Modeling intestinal disorders using zebrafish.

Although the zebrafish was initially developed as a model system to study embryonic development, it has gained increasing attention as an advantageous system to investigate human diseases, including intestinal disorders. Zebrafish embryos develop rapidly, and their digestive system is fully functional and visible by 5days post fertilization. There is a large degree of homology between the intestine of zebrafish and higher vertebrate organisms in terms of its cellular composition and function as both a digestive and immune organ. Furthermore, molecular pathways regulating injury and immune responses are highly conserved. In this chapter, we provide an overview of studies addressing developmental and physiological processes relevant to human intestinal disease. These studies include those related to congenital disorders, host-microbiota interactions, inflammatory diseases, motility disorders, and intestinal cancer. We also highlight the utility of zebrafish to functionally validate candidate genes identified through mutational analyses and genome-wide association studies, and discuss methodologies to investigate the intestinal biology that are unique to zebrafish.

Efficacy and safety of CDX-301, recombinant human Flt3L, at expanding dendritic cells and hematopoietic stem cells in healthy human volunteers.

Fms-like tyrosine kinase-3 ligand (Flt3L) uniquely binds the Flt3 (CD135) receptor expressed on hematopoietic stem cells (HSCs), early progenitor cells, immature thymocytes and steady-state dendritic cells (DCs) and induces their proliferation, differentiation, development and mobilization in the bone marrow, peripheral blood and lymphoid organs. CDX-301 has an identical amino-acid sequence and comparable biological activity to the previously tested rhuFlt3L, which ceased clinical development over a decade ago. This Phase 1 trial assessed the safety, pharmacokinetic, pharmacodynamic and immunologic profile of CDX-301, explored alternate dosing regimens and examined the impact of rhuFlt3L on key immune cell subsets. Thirty healthy volunteers received CDX-301 (1-75 µg/kg/day) over 5-10 days. One event of Grade 3 community-acquired pneumonia occurred. There were no other infections, dose-limiting toxicities or serious adverse events. CDX-301 resulted in effective peripheral expansion of monocytes, hematopoietic stem and progenitor cells and key subsets of myeloid DCs and plasmacytoid DCs, with no clear effect on regulatory T cells. These data from healthy volunteers support the potential for CDX-301, as monotherapy or in combination with other agents, in various indications including allogeneic HSC transplantation and immunotherapy, but the effects of CDX-301 will need to be investigated in each of these patient populations.

Smooth muscle caldesmon modulates peristalsis in the wild type and non-innervated zebrafish intestine.

BACKGROUND: The high molecular weight isoform of the actin-binding protein Caldesmon (h-CaD) regulates smooth muscle contractile function by modulating cross-bridge cycling of myosin heads. The normal inhibitory activity of h-CaD is regulated by the enteric nervous system; however, the role of h-CaD during intestinal peristalsis has never been studied. METHODS: We identified a zebrafish paralog of the human CALD1 gene that encodes an h-CaD isoform expressed in intestinal smooth muscle. We examined the role of h-CaD during intestinal peristalsis in zebrafish larvae by knocking down the h-CaD protein using an antisense morpholino oligonucleotide. We also developed transgenic zebrafish that express inhibitory peptides derived from the h-CaD myosin and actin-binding domains, and examined their effect on peristalsis in wild-type zebrafish larvae and sox10 (colourless) mutant larvae that lack enteric nerves. KEY RESULTS: Genomic analyses identified two zebrafish Caldesmon paralogs. The cald1a ortholog encoded a high molecular weight isoform generated by alternative splicing whose intestinal expression was restricted to smooth muscle. Propulsive intestinal peristalsis was increased in wild-type zebrafish larvae by h-CaD knockdown and by expression of transgenes encoding inhibitory myosin and actin-binding domain peptides. Peristalsis in the non-innervated intestine of sox10 (colourless) larvae was partially restored by h-CaD knockdown and expression of the myosin-binding peptide. CONCLUSIONS & INFERENCES: Disruption of the normal inhibitory function of h-CaD enhances intestinal peristalsis in both wild-type zebrafish larvae and mutant larvae that lack enteric nerves, thus confirming a physiologic role for regulation of smooth muscle contraction at the actin filament.

A monoclonal antibody to the DEC-205 endocytosis receptor on human dendritic cells.

DEC-205 is a multilectin receptor for adsorptive endocytosis, expressed in mouse dendritic cells (DC) and some epithelia. DEC-205 is homologous to the macrophage mannose receptor (MMR). A cDNA for murine DEC-205 was used to identify 3 overlapping human DEC-205 clones from a lymphocyte library. The human homologue is a transmembrane protein of 1722 aminoacids with 10 externally disposed C-type lectin domains having 77% identity to the mouse counterpart. The NH(2) terminal cysteine-rich and fibronectin type II domains were expressed and used to immunize mice. A hybridoma, MG38, which specifically recognized the immunogen was obtained from a DEC-205 knockout mouse. The antibody precipitated a 205 kD protein from metabolically labeled, monocyte-derived DCs. MG38 labeled mature monocyte-derived DCs but showed weak or no labeling of other peripheral blood mononuclear cells. In tissue sections, MG38 identified DEC-205 on thymic cortical epithelium and DCs in the thymic medulla and tonsillar T cell areas. In contrast, an anti-MMR antibody stained DEC-205 negative, macrophages in the thymus cortex, the trabeculae of the thymus and tonsil, as well as efferent lymphatics in the tonsil. Therefore, the MG38 anti-DEC-205 antibody is useful for identifying DCs and reveals clear differences in sites where MMR and DEC-205 are expressed in lymphoid tissues.

Malignant tumors of the small intestine: a review of 144 cases.

Cancer of the small intestine represents less than two per cent of all the malignant tumors of the gastrointestinal tract. Because they are infrequent tumors, a review of a tumor registry was performed to analyze response to treatment of the disease and prognostic factors. A retrospective review of patients with primary cancer of the small intestine was performed using the Department of Defense Tumor Registry. The registry was accessed to determine stage, types of cancer, intervention, and patient outcomes. TNM staging and follow-up were available on 144 patients from 1970 to 1996. Median follow-up was 38.9 months. There were 92 (64%) males and 52 (38%) females. The median age was 55.7 years. The types of small intestinal cancer included 68 patients (47%) with adenocarcinoma, 41 patients (28%) with carcinoid, 18 patients (13%) with leiomyosarcoma, and 17 patients (12%) with lymphoma. The overall 5-year survival was 57 per cent and the median survival was 52 months. Survival of patients with adenocarcinoma was not dependent on location within the small bowel. Survival was best for early-stage tumors and when lesions could be completely resected.

Experimental computer-assisted alloplastic sandwich augmentation of the atrophic mandible.

PURPOSE: This study evaluated the effectiveness of a technique that combined computer-aided surgery with alloplastic augmentation and implant-borne prosthodontic rehabilitation of the atrophic mandible. MATERIALS AND METHODS: Computed tomographic (CT) data from an atrophic cadaver mandible were transferred to a computer-aided design (CAD) system that prepared an anterior sandwich osteotomy. The cranial segment was moved upward and backward to provide an ideal alveolar relationship, and the geometry of the intermediate space was used to design a titanium implant. Furthermore, a surgical template was derived for the osteotomies, and insertion of dental implants was planned to stabilize both the transposed bone and the intermediate implant on the bony base. An identical implant for augmentation was also fabricated from poly-D,L-lactide in a mold as a possible resorbable carrier for osteoinductive proteins. RESULTS: The experimental surgery was successfully performed with maximum precision on the dried mandible. The fabrication of an implant made out of poly-D,L-lactide for the same purpose was also possible. CONCLUSIONS: This preliminary experiment showed that it is possible to use CAD/computer-aided manufacturing (CAM) technology to prepare a prefabricated template and a corresponding titanium implant for mandibular augmentation with a high degree of exactness. Dental implants could be planned and integrated in this procedure as well. The fabrication of a mold using this method also provided the opportunity to give a complex shape to possible carriers of osteoinductive substances.

Integration of periorbital titanium implants in irradiated bone: case report and histologic evaluation.

Extraoral implants are used increasingly frequently in the wake of ablative tumor surgery and adjuvant radiation or chemotherapy for craniofacial rehabilitation with facial prostheses and epitheses. However, high rates of nonintegration and implant loss have been reported for extraoral implants, especially for those in the periorbital region following irradiation. This case report and corresponding histologic evaluation describe the osseointegration pattern in irradiated periorbital bone, based on the example of 3 retrieved, clinically integrated, stable titanium screw implants.

Efficient presentation of phagocytosed cellular fragments on the major histocompatibility complex class II products of dendritic cells.

Cells from the bone marrow can present peptides that are derived from tumors, transplants, and self-tissues. Here we describe how dendritic cells (DCs) process phagocytosed cell fragments onto major histocompatibility complex (MHC) class II products with unusual efficacy. This was monitored with the Y-Ae monoclonal antibody that is specific for complexes of I-Ab MHC class II presenting a peptide derived from I-Ealpha. When immature DCs from I-Ab mice were cultured for 5-20 h with activated I-E+ B blasts, either necrotic or apoptotic, the DCs produced the epitope recognized by the Y-Ae monoclonal antibody and stimulated T cells reactive with the same MHC-peptide complex. Antigen transfer was also observed with human cells, where human histocompatibility leukocyte antigen (HLA)-DRalpha includes the same peptide sequence as mouse I-Ealpha. Antigen transfer was preceded by uptake of B cell fragments into MHC class II-rich compartments. Quantitation of the amount of I-E protein in the B cell fragments revealed that phagocytosed I-E was 1-10 thousand times more efficient in generating MHC-peptide complexes than preprocessed I-E peptide. When we injected different I-E- bearing cells into C57BL/6 mice to look for a similar phenomenon in vivo, we found that short-lived migrating DCs could be processed by most of the recipient DCs in the lymph node. The consequence of antigen transfer from migratory DCs to lymph node DCs is not yet known, but we suggest that in the steady state, i.e., in the absence of stimuli for DC maturation, this transfer leads to peripheral tolerance of the T cell repertoire to self.

Prognostic factors for adenocarcinoma of the gallbladder: an analysis of 162 cases.

Carcinoma of the gallbladder is a rare neoplasm and is associated with a dismal prognosis. To analyze the natural history of this disease and prognostic factors, a large tumor registry database was accessed. During the period 1972 to 1995, 214 patients were entered. Adequate follow-up was available on 162 patients, and this group forms the basis of this review. There were 54 males and 108 females with a median age of 62 years. Median follow-up was 7 months. Right upper quadrant abdominal pain was the most frequent presenting symptom. Fifteen patients had an incidental finding of carcinoma after cholecystectomy. Overall, 5-year survival was 25 per cent, with a median survival time of 9.7 months. Survival was improved for patients with local disease compared with those with regional or metastatic disease. One hundred nine patients underwent surgical therapy. Complete resection was possible in 36 patients, whereas 44 patients had residual disease. Median survival time for patients with no residual disease was 67.2 months, whereas those for patients with microscopic residual tumor and gross residual tumor were 8.9 and 3.8 months, respectively (P < 0.000001). Gallbladder cancer is often diagnosed at an advanced stage and is associated with a poor prognosis. In patients with localized disease, surgical treatment provides the opportunity for long-term survival only when a complete resection can be performed. Prognosis for patients with microscopic residual and gross residual disease is similar.

High levels of a major histocompatibility complex II-self peptide complex on dendritic cells from the T cell areas of lymph nodes.

T lymphocytes recirculate continually through the T cell areas of peripheral lymph nodes. During each passage, the T cells survey the surface of large dendritic cells (DCs), also known as interdigitating cells. However, these DCs have been difficult to release from the lymph node. By emphasizing the use of calcium-free media, as shown by Vremec et al. (Vremec, D., M. Zorbas, R. Scollay, D.J. Saunders, C.F. Ardavin, L. Wu, and K. Shortman. 1992. J. Exp. Med. 176:47-58.), we have been able to release and enrich DCs from the T cell areas. The DCs express the CD11c leukocyte integrin, the DEC-205 multilectin receptor for antigen presentation, the intracellular granule antigens which are recognized by monoclonal antibodies M342, 2A1, and MIDC-8, very high levels of MHC I and MHC II, and abundant accessory molecules such as CD40, CD54, and CD86. When examined with the Y-Ae monoclonal which recognizes complexes formed between I-Ab and a peptide derived from I-Ealpha, the T cell area DCs expressed the highest levels. The enriched DCs also stimulated a T-T hybridoma specific for this MHC II-peptide complex, and the hybridoma underwent apoptosis. Therefore DCs within the T cell areas can be isolated. Because they present very high levels of self peptides, these DCs should be considered in the regulation of self reactivity in the periphery.

Replacement value of betaine for DL-methionine in male broiler chicks.

The effect of DL-methionine and betaine supplementation on growth performance of 2,400 male broilers in the age period of 1 to 38 d, and on carcass composition of a subsample of 384 birds was examined. Three dose levels of DL-methionine (0, 0.05, and 0.10%) and two doses of betaine (0 and 0.04%) were supplemented in different combinations to methioninedeficient diets. Two types of diets were fed as starters and growers: either corn-soybean diets or practical diets typical for the Dutch broiler industry. All diets were fortified with 220 ppm choline in order to avoid a deficiency in methyl groups. Increasing DL-methionine supplementation significantly improved daily weight gain and feed conversion efficiency. Supplemental betaine did not affect bird growth. Betaine slightly improved feed conversion in diets without supplemental DL-methionine, but did not affect this parameter in diets with added DL-methionine. Breast meat yield was significantly increased by about 1.5 percentage points by the addition of 0.05% DL-methionine, whereas 0.04% betaine only tended to increase breast meat yield in the range of 0.3 to 0.6 percentage points. The type of diet did not have any effect on the responses obtained. In summary, there was no evidence for betaine to spare DL-methionine as an essential amino acid supplement in broiler diets.

Effects of dietary protein content, addition of nonessential amino acids and dietary methionine to cysteine balance on responses to dietary sulphur-containing amino acids in broilers.

1. Two experiments were conducted with male broiler chicks from 2 to 5 weeks of age to determine the effect of dietary protein content and amino acid balance on the response to dietary sulphur-containing amino acids (SAA) in terms of performance and carcase quality. 2. In experiment 1, 5 graded amounts of a DL-methionine and L-cysteine (1:1 by weight) mixture were added to basal diets containing 197 or 233 g crude protein/kg. The diets containing 197 g protein/kg were fed with or without the further addition of 36 g crude protein/kg from nonessential amino acids. The amino acid balance of all diets was kept constant for all essential amino acids except the SAA. In experiment 2, 5 graded amounts of SAA from either a crystalline source (DL-methionine or a mixture of DL-methionine and L-cysteine) or from intact proteins were added to a diet containing 208 g protein/kg. 3. At each protein concentration there were significant responses to the SAA addition in weight gain, food conversion efficiency, and carcase quality. Non-linear exponential regression analyses were used to describe bird responses to SAA concentration. The broiler chick's requirement for SAA increased with increasing dietary protein concentrations ranging from 197 to 259 g protein/kg. 4. The utilisation of SAA differed also with differences in origin (crystalline or peptide-bound), and methionine:cysteine balances. Compared to DL-methionine, a 1:1 mixture of DL-methionine and L-cysteine was only 81% or 86% as effective in supporting growth or food conversion, respectively. SAA from added protein was even less effectively utilised. 5. The addition of nonessential amino acids tended to decrease food intake without affecting SAA utilisation. 6. Slaughter yield and breast meat yield were clearly increased while fat deposition was clearly decreased, by SAA addition. The response in breast meat yield suggested an important economic benefit for further meat processing. Nitrogen retention was significantly enhanced by SAA supplementation from crystalline sources, and this led to reductions of up to 30% in the amount of nitrogen excreted per kg weight gain.

Axillary lymph node dissection: does it have a role in primary breast cancer?

The role of elective lymph node dissection has been increasingly questioned for the treatment of primary breast cancer. In an attempt to evaluate whether or not axillary lymph node dissection is of value in early breast cancer, a retrospective review of all breast cancers treated at Eisenhower Army Medical Center was conducted. During that time, 434 patients with breast cancer were treated. Eighty-six of those patients had lesions that were 2.0 cm or smaller. Eighty-one patients underwent axillary lymph node dissection. Twenty-four patients were found to have positive axillary nodes (28%). If the patients were further divided into those with lesions 1.0 centimeters or less versus 1.1-2.0 cm, the incidence of node positivity was 19 per cent and 35 per cent, respectively. Of the patients who underwent axillary lymph node dissection, 60 per cent of those whose lymph nodes were negative received no further treatment, whereas those whose lymph nodes were positive received additional therapy 92 per cent of the time. An additional 8 per cent of the node-negative patients received radiation therapy as the only added therapy after segmental mastectomy with axillary lymph node dissection. Our study demonstrates, or at least suggests, that node positivity did influence subsequent therapy. In addition, the relatively high incidence of positive axillary nodes (28%) in these early breast cancers supports the potential therapeutic benefit of axillary node dissection.

Effects of dietary sulphur-containing amino acids on performance and breast meat deposition of broiler chicks during the growing and finishing phases.

1. Two growth trials were performed to measure the effects of dietary methionine and cystine (SAA) on growth rate, food conversion efficiency and breast meat deposition in male broilers. 2. In experiment 1, broilers were grown on 6 experimental diets covering a range from 6.9 to 9.6 g SAA/kg. The diets were fed from 15 to 33 d of age. Similarly, in experiment 2, 6 diets containing 6.0 to 8.5 g SAA/kg were fed to finishing broilers 33 to 43 d of age. In each experiment 60 birds per treatment were processed, and carcase yield and breast meat percentage were determined. 3. Significant responses in weight gain, efficiency of food conversion and breast meat percentage were detected, which could be described well by exponential regression curves. Dietary SAA requirements to obtain maximum efficiency of food utilisation and maximum breast meat deposition were estimated to be about 9.0 g/kg from 15 to 33 d of age, and about 8.0 g/kg from 33 to 43 d of age. 4. Economic aspects were considered to calculate optimum SAA specifications from the results. In both trials, the dietary optimum of SAA was found to be higher for birds to be further processed than for birds to be marketed as whole carcases.

Bone marrow-derived chimerism in non-irradiated, cyclosporin-treated rats receiving microvascularized limb transplants: evidence for donor-derived dendritic cells in recipient lymphoid tissues.

Tolerance to donor transplantation antigens develops when recipients are made chimeric with donor bone marrow. To establish chimerism, the haemopoietic system of recipients typically is severely compromised. We report on a system in which chimerism develops without ablative therapies. Immunosuppression with cyclosporin A allowed the lower limb of a rat to be replaced by a microvascularized transplant from a fully allogeneic donor. Many donor-derived cells populated recipient lymph nodes and spleen, and most had the large size, irregular shape and strong major histocompatibility complex (MHC) class II expression that typify dendritic cells. Donor cells were not found in the macrophage-rich regions of lymphoid tissues, but instead occupied splenic white pulp and lymph node cortex. The donor cells were derived from radiosensitive marrow precursors, as chimerism was abolished if the grafted limb was irradiated, or if muscle and skin flaps devoid of bone were grafted. Donor cells were rare or not detectable in blood, thymus and liver. Whereas lymphoid chimerism was prominent following limb transfer, donor cells were not detected 1-2 weeks after an injection of two femur equivalents of a marrow suspension. We suggest that dendritic cells that undergo rapid turnover in lymphoid organs are replaced from allogeneic precursors in bone grafts. The combination of cyclosporin and vascularized bone provides a means for inducing chimerism in lymphoid tissues of non-irradiated recipients.

Tissue distribution of the DEC-205 protein that is detected by the monoclonal antibody NLDC-145. II. Expression in situ in lymphoid and nonlymphoid tissues.

The rat monoclonal antibody NLDC-145, which has been utilized as a marker for mouse dendritic cells in numerous studies, binds an antigen that is more broadly distributed. This antigen is a unique 205-kDa integral membrane glycoprotein called DEC-205, which we have recently purified in quantities sufficient for basic biochemical studies, N-terminal sequencing, and immunization of rabbits. In cytofluorographic experiments, both the new polyclonal antibody and the original monoclonal detected DEC-205 on many classes of nondendritic murine leukocytes, particularly B cells. The quantities of DEC-205 on the surfaces of these cells were 10 to 50 times lower than those on epidermal and bone marrow dendritic cells. Here we utilize these reagents to reassess the tissue distribution of DEC-205 by immunohistochemical staining of frozen sections from a variety of organs, and by multiple-organ immunoblotting. Abundant expression of DEC-205 was confirmed histologically on thymic and intestinal epithelia and on dendritic cells in the T cell areas of peripheral lymphoid organs. In addition, DEC-205 was visualized in several other locations: B lymphocytes within B cell follicles, the stroma of the bone marrow, the epithelia of pulmonary airways, and the capillaries of the brain. Immunoblotting confirmed the presence of substantial levels of DEC-205 protein in lysates prepared from lymphoid tissues and from lung, marrow, and intestine. Thus, while DEC-205 is expressed at high levels by dendritic cells, it is also expressed by a number of other cell types in situ.

Response of rainbow trout (Oncorhynchus mykiss) growing from 50 to 150 g to supplements of DL-methionine in a semipurified diet containing low or high levels of cystine.

We studied the effect of increasing dietary concentrations of DL-methionine on growth, feed intake, feed conversion ratio and the composition of gain in rainbow trout. Twenty-four groups of 20 trout initially weighing 51 +/- 0.5 g/trout were fed semipurified diets containing 20.1 MJ digestible energy and either 3.0 or 5.8 g cystine/kg dry matter. At each level of cystine, 12 levels of methionine (2 to 11 g/kg dry matter) were achieved by supplementation with graded quantities of DL-methionine. During an experiment of 49 feeding days, no significant effect of the level of dietary cystine was found for any performance trait. Nonlinear responses to increasing dietary methionine concentrations were found for feed intake, growth rate, protein concentration of gain and protein deposition, whereas fat concentration of gain decreased concurrently. Dietary methionine was utilized most efficiently at a concentration of 3.5 g methionine/kg dry matter or 0.17 g/MJ digestible energy. Ninety-five percent of the plateau deposition of body protein was achieved at a dietary methionine concentration of 8 g/kg dry matter or 0.40 g/MJ digestible energy. For achieving 98%, the required concentration was 9.0 g/kg or 0.49 g/MJ. Recommended dietary methionine concentration will depend on the trait chosen.

Sulfur amino acid requirement of broiler chicks from fourteen to thirty-eight days of age. 2. Economic evaluation.

A calculation model was developed that can be used to derive dietary methionine and cystine (TSAA) levels for maximum profitability in growing broilers. Based on dose-response curves from two broiler experiments, the model calculates additional income from improved feed conversion and from increased breast meat yield. From the comparison of additional income to the additional cost associated with increasing dietary TSAA levels, the TSAA content giving maximum profit can be estimated. Under European price conditions, a dietary level of .95% TSAA was found to be most profitable for broilers grown to 1.7 kg (Experiment 1, 14 to 34 d of age), when only the feed conversion response to dietary TSAA was considered. In broilers grown to 2.2 kg (Experiment 2, 14 to 38 d of age), two situations were simulated. If only the feed conversion response was evaluated, the most profitable TSAA level would be .85%. If both feed conversion and breast meat responses were considered, a higher level of .89% TSAA would be optimum. Changing prices of input and output variables (broiler feed, breast meat, DL-methionine) affected the respective economic optimum level of dietary TSAA only slightly.

Effects of dietary sulfur amino acids and crude protein on the performance of finishing broilers.

The effects of different combinations of dietary methionine + cystine (Met + Cys) and dietary crude protein (CP) in finishing broilers were investigated in two growth studies. In Exp. 1, male broilers 29 to 42 days of age were fed 18 diets containing 16.9%, 18.7%, or 20.4% CP with six levels of Met + Cys within each protein level. Similarly, in Exp. 2 another 12 diets containing either 18.0 or 21.5% CP were fed to male broilers 29 to 48 days of age. In general, the Met + Cys requirement for optimum feed conversion was higher than for maximum growth. In both experiments, between 0.80% and 0.85% methionine + cystine optimized feed conversion. These dietary levels were valid for a 13.05 MJ ME/kg diet fed to broilers growing from 1.2 kg to 2.2 kg (Exp. 1), or for a 13.60 MJ ME/kg diet fed to broilers growing from 1.3 kg to 3.0 kg (Exp. 2). The Met + Cys requirement was not consistently affected by the dietary CP content in Exp. 1. In Exp. 2, increasing dietary CP from 18.0% to 21.5% tended to increase the Met + Cys requirement for optimum feed conversion. A dietary CP level of 18.0% to 18.7% supported performance and carcass fat deposition equal to diets containing 20.4% or 21.5% CP, respectively, when the sulfur amino acid content was adequate.

Expression of B7 costimulator molecules on mouse dendritic cells.

Dendritic cells express most known accessory molecules [ICAM's, LFA's, B7's, and CD40] for binding and stimulating T cells. B7 is the most abundant of these, and B7-2 very much predominates relative to B7-1. B7 expression is regulated, not by LPS, but by some signal [s] that parallels maturation. B7 contributes to the T cell stimulatory function of dendritic cells, as do the other accessory molecules. B7-2 is expressed on dendritic cells and macrophages at several sites in situ, especially dendritic cells in the T cell areas.