In vivo tissue distribution of CD4 lymphocytes in mice determined by radioimmunoscintigraphy with an 111In-labeled anti-CD4 monoclonal antibody.

The tissue distribution of CD4 lymphocytes in normal C57/BL mice and CD4 knockout mice was determined by biodistribution measurements and gamma camera imaging with an 111In-labeled rat IgG2b monoclonal antibody directed against the murine CD-4 antigen. In normal mice high concentrations of antibody accumulated in the spleen and lymph nodes. At 45 hr after injection, the concentration of radiolabel in the spleen and lymph nodes of normal mice were 10- to 20-fold greater than in the corresponding tissue of the CD4 knockout mice and nonlymphoid tissues of both types of mice. At 24 and 45 hr, gamma camera images showed high concentrations of radiolabeled antibody in lymph node and spleen of normal but not knockout mice. These results indicate that radioimmunoscintigraphy with 111In-anti-CD4 is an excellent method for studying tissue distribution of CD lymphocytes in mice. Using an equivalent anti-human CD antibody, this method might be useful for studying the pathophysiology of conditions in which these cells play a critical role and for monitoring therapies for these disorders.

Isolation of the human PC6 gene encoding the putative host protease for HIV-1 gp160 processing in CD4+ T lymphocytes.

Production of infectious HIV-1 virions is dependent on the processing of envelope glycoprotein gp160 by a host cell protease. The protease in human CD4+ T lymphocytes has not been unequivocally identified, yet members of the family of mammalian subtilisin-like protein convertases (SPCs), which are soluble or membrane-bound proteases of the secretory pathway, best fulfill the criteria. These proteases are required for proprotein maturation and cleave at paired basic amino acid motifs in numerous cellular and viral glycoprotein precursors, both in vivo and in vitro. To identify the gp160 processing protease, we have used reverse transcription-PCR and Northern blot analyses to ascertain the spectrum of SPC proteases in human CD4+ T cells. We have cloned novel members of the SPC family, known as the human PC6 genes. Two isoforms of the hPC6 protease are expressed in human T cells, hPC6A and the larger hPC6B. The patterns of SPC gene expression in human T cells has been compared with the furin-defective LoVo cell line, both of which are competent in the production of infectious HIV virions. This comparison led to the conclusion that the hPC6 gene products are the most likely candidates for the host cell protease responsible for HIV-1 gp160 processing in human CD4+ T cells.

A novel strategy for generating monoclonal antibodies from single, isolated lymphocytes producing antibodies of defined specificities.

We report a novel approach to the generation of monoclonal antibodies based on the molecular cloning and expression of immunoglobulin variable region cDNAs generated from single rabbit or murine lymphocytes that were selected for the production of specific antibodies. Single cells secreting antibodies for a specific peptide either from gp116 of the human cytomegalovirus or from gp120 of HIV-1 or for sheep red blood cells were selected using antigen-specific hemolytic plaque assays. Sheep red blood cells were coated with specific peptides in a procedure applicable to any antigen that can be biotinylated. Heavy- and light-chain variable region cDNAs were rescued from single cells by reverse transcription-PCR and expressed in the context of human immunoglobulin constant regions. These chimeric murine and rabbit monoclonal antibodies replicated the target specificities of the original antibody-forming cells. The selected lymphocyte antibody method exploits the in vivo mechanisms that generate high-affinity antibodies. This method can use lymphocytes from peripheral blood, can exploit a variety of procedures that identify individual lymphocytes producing a particular antibody, and is applicable to the generation of monoclonal antibodies from many species, including humans.

Targeting of proteins to granule subsets is determined by timing and not by sorting: The specific granule protein NGAL is localized to azurophil granules when expressed in HL-60 cells.

The mechanism of protein targeting to individual granules in cells that contain different subsets of storage granules is poorly understood. The neutrophil contains two highly distinct major types of granules, the peroxidase positive (azurophil) granules and the peroxidase negative (specific and gelatinase) granules. We hypothesized that targeting of proteins to individual granule subsets may be determined by the stage of maturation of the cell, at which the granule proteins are synthesized, rather than by individual sorting information present in the proteins. This was tested by transfecting the cDNA of the specific granule protein, NGAL, which is normally synthesized in metamyelocytes, into the promyelocytic cell line HL-60, which is developmentally arrested at the stage of formation of azurophil granules, and thus does not contain specific and gelatinase granules. Controlled by a cytomegalovirus promoter, NGAL was constitutively expressed in transfected HL-60 cells. This resulted in the targeting of NGAL to azurophil granules as demonstrated by colocalization of NGAL with myeloperoxidase, visualized by immunoelectron microscopy. This shows that targeting of proteins into distinct granule subsets may be determined solely by the time of their biosynthesis and does not depend on individual sorting information present in the proteins.

Expression of a candidate cadherin in T lymphocytes.

Cadherins are homotypic adhesion molecules that classically mediate interactions between cells of the same type in solid tissues. In addition, E-cadherin is able to support homotypic adhesion of epidermal Langerhans cells to keratinocytes (Tang, A., Amagai, M., Granger, L. G., Stanley, J. R. & Udey, M. C. (1993) Nature (London) 361, 82-85) and heterotypic adhesion of mucosal epithelial cells to E-cadherin-negative intestinal intraepithelial T lymphocytes. Thus, we hypothesized that cadherins may play a wider role in cell-to-cell adhesion events involving T lymphocytes. We searched for a cadherin or cadherins in T lymphocytes with a pan-cadherin antiserum and antisera against alpha- or beta-catenin, molecules known to associate with the cytoplasmic domain of cadherins. The anti-beta-catenin antisera coimmunoprecipitated a radiolabeled species in T-lymphocyte lines that had a molecular mass of 129 kDa and was specifically immunoblotted with the pan-cadherin antiserum. Also, the pan-cadherin antiserum directly immunoprecipitated a 129-kDa radiolabeled species from an 125I surface-labeled Jurkat human T-cell leukemic cell line. After V8 protease digestion, the peptide map of this pan-cadherin-immunoprecipitated, 129-kDa species exactly matched that of the 129-kDa species coimmunoprecipitated with the beta-catenin antiserum. These results demonstrate that T lymphocytes express a catenin-associated protein that appears to be a member of the cadherin superfamily and may contribute to T cell-mediated immune surveillance.

The association between glycosylphosphatidylinositol-anchored proteins and heterotrimeric G protein alpha subunits in lymphocytes.

Glycosylphosphatidylinositol (GPI)-anchored proteins are nonmembrane spanning cell surface proteins that have been demonstrated to be signal transduction molecules. Because these proteins do not extend into the cytoplasm, the mechanism by which cross-linking of these molecules leads to intracellular signal transduction events is obscure. Previous analysis has indicated that these proteins are associated with src family member tyrosine kinases; however, the role this interaction plays in the generation of intracellular signals is not clear. Here we show that GPI-anchored proteins are associated with alpha subunits of heterotrimeric GTP binding proteins (G proteins) in both human and murine lymphocytes. When the GPI-anchored proteins CD59, CD48, and Thy-1 were immunoprecipitated from various cell lines or freshly isolated lymphocytes, all were found to be associated with a 41-kDa phosphoprotein that we have identified, by using specific antisera, as a mixture of tyrosine phosphorylated G protein alpha subunits: a small amount of Gialpha1, and substantial amounts of Gialpha2 and Gialpha3. GTP binding assays performed with immunoprecipitations of CD59 indicated that there was GTP-binding activity associated with this molecule. Thus, we have shown by both immunochemical and functional criteria that GPI-anchored proteins are physically associated with G proteins. These experiments suggest a potential role of G proteins in the transduction of signals generated by GPI-anchored molecules expressed on lymphocytes of both mouse and human.

Selective expansion of high- or low-avidity cytotoxic T lymphocytes and efficacy for adoptive immunotherapy.

The conventional approach to cytotoxic T-lymphocyte (CTL) induction uses maximal antigen concentration with the intent of eliciting more CTL. However, the efficacy of this approach has not been systematically explored with regard to the quality of the CTLs elicited or their in vivo functionality. Here, we show that a diametrically opposite approach elicits CTLs that are much more effective at clearing virus. CTLs specific for a defined peptide epitope were selectively expanded with various concentrations of peptide antigen. CTLs generated with exceedingly low-dose peptide lysed targets sensitized with > 100-fold less peptide than CTLs generated with high-dose peptide. Differences in expression of T-cell antigen receptors or a number of other accessory molecules did not account for the functional differences. Further, high-avidity CTLs adoptively transferred into severe combined immunodeficient mice were 100- to 1000-fold more effective at viral clearance than the low-avidity CTLs, despite the fact that all CTL lines lysed virus-infected targets in vitro. Thus, the quality of CTLs is as important as the quantity of CTLs for adoptive immunotherapy, and the ability to kill virally infected targets in vitro is not predictive of in vivo efficacy, whereas the determinant density requirement described here is predictive. Application of these principles may be critical in developing effective adoptive cellular immunotherapy for viral infections and cancer.

cAMP inducibility of transcriptional repressor ICER in developing and mature human T lymphocytes.

Stimulation of the cAMP-dependent signaling pathway exerts an inhibitory effect on the proliferation and effector functions of T cells. The ability of T cells to form high intracellular levels of cAMP is acquired during development in the human thymus and is retained by the majority of mature peripheral T lymphocytes. Here we show that elevated cAMP levels in T cells correlate with the expression of the potent transcriptional repressor ICER (inducible cAMP early repressor) previously described in the hypothalamic-pituitary-gonadal axis. Further, in transcriptional assays in vivo, ICER inhibits calcineurin-mediated expression of the interleukin 2 promoter as well as Tax-mediated transactivation of the human T-lymphotropic virus type I (HTLV-I) promoter. Thus, the induction of ICER in T cells may play an important role in the cAMP-induced quiescence and the persistent latency of HTLV-I.

Interleukin 2 (IL-2) and interleukin 7 (IL-7) reciprocally induce IL-7 and IL-2 receptors on gamma delta T-cell receptor-positive intraepithelial lymphocytes.

In this study, we describe the interaction between cytokine and cytokine receptor (R) for the activation and proliferation of gamma delta T-cell receptor-positive T cells (gamma delta T cells). gamma delta T cells isolated from murine intestinal intraepithelial lymphocytes (IELs) were separated into gamma delta (Dim) and gamma delta (Bright) fractions according to the intensity of gamma delta T-cell receptor expression. The gamma delta T cells express low levels of IL-2R and IL-7R as shown by flow cytometry and reverse transcriptase-PCR analysis, whereas gamma delta (Bright) T cells did not express either receptor. Our study also revealed that recombinant marine (rm)IL-2 and rmIL-7 reciprocally induced high expressions of IL-7R and IL-2R, respectively, on gamma delta (Dim) T cells but not on gamma delta (Bright) cells. Thus, treatment of gamma delta (Dim) T cells with rmIL-2 and rmIL-7 resulted in high proliferative responses, whereas gamma delta (Bright) T cells did not respond to these two cytokines. The sources of these two cytokines for gamma delta T cells were neighboring epithelial cells (IL-7) and alpha beta T cells (IL-2 and IL-7). Cytokine signaling by IL-2 and IL-7 from alpha beta T cells and epithelial cells was necessary for the expression of IL-7R and IL-2R, respectively, on a subset of gamma delta T cells (e.g., gamma delta (Dim) T cells) in mucosa-associated tissue for subsequent activation and cell division.

Hypothesis: "Rogue cell"-type chromosomal damage in lymphocytes is associated with infection with the JC human polyoma virus and has implications for oncopenesis.

The hemagglutination inhibition antibody titers against the JC and BK polyoma viruses (JCV and BKV, respectively) are significantly elevated in individuals exhibiting "rogue" cells among their cultured lymphocytes. However, the elevation is so much greater with respect to JCV that the BKV elevation could readily be explained by cross reactivity to the capsid protein of these two closely related viruses. The JCV exhibits high sequence homology with the simian papovavirus, simian virus 40 (SV40), and inoculation of human fetal brain cells with JCV produces polyploidy and chromosomal damage very similar to that produced by SV40. We suggest, by analogy with the effects of SV40, that these changes are due to the action of the viral large tumor antigen, a pluripotent DNA binding protein that acts in both transcription and replication. The implications of these findings for oncogenesis are briefly discussed.

CpG motifs present in bacteria DNA rapidly induce lymphocytes to secrete interleukin 6, interleukin 12, and interferon gamma.

Bacterial infection stimulates the host to mount a rapid inflammatory response. A 6-base DNA motif consisting of an unmethylated CpG dinucleotide flanked by two 5' purines and two 3' pyrimidines was shown to contribute to this response by inducing polygonal B-cell activation. This stimulatory motif is 20 times more common in the DNA of bacteria than higher vertebrates. The current work shows that the same motif induces the rapid and coordinated secretion of interleukin (IL) 6, IL-12, and interferon gamma (but not IL-2, IL-3, IL-4, IL-5, or IL-10) in vivo and in vitro. Stimulatory CpG DNA motifs induced B, T, and natural killer cells to secrete cytokine more effectively than did lipopolysaccharide. Thus, immune recognition of bacterial DNA may contribute to the cytokine, as well as the antibody production characteristic of an innate inflammatory response.

Activation of CD4+ T lymphocytes form interleukin 2-deficient mice by costimulatory B7 molecules.

Interleukin 2 (IL-2)-deficient (IL-2-/-) mice develop hemolytic anemia and chronic inflammatory bowel disease. Importantly, the induction of disease in IL-2-deficient mice is critically dependent on CD4+ T cells. We have studied the requirements of T cells from IL-2-deficient mice for costimulation with B7 antigens. Stable B7-1 or B7-2 chinese hamster ovary (CHO) cell transfectants could synergize with anti-CD3 monoclonal antibody (mAb) to induce the proliferation of CD4+ T cells from IL-2-/- mutant mice. Further mechanistic studies established that B7-induced activation resulted in surface expression of the alpha chain of the IL-2 receptor. B7-induced proliferation occurred independently of IL-4 and was largely independent of the common gamma chain of the IL-2, IL-4, IL-7, IL-9, and IL-15 receptors. Finally, anti-B7-2 but not anti-B7-1 mAb was able to inhibit the activation of IL-2-/- T cells induced by anti-CD3 mAb in the presence of syngeneic antigen-presenting cells. The results of our experiments indicate that IL-2-/- CD4+ T cells remain responsive to B7 stimulation and raise the possibility that B7 antagonists have a role in the prevention/treatment of inflammatory bowel disease.

gamma/delta and other unconventional T lymphocytes: what do they see and what do they do?

T lymphocytes recognize specific ligands by clonally distributed T-cell receptors (TCR). In humans and most animals, the vast majority of T cells express a TCR composed of an alpha chain and a beta chain, whereas a minor T-cell population is characterized by the TCR gamma/delta. Almost all of our knowledge about T cells stems from alpha/beta T cells and only now are we beginning to understand gamma/delta T cells. In contrast to conventional alpha/beta T cells, which are specific for antigenic peptides presented by gene products of the major histocompatibility complex, gamma/delta T cells directly recognize proteins and even nonproteinacious phospholigands. These findings reveal that gamma/delta T cells and alpha/beta T cells recognize antigen in a fundamentally different way and hence mitigate the dogma of exclusive peptide-major histocompatibility complex recognition by T cells. A role for gamma/delta T cells in antimicrobial immunity has been firmly established. Although some gamma/delta T cells perform effector functions, regulation of the professional and the nonprofessional immune system seems to be of at least equal importance. The prominent residence of gamma/delta T cells in epithelial tissues and the rapid mobilization of gamma/delta T cells in response to infection are consistent with such regulatory activities under physiological and pathologic conditions. Thus, although gamma/delta T cells are a minor fraction of all T cells, they are not just uninfluential kin of alpha/beta T cells but have their unique raison d'être.

Potent immunogenicity of the B subunits of Escherichia coli heat-labile enterotoxin: receptor binding is essential and induces differential modulation of lymphocyte subsets.

The importance of receptor binding in the potent immunogenicity of Escherichia coli heat-labile enterotoxin B subunit (EtxB) was tested by comparing its immunogical properties with those of a receptor binding mutant, EtxB(G33D). Subcutaneous immunization of EtxB(G33D) resulted in 160-fold reduction in antibody titer compared with wild-type EtxB, whereas its oral delivery failed to provoke any detectable secretory or serum anti-B subunit responses. Moreover, the two proteins induced strikingly different effects on lymphocyte cultures in vitro. EtxB, in comparison with EtxB(G33D), caused an increase in the proportion of B cells, many of which were activated (CD25+); the complete depletion of CD8+ T cells; an increase in the activation of CD4+ T cells; and an increase in interleukin 2 and a decrease in interferon gamma. These data indicate that EtxB exerts profound effects on immune cells, suggesting that its potent immunogenicity is dependent not only on efficient receptor-mediated uptake, but also on direct receptor-mediated immunomodulation of lymphocyte subsets.

Expression of a single-chain HLA class I molecule in a human cell line: presentation of exogenous peptide and processed antigen to cytotoxic T lymphocytes.

We have synthesized a recombinant gene encoding a single-chain HLA-A2/beta 2-microglobulin (beta 2m) molecule by linking beta 2m through its carboxyl terminus via a short peptide spacer to HLA-A2 (A*0201). This gene has been expressed in the beta 2m-deficient colorectal tumor cell line DLD-1. Transfection of this cell with the single-chain construct was associated with conformationally correct cell surface expression of a class I molecule of appropriate molecular mass. The single-chain HLA class I molecule presented either exogenously added peptide or (after interferon-gamma treatment) endogenously processed antigen to an influenza A matrix-specific, HLA-A2-restricted cytotoxic T-lymphocyte line. The need for interferon gamma for the processing and presentation of endogenous antigen suggests that DLD-1 has an antigen-processing defect that can be up-regulated, a feature that may be found in other carcinomas. Our data indicate that single-chain HLA class I constructs can form functional class I molecules capable of presenting endogenously processed antigens. Such molecules should be of use for functional studies, as well as providing potential anticancer immunotherapeutic agents or vaccines.