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.

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.

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.

Analysis of SH2D1A mutations in patients with severe Epstein-Barr virus infections, Burkitt's lymphoma, and Hodgkin's lymphoma.

Mutations or deletions in the SH2D1A (src homology 2 domain protein 1A) gene result in a severe immunodeficiency called X-linked lymphoproliferative (XLP) disease. XLP is primarily characterized by a defective immune response against the Epstein-Barr virus (EBV), resulting in an unusually severe and often fatal clinical course following EBV infection. The second major cause of death is the development of B cell lymphomas, both in EBV-infected and EBV-negative patients. To study whether the clinical manifestation of XLP gene defects and/or polymorphisms extends beyond the classically recognized phenotype, we analyzed patients for the presence of SH2D1A gene alterations who presented with fatal or nonfatal, yet unusually severe or chronic EBV infections, and other possibly EBV-associated diseases, such as Hodgkin's lymphomas or nonendemic Burkitt's lymphomas and Burkitt-type leukemias. We identified mutations of the SH2D1A gene only in the majority of patients presenting with fatal mononucleosis or an XLP family history, but not in any of the other patients studied. The only alteration determined was a polymorphism in the 5' region of the SH2D1A gene both in patient groups as well as in controls.

Señalización mediada por el receptor para el antígeno de los linfocitos T (TCR): CD3-epsilon es algo más que un amplificador de señales / Insights into T cell antigen receptor (TCR) signaling: CD3-epsilon is more than a signal amplifier

Para que se produzca el reclutamiento de tirosincinasas y otras moléculas adaptadoras o efectoras al receptor para el antígeno de los linfocitos T (complejo TCR/CD3) se necesita la fosforilación de las tirosinas de un motivo de activación presente en todas las subunidades CD3 del complejo. Este motivo es conocido por su acrónimo ITA M (del inglés Immuno receptor Ty rosine-based Activation Motif). En los últimos diez años se ha investigado a fondo el papel de los ITAM de CD3 en la activación de los linfocitos T y en la selección tímica. Sin embargo, la función de los ITAM de las otras subunidades CD3 es menos conocida. En esta revisión se pondrá de manifiesto el potencial señalizador del dominio intracitoplásmico de CD3 con especial hincapié en el papel que tienen las interacciones proteína - proteína y proteína-lípidos en la regulación de la activación de linfocito T. También se discutirá la capacidad del ITAM de CD3 para actuar como un regulador negativo de la señalización mediada por el T C R (AU)

Structural basis for the interaction of the free SH2 domain EAT-2 with SLAM receptors in hematopoietic cells.

The T and natural killer (NK) cell-specific gene SAP (SH2D1A) encodes a 'free SH2 domain' that binds a specific tyrosine motif in the cytoplasmic tail of SLAM (CD150) and related cell surface proteins. Mutations in SH2D1A cause the X-linked lymphoproliferative disease, a primary immunodeficiency. Here we report that a second gene encoding a free SH2 domain, EAT-2, is expressed in macrophages and B lympho cytes. The EAT-2 structure in complex with a phosphotyrosine peptide containing a sequence motif with Tyr281 of the cytoplasmic tail of CD150 is very similar to the structure of SH2D1A complexed with the same peptide. This explains the high affinity of EAT-2 for the pTyr motif in the cytoplasmic tail of CD150 but, unlike SH2D1A, EAT-2 does not bind to non-phosphorylated CD150. EAT-2 binds to the phosphorylated receptors CD84, CD150, CD229 and CD244, and acts as a natural inhibitor, which interferes with the recruitment of the tyrosine phosphatase SHP-2. We conclude that EAT-2 plays a role in controlling signal transduction through at least four receptors expressed on the surface of professional antigen-presenting cells.

Development of chronic colitis is dependent on the cytokine MIF.

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohn's disease, these data suggested that MIF is a new target for intervention in Crohn's disease.

Molecular genetics of ulcerative colitis-associated colon cancer in the interleukin 2- and beta(2)-microglobulin-deficient mouse.

Mice deficient in beta(2)-microglobulin and interleukin 2 (beta(2)m(null) x IL-2(null)) spontaneously develop colon cancer in the setting of chronic ulcerative colitis (UC). We investigated mutations of the Apc and p53 genes and microsatellite instability in colonic adenocarcinomas arising in this model. Mutations of the Apc and p53 genes in the regions corresponding to mutation hot spots in human colorectal cancer were determined by sequencing in 11 colonic adenocarcinomas. Microsatellite instability was determined in matched normal and neoplastic DNA at five loci. All 11 adenocarcinomas harbored Apc mutations. Of these 11 tumors, 5 harbored truncating mutations. A total of 67 Apc mutations were found in these 11 tumors; 59 were missense mutations, whereas 8 were frameshift or nonsense mutations. Six of the 11 adenocarcinomas harbored p53 mutations. A total of seven p53 mutations were found in these 11 tumors; all mutations were transitions, 4 of which were C:G-->T:A transitions occurring in codon 229 at cytosine-guanine dinucleotides. Nine adenocarcinomas exhibited microsatellite instability in at least one of the five loci examined; 1 tumor had microsatellite instability in two loci. Molecular genetics, as well as clinical features, of colon cancer in the beta(2)m(null) x IL-2(null) mice are similar to those of human UC-associated colorectal cancer. As such, this model appears to be an excellent animal model to study UC-associated colorectal carcinogenesis.

CD150 is a member of a family of genes that encode glycoproteins on the surface of hematopoietic cells.

Human CD150 (SLAM) is a glycoprotein expressed on the surface of T, B, natural killer, and dendritic cells. The extracellular domain of CD150 is the receptor for measles virus and CD150 acts as a co-activator on T and B cells. We characterized the mouse and human CD150 genes, each of which comprises seven exons spanning approximately 32 kb. Mouse CD150 mRNA was detected in T cells and in most thymocyte subsets, except CD4-8- cells. Surprisingly, the CD4-8- thymocytes of CD3gammadeltanull mice, but not of Ragnull or severe combined immunodeficiency mice, expressed CD150. Whereas high levels of CD150 were found in Th1 cells, only small amounts were detectable in Th2 cells. CD150 expression was up-regulated upon in vitro activation of mouse T cells by anti-CD3. The complete mouse CD150 gene is highly homologous to its human orthologue in terms of nucleotide sequences and intron/exon organization. The human genomic sequences indicate that all isoforms detected so far have arisen from alternative splicing events. As judged by fluorescence in situ hybridization, mouse CD150 mapped to Chromosome (Chr) 1, band 1H2.2-2.3, and human CD150 was found on Chr 1q22. Human and mouse CD150 share sequence homologies with six other genes, five of which - CD84, CD229 (Ly-9), CD244 (2B4), CD48, and 19A - are localized in a 250-kb segment in close proximity to the human gene. Their location and their sequence similarities strongly suggest that the CD150 family of cell surface receptors arose via successive duplications of a common ancestral gene.

Alterations of the X-linked lymphoproliferative disease gene SH2D1A in common variable immunodeficiency syndrome.

X-linked lymphoproliferative (XLP) disease is a primary immunodeficiency caused by a defect in the SH2D1A gene. At least 3 major manifestations characterize its clinical presentation: fatal infectious mononucleosis (FIM), lymphomas, and immunoglobulin deficiencies. Common variable immunodeficiency (CVID) is a syndrome characterized by immunoglobulin deficiency leading to susceptibility to infection. In some patients with CVID, a defective btk or CD40-L gene has been found, but most often there is no clearly identified etiology. Here, 2 unrelated families in whom male members were affected by CVID were examined for a defect in the XLP gene. In one family previously reported in the literature as having progressive immunoglobulin deficiencies, 3 brothers were examined for recurrent respiratory infections, whereas female family members showed only elevated serum immunoglobulin A levels. A grandson of one of the brothers died of a severe Aspergillus infection secondary to progressive immunoglobulin deficiency, FIM, aplastic anemia, and B-cell lymphoma. In the second family, 2 brothers had B lymphocytopenia and immunoglobulin deficiencies. X-linked agammaglobulinemia syndrome was excluded genetically, and they were classified as having CVID. The occurrence of FIM in a male cousin of the brothers led to the XLP diagnosis. Because the SH2D1A gene was found altered in both families, these findings indicate that XLP must be considered when more than one male patient with CVID is encountered in the same family, and SH2D1A must be analyzed in all male patients with CVID. Moreover, these data link defects in the SH2D1A gene to abnormal B-lymphocyte development and to dysgammaglobulinemia in female members of families with XLP disease.

Characterization of SH2D1A missense mutations identified in X-linked lymphoproliferative disease patients.

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency characterized by extreme susceptibility to Epstein-Barr virus. The XLP disease gene product SH2D1A (SAP) interacts via its SH2 domain with a motif (TIYXXV) present in the cytoplasmic tail of the cell-surface receptors CD150/SLAM, CD84, CD229/Ly-9, and CD244/2B4. Characteristically, the SH2D1A three-pronged interaction with Tyr(281) of CD150 can occur in absence of phosphorylation. Here we analyze the effect of SH2D1A protein missense mutations identified in 10 XLP families. Two sets of mutants were found: (i) mutants with a marked decreased protein half-life (e.g. Y7C, S28R, Q99P, P101L, V102G, and X129R) and (ii) mutants with structural changes that differently affect the interaction with the four receptors. In the second group, mutations that disrupt the interaction between the SH2D1A hydrophobic cleft and Val +3 of its binding motif (e.g. T68I) and mutations that interfere with the SH2D1A phosphotyrosine-binding pocket (e.g. C42W) abrogated SH2D1A binding to all four receptors. Surprisingly, a mutation in SH2D1A able to interfere with Thr -2 of the CD150 binding motif (mutant T53I) severely impaired non-phosphotyrosine interactions while preserving unaffected the binding of SH2D1A to phosphorylated CD150. Mutant T53I, however, did not bind to CD229 and CD224, suggesting that SH2D1A controls several critical signaling pathways in T and natural killer cells. Because no correlation is present between identified types of mutations and XLP patient clinical presentation, additional unidentified genetic or environmental factors must play a strong role in XLP disease manifestations.

Modulación negativa del TCR por un mecanismo de todo-o-nada / All-or-none downregulation of the T cell antigen receptor

El contacto del TCR con MHC/antígeno resulta en su modulación y desaparición de la superficie celular. Recientemente hemos descrito que este proceso ocurre por al menos dos mecanismos: uno es dependiente de transmisión de señales, predomina a bajas concentraciones de antígeno y resulta en la modulación en trans de moléculas de TCR no contactadas. El otro requiere contacto directo y es independiente de transmisión de señales. En este artículo describimos que el TCR es modulado en una forma discontinua, es decir las células estimuladas oscilan de un estado no-modulado a otro completamente modulado sin transición aparente por estados intermedios, cuando las células T son estimuladas con altas dosis de antígeno o de anticuerpos anti-TCR. El fenómeno se reproduce cuando un receptor quimérico, que contiene la parte extracelular y transmembránica de CD8 y el tallo citoplásmico de CD3 , es entre cruzado con anticuerpos inmovilizados a un substrato. Este proceso de modulación de "todo-o-nada" no requiere de transmisión de señales o de polimerización del citoesqueleto de actina. El análisis por microscopía confocal muestra que el anticuerpo estimulante es tomado del substrato y concentrado junto con la quimera en un polo de la célula donde se constituye un sitio de nucleación para la formación de vesículas endocíticas. El efecto de "todo-o-nada" puede explicarse por la concentración lenta del TCR o de la quimera, seguido de la internalización rápida de los receptores agregados (AU)

Cell surface receptors Ly-9 and CD84 recruit the X-linked lymphoproliferative disease gene product SAP.

X-linked lymphoproliferative disease (XLP) is a rare immune disorder commonly triggered by infection with Epstein-Barr virus. Major disease manifestations include fatal acute infectious mononucleosis, B-cell lymphoma, and progressive dys-gammaglobulinemia. SAP/SH2D1A, the product of the gene mutated in XLP, is a small protein that comprises a single SH2 domain and a short tail of 26 amino acids. SAP binds to a specific motif in the cytoplasmic tails of the cell surface receptors SLAM and 2B4, where it blocks recruitment of the phosphatase SHP-2. Here it is reported that Ly-9 and CD84, 2 related glycoproteins differentially expressed on hematopoietic cells, also recruit SAP. Interactions between SAP and Ly-9 or CD84 were analyzed using a novel yeast 2-hybrid system, by COS cell transfections and in lymphoid cells. Recruitment of SAP is most efficient when the specific tyrosine residues in the cytoplasmic tails of Ly-9 or CD84 are phosphorylated. It is concluded that in activated T cells, the SAP protein binds to and regulates signal transduction events initiated through the engagement of SLAM, 2B4, CD84, and Ly-9. This suggests that combinations of dysfunctional signaling pathways initiated by these 4 cell surface receptors may cause the complex phenotypes of XLP. (Blood. 2001;97:3867-3874)

SAP controls T cell responses to virus and terminal differentiation of TH2 cells.

SH2D1A, which encodes signaling lymphocyte activation molecule (SLAM)-associated protein (SAP), is altered in patients with X-linked lymphoproliferative disease (XLP), a primary immunodeficiency. SAP-deficient mice infected with lymphocytic choriomeningitis virus had greatly increased numbers of CD8+ and CD4+ interferon-gamma-producing spleen and liver cells compared to wild-type mice. The immune responses of SAP-deficient mice to infection with Leishmania major together with in vitro studies showed that activated SAP-deficient T cells had an impaired ability to differentiate into T helper 2 cells. The aberrant immune responses in SAP-deficient mice show that SAP controls several distinct key T cell signal transduction pathways, which explains in part the complexity of the XLP phenotypes.

Continuous stimulation by normal luminal bacteria is essential for the development and perpetuation of colitis in Tg(epsilon26) mice.

BACKGROUND & AIMS: Normal resident bacteria are required for development of colitis in several rodent models. We determined whether bacterial stimulation is necessary for both induction and perpetuation of mucosal inflammation and T-cell activation in Tg(epsilon26) mice, in which transplantation of wild-type bone marrow (BM-->Tg(epsilon26)) causes colitis under specific pathogen-free (SPF) conditions. METHODS: BM from (C57BL/6 X CBA/J) F1 mice was transplanted into germfree (GF) or SPF Tg(epsilon26) mice. Mesenteric lymph node (MLN) cells from these mice were then transferred into SPF or GF recipients. Colitis and activation of MLN cells were measured by histologic scores, membrane marker analysis, and intracellular cytokine staining. Cytokine secretion by MLN cells stimulated by anti-CD3 or by luminal or epithelial antigens was measured by ELISA. RESULTS: Colitis did not develop when BM was transferred into GF recipient mice (BM-->GF Tg(epsilon26)). T lymphocytes that secreted interferon gamma upon activation were present in the MLN of BM-->GF Tg(epsilon26) mice, albeit in lower frequency than in control BM-->SPF Tg(epsilon26) mice. Furthermore, transfer of MLN cells from BM-->SPF Tg(epsilon26) mice into SPF Tg(epsilon26) recipients induced active colitis, but not if the same cells were transferred into GF Tg(epsilon26) recipients. Although CD4 T cells were detected in the colonic mucosa of GF recipients, no inflammation was observed for at least 31 weeks. In a reciprocal experiment, MLN cells from BM-->GF Tg(epsilon26) mice without colitis transferred disease to SPF Tg(epsilon26) recipients within 2-4 weeks. CONCLUSIONS: Activated T cells are present in the mucosa of BM-->GF Tg(epsilon26) mice but are incapable of inducing disease unless colonic bacteria are present. Moreover, pathogenic T cells require the continuous presence of colonic bacteria to sustain colitis.

X-linked lymphoproliferative disease: a progressive immunodeficiency.

Our understanding of the X-linked lymphoproliferative syndrome (XLP) has advanced significantly in the last two years. The gene that is altered in the condition (SAP/SH2D1A) has been cloned and its protein crystal structure solved. At least two sets of target molecules for this small SH2 domain-containing protein have been identified: A family of hematopoietic cell surface receptors, i.e. the SLAM family, and a second molecule, which is a phosphorylated adapter. A SAP-like protein, EAT-2, has also been found to interact with this family of surface receptors. Several lines of evidence, including structural studies and analyses of missense mutations in XLP patients, support the notion that SAP/SH2D1A is a natural inhibitor of SH2-domain-dependent interactions with members of the SLAM family. However, details of its role in signaling mechanisms are yet to be unravelled. Further analyses of the SAP/SH2D1A gene in XLP patients have made it clear that the development of dys-gammaglobulinemia and B cell lymphoma can occur without evidence of prior EBV infection. Moreover, preliminary results of virus infections of a mouse in which the SAP/SH2D1A gene has been disrupted suggest that EBV infection is not per se critical for the development of XLP phenotypes. It appears therefore that the SAP/SH2D1A gene controls signaling via the SLAM family of surface receptors and thus may play a fundamental role in T cell and APC interactions during viral infections.

Potential pathways for regulation of NK and T cell responses: differential X-linked lymphoproliferative syndrome gene product SAP interactions with SLAM and 2B4.

SAP, the gene that is altered or absent in the X-linked lymphoproliferative syndrome (XLP), encodes a small protein that comprises a single SH2 domain and binds to the cell-surface protein SLAM which is present on activated or memory T and B cells. Because defective NK cell activity also has been reported in XLP patients, we studied the SAP gene in NK cells. SAP was induced upon viral infection of SCID mice and shown to be expressed in NK cells by in vitro culturing in the presence of IL-2. Moreover, SAP was expressed in the NK cell lines YT and RNK 16. Because SLAM, the cell-surface protein with which SAP interacts, and 2B4, a membrane protein having sequence homologies with SLAM, also were found to be expressed on the surfaces of activated NK and T cell populations, they may access SAP functions in these populations. Whereas we found that 2B4 also binds SAP, 2B4-SAP interactions occurred only upon tyrosine phosphorylation of 2B4. By contrast, SLAM-SAP interactions were independent of phosphorylation of Y281 and Y327 on SLAM. As CD48, the ligand for 2B4, is expressed on the surface of Epstein-Barr virus (EBV)-infected B cells, it is likely that SAP regulates signal transduction through this pair of cell-surface molecules. These data support the hypothesis that XLP is a result of both defective NK and T lymphocyte responses to EBV. The altered responses may be due to aberrant control of the signaling cascades which are initiated by the SLAM-SLAM and 2B4-CD48 interactions.