Structural and functional studies of the early T lymphocyte activation 1 (Eta-1) gene. Definition of a novel T cell-dependent response associated with genetic resistance to bacterial infection

Comparative susceptibility to mouse interferons of Rickettsia tsutsugamushi strains with different virulence in mice and of Rickettsia rickettsii

Three strains of Rickettsia tsutsugamushi (Karp, Gilliam, and TA716, representing three virulence types in mice) were examined for their sensitivity to the inhibitory effects of recombinant gamma interferon (IFN-gamma) and purified IFN-alpha/beta in two cultured mouse fibroblast cell lines. The susceptibilities of another species, Rickettsia rickettsii, and of encephalomyocarditis virus (EMCV) were also tested for comparative purposes. IFN-gamma inhibited rickettsial replication in only one of the six combinations of R. tsutsugamushi strains and mouse cells (strain Gilliam and the BALB/c mouse-derived cell line). In contrast, R. rickettsii and EMCV replication were markedly inhibited in both cell types, but to a greater extent in the BALB/c line than in the C3H cells. IFN-alpha/beta (300 to 450 U/ml) was uniformly ineffective in three of the combinations of R. tsutsugamushi strains and mouse cells (Gilliam in C3H cells and Karp in both C3H and BALB/c cells); in the remaining sets, IFN-alpha/beta-mediated inhibition of rickettsial replication was variable and in no case was it very pronounced. The tests with R. rickettsii in both cell types also indicated slight, variable sensitivity to IFN-alpha/beta. EMCV, on the other hand, was very susceptible to IFN-alpha/beta, confirming the potency of the preparation used; as with IFN-gamma, virus replication was inhibited to a greater degree in the BALB/c cell line than in the C3H cultures. These results are discussed in terms of their relationship to the virulence properties of the R. tsutsugamushi strains in BALB/c and C3H mice and to the known IFN-sensitivities of the more widely studied Rickettsia prowazekii.

Susceptibility of Rickettsia tsutsugamushi Gilliam to gamma interferon in cultured mouse cells

Recombinant rodent gamma interferon (IFN-gamma) inhibited the infection of cultured BALB/3T3 mouse fibroblasts by Rickettsia tsutsugamushi Gilliam, apparently mainly by clearance of intracellular rickettsiae. No significant effect on rickettsial entry into the cells was noted; IFN-gamma was toxic to infected cells, as measured by the capacity of treated, infected cells to attach to the surfaces of culture vessels. In a small proportion of IFN-gamma-treated cells, rickettsial replication appeared to persist at normal levels. A fraction (28%) of rickettsiae clonally isolated from cultures treated with IFN-gamma was resistant to IFN-gamma-mediated inhibition, but four serial passages of these resistant clones in the absence of additional IFN-gamma resulted in the loss of resistance. In several respects, therefore, the IFN-gamma-mediated inhibition of scrub typhus rickettsiae in cultured fibroblasts was similar to that reported for Rickettsia prowazekii.

Genetics of the immune response to infectious pathogens

In this selective review of the recent literature in the field of genetically determined host resistance to infection, we highlight five areas in which research is directed towards the search for proteins encoded by genes that function to maintain a 'resistant' phenotype in the face of challenge by a variety of pathogenic organisms. In particular, we discuss newly described genes that may regulate host resistance, newly described functions of genes previously identified, the reverse genetics approach to cloning an elusive gene, a direct genetics approach to a similar problem, and the role of the major histocompatibility complex in regulating our ability to resist challenge by infectious organisms.

Osteopontin, a substrate for transglutaminase and factor XIII activity

Osteopontin (OPN), an extracellular matrix cell adhesion protein, was found to serve as a substrate for the incorporation of radiolabelled putrescine mediated by a commercial preparation of guinea pig liver transglutaminase. Preliminary evidence also suggests that OPN serves as a substrate for the plasma transglutaminase, Factor XIIIa. While the protein substrates to which OPN is linked in vivo have not been identified, it is reasonable to speculate that this capacity of OPN may dictate its extracellular location and thereby affect its role in bone homeostasis, tumorigenesis, metastasis, resistance to bacterial infections or, perhaps, wound repair.

Differential regulation of the 55 and 44 kDa forms of secreted phosphoprotein 1 (SPP-1, osteopontin) in normal and transformed rat bone cells by osteotropic hormones, growth factors and a tumor promoter

Confluent cultures of rat bone cells synthesize several forms of secreted phosphoprotein 1 (SPP-1, osteopontin), the major phosphorylated forms of which migrate at 55 and 44 kDa on 15% cross-linked SDS-PAGE gels and correspond to the transformation-associated proteins pp 69 and pp 62. A clonal rat calvarial cell line (RCA 11), which expressed the highest level of SPP-1, produced only the 55 kDa form of the phosphorylated protein, whereas normal rat calvarial cells enriched in osteoblastic cells (RC IV cells) produced mostly the 55 kDa form, with small amounts of the 44 kDa form. In contrast, a 44 kDa form was the major [32PO4]-labelled SPP-1 synthesized by a rat osteocarcoma cell line (ROS 17/2.8 cells) with lesser amounts of the 55 kDa SPP-1. When [35S]methionine was used to measure protein synthesis, only the 55 kDa SPP-1 could be clearly detected in confluent cultures of each cell population, indicating that the 55 kDa SPP-1 is the prominent form of SPP-1 synthesized by each cell population. Following treatment of the normal rat bone cells for 24 h with osteotropic hormones (vit D3, PTH and RA), growth factors (PDGF, EGF, TGF-beta), a tumor promoter (TPA) and a plant lectin (Con A), the 55 kDa [35S]methionine labelled SPP-1 was increased 1.7-8.3-fold. Similar, but generally lower responses were observed in the clonal RCA 11 cell line, whereas the ROS 17/2.8 cells were more refractory, showing only a strong response to vit D3. In general, vit D3 produced the strongest stimulation in all populations with TGF-beta producing a good response in the non-transformed cells and RA in the RC IV cells. In contrast, PTH was inhibitory in both RCA 11 and ROS 17/2.8 cells. In most, but not all, cases the alteration in SPP-1 synthesis reflected similar changes in SPP-1 mRNA and in the intensity of the [32PO4]-labelled 55 kDa SPP-1. Collectively, these studies demonstrate that bone cells produce several forms of SPP-1 which are differentially regulated in normal and transformed cells through both transcriptional and posttranscriptional mechanisms.

Differential induction of interferon gamma gene expression after activation of CD4+ T cells by conventional antigen and Mls superantigen

We have analyzed cytokine gene expression by a murine CD4+ T-cell clone that expresses three forms of T-cell recognition. The clone employs a V beta 6-containing T-cell receptor to recognize (i) a self class II major histocompatibility complex and an ovalbumin-derived peptide (OVA), (ii) an I-Ab alloantigen, and (iii) Mls-1a. All three responses are accompanied by similar levels of cell proliferation. However, although interferon gamma gene expression is strongly induced during both physiological recognition of the OVA peptide and allogeneic major histocompatibility complex recognition, expression of this gene was not detected during the Mls response. These studies indicate that Mls recognition is functionally distinct from T-cell recognition of peptides and alloantigens and leads to an alternative pattern of cytokine gene expression. They also suggest the possibility that encounter with these two classes of T-cell antigen in vivo may generate subsets of T helper cells that display different patterns of cytokine gene expression.

The murine gene encoding secreted phosphoprotein 1 (osteopontin): promoter structure, activity, and induction in vivo by estrogen and progesterone

Secreted phosphoprotein 1 (Spp-1) is a 41.5-kDa bone sialoprotein presumed to be important in the development and functioning of a number of mammalian organs and possibly also in the progression of malignancies. We report here the isolation of a phage lambda genomic clone of the murine Spp-1 gene containing the promoter and first six exons (4.6 kb of the 5.7-kb gene). We have found another exon located 5' to the 'exon 1' reported by Miyazaki et al. [J. Biol. Chem. 265 (1990) 14432-14438]. The DNA upstream from this 5' exon functions as a promoter in epidermal fibroblast and osteoblast-like cells, as demonstrated by transient transfection assays, S1 mapping of the transcription start point, and sequence analysis revealing TATA-like (TTTAAA) and CAAT (its inverse complement) boxes. A small region of the promoter (nt -253 to +79) was able to direct high-level expression of a fused cat reporter gene in JB6 mouse epidermal cells. The transient transfection assays indicated the presence of a positive transcription element between nt -543 and -253 and a negative transcription element between nt -777 and -543. Addition of the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), resulted in a 1.5-3-fold induction of transcription, depending on the promoter construct and the TPA concentration. The Spp-1 mRNA was localized in several tissues, consistent with previous reports, and to novel sites in ovary, and in the skin and ventral fatty tissue of pregnant and lactating mice. The induction of Spp-1 mRNA was partially mimicked by painting beta-estradiol or progesterone on the skin of nonpregnant females.

Dysregulated expression of the T cell cytokine Eta-1 in CD4-8- lymphocytes during the development of murine autoimmune disease

The development of autoimmune disease in the MRL/MpJ-lpr inbred mouse strain depends upon the maturation of a subset of T lymphocytes that may cause sustained activation of immunological effector cells such as B cells and macrophages. We tested the hypothesis that abnormal effector cell activation reflects constitutive overexpression of a T cell cytokine. We found that a newly defined T cell cytokine, Eta-1, is expressed at very high levels in T cells from MRL/l mice but not normal mouse strains and in a CD4-8- 45R+ T cell clone. The Eta-1 gene encodes a secreted protein that binds specifically to macrophages, possibly via a cell adhesion receptor, resulting in alterations in the mobility and activation state of this cell type (Patarca, R., G. J. Freeman, R. P. Singh, et al. 1989. J. Exp. Med. 170:145; Singh, R. P., R. Patarca, J. Schwartz, P. Singh, and H. Cantor. 1990. J. Exp. Med. 171:1931). In addition, recent studies have indicated that Eta-1 can enhance secretion of IgM and IgG by mixtures of macrophages and B cells (Patarca, R., M. A. Lampe, M. V. Iregai, and H. Cantor, manuscript in preparation). Dysregulation of Eta-1 expression begins at the onset of autoimmune disease and continues throughout the course of this disorder. Maximal levels of Eta-1 expression and the development of severe autoimmune disease reflect the combined contribution of the lpr gene and MRL background genes.

Definition of a specific interaction between the early T lymphocyte activation 1 (Eta-1) protein and murine macrophages in vitro and its effect upon macrophages in vivo

The Eta-1 gene specifies a secreted product of activated T cells and is associated with genetic resistance to infection by an obligate intracellular bacterium. Previous studies have suggested that eta-1 might affect the ability of macrophages to migrate to the site of bacterial infection and/or to inhibit intracellular bacterial growth. We therefore examined the interaction of eta-1 with macrophages in vitro and in vivo. We find that macrophages express approximately 10(4) eta-1 receptors/cell and each receptor has a Kd of approximately 5 x 10(-10) M. The subsequence of eta-1 containing an RGD motif is required for binding because a synthetic peptide containing the eta-1 RGD domain inhibited protein attachment to macrophages. We also found that subcutaneous inoculation of mice with eta-1 resulted in a cellular infiltrate comprised primarily of macrophages. We propose that the interaction between eta-1 and its receptor on macrophages results in a change in macrophage physiology resulting in accumulation of these cells at extravascular sites.