Development of a europium nanoparticles lateral flow immunoassay for NGAL detection in urine and diagnosis of acute kidney injury.

BACKGROUND: AKI is related to severe adverse outcomes and mortality with Coronavirus Disease 2019 (COVID-19) patients, that early diagnosed and intervened is imperative. Neutrophil gelatinase-associated lipocalin (NGAL) is one of the most promising biomarkers for detection of acute kidney injury (AKI), but current detection methods are inadequacy, so more rapid, convenient and accuracy methods are needed to detect NGAL for early diagnosis of AKI. Herein, we established a rapid, reliable and accuracy lateral flow immunoassay (LFIA) based on europium nanoparticles (EU-NPS) for the detection of NGAL in human urine specimens. METHODS: A double-antibody sandwich immunofluorescent assay using europium doped nanoparticles was employed and the NGAL monoclonal antibodies (MAbs) conjugate as labels were generated by optimizing electric fusion parameters. Eighty-three urine samples were used to evaluate the clinical application efficiency of this method. RESULTS: The quantitative detection range of NGAL in AKI was 1-3000 ng/mL, and the detection sensitization was 0.36 ng/mL. The coefficient of variation (CV) of intra-assay and inter-assay were 2.57-4.98 % and 4.11-7.83 %, respectively. Meanwhile, the correlation coefficient between europium nanoparticles-based lateral fluorescence immunoassays (EU-NPS-LFIA) and ARCHITECT analyzer was significant (R2 = 0.9829, n = 83, p < 0.01). CONCLUSIONS: Thus, a faster and easier operation quantitative assay of NGAL for AKI has been established, which is very important and meaningful to diagnose the early AKI, suggesting that the assay can provide an early warning of final outcome of disease.

Remote sensing assessment of oil spills near a damaged platform in the Gulf of Mexico.

An oil platform in the Mississippi Canyon 20 (MC-20) site was damaged by Hurricane Ivan in September 2004. In this study, we use medium- to high-resolution (10-30 m) optical remote sensing imagery to systematically assess oil spills near this site for the period between 2004 and 2016. Image analysis detects no surface oil in 2004, but ~40% of the cloud-free images in 2005 show oil slicks, and this number increases to ~70% in 2006-2011, and >80% since 2012. For all cloud-free images from 2005 through 2016 (including those without oil slicks), delineated oil slicks show an average oil coverage of 14.9 km2/image, with an estimated oil discharge rate of 48 to ~1700 barrels/day, and a cumulative oil-contaminated area of 1900 km2 around the MC-20 site. Additional analysis suggests that the detected oil slick distribution can be largely explained by surface currents, winds, and density fronts.

The Anti-Inflammatory Effects of Vitamin D in Tumorigenesis.

In conjunction with the classical functions of regulating intestinal, bone, and kidney calcium and phosphorus absorption, as well as bone mineralization of vitamin D, the population-based association between low vitamin D status and increased cancer risk is now generally accepted. Inflammation is causally related to oncogenesis. It is widely thought that vitamin D plays an important role in the modulation of the inflammation system by regulating the production of inflammatory cytokines and immune cells, which are crucial for the pathogenesis of many immune-related diseases. Mechanistic studies have shown that vitamin D influences inflammatory processes involved in cancer progression, including cytokines, prostaglandins, MAP kinase phosphatase 5 (MKP5), the nuclear factor kappa B (NF-κB) pathway, and immune cells. Multiple studies have shown that vitamin D has the potential to inhibit tumor development by interfering with the inflammation system. The present review summarizes recent studies of the mechanisms of vitamin D on regulating the inflammation system, which contributes to its potential for cancer prevention and therapy. This review helps answer whether inflammation mediates a causal relationship between vitamin D and tumorigenesis.

Downregulation of ATG5-dependent macroautophagy by chaperone-mediated autophagy promotes breast cancer cell metastasis.

Recent data have shown that the expression of lysosome-associated membrane protein type 2 A (LAMP2A), the key protein in the chaperone-mediated autophagy (CMA) pathway, is elevated in breast tumor tissues. However, the exact effects and mechanisms of CMA during breast cancer metastasis remain largely unknown. In this study, we found that the LAMP2A protein level was significantly elevated in human breast cancer tissues, particularly in metastatic carcinoma. The increased LAMP2A level was also positively correlated with the histologic grade of ductal breast cancer. High LAMP2A levels also predicted shorter overall survival of breast cancer patients. Downregulation of CMA activity by LAMP2A knockdown significantly inhibited the growth and metastasis of both MDA-MB-231 and MDA-MB-468 breast cancer cells in vivo and in vitro, while upregulation of CMA activity by LAMP2A overexpression had the opposite effect. Mechanistically, we found that elevated CMA activity mediated increased growth and metastasis of human breast cancer cells by downregulating the activity of autophagy-related gene 5 (ATG5)-dependent macroautophagy. Collectively, these results indicate that the anti-macroautophagic property is a key feature of CMA-mediated tumorigenesis and metastasis and may, in some contexts, serve as an attractive target for breast cancer therapies.

Sargassum coverage in the northeastern Gulf of Mexico during 2010 from Landsat and airborne observations: Implications for the Deepwater Horizon oil spill impact assessment.

Using high-resolution airborne measurements and more synoptic coverage of Landsat measurements, we estimated the total Sargassum coverage in the northeastern Gulf of Mexico (NE GOM) during 2010, with the ultimate purpose to infer how much Sargassum might have been in contact with oil from the Deepwater Horizon oil spill. Mean Sargassum coverage during the four quarters of 2010 for the study region was estimated to range from ~3148±2355km(2) during January-March to ~7584±2532km(2) during July-September (95% confidence intervals) while estimated Sargassum coverage within the integrated oil footprint ranged from 1296±453km(2) (for areas with >5% thick oil) to 736±257km(2) (for areas with >10% thick oil). Similar to previous studies on estimating Sargassum coverage, a direct validation of such estimates is impossible given the heterogeneity and scarcity of Sargassum occurrence. Nonetheless, these estimates provide preliminary information to understand relative Sargassum abundance in the NE GOM.

Oil slick morphology derived from AVIRIS measurements of the Deepwater Horizon oil spill: Implications for spatial resolution requirements of remote sensors.

Using fine spatial resolution (~7.6m) hyperspectral AVIRIS data collected over the Deepwater Horizon oil spill in the Gulf of Mexico, we statistically estimated slick lengths, widths and length/width ratios to characterize oil slick morphology for different thickness classes. For all AVIRIS-detected oil slicks (N=52,100 continuous features) binned into four thickness classes (≤50 µm but thicker than sheen, 50-200 µm, 200-1000 µm, and >1000 µm), the median lengths, widths, and length/width ratios of these classes ranged between 22 and 38 m, 7-11 m, and 2.5-3.3, respectively. The AVIRIS data were further aggregated to 30-m (Landsat resolution) and 300-m (MERIS resolution) spatial bins to determine the fractional oil coverage in each bin. Overall, if 50% fractional pixel coverage were to be required to detect oil with thickness greater than sheen for most oil containing pixels, a 30-m resolution sensor would be needed.

Surface oil footprint and trajectory of the Ixtoc-I oil spill determined from Landsat/MSS and CZCS observations.

The Ixtoc-I oil spill occurred in 1979 in shallow waters (50 m) of the Bay of Campeche, Mexico. Although it is known that a large portion of the released oil from this second largest accidental marine oil spill in history reached the surface, to date there has been no attempt to document the surface footprint and trajectory of the released oil. Our study attempts to fill this knowledge gap using remote sensing data collected by Landsat/MSS and CZCS. Both showed the same general patterns of oil trajectory to the northwest and north, nearly parallel to the coastline of the western Gulf of Mexico (GoM) with possible oil landing on Mexican and Texas beaches. Field observations at selected beaches and islands along the coast of the western and southern GoM during and after the spill confirmed these satellite-based findings, which were also used to help in planning a recent field campaign to collect sediment samples in the southern GoM.

Identification of broadly conserved cross-species protective Leishmania antigen and its responding CD4+ T cells.

There is currently no clinically effective vaccine against leishmaniasis because of poor understanding of the antigens that elicit dominant T cell immunity. Using proteomics and cellular immunology, we identified a dominant naturally processed peptide (PEPCK335-351) derived from Leishmania glycosomal phosphoenolpyruvate carboxykinase (PEPCK). PEPCK was conserved in all pathogenic Leishmania, expressed in glycosomes of promastigotes and amastigotes, and elicited strong CD4(+) T cell responses in infected mice and humans. I-A(b)-PEPCK335-351 tetramer identified protective Leishmania-specific CD4(+) T cells at a clonal level, which comprised ~20% of all Leishmania-reactive CD4(+) T cells at the peak of infection. PEPCK335-351-specific CD4(+) T cells were oligoclonal in their T cell receptor usage, produced polyfunctional cytokines (interleukin-2, interferon-γ, and tumor necrosis factor), and underwent expansion, effector activities, contraction, and stable maintenance after lesion resolution. Vaccination with PEPCK peptide, DNA expressing full-length PEPCK, or rPEPCK induced strong durable cross-species protection in both resistant and susceptible mice. The effectiveness and durability of protection in vaccinated mice support the development of a broadly cross-species protective vaccine against different forms of leishmaniasis by targeting PEPCK.

Exploring the potential of optical remote sensing for oil spill detection in shallow coastal waters--a case study in the Arabian Gulf.

Remote sensing provides an effective tool for timely oil pollution response. In this paper, the spectral signature in the optical and infrared domains of oil slicks observed in shallow coastal waters of the Arabian Gulf was investigated with MODIS, MERIS, and Landsat data. Images of the Floating Algae Index (FAI) and estimates of sea currents from hydrodynamic models supported the multi-sensor oil tracking technique. Scenes with and without sunglint were studied as the spectral signature of oil slicks in the optical domain depends upon the viewing geometry and the solar angle in addition to the type of oil and its thickness. Depending on the combination of those factors, oil slicks may exhibit dark or bright contrasts with respect to oil-free waters. Three oil spills events were thoroughly analyzed, namely, those detected on May 26 2000 by Landsat 7 ETM + and MODIS/Terra, on October 21 2007 by MERIS and MODIS, and on August 17 2013 by Landsat 8 and MODIS/Aqua. The oil slick with bright contrast observed by Landsat 7 ETM + on May 26 2000 showed lower temperature than oil-free areas. The spectral Rayleigh-corrected reflectance (R(rc)) signature of oil-covered areas indicated higher variability due to differences in oil fractions while the R(rc) spectra of the oil-free area were persistent. Combined with RGB composites, FAI images showed potentials in differentiating oil slicks from algal blooms. Ocean circulation and wind data were used to track oil slicks and forecast their potential landfall. The developed oil spill maps were in agreement with official records. The synergistic use of satellite observations and hydrodynamic modeling is recommended for establishing an early warning and decision support system for oil pollution response.

[The effect of LAMP2A shRNA on the resistance of breast cancer cells to paclitaxel].

OBJECTIVE: To prepare a recombinant lentiviral carring human lysosome-associated membrane protein type 2A (LAMP2A) gene shRNA, establish MDA-MB-231 cell line with a low expression of LAMP2A and observe the change in cell resistance to paclitaxel. METHODS: Four shRNAs were designed according to the sequencing analysis of LAMP2A mRNA. The pGLV-EGFP-shRNA lentiviral vector was established by gene recombination technology and was confirmed by DNA sequencing. The lentiviral vector and the packaging vector were used to cotransfect the HEK293T cells to obtain the lentivirus against LAMP2A mRNA, and the titer of the virus was determined. The constructed shRNA lentivirus was applied to infect human breast cancer cell line MDA-MB-231, and then the cells were screened with puromycin for two weeks. The inhibitive efficacy of the shRNA on the LAMP2A protein was determined by Western blotting. After the breast cancer cell line with a low expression of LAMP2A was treated with three different concentrations of paclitaxel (1, 10, 100 nmol/L), MTT assay was performed to observe the difference in the proliferation ability between the control group and the low LAMP2A expression groups. RESULTS: DNA sequencing revealed that the recombinant lentiviral plasmid was correctly constructed with the virus titer reaching 2×10(8); TU/mL. The LAMP2A protein expression in the obtained breast cancer cell line dropped drastically. After the treatment with paclitaxel at 10 and 100 nmol/L respectively, the drug resistance of cells with a low expression of LAMP2A was notably weaker than that of the control group (P<0.05). CONCLUSION: The recombinant shRNA lentiviral vector against human LAMP2A gene was successfully constructed, and the breast cancer cell line MDA-MB-231 transfected with it stably expressed a low level of LAMP2A. It was proved that the down-regulation of LAMP2A could reduce the resistance of breast cancer cells to paclitaxel.

A monoclonal antibody specific to the non-epitope region of hepatitis B virus preS1 contributes to more effective HBV detection.

OBJECTIVES: The hepatitis B virus (HBV) preS1 protein is divided into an epitope region and a non-epitope region based on the respective antigenicities of these regions. Most of the antibodies that are currently used to detect the large surface protein of HBV (HBV LHB) are specific to the epitope region of preS1, which may contribute to the false negative results of HBV LHB detection assays. Here, we established a mouse monoclonal antibody (mAb) that could improve the efficiency of HBV LHB detection. DESIGN AND METHODS: The HBV preS1 protein was expressed in E. coli strain BL21 and used to screen hybridoma clones. HBV preS1-specific mAb was produced by immunizing mice with a chemically synthesized peptide antigen derived from the non-epitope region of HBV preS1. The mAb was characterized by ELISA, Western blot, and immunocytochemistry and was subsequently used in serum sample tests. RESULTS: Based on in silico B cell epitope predictions, the HBV preS1 aa 91-117 peptide was synthesized as an antigen. Recombinant HBV preS1 was expressed in E. coli and identified by SDS-PAGE. The mAb D8 (IgG2b) recognized the recombinant preS1 protein in both ELISA and Western blot assays and also recognized the preS1 protein expressed in plasmid-transfected HepG2.2.15 cells by immunocytochemistry. Furthermore, the D8 mAb, which is specific for the non-epitope region of preS1, contributed to the improved sensitivity and specificity of HBV detection. CONCLUSIONS: We established an mAb that is specific to the non-epitope region of HBV preS1 and improved the detection of HBV LHB in an ELISA assay. This mAb could help increase the accuracy of the clinical measurement of preS1.

Ectopically expressed IBP promotes cell proliferation in oral squamous cell carcinoma.

IFN regulatory factor 4 binding protein (IBP) has been shown to play an important role in the progression of malignant tumors such as breast cancer cells, but its function in oral squamous cell carcinoma (OSCC) remains unclear. We found that IBP ectopically expressed in some OSCC specimens but not in normal oral mucosa epithelium tissues. IBP expression was significantly correlated with tumor size, differentiation, clinical stage, and distant metastasis. Furthermore, IBP markedly promoted OSCC cell proliferation, shortened the G1 interval in the cell cycle, and increased cyclin D1 expression. These findings suggest that IBP may be a potential therapeutic target for OSCC.

Interferon regulatory factor 4 binding protein is a novel p53 target gene and suppresses cisplatin-induced apoptosis of breast cancer cells.

BACKGROUND: Our previous work demonstrated that ectopic expression of interferon regulatory factor 4 binding protein (IBP) was correlated with the malignant behaviour of human breast cancer cells. The mechanisms controlling differential expression of IBP in breast cancer still remain unknown. RESULTS: To investigate the mechanism of IBP dysregulation in breast cancer, we identified IBP was a novel p53 target gene. IBP expression was negatively regulated by wild-type p53 and was p53 dependently suppressed by DNA damage agent cisplatin. Furthermore, high levels of IBP were found to decrease cisplatin-induced growth suppression and apoptotic cell death, which was associated with decreased p53 activity and imbalanced Bcl-2 family member expression. CONCLUSIONS: IBP is a novel p53 target gene which suppresses cisplatin-mediated apoptosis of breast cancer cells via negative feedback regulation of the p53 signalling pathway, suggesting IBP may serve as a target for pharmacologic intervention of breast cancer resistant to cisplatin therapy.

Elevation of plasma soluble CD26 levels during pregnancy.

AIM: CD26 is a type II transmembrane protein with dipeptidyl peptidase IV (DPPIV) activity expressed on a variety of cell types. Recent studies have indicated that CD26 or enzymatic activity levels were previously associated with immune-mediated disorders. As immunoregulation is very important for a successful pregnancy, we hypothesize that CD26 may play an important role during pregnancy, and herein, we sought to determine the association between circulating levels of soluble CD26 (sCD26) and pregnancy outcome. MATERIAL AND METHODS: In this study, a stable hybridoma cell line 1F1 was produced by fusion of murine splenocytes and myeloma cells. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed for the detection of the maternal plasma sCD26. We measured the plasma levels of sCD26 in 80 normal pregnant women and 45 non-pregnant women. RESULTS: Our results indicated that the plasma level of sCD26 was significantly higher in the pregnant group (P < 0.001) than that in the non-pregnant group. CONCLUSION: These findings hinted that CD26 may play a role in successful pregnancy and it is not an absolute surrogate marker for the Th1-type immunity as the dominant Th2-type immunity during pregnancy.

Characterization, epitope identification and mechanisms of the anti-septic capacity of monoclonal antibodies against macrophage migration inhibitory factor.

Sepsis is characterized by uncontrolled inflammatory responses. Macrophage migration inhibitory factor (MIF) has been shown to play an important role in the progression of sepsis thus is a potential therapeutic target. The aim of this study is to produce IgG anti-MIF monoclonal antibodies (mAbs) with anti-septic abilities in vivo and to determine mechanisms of their function. We generated 8 IgG anti-MIF mAbs with high specificity and 3 of them showed potent protective abilities in murine lethal peritonitis induced by cecal ligation and puncture (CLP). One anti-MIF mAb, F11, showed 100% protection within 72 h after sepsis induction and 72% mice treated with this mAb survived up to 84 h with reduced lung and kidney pathology. F11 treatment also reduced tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels in septic mice. We further found that all 8 anti-MIF mAbs recognized the same epitope located in the amino acid residue 1-20 region of the N terminus of the MIF protein. Three of the mAbs, F11 in particular, inhibited tautomerase activity in association with their protective effect on CLP mice. Thus, we have produced anti-MIF mAbs that protected mice from CLP-induced sepsis by recognizing the same epitope domains in MIF. These mAbs are promising candidates for further development of therapeutics against inflammatory diseases.

Overexpression of the Interferon regulatory factor 4-binding protein in human colorectal cancer and its clinical significance.

BACKGROUND: IFN regulatory factor 4-binding protein (IBP) is a novel type of activator of Rho GTPases. It has been linked with differentiation and apoptosis of lymphocytes, but its function in oncogenesis remains unclear. Here we studied the expression of endogenous IBP in four human colorectal cancer cell lines, normal, adenoma and tumor colorectal tissues. METHODS: Molecular (Western blot and RT-PCR), and confocal analyses were used to investigate IBP expression in human colorectal cancer cell lines. Matched normal and tumor tissue sections of 63 patients and 15 adenoma tissue sections were analyzed for IBP expression by immunohistochemistry (IHC). RESULTS: IBP was ubiquitely expressed in human colorectal cancer cell lines. The expression of IBP can be detected at both the mRNA and protein level in SW480, SW620 and HT29 cells. Clinically, IBP were elevated in human colorectal cancer specimens in comparison to normal colorectal tissues. Substantial high expression of IBP was observed in colorectal cancer tissues (67%), whereas corresponding normal tissues and 15 adenoma tissues showed consistently absent immunoreactivity of IBP. Moreover, IBP expression is correlated with the differentiation level of colorectal cancer cells (p<0.05) and clinical stage of patients (p<0.01). CONCLUSIONS: Our data show, for the first time, a dysregulated expression of IBP in human colorectal cancer, offering new perspectives for its role in cancer development and progression. IBP may be a novel tumor marker and a therapeutic target for colorectal cancer.

c-Rel is a transcriptional repressor of EPHB2 in colorectal cancer.

The receptor tyrosine kinase EPHB2 has recently been identified as a TCF4 transcriptional target that controls the intestinal epithelial architecture through repulsive interactions with Ephrin-B ligands. Many reports have demonstrated that most human colorectal cancers lose EPHB2 expression despite constitutive Wnt activation. Therefore, we investigated the mechanisms that cause EPHB2 down-regulation in colorectal cancer. In this study, we demonstrate that DNA hypermethylation was not responsible for the frequent loss of EPHB2 expression in colorectal cancer. Cloning and functional characterization of the EPHB2 gene 5'-flanking region revealed a potential negative regulatory element in the distal regulatory region. In vitro electrophoretic gel mobility shift and in vivo chromatin immunoprecipitation assays demonstrated that c-Rel directly binds to the putative element. Inhibiting c-Rel activity or knocking down c-Rel expression by RNA interference in colon cancer cells was sufficient to induce EPHB2 expression. Furthermore, transient transfection assays demonstrated that c-Rel over-expression repressed endogenous EPHB2 expression in colon cancer cells. We demonstrate for the first time that c-Rel acts as a transcriptional repressor of EPHB2 and plays an active role in EPHB2 down-regulation in colorectal cancers.

The ectopic expression of IFN regulatory factor 4-binding protein is correlated with the malignant behavior of human breast cancer cells.

Many proteins that are aberrantly expressed in malignant tumors play important roles in promoting tumorigenesis, metastasis and immune escape. IFN regulatory factor 4-binding protein (IBP), which is a novel PH-DH-like protein related to SWAP-70, and functions as an upstream activator of Rho GTPases. It is widely expressed in cells of the immune system and is involved in coupling activated cell receptors to downstream signaling events that mediate cell proliferation, differentiation and polarization. Although IBP was detected in human chondrosarcoma, its function in tumor cells remains unknown. In this study, newly generated monoclonal anti-IBP antibodies were employed and they detected higher level expression of IBP in some human invasive breast carcinoma tissues and in two breast cancer cell lines that form highly invasive tumors in nude mice. In contrast, the levels of IBP mRNA and protein were low or undetectable in normal human breast tissues, benign breast lesions or low-tumorigenic breast cancer cell lines. Over-expression of wild-type IBP in an IBP-negative breast cancer cell line markedly increased its proliferation and invasiveness in vitro. Conversely, RNA interference-mediated knockdown of IBP expression in an IBP-positive breast cancer cell line significantly reduced cell growth and invasiveness. Our results indicate that IBP is expressed in more highly invasive human breast cancer cells, such as MCF-7 and MDA-MB-231, with lower expression in normal breast tissue, benign tumors and less aggressive breast cancer cells, such as SKBR3 and MDA-MB-453. Thus, expression of IBP is correlated with the degree of malignant breast tumors. Nevertheless, it should be pointed our that further study with more tumor types is required to fully elucidate the role of IBP in tumorigenesis and the potential of IBP as a marker for more highly malignant tumors.

T cell receptor engagement leads to the recruitment of IBP, a novel guanine nucleotide exchange factor, to the immunological synapse.

Reorganization of the actin cytoskeleton is crucial to the formation and function of the immunological synapse. Rho GTPases are critical mediators of cytoskeletal reorganization, and their activity at the synapse is likely to be stringently regulated. Guanine nucleotide exchange factors (GEFs) belonging to the Dbl family of proteins represent one major class of proteins that regulate the activity of Rho GTPases. Here we demonstrate that IBP, a homologue of SWAP-70, is a novel GEF for Rac1 and Cdc42 in T lymphocytes, which is recruited to the immunological synapse upon engagement of the antigen receptor. Mutational analysis supports a model whereby IBP is inactive in unstimulated cells. Upon engagement of the T cell receptor, its GEF activity is enhanced by tyrosine phosphorylation, as well as by binding newly generated phosphatidylinositol 3,4,5-trisphosphate. Although it is known that T cell receptor engagement leads to the recruitment of Vav to the immunological synapse, these findings indicate that other GEFs, such as IBP, also relocalize to this intercellular region. The recruitment and activation of distinct classes of GEFs may allow for precise control of Rho GTPase function at the crucial interface between T cells and antigen presenting cells.

Molecular cloning of IBP, a SWAP-70 homologous GEF, which is highly expressed in the immune system.

Rho GTPases play a fundamental role in a variety of biological processes ranging from the reorganization of the actin cytoskeleton to the regulation of cell proliferation. The activation of Rho GTPases is regulated by guanine nucleotide exchange factors (GEFs) belonging to the Dbl family of proteins. The hallmark of this large family of GEFs is the presence of a tandem DH-PH module in which a pleckstrin-homology (PH) domain is located at the C-terminus of a Dbl-homology (DH) domain. Recent studies have demonstrated that SWAP-70 constitutes a novel class of Rac-GEF, in which the PH domain is located at the N-terminus, rather than the C terminus, of the DH domain. Here we report the molecular cloning of human IBP (IRF-4 binding protein), a new member of this novel family of GEFs. The IBP gene maps to human chromosome 6p21.31 centromeric to the MHC locus. Isolation of the murine IBP cDNA reveals a very high degree of homology with the human IBP cDNA suggesting that IBP is evolutionarily conserved. The 5' portion of the murine IBP cDNA is furthermore identical to the Def-6 cDNA fragment, which was identified in the course of a search for genes differentially expressed in the murine hematopoietic system. IBP is broadly expressed in the immune system and can be detected in both T and B cell compartments in contrast to SWAP-70 whose expression is primarily restricted to B cells. Taken together these findings indicate that IBP is a novel type of GEF, which participates in the activation of Rho GTPases in lymphoid tissues.