The relationship between the L1 and L2 domains of the insulin and epidermal growth factor receptors and leucine-rich repeat modules

Background  

Leucine-rich repeats are one of the more common modules found in proteins. The leucine-rich repeat consensus motif is LxxLxLxxNxLxxLxxLxxLxx- where the first 11–12 residues are highly conserved and the remainder of the repeat can vary in size Leucine-rich repeat proteins have been subdivided into seven subfamilies, none of which include members of the epidermal growth factor receptor or insulin receptor families despite the similarity between the 3D structure of the L domains of the type I insulin-like growth factor receptor and some leucine-rich repeat proteins.     

CD134 as target for specific drug delivery to auto-aggressive CD4<Superscript>+</Superscript>T cells in adjuvant arthritis

T cells have an important role during the development of autoimmune diseases. In adjuvant arthritis, a model for rheumatoid arthritis, we found that the percentage of CD4⁺ T cells expressing the activation marker CD134 (OX40 antigen) was elevated before disease onset. Moreover, these CD134⁺ T cells showed a specific proliferative response to the disease-associated epitope of mycobacterial heat shock protein 60, indicating that this subset contains auto-aggressive T cells. We studied the usefulness of CD134 as a molecular target for immune intervention in arthritis by using liposomes coated with a CD134-directed monoclonal antibody as a drug targeting system. Injection of anti-CD134 liposomes subcutaneously in the hind paws of pre-arthritic rats resulted in targeting of the majority of CD4⁺CD134⁺ T cells in the popliteal lymph nodes. Furthermore, we showed that anti-CD134 liposomes bound to activated T cells were not internalized. However, drug delivery by these liposomes could be established by loading anti-CD134 liposomes with the dipalmitate-derivatized cytostatic agent 5'-fluorodeoxyuridine. These liposomes specifically inhibited the proliferation of activated CD134⁺ T cells in vitro, and treatment with anti-CD134 liposomes containing 5'-fluorodeoxyuridine resulted in the amelioration of adjuvant arthritis. Thus, CD134 can be used as a marker for auto-aggressive CD4⁺ T cells early in arthritis, and specific liposomal targeting of drugs to these cells via CD134 can be employed to downregulate disease development.     

Soil applications of sulfureous compounds to control tipburn of head lettuce in the field

Summary Different levels of sulfureous compounds were applied to the soil before sowing or four to six weeks after sowing seeds of head lettuce (Lactuca sativa var.capitata L.) in five field plots throughout Arizona during 1979 and 1983. Plants were rated for tipburn incidence at harvest. Tipburn severity values were consistently lower in cultivars, Calmar, Vanguard and Empire and higher in cultivar Green bud in treated plots compared to non-treated plots. However, disease severity ratings in treated and non-treated plots were not significantly different at the 5% level. Attempts to control lettuce tipburn by foliar and soil application of calcium salts have been successful in the greenhouse and in the laboratory^{3, 6, 7}, but not in the field^{1, 2, 4}. Therefore, we undertook the present study to determine if the disease can be managed by soil application of sulfureous compounds. Our rational for using sulfureous compounds was based on the assumption that these compounds may convert a portion of the relatively water insoluble calcium carbonate (present in large quantities in the calcereous soils of Arizona and California) into more water soluble calcium sulfate by causing a slight drop in soil pH. Moreover, different formulations of sulfureous compounds, including those used in this study, are being used by some lettuce growers as soil conditioners and fertilizers. Journal Series Paper of the Arizona Agricultural Experimental Station, Tucson, AZ, USA     

TIM-3 Suppresses Anti-CD3/CD28-Induced TCR Activation and IL-2 Expression through the NFAT Signaling Pathway

TIM-3 (T cell immunoglobulin and mucin-domain containing protein 3) is a member of the TIM family of proteins that is preferentially expressed on Th₁ polarized CD4⁺ and CD8⁺ T cells. Recent studies indicate that TIM-3 serves as a negative regulator of T cell function (i.e. T cell dependent immune responses, proliferation, tolerance, and exhaustion). Despite having no recognizable inhibitory signaling motifs, the intracellular tail of TIM-3 is apparently indispensable for function. Specifically, the conserved residues Y265/Y272 and surrounding amino acids appear to be critical for function. Mechanistically, several studies suggest that TIM-3 can associate with interleukin inducible T cell kinase (ITK), the Src kinases Fyn and Lck, and the p85 phosphatidylinositol 3-kinase (PI3K) adaptor protein to positively or negatively regulate IL-2 production via NF-κB/NFAT signaling pathways. To begin to address this discrepancy, we examined the effect of TIM-3 in two model systems. First, we generated several Jurkat T cell lines stably expressing human TIM-3 or murine CD28-ECD/human TIM-3 intracellular tail chimeras and examined the effects that TIM-3 exerts on T cell Receptor (TCR)-mediated activation, cytokine secretion, promoter activity, and protein kinase association. In this model, our results demonstrate that TIM-3 inhibits several TCR-mediated phenotypes: i) NF-kB/NFAT activation, ii) CD69 expression, and iii) suppression of IL-2 secretion. To confirm our Jurkat cell observations we developed a primary human CD8⁺ cell system that expresses endogenous levels of TIM-3. Upon TCR ligation, we observed the loss of NFAT reporter activity and IL-2 secretion, and identified the association of Src kinase Lck, and PLC-γ with TIM-3. Taken together, our results support the conclusion that TIM-3 is a negative regulator of TCR-function by attenuating activation signals mediated by CD3/CD28 co-stimulation.     

Genetic Analysis of the Aspergillus flavus Vegetative Compatibility Group to Which a Biological Control Agent That Limits Aflatoxin Contamination in U.S. Crops Belongs

Some filamentous fungi in Aspergillus section Flavi produce carcinogenic secondary compounds called aflatoxins. Aflatoxin contamination is routinely managed in commercial agriculture with strains of Aspergillus flavus that do not produce aflatoxins. These non-aflatoxin-producing strains competitively exclude aflatoxin producers and reshape fungal communities so that strains with the aflatoxin-producing phenotype are less frequent. This study evaluated the genetic variation within naturally occurring atoxigenic A. flavus strains from the endemic vegetative compatibility group (VCG) YV36. AF36 is a strain of VCG YV36 and was the first fungus used in agriculture for aflatoxin management. Genetic analyses based on mating-type loci, 21 microsatellite loci, and a single nucleotide polymorphism (SNP) in the aflC gene were applied to a set of 237 YV36 isolates collected from 1990 through 2005 from desert legumes and untreated fields and from fields previously treated with AF36 across the southern United States. One haplotype dominated across time and space. No recombination with strains belonging to VCGs other than YV36 was detected. All YV36 isolates carried the SNP in aflC that prevents aflatoxin biosynthesis and the mat1-2 idiomorph at the mating-type locus. These results suggest that VCG YV36 has a clonal population structure maintained across both time and space. These results demonstrate the genetic stability of atoxigenic strains belonging to a broadly distributed endemic VCG in both untreated populations and populations where the short-term frequency of VCG YV36 has increased due to applications of a strain used to competitively exclude aflatoxin producers. This work supports the hypothesis that strains of this VCG are not involved in routine genetic exchange with aflatoxin-producing strains.     

Variation in polygalacturonase production among Aspergillus flavus isolates

Pectinase production by Aspergillus flavus was determined by measuring clear zones formed around colonies stained with ruthenium red. Several isolates produced red zones instead of clear zones. Red zones were reproduced with pectinesterase and correlated with absence of specific polygalacturonases. Of 87 isolates tested, 15 produced red zones.     

Primary antibody-forming cells and secondary B cells are generated from separate precursor cell subpopulations

Two precursor cell subpopulations have been isolated from the spleen cells of nonimmune mice. The major B cell subpopulation binds high levels of the J11D monoclonal antibody and, upon T cell-dependent antigenic stimulation, gives rise to primary antibody-forming cell clones but not secondary B cells. A minority of the 10%-14% of Ia+ precursors that bind low levels of J11D (J11Dlo) also generate antibody-forming cell clones after primary stimulation. However, over 70% of J11Dlo precursors yield no primary antibody-forming cell clones but instead give rise to secondarily responsive B cells. The existence of a distinct precursor cell subpopulation that is responsible for the generation of B cell memory is further evidenced by the distribution of variable region clonotypes among J11Dlo primary precursors, which resembles the clonotype patterns of secondary B cells, and by the accumulation of somatic mutations in their clonal progeny.