response to IL-5 in B-cell chronic lymphocytic leukemia.

In B-cell chronic lymphocytic leukemia, neoplastic B-lymphocytes are arrested in development. Since interleukins are essential for B-cell differentiation, we examined whether B-CLL cells were capable of responding normally to interleukins. Purified B-lymphocytes from B-CLL patients and controls were compared for their ability to proliferate and differentiate after stimulation with MCAT or SAC plus rhIL-2 or rhIL-5. When rhIL-5 was added to MCAT-stimulated cells, 8 of 10 controls showed a substantial increase in IgM production, compared with only 1 of 10 B-CLL patients. Lack of IL-5 responsiveness could provide insight into the arrested B-lymphocyte development of some B-CLL patients.

Efficient synthesis of adeno-associated virus structural proteins requires both adenovirus DNA binding protein and VA I RNA.

We have shown previously that replication of defective parvoviruses [adeno-associated viruses (AAV)] requires several early adenovirus (Ad) gene products [J. E. Janik, M. M. Huston, and J. A. Rose (1981) Proc. Natl. Acad. Sci. USA 78, 1925-1929]. To examine their possible roles in the transcription and translation of AAV mRNA, 293-31 cells, a human embryonic kidney cell line that constitutively expresses the Ad early region IA and IB gene products, were transfected with a pBR325 plasmid (pLH1) that contains a duplex AAV2 DNA segment (0.03-0.97 map units) which encompasses the promoters and coding sequences necessary for expression of all AAV polypeptides. When cells were transfected with pLH1 alone, both spliced and unspliced AAV-specific cytoplasmic RNAs accumulated. These transcripts were capable of directing synthesis of the three AAV capsid polypeptides in vitro, whereas in vivo synthesis of AAV protein was not detected by immunofluorescence or immunoprecipitation. When cells were cotransfected with pLH1 and intact Ad DNA, the level of cytoplasmic AAV RNA was enhanced and AAV protein was synthesized in vivo. Additional experiments demonstrated that in vivo AAV protein synthesis also could be induced when pLH1 was cotransfected with plasmids that contain the Ad DNA-binding protein (pDBP) and VA I RNA (p2BalM) genes; however, a low level of in vivo AAV capsid protein was occasionally detected in cotransfections with pLH1 and a plasmid that contains both VA I and VA II RNA coding sequences (p2SalC). Cotransfection of pLH1 and pDBP or pLH1 and p2SalC showed complex alterations in the steady-state patterns of AAV cytoplasmic transcripts. In both cases, increased levels of transcripts, particularly the 2.3-kb spliced species, were detected in comparison to levels seen in cells transfected with pLH1 alone. Despite these increases, however, there was little, if any, induction of AAV protein synthesis unless both the DNA-binding protein (DBP) and VA I RNA coding sequences were present in cotransfection with pLH1. We conclude that, in 293-31 cells, the Ad VA I RNA and DBP gene products regulate AAV capsid protein synthesis at least at two levels: (i) by increasing the steady-state levels of structural protein transcripts in the cytoplasm, especially the spliced species, and (ii) by enhancing the translation of these messages.

Mitochondrial modulation of maternally transmitted antigen: analysis of cell hybrids.

Maternally transmitted antigen (Mta) is a murine cell surface class I-like antigen that is defined by specific cytotoxic lymphocyte reactivity. Mta is unique in that its expression requires cooperation between genetic elements both in the Qa/Tla region of chromosome 17 and in the cytoplasm. In view of the known cytoplasmic, and thus maternal, inheritance of mitochondria, we have directly assessed their potential involvement in Mta expression. The mitochondria-specific lethal dye rhodamine 6G (R6G) was used to control the input of mitochondria into cell hybrids. The parental lines, one of BALB/c and one of NZB origin, were known to differ in Mta and mtDNA phenotype. Our data show that most control BALB/c-NZB hybrids expressed the BALB/c Mta phenotype and likewise contained only BALB/c-type mtDNA. The NZB Mta phenotype was not coexpressed in the control hybrids. However, when the mitochondrial contribution from BALB/c was prevented by R6G treatment, the majority of the resultant hybrids expressed only the NZB Mta type and likewise contained only NZB mtDNA. The exceptional R6G-treated hybrids that continued to express the BALB/c Mta phenotype likewise contained only BALB/c mtDNA. Thus, in every case the mtDNA phenotype correlated with the Mta phenotype of the cells. Together, the data support the remarkable conclusion that mitochondria modulate the phenotypic expression of a cell surface molecule.

Adeno-associated virus proteins: origin of the capsid components.

The three primary capsid proteins (A, B, and C) of adeno-associated viruses have been shown previously to contain overlapping amino acid sequences (R. McPherson and J. Rose, J. Virol. 46:523-529, 1983). In the present study we demonstrate definitively that these proteins are encoded in the right half of the adeno-associated virus 2 genome, and one or both of the smallest adeno-associated RNA species (2.3- or 2.6-kilobase RNA) account for their synthesis. Protein A (90 kilodaltons) apparently initiates from a site within the intervening sequence, which is intact in the larger (unspliced) 2.6-kilobase mRNA, and may read through one or more termination codons, including a strong stop signal (UAA) that lies 31 bases downstream from the end of the intervening sequence. Proteins B (72 kilodaltons) and C (60 kilodaltons) are not derived from protein A but apparently originate from independent, in-frame initiations that lie downstream from the splice junction. It thus seems likely that production of the three adeno-associated virus capsid proteins involves at least two mRNA species. The B and C proteins presumably arise from the spliced 2.3-kilobase RNA, whereas protein A should be generated by the 2.6-kilobase RNA or a hitherto unidentified spliced RNA species.

Mitochondria control expression of a murine cell surface antigen.

Maternally transmitted antigen (Mta) is a murine cell-surface molecule defined by the reactivity of specific H-2 nonrestricted cytotoxic T lymphocytes (CTL-s). Maternal transmission appears to be under control of a stable genetic factor in the cytoplasm of the ovum. In view of the known maternal inheritance of mitochondria we have assessed their involvement in Mta expression using the mitochondria specific poison Rhodamine 6G (R6G). We report here that Mta expression in somatic cell hybrids requires functional mitochondria from the Mta+ parent cell line. Mta expression was dominant in hybrids from the fusion of Mta+ and Mta- cells. However, pretreatment of the Mta+ parent with R6G resulted in hybrids which were Mta-, or diminished in Mta expression. These data strongly implicate mitochondrial DNA (mtDNA) in the expression of a cell-surface molecule, and define a system for studying a previously unrecognized mitochondrial function. To our knowledge, this is the first evidence for mitochondrial control of the expression of a cell membrane molecule in eukaryotes.

Differences in maternal lineages of New Zealand Black mice defined by restriction endonuclease analysis of mitochondrial DNA and by expression of maternally transmitted antigen.

Two substrains of New Zealand Black (NZB) mice have been compared with respect to expression of a maternally transmitted cell surface antigen, Mta, defined by cloned cytolytic T cells, and for restriction enzyme polymorphisms of mitochondrial DNA (mtDNA). These independent assays of maternal cytoplasmic inheritance provide strong evidence for genetic contamination of the NZB/BlPt substrain (NZB/Bl mice from Michael Potter's separate colony at the National Institutes of Health), in which the typical NZB immunologic abnormalities are at least partially ameliorated. The decisive data are the restriction enzyme maps of mtDNA for NZB/BlPt, which were identical with those of the common "old inbred" strains and quite different from those of NZB/BlN (NZB/Bl mice from the breeding facility at the National Institutes of Health). It is probable that the contamination of the NZB/BlPt substrain is related to phenotypic changes in their autoimmune state. More interestingly, the data are consistent with, although they do not prove, involvement of the mitochondrial genome in expression of a cell surface molecule.

Locations of adenovirus genes required for the replication of adenovirus-associated virus.

We have used DNA transfection to identify several regions of the adenovirus genome needed to induce replication of the defective parvovirus, adenovirus-associated virus (AAV). Previous studies have indicated that only early adenovirus functions are needed to aid the replication of AAV. In this report, we demonstrate that three restriction endonuclease fragments of adenovirus DNA are necessary for production of infectious AAV in 293-31 cells (an adenovirus type 5-transformed human embryonic kidney cell line). These fragments map from 28.5 to 29.4, 59.5 to 75.9, and 89.7 to 100 map units on the adenovirus type 2 genome and correspond to the locations of the VAI RNA gene, early region 2, and early region 4, respectively. The 293-31 cell line, which has been found to express early region 1A and 1B proteins, alone is incapable of supporting AAV replication or even AAV DNA synthesis. Additional experiments with adenovirus type 5 host range mutants (group I, hr1 and group II, hr7) indicate, however, that early region 1A provides an essential function(s) for AAV replication, whereas early region 1B probably does not.