A T-cell-derived lymphokine was identified by its ability to support the growth of a subset of B-cell hybridomas. Hybrids that failed to survive in the absence of this molecule represented a major proportion of rat-mouse hybridomas but were very rare among mouse-mouse B-cell hybrids. Stable factor-dependent B-cell hybridomas were used to monitor the purification of the growth factor from the supernatant of a clonotypically stimulated mouse helper T-cell clone. Sequential fractionation using gel filtration, anionexchange chromatography, and reversed-phase HPLC resolved the factor from other B-cell growth factors and yielded a single-chain protein characterized by a major charge (pI = 5-7) and molecular mass (22-to 29-kDa) heterogeneity, probably due to variations in glycosylation. The NH2-terminal amino acid sequence of this protein, which is active on B-cell hybridomas in the 0.1 pM range, showed no significant homology with that of known lymphokines. Because the purified factor also supported the growth and survival in vitro of murine plasmacytomas (to be published elsewhere), it was provisionally designated interleukin-HP1 (where H stands for hybridoma and P stands for plasmacytoma).

A factor that promotes the growth of certain B cell hybridomas and of plasmacytomas is shown to be produced by normal human fibroblasts and by a line of human osteosarcoma cells (MG-63) after treatment with IL-1 or TNF. The hybridoma-plasmacytoma growth factor (HPGF) is identified with a 26 kD protein whose mRNA was previously shown to be induced in the same cells by the same inducers. First, poly(A)-rich RNA extracted from IL-1-treated cells could be enriched in HPGF-mRNA content by hybridization to 26 kD cDNA. Second, MG-63-derived HPGF purified to electrophoretic homogeneity was subjected to amino acid sequence analysis, whereby the NH2-terminal sequence was found to match the nucleotide sequence of a 26 kD cDNA clone.

We examined the effect of interleukin (IL)-9, a cytokine active on B and T lymphocytes and associated with bronchial asthma, on the development of lung fibrosis induced by crystalline silica particles. Therefore, we compared the response to silica (1 and 5 mg/animal, intratracheally) in transgenic mice that constitutively express high levels of IL-9 (Tg5) and their wild-type counterparts (FVB). At 2 and 4 mo after treatment with silica, histologic examination and measurement of lung hydroxyproline content showed that the severity of fibrosis was significantly less important in Tg5 mice than in their wild-type counterparts. Intraperitoneal injection of IL-9 in C57BL/6 mice also reduced the amplitude of silica-induced lung fibrosis. The reduction of lung fibrosis by IL-9 was associated with a significant expansion of the B-lymphocyte population, both in bronchoalveolar lavage (BAL) and in the pulmonary parenchyma. In wild-type animals, silica-induced fibrosis correlated with markers of a T helper 2-like response such as upregulation of IL-4 levels in lung tissue and an increased immunoglobulin (Ig) G1/IgG2a ratio in BAL. Immunohistochemical studies demonstrated that the upregulation of IL-4 associated with the development of fibrosis was mainly localized in inflammatory alveolar macrophages. In transgenic mice, the level of IL-4 in lung homogenates was not significantly affected by silica treatment, and a reduced IgG1/IgG2a ratio was observed upon treatment with silica. The levels of interferon-gamma were significantly decreased after silica treatment in both strains. Together, these observations point to an antifibrotic effect of IL-9 in pulmonary fibrosis associated with a limitation of the type 2 polarization which accompanies lung fibrosis.

Murine IgG antiviral antibodies elicited by infection have recently been shown to belong predominantly to the IgG2a subclass (1). This isotypic distribution ofantiviral antibodies contrasts sharply with that ofantisoluble protein or anticarbohydrate antibodies, which are usually restricted to the IgG1 and IgG3 subclasses, respectively (1-3). Such an isotypic bias of antiviral antibodies could be due to intrinsic biochemical characteristics of viral antigens or, alternatively, to regulatory mechanisms elicited by the infectious process itself. To address this question, we analyzed the effect of infection on the isotypic pattern of antibodies not directed against the viral antigens. Our results indicate that viruses can influence the subclass distribution of IgG antibodies produced in the course of the infection, irrespective of their specificity. Materials and MethodsMice. CBA/Rij and 129/Sv mice, bred at our institute by Dr. G. Warnier, were maintained in specific pathogen-free conditions and used when 6-10 wk old.Viruses. Infections were performed as described in (1). In addition, K virus (a gift ofDr. W. P. Rowe, Bethesda, MD, No. 3134/KS) and EDIM virus (a gift ofDr. T. H. Flewett, Birmingham, UK) were used . For the absorption experiments, pooled sera from infected mice were diluted 100-fold in PBS (120 mM NACI, 5 mM Na2HPO4, 3 mM KH2PO4, pH 7.2) containing 2% FCS and incubated for 2 h at 4°C with serial doses of purified virus or with buffer only. Viral particles were then removed from sera by centrifugation through a 15% sucrose cushion (35,000 rpm for 90 min in an SW41 rotor, Beckman Instruments, Inc., Palo Alto, CA) and remaining Igs were measured in supernatant by ELISA.Immunoglobulin Determinations. Total IgM and IgA levels were determined by RIA as described previously (4) and total IgG subclass levels were measured by ELISA . For the ELISA, polystyrene plates (Greneir, Nurtingen, FRG) were coated overnight with an anti-mouse IgG3 rat mAb (2E .6, American Type Culture Collection, Rockville, MD) (5 Wg/ml in 0.02 M glycine, 0.03 M NaCl, pH 9.2) or with affinity-purified goat antibodies specific for rabbit IgG, followed by rabbit antibodies specific for mouse IgG subclasses (4). After overnight incubation with sera serially diluted in Tris-buffered saline (10 mM Tris, 10 mM merthiolate, 130