Experimental evolution of protozoan traits in response to interspecific competition.

Decades of experiments have demonstrated the ecological effect of competition, but experimental evidence for competitive effects on trait evolution is rare. I measured the evolution of six protozoan traits in response to competitors from the inquiline community of pitcher plants. Replicate populations of Colpoda, a ciliated protozoan, were allowed to evolve in response to intra- and interspecific competition for 20 days (approximately 100 generations), before traits were measured in two common garden environments. Populations that evolved with interspecific competition had smaller cell sizes, produced fewer cysts and had higher population growth rates relative to populations grown in monoculture. The presence of interspecific competitors led to differential lineage sorting, most likely by increasing the strength of selection. These results are the first to demonstrate protozoan evolution in response to competition and may have implications for species coexistence in this system.

Requirement for natural killer cell-produced interferon gamma in defense against murine cytomegalovirus infection and enhancement of this defense pathway by interleukin 12 administration.

The presence of natural killer (NK) cells contributes to early defense against murine cytomegalovirus (MCMV) infection. Although NK cells can mediate in vivo protection against MCMV, the mechanism by which they do so has not been defined. The studies presented here evaluate cytokine production by NK cells activated during MCMV infection and the role of NK cell-produced cytokines in early in vivo antiviral defenses. Experiments with normal C57BL/6, T cell-deficient C57BL/6 nude, and severe combined immunodeficient mice lacking T and B cells demonstrated that both interferon gamma (IFN-gamma) and tumor necrosis factor (TNF) production were induced at early times after infection with MCMV. Conditioned media samples prepared with cells from these mice, on day 2 after infection, produced 11-43 pg/million cells of IFN-gamma and 12-19 pg/million cells of TNF as evaluated by specific protein enzyme-linked immunosorbent assays. Studies in the NK- and T cell-deficient mouse line, E26, in mice that had been depleted in vivo of NK cells by treatment with antibodies eliminating NK cells, anti-asialo ganglio-N-tetraosylceramide or anti-NK1.1, and with populations of cells that had been depleted of NK cells by complement treatment with the anti-NK cell antibody, SW3A4, demonstrated that NK cells were solely responsible for the IFN-gamma but were not required for TNF production. The in vivo absence of NK cells was accompanied by increased viral hepatitis and viral replication in both immunocompetent and immunodeficient mice, as well as decreased survival time of immunodeficient mice. In vivo treatments with antibodies neutralizing IFN-gamma demonstrated that this factor contributed to the NK cell-mediated antiviral defense and reduced the measured parameters of viral defense to levels indistinguishable from those observed in NK cell-deficient mice. These effects appeared to be independent of cytolytic activity, as NK cells isolated from anti-IFN-gamma-treated mice mediated killing at levels comparable to those observed in control-treated mice. The consequences of interleukin 12 (IL-12) administration, a known potent inducer of IFN-gamma production by NK cells, were evaluated in MCMV-infected mice. Low IL-12 doses, i.e., 1 ng/d, increased NK cell cytotoxicity and IFN-gamma production up to twofold and resulted in improved antiviral status; virus-induced hepatitis was decreased as much as fivefold, and viral burdens were decreased to levels below detection.(ABSTRACT TRUNCATED AT 400 WORDS)

Essential and partially overlapping role of CD3gamma and CD3delta for development of alphabeta and gammadelta T lymphocytes.

CD3gamma and CD3delta are two highly related components of the T cell receptor (TCR)-CD3 complex which is essential for the assembly and signal transduction of the T cell receptor on mature T cells. In gene knockout mice deficient in either CD3delta or CD3gamma, early thymic development mediated by pre-TCR was either undisturbed or severely blocked, respectively, and small numbers of TCR-alphabeta+ T cells were detected in the periphery of both mice. gammadelta T cell development was either normal in CD3delta-/- mice or partially blocked in CD3gamma-/- mice. To examine the collective role of CD3gamma and CD3delta in the assembly and function of pre-TCR and in the development of gammadelta T cells, we generated a mouse strain with a disruption in both CD3gamma and CD3delta genes (CD3gammadelta-/-). In contrast to mice deficient in either CD3gamma or CD3delta chains, early thymic development mediated by pre-TCR is completely blocked, and TCR-alphabeta+ or TCR-gammadelta+ T cells were absent in the CD3gammadelta-/- mice. Taken together, these studies demonstrated that CD3gamma and CD3delta play an essential, yet partially overlapping, role in the development of both alphabeta and gammadelta T cell lineages.

T cell-mediated pathology in two models of experimental colitis depends predominantly on the interleukin 12/Signal transducer and activator of transcription (Stat)-4 pathway, but is not conditional on interferon gamma expression by T cells.

The requirements for interleukin (IL)-12/signal transducer and activator of transcription (Stat)-4 signaling and induction of T cell-specific interferon (IFN)-gamma expression in the development of T helper cell (Th)1-type pathology were examined in two different models of experimental colitis. In each model, abnormal reconstitution of the T cell compartment in immunodeficient mice by adoptive cell transfer leads to a wasting syndrome and inflammation of the colon, induced by IFN-gamma and tumor necrosis factor (TNF)-alpha-producing T cells. We show here that treatment with anti-IL-12 antibodies in one of the models, or reconstitution with T cells from Stat-4-deficient (Stat-4(null)) mice in both models resulted in a milder disease in the majority of recipient animals, compared with those that were left untreated or that had been reconstituted with wt cells. Protected mice in each group also harbored lower frequencies of IFN-gamma-producing T cells than did diseased mice, suggesting that effects on wasting and colitis resulted from the attenuation of IFN-gamma expression by T cells. To test whether the development of pathogenic T cells in the two colitis models was directly dependent on T cell-specific IFN-gamma expression, IFN-gammanull donors were used for T cell reconstitution in each system. Surprisingly, large numbers of IFN-gammanull-reconstituted mice developed wasting and colitis, which in many cases was of comparable severity to that seen in animals reconstituted with wt cells. Furthermore, T cells from these animals expressed TNF-alpha, demonstrating that they had retained the ability to produce another proinflammatory cytokine. Taken together, these results demonstrate that in some forms of chronic experimental colitis the development of pathogenic T cells is influenced predominantly, though not exclusively, by IL-12 via the actions of Stat-4 proteins. Furthermore, our data suggest that in the models of colitis studied here the effects of IL-12/Stat-4 or other Th1 promoting pathways are not limited to the induction of IFN-gamma gene expression in T lymphocytes.

Expression and function of a variant T cell receptor complex lacking CD3-gamma.

A T cell line termed DIL2 has been derived from an infant with a polyclonal T cell receptor (TCR)/CD3 cell surface expression defect. Indirect immunofluorescence showed that the expression of certain TCR/CD3 epitopes (like those detected by WT31 and BMA031 monoclonals) was strongly reduced (around five-fold) on DIL2, whereas other epitopes (like those detected by SP34 and Leu4) were only around two-fold lower than in normal T cell lines. Specific immunoprecipitates of surface-radioiodinated DIL2 cells contained TCR-alpha, TCR-beta, CD3-delta, CD3-epsilon and TCR-zeta chains, but lacked CD3-gamma. This structural TCR/CD3 variant was, however, capable of transducing certain activation signals, since normal proliferation and a low but significant calcium flux was observed in DIL2 cells after engagement with specific antibodies. Our data suggest that a functional TCR/CD3 complex can be expressed on the surface of T cells in the absence of CD3-gamma.

Gliadin-primed CD4+CD45RBlowCD25- T cells drive gluten-dependent small intestinal damage after adoptive transfer into lymphopenic mice.

BACKGROUND AND AIMS: Coeliac disease is a common small intestinal inflammatory disorder that results from a breach of intestinal tolerance to dietary gluten proteins, driven by gluten-reactive effector T cells. We aimed to assess the pathogenic role of gluten-reactive T cells and to generate a model of gluten-induced enteropathy. METHODS: CD4+CD25- T cell fractions were adoptively transferred into lymphopenic mice, leading to "baseline" small intestinal inflammation. RESULTS: Rag1-/- recipients of gliadin-presensitised CD4+CD45RBlowCD25- T cells, but not CD4+CD45RBhigh naive T cells, gained less weight and suffered from more severe duodenitis when challenged with oral gluten than recipients on gluten-free diet, or recipients of control (ovalbumin)-presensitised T cells. This was accompanied by deterioration of mucosal histological features characteristic of coeliac disease, and increased Th1/Th17 cell polarisation in the duodenum and the periphery. Interestingly, reintroduction of a gluten-free diet led to weight gain, improvement of histological duodenitis, and a decrease in duodenal interferon gamma and interleukin 17 transcripts. Moreover, B cell-competent nude recipients of gliadin-presensitised CD4+CD45RBlowCD25- T cells produced high levels of serum anti-gliadin immunoglobulin A (IgA) and IgG1/IgG2c only when challenged with oral gluten. CONCLUSIONS: CD4+ T cell immunity to gluten leads to a breach of oral gluten tolerance and small intestinal pathology in lymphopenic mice, similar to human coeliac disease. This model will be useful for the study of coeliac disease pathogenesis, and also for testing novel non-dietary therapies for coeliac disease.

The ghost of competition present.

Communities have been viewed as the end product of an assembly process that results in increasing stability through time as progressively better competitors eventually dominate the other species that can emigrate from a regional pool. Previous work has explained species assemblages based on the traits of the successful species. We suggest that the traits of unsuccessful species in the regional pool may also be important for understanding which species are successful in communities. We constructed a simulation model to study what distinguishes stable, uninvasible assemblages from other possible assemblages from a regional pool of species. Our model demonstrates that both the interactions among the successful species and the interactions between these species and unsuccessful species attempting to invade the community contribute significantly to determining success in the final stable community. Understanding the structure of natural communities may require some knowledge of the unobserved "ghost" species that fail to establish in that same community yet still have significant effects on structure.

Associations between subunit ectodomains promote T cell antigen receptor assembly and protect against degradation in the ER.

The T cell antigen receptor (TCR) is an oligomeric protein complex made from at least six different integral membrane proteins (alpha beta gamma delta epsilon and zeta). The TCR is assembled in the ER of T cells, and correct assembly is required for transport to the cell surface. Single subunits and partial receptor complexes are retained in the ER where TCR alpha, beta, and CD3 delta chains are degraded selectively. The information required for the ER degradation of the TCR beta chain is confined to the membrane anchor of the protein (Wileman et al., 1990c; Bonifacino et al., 1990b). In this study we show that the rapid degradation of the TCR beta chain is inhibited when it assembles with single CD3 gamma, delta, or epsilon subunits in the ER, and have started to define the role played by transmembrane anchors, and receptor ectodomains, in the masking proteolytic targeting information. Acidic residues within the membrane spanning domains of CD3 subunits were essential for binding to the TCR beta chain. TCR beta chains and CD3 subunits therefore interact via transmembrane domains. However, when sites of binding were restricted to the membrane anchor of the TCR beta chain, stabilization by CD3 subunits was markedly reduced. Interactions between membrane spanning domains were not, therefore, sufficient for the protection of the beta chain from ER proteolysis. The presence of the C beta domain, containing the first 150 amino acids of the TCR ectodomain, greatly increased the stability of complexes formed in the ER. For assembly with CD3 epsilon, stability was further enhanced by the V beta amino acids. The results showed that the efficient neutralization of transmembrane proteolytic targeting information required associations between membrane spanning domains and the presence of receptor ectodomains. Interactions between receptor ectodomains may slow the dissociation of CD3 subunits from the beta chain and prolong the masking of transmembrane targeting information. In addition, the close proximity of TCR and CD3 ectodomains within the ER may provide steric protection from the action of proteases within the ER lumen.

The gamma and epsilon subunits of the CD3 complex inhibit pre-Golgi degradation of newly synthesized T cell antigen receptors.

The T cell receptor for antigen (TCR) is composed of six different transmembrane proteins. T cells carefully control the intracellular transport of the receptor and allow only complete receptors to reach the plasma membrane. In an attempt to understand how T cells regulate this process, we used c-DNA transfection and subunit-specific antibodies to follow the intracellular transport of five subunits (alpha beta gamma delta epsilon) of the receptor. In particular, we assessed the intracellular stability of each chain. Our results showed that the chains were markedly different in their susceptibility to intracellular degradation. TCR alpha and beta and CD3 delta were degraded rapidly, whereas CD3 gamma and epsilon were stable. An analysis of the N-linked oligosaccharides of the glycoprotein subunits suggested that the chains were unable to reach the medial Golgi during the metabolic chase. This was supported by immunofluorescence micrographs that showed both the stable CD3 gamma and unstable CD3 delta chain localized in the endoplasmic reticulum. To study the effects of subunit associations on intracellular transport we used cotransfection to reconstitute precise combinations of subunits. Associations between stable and unstable subunits expressed in the same cell led to the formation of stable complexes. These complexes were retained in or close to the endoplasmic reticulum. The results suggested that the intracellular transport of the T cell receptor could be regulated by two mechanisms. The TCR alpha and beta and CD3 delta subunits were degraded rapidly and as a consequence failed to reach the plasma membrane. CD3 gamma or epsilon were stable but were retained inside the cell. The results also demonstrated that there was an interplay between the two pathways such that the CD3 gamma and epsilon subunits were able to protect labile chains from rapid intracellular degradation. In this way, they could seed subunit assembly in or close to the endoplasmic reticulum and allow a stable receptor to form before its transport to the plasma membrane.

Reconstitution of T cell receptor zeta-mediated calcium mobilization in nonlymphoid cells.

T cell antigen receptor (TCR) activation involves interactions between receptor subunits and nonreceptor protein tyrosine kinases (PTKs). Early steps in signaling through the zeta chain of the TCR were examined in transfected COS-1 cells. Coexpression of the PTK p59fynT, but not p56lck, with zeta or with a homodimeric TCR beta-zeta fusion protein produced tyrosine phosphorylation of both zeta and phospholipase C (PLC)-gamma 1, as well as calcium ion mobilization in response to receptor cross-linking. CD45 coexpression enhanced these effects. No requirement for the PTKZAP-70 was observed. Thus, p59fynT may link zeta directly to the PLC-gamma 1 activation pathway.

Biochemical analysis of human T lymphocyte differentiation antigens T4 and T5.

Two major functionally distinct T cell subsets in man have been defined with heteroantiserums and monoclonal antibodies directed against stable cell surface antigens that appear during thymic ontogeny. A monoclonal antibody to T4 antigen (anti-T4) is reactive with the peripheral inducer T cell population while a monoclonal antibody to T5 antigen (anti-T5) is reactive with the cytotoxic and suppressor population. Immunoprecipitation and electrophoresis on sodium dodecyl sulfate polyacrylamide gel were used to show that on human thymocytes or peripheral T cells the T4 antigen is a single 62,000-dalton glycoprotein while the T5 antigen is a complex of two glycoproteins, one being 30,000 daltons and the other 32,000 daltons. Similar glycoproteins have been isolated with antibodies to murine Lyt 1 and Lyt 2,3 antigens. Both the antigens defining the phenotypes of inducer and suppressor populations in man and mouse are structurally homologous.

Alloantigen recognition is preceded by nonspecific adhesion of cytotoxic T cells and target cells.

T-cell receptors bind antigens only when the antigens are exposed on the cell surface. This can be studied best in the interaction of cytolytic T lymphocytes (CTL) with target cells because the recognition and binding event can be separated from the lytic phase. Studies with CTL clones specific for HLA-A2 and HLA-B7 demonstrated that conjugates of CTL's and target cells can be formed in the absence of specific antigen recognition. Furthermore, T-cell receptor and target antigen cannot interact unless there is conjugate formation. This indicates that nonspecific conjugate formation between CTL's and target cells precedes the recognition of specific antigen by the T-cell receptor.

Expression of murine CD1 on gastrointestinal epithelium.

Cluster of differentiation 1 (CD1) in humans is a family of major histocompatibility complex (MHC) class I-like molecules expressed on the surface of immature thymocytes, Langerhans cells, and a subpopulation of B cells. The only function identified for human CD1 is as a ligand recognized by a subpopulation of T lymphocytes. In order to study the distribution and function of these molecules in the mouse, a murine CD1 complementary DNA was expressed in mouse fibroblasts and used to produce monoclonal antibodies. These antibodies revealed prominent expression of murine CD1 only on gastrointestinal tract epithelium and in the cytoplasm of hepatocytes. Low levels of expression were also detected on thymocytes and peripheral lymphocytes. The gastrointestinal distribution of murine CD1 suggests that this molecule may be important in epithelial immunity.

Monoallelic expression of the interleukin-2 locus.

The lymphokine interleukin-2 (IL-2) is responsible for autocrine cell cycle progression and regulation of immune responses. Uncontrolled secretion of IL-2 results in adverse reactions ranging from anergy, to aberrant T cell activation, to autoimmunity. With the use of fluorescent in situ hybridization and single-cell polymerase chain reaction in cells with different IL-2 alleles, IL-2 expression in mature thymocytes and T cells was found to be tightly controlled by monoallelic expression. Because IL-2 is encoded at a nonimprinted autosomal locus, this result represents an unusual regulatory mode for controlling the precise expression of a single gene.

Recognition of HLA-A2 by cytotoxic T lymphocytes after DNA transfer into human and murine cells.

A gene coding for the major histocompatibility antigen HLA-A2 was transferred into human HLA-A2 negative M1 cells and murine L cells. Following transfection, these cells expressed molecules at the cell surface that are biochemically indistinguishable from HLA-A2 antigens on the human cell line JY from which the HLA-A2 gene was isolated. The M1A2 cells were recognized and lysed by a cytolytic T-cell clone specific for HLA-A2. The transfected L cells which express HLA-A2 in association with human beta 2-microglobulin were not lysed by this T-cell clone. The specific cytolysis of M1A2 cells could be inhibited by monoclonal antibodies to HLA-A2, and monoclonal antibodies to T3, T8, and LFA-1 on cytotoxic T lymphocytes. These results suggest that killing by allospecific T cells requires HLA-A2 antigens as well as other species-specific structures on the target cell surface.

Association of LY9 in UK and Canadian SLE families.

Systemic lupus erythematosus (SLE) is a complex disease trait of unknown aetiology. Genome-wide linkage studies in human SLE identified several linkage regions, including one at 1q23, which contains multiple susceptibility genes, including the members of the signalling lymphocyte activation molecule (SLAM) locus. In mice there is a syntenic linkage region, Sle1. The SLAM genes are functionally related cell-surface receptors, which regulate signal transduction of cells in the immune system. Family-based association study in UK and Canadian SLE families identified variants in the promoter and coding region of SLAMF7 and LY9 contributing to SLE disease susceptibility. The strongest association was from rs509749, in exon 8 of LY9 (P=0.00209). rs509749 encodes a Val/Met nonsynonymous change in amino acid 602 in the cytoplasmic domain of LY9. In the parents and affected individuals from the Canadian SLE families, the risk allele of rs509049 skews the T-cell population by increasing the number of CD8+ memory T cells, while decreasing the proportion of CD4+ naïve T cells and activated T cells. Since rs509749 lies within the consensus binding site for SAP/SH2D1a, which influences downstream signalling events from LY9, the mechanism for increased CD8+ memory T cells may include differential binding SAP/SH2D1a to the cytoplasmic domain of LY9.

Deficiency of a leukocyte surface glycoprotein (LFA-1) in two patients with Mo1 deficiency. Effects of cell activation on Mo1/LFA-1 surface expression in normal and deficient leukocytes.

Mo1, a phagocyte surface glycoprotein heterodimer, is involved in a number of phagocyte adhesion functions such as binding and ingestion of serum-opsonized particles, zymosan-induced degranulation, and superoxide generation. Deficiency of this antigen in humans has been associated with increased susceptibility to recurrent bacterial infections. The beta subunit of Mo1 is shared by another surface glycoprotein named LFA-1, which is involved in lymphocyte proliferation, cytolytic T cell, and natural killing activities. Two unrelated patients with Mo1 deficiency were found to be deficient in LFA-1 as well as in the common beta subunit. Investigation of lymphocyte functions in these two patients revealed normal mixed leukocyte culture-generated cytolytic T cell and natural killing activities and significantly reduced proliferative response to phytohemagglutinin. LFA-1-deficient cells also proliferated in response to soluble antigen and different alloantigens. These responses were partially blocked by anti-LFA-1 antibody. Whereas LFA-1 was undetectable by immunofluorescence and immunoprecipitation on the patients' resting T cells, significantly reduced (approximately 5% of normal) but detectable amounts of the heterodimeric LFA-1 antigen were found on mitogen and alloantigen-activated T cells. On granulocytes, Mo1 surface expression was also dependent on the state of cellular activation. The amount of surface Mo1 present on resting normal granulocytes increased by 3-10-fold following exposure to stimuli that induced degranulation, suggesting the presence of a major intracellular pool for this antigen. Analysis of subcellular fractions from granulocytes showed that intracellular Mo1 is located primarily in the specific granule fraction. Activated granulocytes had little or no increase in their surface expression of LFA-1 antigen. Deficient granulocytes had significantly increased numbers of Mo1 antigen expressed on the surface following stimulation with calcium ionophore (1 microM). However, the amount expressed continued to be significantly reduced compared with normal cells. Quantitation of surface Mo1 on granulocytes exposed to calcium ionophore (1 microM) showed that both parents in one family but only the mother in the other family had significantly reduced levels of Mo1, suggesting heterogeneity in the inheritance of this disorder. Whereas LFA-1 deficiency on lymphocytes was associated with normal alloantigen-induced cytolytic T cell and natural killing activities in these two patients, functions which were in part dependent on small amounts of detectable LFA-1 antigen, the Mo1 deficiency state led to significant defects in phagocyte adhesion functions. Hence, the clinical symptoms associated with this combined deficiency state reflect a more profound phagocyte than lymphocyte disorder.

The gene defective in X-linked lymphoproliferative disease controls T cell dependent immune surveillance against Epstein-Barr virus.

Our understanding of the X-linked lymphoproliferative syndrome (XLP) has advanced significantly in the past two years. The gene that is aberrant in the condition - SH2D1A/SAP, which encodes SAP (signaling lymphocytic activation molecule [SLAM]-associated protein) - was cloned, the crystal structure of its product was solved and insights into the signaling mechanisms of this small SH2-domain-containing protein via the cell surface receptors SLAM and 2B4 have been provided. SAP mutation, and not Epstein-Barr virus infection per se, may be critical for XLP.

Binding of ZAP-70 to phosphorylated T-cell receptor zeta and eta enhances its autophosphorylation and generates specific binding sites for SH2 domain-containing proteins.

ZAP-70 is a protein tyrosine kinase thought to play a critical role in T-cell receptor (TCR) signal transduction. During T-cell activation, ZAP-70 binds to a conserved signalling motif known as the immune receptor tyrosine activating motif (ITAM) and becomes tyrosine phosphorylated. To determine whether binding of ZAP-70 to the phosphorylated ITAM was able to activate its kinase activity, we measured the kinase activity of ZAP-70 both when it was bound and when it was unbound to phosphorylated TCR subunits. The ability of ZAP-70 to phosphorylate itself, but not exogenous substrates, was enhanced when it was bound to the tyrosine-phosphorylated TCR zeta and eta chains or to a construct that contained duplicated epsilon ITAMs. No enhanced ZAP-70 autophosphorylation was noted when it was bound to tyrosine-phosphorylated CD3 gamma or epsilon. In addition, autophosphorylation of ZAP-70 when bound to zeta or eta resulted in the generation of multiple distinct ZAP-70 phosphorylated tyrosine residues which had the capacity to bind the SH2 domains of fyn, lck, GAP, and abl. As the effect was noted only when ZAP-70 was bound to TCR subunits containing multiple ITAMs, we propose that one of the roles of the tandem ITAMs is to facilitate the autophosphorylation of ZAP-70. Tyrosine-phosphorylated ZAP-70 then mediates downstream signalling by recruiting SH2 domain-containing signalling proteins.