The role of CCR7 in TH1 and TH2 cell localization and delivery of B cell help in vivo

Subsets of murine CD4+ T cells localize to different areas of the spleen after adoptive transfer. Naïve and T helper 1 (TH1) cells, which express the chemokine receptor CCR7, are home to the periarteriolar lymphoid sheath, whereas activated TH2 cells, which lack CCR7, form rings at the periphery of the T cell zones near B cell follicles. Retroviral transduction of TH2 cells with CCR7 forces them to localize in a TH1-like pattern and inhibits their participation in B cell help in vivo but not in vitro. Thus, differential expression of chemokine receptors results in unique cellular migration patterns that are important for effective immune responses.

Cooperation between Th1 and Th2 cells in a murine model of eosinophilic airway inflammation

We have studied the actions of helper T lymphocyte-1 and -2 (Th1 and Th2) cells in an acute model of eosinophilic airway inflammation by infusing chicken ovalbumin-specific (OVA-specific) Th1 cells, Th2 cells, or both into unsensitized mice and challenging the mice with an OVA aerosol. OVA challenge after infusion of Th1 cells alone resulted in airway inflammation with lymphocytes and monocytes. Challenge after the infusion of Th2 cells alone resulted in minimal inflammation. In contrast, when Th1 and Th2 cells were transferred together, they cooperated to promote a robust eosinophil-predominant inflammatory response. Th1 cells alone were readily recruited to the airways after challenge, but in the absence of Th1 cells, Th2 cells did not accumulate in the airways. When transferred together, both Th1 and Th2 cells, as well as endogenous eosinophils, were effectively recruited. This recruitment was correlated with increased VCAM-1 expression in the medium- and large-sized vessels of the lung and could be inhibited by treating the mice with neutralizing antibodies to TNF-alpha or VCAM-1. These data indicate that Th2 cells require signals in addition to antigen for their effective recruitment to the airways. Th1 cells can provide these signals.

Modulation of airway inflammation by passive transfer of allergen-specific Th1 and Th2 cells in a mouse model of asthma

Although evidence is strong that Th cells play a major role in mediating the airway inflammation observed in asthma, the relative contributions of the Th cell subsets, Th1 and Th2, are unclear. It has been suggested that asthma is driven by Th2 predominant responses in the lung, but other data suggest a role for Th1 cells as well. Here we show by intracellular cytokine staining and flow cytometric analysis that in the murine model of OVA-induced airway inflammation, both Th1 and Th2 cells are recruited to the airways. Th1 cells predominate early in the response and Th2 cells predominate late. We further show that increasing the number of Th1 cells by passive transfer of OVA-specific Th1 cells results in increased inflammation. This effect is observed regardless of whether the T cells are transferred before sensitization or after airway inflammation is already in progress. Transfer of Th1 cells also results in increased recruitment of host T cells of both Th1 and Th2 phenotypes. Passive transfer of Th2 cells results in little change in the inflammatory response. These results demonstrate that Ag-specific Th1 cells are not protective in this model of asthma, but rather may potentiate the inflammatory response.

Affinity maturation without germinal centres in lymphotoxin-alpha-deficient mice

Affinity maturation by somatic hypermutation is thought to occur within germinal centres. Mice deficient in lymphotoxin-alpha (LT alpha-/- mice) have no lymph nodes or Peyer's patches, and fail to form germinal centres in the spleen. We tested whether germinal centres are essential for maturation of antibody responses to T-cell-dependent antigens. LT alpha-/- mice immunized with low doses of (4-hydroxy-3-nitrophenyl)acetyl-ovalbumin (NP-OVA) showed dramatically impaired production of high-affinity anti-NP IgG1. However, LT alpha-/- mice immunized with high doses of NP-OVA, even though they failed to produce germinal centres, manifested a high-affinity anti-NP IgG1 response similar to wild-type mice. Furthermore, when LT alpha-/- mice were multiply immunized with high doses of NP-OVA, the predominantly expressed anti-NP VH gene segment VH186.2 showed somatic mutations typical of affinity maturation. Thus, B-cell memory and affinity maturation are not absolutely dependent on the presence of germinal centres.

Characterization of deletion and truncation mutants of the rat glucagon receptor. Seven transmembrane segments are necessary for receptor transport to the plasma membrane and glucagon binding

Glucagon receptor mutants were characterized with the aim of elucidating minimal structural requirements for proper biosynthesis, ligand binding, and adenylyl cyclase coupling. One N-terminal deletion mutant and five truncation mutants with progressively shorter C termini were expressed in transiently transfected monkey kidney (COS-1) cells. Each truncation mutant was designed so that the truncated C-terminal tail would remain on the cytoplasmic surface of the receptor. In order to characterize the cellular location of the expressed receptor mutants, a highly specific, high affinity antipeptide antibody was prepared against the extracellular, N-terminal tail of the receptor. Immunoblot analysis and immunofluorescence microscopy showed that the presence of all seven putative transmembrane segments, but not not an intact N-terminal tail, was required for cell surface expression of the receptor. Membranes from cells expressing receptor mutants lacking a large portion of the N-terminal tail or any of the seven putative transmembrane segments failed to bind glucagon. Membranes from cells expressing the C-terminal tail truncation mutants, which retained all seven transmembrane segments, bound glucagon with affinities similar to that of the native receptor and activated cellular adenylyl cyclase in response to glucagon. These results indicate that all seven helices are necessary for the proper folding and processing of the glucagon receptor. Glycosylation is not required for the receptor to reach the cell surface, and it may not be required for ligand binding. However, the N-terminal extracellular portion of the receptor is required for ligand binding. Most of the distal C-terminal tail is not necessary for ligand binding, and the absence of the tail may increase slightly the receptor binding affinity for glucagon. The C-terminal tail is also not necessary for adenylyl cyclase coupling and therefore does not play a direct role in G protein (GS) activation by the glucagon receptor.

Synthesis and expression of a gene for the rat glucagon receptor. Replacement of an aspartic acid in the extracellular domain prevents glucagon binding

In order to facilitate structure-function studies of the glucagon receptor by site-directed mutagenesis, we have designed and synthesized a gene for the rat glucagon receptor. The gene codes for the native 485-amino-acid protein but contains 91 unique restriction sites. To characterize gene expression, a highly specific, high affinity antipeptide antibody was prepared against the receptor. The synthetic gene was expressed in transiently transfected monkey kidney (COS-1) cells. COS cells expressing the synthetic receptor gene bound glucagon with affinity and specificity similar to that of hepatocytes containing native receptor. The transfected COS cells also showed increased intracellular cAMP levels in response to glucagon. The functional role of an aspartic acid residue in the NH2-terminal tail of the receptor was tested by site-directed mutagenesis. This site in the related growth hormone releasing factor receptor was shown to be responsible for the little mouse (lit) genetic defect that results in mice of small size with hypoplastic pituitary glands. Mutant glucagon receptors with amino acid replacements of Asp64 were expressed at normal levels in COS cells but failed to bind glucagon. These results indicate that amino acid Asp64 may play a key role in glucagon binding to receptor.

Production and characterization of human hybridoma monoclonal anti-Sm and anti-U1RNP antibodies spontaneously produced from normal human lymphocytes

A panel of human:human hybridomas secreting monoclonal anti-Sm/RNP antibodies was established by the fusion of normal human tonsillar lymphocytes to the lymphoblastoid B cell line GM4672. The specificity of these antibodies was studied by direct binding and competitive inhibition in enzyme linked immunosorbent assays (ELISAs), and by immunoblotting. The stable subclones of these hybridoma monoclonal anti-Sm/RNP antibodies could be classified into four groups according to ELISA. Group I bound Sm/RNP only, group II bound Sm-RNP, Ro/SS-A and La/SS-B, group III bound Sm/RNP and ssDNA, and group IV bound Sm/RNP, Ro/SS-A, La/SS-B and ssDNA. When antibodies from each of the groups were tested by immunoblotting, the following pattern of reactivity emerged. Group II and IV antibodies reacted with U1RNP-A, Sm-B'/B, Sm-D and Sm-E proteins, as well as the Ro/SS-A and La/SS-B proteins. In contrast, group I and III antibodies did not bind to any individual protein components of Sm/RNP,Ro/SS-A or La/SS-B antigens, but recognized their conformational epitopes. These results, therefore, directly demonstrate for the first time that normal-derived B cells have the genetic potential, revealed here by somatic cell hybridization, to produce anti-Sm/RNP antibody responses which are ordinarily only associated with systemic lupus erythematosus (SLE) and related connective tissue diseases.