Disruption of T cell signaling networks and development by Grb2 haploid insufficiency

The developmental processes of positive and negative selection in the thymus shape the T cell antigen receptor (TCR) repertoire and require the integration of multiple signaling networks. These networks involve the efficient assembly of macromolecular complexes and are mediated by multimodular adaptor proteins that permit the functional integration of distinct signaling molecules. We show here that decreased expression of the adaptor protein Grb2 in Grb2+/- mice weakens TCR-induced c-Jun N-terminal kinase (JNK) and p38, but not extracellular signal-regulated kinase (ERK), activation. In turn, this selective effect decreases the ability of thymocytes to undergo negative, but not positive, selection. We also show that there are differences in the signaling thresholds of the three mitogen-activated protein kinase (MAPK) families. These differences may provide a mechanism by which quantitative differences in signal strength can alter the balance of downstream signaling pathways to induce the qualitatively distinct biological outcomes of proliferation, differentiation or apoptosis.

Morphological analysis of adrenal glands: a prospective analysis

There is a lack of studies to document the weight range of normal adrenal glands. The aims of the current study are to find out the weight range of normal adrenal glands in Chinese patients and to analyze any potential factors affecting it. Adrenal glands not affected by disease were prospectively collected from autopsies on 333 Chinese patients (208 men, 125 women). The weight and longest dimension of each adrenal gland were noted. The impact of various clinicopathological factors on the adrenal weight was studied. In addition, the morphometric features of these adrenal glands were compared with that of 28 surgically resected adrenal glands with cortical adenomas. The mean combined weight of adrenal glands was 11.8 g (range = 5.8 g to 19.9 g). The left adrenal gland was often heavier than the right (mean weight = 6.1 g and 5.7 g respectively) and with a greater longitudinal length than the right (mean length = 5.2 cm and 4.8 cm respectively). Adrenal glands were often heavier in male, younger age group (less than 60-yr-old) and patients with history of hypertension or lung cancers. In comparison, the mean weight of right adrenal gland with cortical adenoma was 11.7 g (range = 6 g to 26 g) and that of left adrenal gland with cortical adenoma was 9.4 g (range = 4.6 g to 25 g). This is the first study in the English literature that provides data on the weight of normal adrenal glands in a solely Chinese population. Adrenal weight may be affected by patients' gender, age, laterality of adrenal gland and presence of systemic disease.

An unusual case of double tuberculous broncho-oesophageal fistulas in an adult

Broncho-oesophageal fistula associated with tuberculosis is rarely reported in the literature and has not been reported in Hong Kong. We describe a 30-year-old Chinese human immunodeficiency virus (HIV)-negative man with double tuberculous broncho-oesophageal fistulas proven by histology. Constitutional symptoms of active tuberculosis were absent and chest radiograph did not show an obvious lung lesion. Our case shows that broncho-oesophageal fistula can be the sole manifestation of active tuberculosis and that the diagnosis should be suspected in patients who are seen with chronic respiratory symptoms in areas where the prevalence of tuberculosis is high.

Is it safe to reuse disposable laparoscopic trocars? An in vitro testing

BACKGROUND

The reuse of disposable laparoscopic instruments carries a risk of transmitting infectious diseases such as hepatitis and HIV. We evaluated the safety of reusing disposable trocars by studying the chances of their harboring infectious viruses after resterilization in an in vitro setting.

METHODS

Disposable laparoscopic trocars were exposed to horse blood contaminated with high or low viral concentrations of herpes simplex virus type 1 (HSV1) and attenuated polio virus type 1 at room temperature for 2 h. HSV1 was chosen as the surrogate for lipid viruses that include hepatitis B and HIV virus; polio virus represented the nonlipid viruses that cause infections in immunocompromised patients and are more resistant to sterilization. The trocars were subsequently cleaned and resterilized by low-temperature steam and formaldehyde at 80 degrees C for 3 h. Viral cultures were then repeated after sterilization.

RESULTS

A cytopathic effect (CPE) was demonstrated at both concentrations for HSV1 in all trocars before but not after sterilization. For the polio virus, CPE was evident in 50% of the trocars (two of four) exposed to high viral concentration after sterilization.

CONCLUSION

Disposable trocars are difficult to resterilize and may harbor infectious viruses after their initial use. Therefore, the reuse of disposable trocars in laparoscopic surgery cannot be recommended.

Pulmonary sclerosing hemangioma consistently expresses thyroid transcription factor-1 (TTF-1): a new clue to its histogenesis

The histogenesis of pulmonary sclerosing hemangioma has remained controversial despite extensive studies by many investigators. The availability of an antibody to thyroid transcription factor-1 (TTF-1), which is expressed in type II pneumocytes and Clara cells, has prompted us to readdress this issue. Sixteen cases were immunostained with a panel of antibodies including TTF-1. The patients were predominantly women with an age range of 30 to 73 years (mean, 52 yrs). All tumors were solitary. The single male patient showed regional lymph node metastases, an unusual occurrence reported only once in the literature. All cases exhibited the classic histologic features, with variegated patterns. TTF-1 expression was observed in both the surface lining cells and the pale polygonal cells. The surface lining cells were epithelial membrane antigen (EMA)+ cytokeratin+ surfactant apoprotein A+, whereas the polygonal cells were EMA+ cytokeratin- surfactant apoprotein A-. The neuroendocrine markers synaptophysin and chromogranin were both negative. The metastatic deposits in the lymph nodes comprised only polygonal cells and exhibited an EMA+ cytokeratin- surfactant apoprotein A- TTF- 1+ immunophenotype. These results suggest that pulmonary sclerosing hemangioma is an epithelial neoplasm derived from primitive respiratory epithelium or incompletely differentiated type II pneumocyte or Clara cell.

Functional complementation of BLNK by SLP-76 and LAT linker proteins

Recent studies have demonstrated a requirement for the SLP-76 (SH2 domain-containing leukocyte protein of 76 kDa) and LAT (linker for activation of T cells) adaptor/linker proteins in T cell antigen receptor activation and T cell development as well as the BLNK (B cell linker) linker protein in B cell antigen receptor (BCR) signal transduction and B cell development. Whereas the SLP-76 and LAT adaptor proteins are expressed in T, natural killer, and myeloid cells and platelets, BLNK is preferentially expressed in B cells and monocytes. Although BLNK is structurally homologous to SLP-76, BLNK interacts with a variety of downstream signaling proteins that interact directly with both SLP-76 and LAT. Here, we demonstrate that neither SLP-76 nor LAT alone is sufficient to restore the signaling deficits observed in BLNK-deficient B cells. Conversely, the coexpression of SLP-76 and LAT together restored BCR-inducible calcium responses as well as activation of all three families of mitogen-activated protein kinases. Together, these data suggest functional complementation of SLP-76 and LAT in T cell antigen receptor function with BLNK in BCR function.

Transhepatic balloon sphincteroplasty for bile duct stones after total gastrectomy

Previous upper gastrointestinal surgery with the construction of a Roux-en-Y jejunal loop may prevent endoscopic access to the second part of the duodenum. We report a technique of percutaneous transhepatic balloon sphincteroplasty to facilitate the removal of common bile duct (CBD) stones. A 67-year-old woman presented with a 1-week history of right upper quadrant abdominal pain and fever, deranged liver function tests, and dilated intrahepatic ducts. The patient had previously had a total gastrectomy with Roux-en-Y reconstruction for a high-grade B-cell lymphoma of the stomach. Peroral endoscopic access to the biliary tree was unsuccessful. Percutaneous transhepatic cholangiography confirmed the presence of CBD stones. Over a period of 8 weeks, sequential dilatation of the percutaneous tract was undertaken. After a further 2 weeks, percutaneous choledochoscopy was performed. Several large stones were visualized and then fragmented. The choledochoscope would not pass through to the duodenum due to postinflammatory stenosis of the papilla, so the papilla was dilated with an endoscopic balloon. The remaining fragments were pushed through, and the duct was thoroughly irrigated with saline. Repeat cholangiography confirmed a clear CBD. Balloon catheter sphincteroplasty and biliary stone extrusion into the duodenum is a novel technique that enabled clearance of the CBD in an elderly patient who may otherwise have required open surgical exploration.

Involvement of LAT, Gads, and Grb2 in compartmentation of SLP-76 to the plasma membrane

B cell linker protein (BLNK) and Src homology 2 domain-containing leukocyte protein of 76 kD (SLP-76) are adaptor proteins required for B cell receptor (BCR) and T cell receptor function, respectively. Here, we show that expression of SLP-76 cannot reconstitute BCR function in Zap-70(+)BLNK(-) B cells. This could be attributable to inability of SLP-76 to be recruited into glycolipid-enriched microdomains (GEMs) after antigen receptor cross-linking. Supporting this idea, the BCR function was restored when a membrane-associated SLP-76 chimera was enforcedly localized to GEMs. Moreover, we demonstrate that addition of both linker for activation of T cells (LAT) and Grb2-related adaptor downstream of Shc (Gads) to SLP-76 allow SLP-76 to be recruited into GEMs, whereby the BCR function is reconstituted. The Gads function was able to be replaced by overexpression of Grb2. In contrast to SLP-76, BLNK did not require Grb2 families for its recruitment to GEMs. Hence, these data suggest a functional overlap between BLNK and SLP-76, while emphasizing the difference in requirement for additional adaptor molecules in their targeting to GEMs.

Neck ultrasound in staging squamous oesophageal carcinoma - a high yield technique

AIM

This study evaluates the use of neck ultrasound in staging squamous oesophageal carcinoma.

MATERIALS AND METHODS

A prospective analysis of the clinical, neck ultrasound (US) and thoraco-abdominal computed tomography (CT) findings in 121 patients with squamous oesophageal carcinoma at presentation was performed. The relationship between malignant neck nodes, mediastinal and abdominal adenopathy, location and size of the primary tumour was analysed.

RESULTS

Ten of 121 patients (8%) had clinically palpable neck nodes which were deemed malignant in six (5%) following US and fine-needle aspiration for cytology. Of those 111 patients with no palpable neck nodes, 31 (28%) had malignant nodes shown on US. The more cephalad the location of the primary tumour, the higher the frequency of malignant neck nodes which were found in 80%, 52%, 29% and 9% of cervical, upper thoracic, mid-thoracic and lower thoracic oesophageal tumours, respectively. Eleven (29%) of the 38 patients with malignant neck nodes shown on US had no CT evidence of additional adenopathy in the mediastinum or upper abdomen. Neck US altered TNM staging in 22/121 (18%) patients at presentation.

CONCLUSION

Neck US frequently detects clinically impalpable metastatic nodes leading to altered TNM staging in patients with squamous oesophageal carcinoma. We advocate its routine use when staging squamous oesophageal carcinoma.

Effect of intravenous omeprazole on recurrent bleeding after endoscopic treatment of bleeding peptic ulcers

BACKGROUND

After endoscopic treatment of bleeding peptic ulcers, bleeding recurs in 15 to 20 percent of patients.

METHODS

We assessed whether the use of a high dose of a proton-pump inhibitor would reduce the frequency of recurrent bleeding after endoscopic treatment of bleeding peptic ulcers. Patients with actively bleeding ulcers or ulcers with nonbleeding visible vessels were treated with an epinephrine injection followed by thermocoagulation. After hemostasis had been achieved, they were randomly assigned in a double-blind fashion to receive omeprazole (given as a bolus intravenous injection of 80 mg followed by an infusion of 8 mg per hour for 72 hours) or placebo. After the infusion, all patients were given 20 mg of omeprazole orally per day for eight weeks. The primary end point was recurrent bleeding within 30 days after endoscopy.

RESULTS

We enrolled 240 patients, 120 in each group. Bleeding recurred within 30 days in 8 patients (6.7 percent) in the omeprazole group, as compared with 27 (22.5 percent) in the placebo group (hazard ratio, 3.9; 95 percent confidence interval, 1.7 to 9.0). Most episodes of recurrent bleeding occurred during the first three days, which made up the infusion period (5 in the omeprazole group and 24 in the placebo group, P<0.001). Three patients in the omeprazole group and nine in the placebo group underwent surgery (P=0.14). Five patients (4.2 percent) in the omeprazole group and 12 (10 percent) in the placebo group died within 30 days after endoscopy (P=0.13).

CONCLUSIONS

After endoscopic treatment of bleeding peptic ulcers, a high-dose infusion of omeprazole substantially reduces the risk of recurrent bleeding.

Odontogenic keratocysts: a clinicopathological study in Hong Kong Chinese

OBJECTIVE

To analyze the clinicopathological features of odontogenic keratocysts in Chinese patients.

STUDY DESIGN

Retrospective analysis.

METHODS

The clinical records and pathological features of odontogenic keratocysts from 69 ethnic Hong Kong Chinese patients (40 male and 29 female patients) were reviewed.

RESULTS

The male-to-female ratio was 1.4:1; patient age ranged from 6 to 69 years with a modal peak in the third decade (mean age, 28 y; median age, 23 y). The preoperative diagnosis was correct in 78% of the cases and the most common misdiagnosis was dentigerous cyst. Sixty-two percent of the cysts were found in the mandible, and 38% in the maxilla. Multiple cysts occurred in 9% (including three cases of basal cell nevus syndrome). Histologically, 82.6%, 5.8%, and 11.6% of the cysts were parakeratinized, orthokeratinized, and mixed types, respectively. Patients with multiple cysts all showed parakeratinization. The majority (80%) of the cysts were lined by epithelia with a thickness of five to eight cells. Surface corrugation, subepithelial split, suprabasal split, satellite microcysts, epithelial islands, significant inflammation, hyaline bodies, and dystrophic calcification were present in 10%, 81%, 25%, 38%, 42%, 46%, 7%, and 10% of cysts, respectively. The overall recurrence rate was 240%, with a median time for first recurrence of 19 months (range, 1 mo-22 y). Cysts showing orthokeratinization or mixed types of keratinization recurred less often than parakeratinized cysts. Recurrence had the same type of keratinization as the initial cyst.

CONCLUSIONS

Pathological examination of keratocysts is important, because keratocysts have different clinicopathological features and carry a risk for clinical misdiagnosis.

Regulation of B cell function by linker proteins

Studies over the past few years have demonstrated the importance of linker or adaptor proteins in the signaling pathways activated by the B cell antigen-receptor. These proteins direct the appropriate subcellular localization of enzymatic complexes, amplify signaling pathways and integrate the functions of distinct signaling complexes. Many of the recently identified linker proteins function through these distinct mechanisms to upregulate the BCR signaling pathway. In addition, linker proteins facilitate the influences of co-receptors that augment or dampen the BCR signaling pathway.

Diagnostic and therapeutic fistuloscopy: an adjuvant management in postoperative fistulas and abscesses after upper gastrointestinal surgery

BACKGROUND AND STUDY AIMS

Postoperative fistulas and abscesses pose difficult management problems. We report our experience in the use of fistuloscopy in postoperative fistulas and abscesses after upper gastrointestinal surgery.

PATIENTS AND METHODS

From June 1993 to January 1997, nine patients (seven men, two women; mean age 65) with postoperative fistulas and abscesses were treated with therapeutic fistuloscopy. Diagnostic fistuloscopy was carried out using a 5-mm choledochoscope under fluoroscopic guidance. Therapeutic procedures included mechanical debridement, irrigation, and sealing of fistula with fibrin sealant and gelatin sponge.

RESULTS

The patients were suffering from duodenal stump fistula (three cases), gastrojejunostomy dehiscence after gastrectomy (three cases), gastropleurocutaneous fistula (two cases), and subphrenic abscesses (two cases). Fistuloscopy was performed 4-19 days (mean 12 days) after the diagnosis of the fistula. The median number of sessions required was 2 (range 1-4). The average daily fistula output prior to fistuloscopy was 154 ml (range 30-560 ml), and all fistulas healed in an average of 18.7 days (range 2-46 days) after index fistuloscopy. No procedure-related complications occurred. The mean hospital stay was 61 days. During a mean follow-up period of 12 months, no recurrent abscesses or fistulas developed.

CONCLUSIONS

Fistuloscopy provides a new means of managing patients with postoperative fistula and abscess formation.

Incidence and pathology of primary brain lymphoma in Hong Kong Chinese patients

Primary brain lymphoma (PBL) is an uncommon extranodal lymphoma. Its incidence is rapidly increasing in both immunocompromised and immunocompetent patients in Western countries. Eighteen cases of PBL were identified during a 16-year period among HIV negative patients in Queen Mary Hospital, Hong Kong. One case of post-transplantation lymphoproliferative disease (PTLD) was positive for Epstein Barr virus (EBV) encoded RNA (EBER) by in situ hybridization. All the remaining 17 immunocompetent cases were classified as diffuse large B-cell lymphoma, except for one case of Burkitt's lymphoma. EBER expression was negative in all 13 cases tested. Immunostaining for bcl-2 and bcl-6 was positive in 8/11 and 6/11 cases tested, with heterogeneous combination of expression and intensity. The incidence rate of PBL in immunocompetent patients was stable at 1.03 per million per year. The incidence of PBL in post transplantation (0.16%) and HIV related setting (0.29%) is also low in Chinese. PBL in Chinese patients is almost uniformly represented by EBV negative, diffuse large B-cell lymphoma, confined to the brain. However, the molecular pathogenesis may be heterogeneous.

Membrane cofactor protein (MCP; CD46): isoform-specific tyrosine phosphorylation

Membrane cofactor protein (MCP; CD46) is a widely expressed type 1 transmembrane glycoprotein that inhibits complement activation on host cells. It also is a receptor for several pathogens including measles virus, Streptococcus pyogenes, Neisseria gonorrhea, and Neisseria meningitidis. That MCP may have signaling capability was suggested by its microbial interactions. That is, binding of MCP on human monocytes by measles virus hemagglutinin or cross-linking by an anti-MCP Ab resulted in IL-12 down-regulation, while binding to MCP by Neisseria on epithelial cells produced a calcium flux. Through alternative splicing, MCP is expressed on most cells with two distinct cytoplasmic tails of 16 (CYT-1) or 23 (CYT-2) amino acids. These play pivotal roles in intracellular precursor processing and basolateral localization. We investigated the putative signal transduction pathway mediated by MCP and demonstrate that CYT-2, but not CYT-1, is phosphorylated on tyrosine. We examined MCP tail peptides and performed Ab cross-linking experiments on several human cell lines and MCP isoform transfectants. We found an MCP peptide of CYT-2 was phosphorylated by a src kinase system. Western blots of the cells lines demonstrated that cells bearing CYT-2 were also phosphorylated on tyrosine. Additionally, we provide genetic and biochemical evidence that the src family of kinases is responsible for the latter phosphorylation events. In particular, the src kinase, Lck, is required for phosphorylation of MCP in the Jurkat T cell line. Taken together, these studies suggest a src family-dependent pathway for signaling through MCP.

Adapter proteins SLP-76 and BLNK both are expressed by murine macrophages and are linked to signaling via Fcgamma receptors I and II/III

The SLP-76 (Src homology 2 domain-containing leukocyte protein of 76 kDa) adapter protein is expressed in T cells and myeloid cells, whereas its homologue BLNK (B cell linker protein) is expressed in B cells. SLP-76 and BLNK link immunoreceptor tyrosine-based activation motif-containing receptors to signaling molecules that include phospholipase C-gamma, mitogen-activated protein kinases, and the GTPases Ras and Rho. SLP-76 plays a critical role in T cell receptor, FcvarepsilonRI and gpVI collagen receptor signaling, and participates in signaling via FcgammaR and killer cell inhibitory receptors. BLNK plays a critical role in B cell receptor signaling. We show that murine bone marrow-derived macrophages express both SLP-76 and BLNK. Selective ligation of FcgammaRI and FcgammaRII/III resulted in tyrosine phosphorylation of both SLP-76 and BLNK. SLP-76(-/-) bone marrow-derived macrophages display FcgammaR-mediated tyrosine phosphorylation of Syk, phospholipase C-gamma2, and extracellular signal regulated kinases 1 and 2, and normal FcgammaR-dependent phagocytosis. These data suggest that both SLP-76 and BLNK are coupled to FcgammaR signaling in murine macrophages.

Eradication of Helicobacter pylori prevents recurrence of ulcer after simple closure of duodenal ulcer perforation: randomized controlled trial

OBJECTIVE

In this randomized trial, the authors sought to determine whether eradication of Helicobacter pylori could reduce the risk of ulcer recurrence after simple closure of perforated duodenal ulcer.

BACKGROUND DATA

Immediate acid-reduction surgery has been strongly advocated for perforated duodenal ulcers because of the high incidence of ulcer relapse after simple patch repair. Although H. pylori eradication is now the standard treatment of uncomplicated and bleeding peptic ulcers, its role in perforation remains controversial. Recently a high prevalence of H. pylori infection has been reported in patients with perforations of duodenal ulcer. It is unclear whether eradication of the bacterium confers prolonged ulcer remission after simple repair and hence obviates the need for an immediate definitive operation.

METHODS

Of 129 patients with perforated duodenal ulcers, 104 (81%) were shown to be infected by H. pylori. Ninety-nine H. pylori-positive patients were randomized to receive either a course of quadruple anti-helicobacter therapy or a 4-week course of omeprazole alone. Follow-up endoscopy was performed 8 weeks, 16 weeks (if the ulcer did not heal at 8 weeks), and 1 year after hospital discharge for surveillance of ulcer healing and determination of H. pylori status. The endpoints were initial ulcer healing and ulcer relapse rate after 1 year.

RESULTS

Fifty-one patients were assigned to the anti-Helicobacter therapy and 48 to omeprazole alone. Nine patients did not undergo the first follow-up endoscopy. Of the 90 patients who did undergo follow-up endoscopy, 43 of the 44 patients in the anti-Helicobacter group and 8 of the 46 in the omeprazole alone group had H. pylori eradicated; initial ulcer healing rates were similar in the two groups (82% vs. 87%). After 1 year, ulcer relapse was significantly less common in patients treated with anti-Helicobacter therapy than in those who received omeprazole alone (4.8% vs. 38.1%).

CONCLUSIONS

Eradication of H. pylori prevents ulcer recurrence in patients with H. pylori-associated perforated duodenal ulcers. Immediate acid-reduction surgery in the presence of generalized peritonitis is unnecessary.

Cytokeratin-Positive Malignant Tumors With Reticulum Cell Morphology

Cytokeratin-positive interstitial reticulum cells (CIRCs) have been described as a subset of fibroblastic reticulum cells (FBRCs) normally found in lymph nodes, the spleen, and tonsils. Although tumors derived form other reticulum (dendritic) cells, specifically follicular dendritic cells, interdigitating dendritic cells, and cytokeratin-negative FBRCs, have been well documented and are now accepted, this is not the case for tumors of CIRCs. A possible reason for this failure is the difficulty in distinguishing them from other tumors, particularly carcinoma. We report three cases of cytokeratin-positive malignant tumors with a reticulum cell morphology: two located in the mediastinum and one in the soft tissue in the proximal forearm. All cases coexpressed vimentin, and one case coexpressed smooth muscle actin and desmin, resulting in a phenotype similar to that of some normal CIRCs. Although metastatic carcinoma from an occult or regressed primary tumor cannot be excluded completely, we raise the possibility of a CIRC origin for these cases.

Clinical Utility of FDG-PET in Detecting Head and Neck Tumors. A Comparison of Diagnostic Methods and Modalities

Positron emission tomography (PET) using F-18-fluoro-2-deoxy-d-glucose(F-18-FDG) is gaining acceptance as a useful imaging method for head and neck tumors. Results of 59 PET scans done on 45 patients with head and neck tumors were evaluated retrospectively. Thirty-six patients had prior treatment consisting of surgery, radiation therapy, chemotherapy, or a combination of these modalities. PET results were compared to computed tomography and magnetic resonance imaging results and validated by histologic findings or survival. PET identified 36 out of 37 tumors (sensitivity 97%) and 18 of 22 benign processes (specificity 82%). Tumor was ruled out in 18 out of 19 patients. For CT, the sensitivity was 80% (20/25) and specificity was 31% (4/13). FDG-PET facilitates differentiation of recurrent head and neck tumors from treatment related changes sometimes difficult to characterize by CT or MRI and may have a significant impact on the management of patients reducing morbidity and costs.

Parathyroid adenomas with pronounced lymphocytic infiltration: no evidence of autoimmune pathogenesis

Pronounced lymphocytic infiltration in parathyroid adenoma is rare, with only six previously reported cases in the literature. The aims of this study are to review the features and investigate the pathogenesis of this rare entity. Two solitary parathyroid adenomas having this feature were reported, and the clinicopathologic features of all the documented cases were reviewed. The nature of the lymphoid infiltrate and the presence of Epstein-Barr virus (EBV) were analyzed to unveil the pathogenesis of this infiltrate. One adenoma was found in a 70-yr-old woman with primary hyperparathyroidism and valvular heart disease. The other was an autopsy finding in a 48-yr-old man who had presented with hypercalcemic crisis. The lymphoid cell population within the tumors was composed of B cells and different subsets of T cells. EBV was not detected in the infiltrates. The lymphocytic infiltrate in parathyroid adenoma is an unusual histologic entity. Its presence is unlikely to imply an autoimmune disorder. We hypothesize that the lesion may be a result of local tissue response to parathyroid adenoma.

Requirement for B cell linker protein (BLNK) in B cell development

Linker proteins function as molecular scaffolds to localize enzymes with substrates. In B cells, B cell linker protein (BLNK) links the B cell receptor (BCR)-activated Syk kinase to the phosphoinositide and mitogen-activated kinase pathways. To examine the in vivo role of BLNK, mice deficient in BLNK were generated. B cell development in BLNK-/- mice was blocked at the transition from B220+CD43+ progenitor B to B220+CD43- precursor B cells. Only a small percentage of immunoglobulin M++ (IgM++), but not mature IgMloIgDhi, B cells were detected in the periphery. Hence, BLNK is an essential component of BCR signaling pathways and is required to promote B cell development.

An essential role for BLNK in human B cell development

The signal transduction events that control the progenitor B cell (pro-B cell) to precursor B cell (pre-B cell) transition have not been well delineated. In evaluating patients with absent B cells, a male with a homozygous splice defect in the cytoplasmic adapter protein BLNK (B cell linker protein) was identified. Although this patient had normal numbers of pro-B cells, he had no pre-B cells or mature B cells, indicating that BLNK plays a critical role in orchestrating the pro-B cell to pre-B cell transition. The immune system and overall growth and development were otherwise normal in this patient, suggesting that BLNK function is highly specific.