Importance of immunoglobulin isotype in human antibody-dependent, cell-mediated cytotoxicity directed by murine monoclonal antibodies.

Using the fluorescence activated cell sorter to select rare IgG2a- and IgG2b-producing variants, we developed switch variant families of hybridomas from IgG1-producing hybridomas, ME1 and MA2.1. The IgG2a and IgG2b antibodies produced by such switch variants have the same binding activities for HLA as the IgG1 antibodies produced by the parent hybridomas. Using these antibodies, we directly compared the IgG1, IgG2a, and IgG2b murine Ig isotypes for their capacities to direct human peripheral blood lymphocytes (PBL) in antibody-dependent cell-mediated cytotoxicity (ADCC) against a B lymphoblastoid cell line. We demonstrate that, for antibodies of identical binding affinity and specificity, the murine IgG2a isotype is the most effective in directing ADCC by human effector cells. The murine IgG2b directs intermediate levels of ADCC activity while IgG1 is inactive. We identified the effector cells in human PBL that mediate IgG2a or IgG2b ADCC as nonadherent killer (K) cells. These cells express the C3bi receptor and have cytolytic activity which is specifically blocked by a monoclonal antibody (anti-Leu-11a) that binds the Fc receptor (FcR) of such cells. Finally, FcR-bearing K cells bind to target cell-bound, rather than free, IgG2a or IgG2b molecules.

Stoichiometry of the T cell antigen receptor (TCR) complex: each TCR/CD3 complex contains one TCR alpha, one TCR beta, and two CD3 epsilon chains.

The stoichiometry of the subunits that comprise the T cell antigen receptor (TCR) complex is not completely known. In particular, it is uncertain whether TCR alpha and TCR beta proteins are present in the TCR complex as one or multiple heterodimeric pairs. In this study we have used mice transgenic for two different TCR alpha and two different TCR beta proteins to determine the number of TCR alpha and TCR beta chains in a single TCR complex. Individual thymocytes and splenic T cells from double TCR transgenic mice simultaneously expressed all four transgenic TCR proteins on their surfaces. Because the individual TCR alpha and individual TCR beta proteins were biochemically distinguishable, we were able to examine association among the transgenic TCR products. We found that each TCR alpha chain paired with each TCR beta chain, but that each TCR complex contained only one TCR alpha and one TCR beta protein. Furthermore, quantitative immunofluorescence revealed that T cells expressed twice as many CD3 epsilon as TCR beta proteins. These findings demonstrate that there are precisely one TCR alpha, one TCR beta, and two CD3 epsilon chains in each TCR/CD3 complex expressed on the surfaces of both thymocytes and mature T cells.

T cell receptor (TCR)-induced death of immature CD4+CD8+ thymocytes by two distinct mechanisms differing in their requirement for CD28 costimulation: implications for negative selection in the thymus.

Negative selection is the process by which the developing lymphocyte receptor repertoire rids itself of autoreactive specificities. One mechanism of negative selection in developing T cells is the induction of apoptosis in immature CD4+CD8+ (DP) thymocytes, referred to as clonal deletion. Clonal deletion is necessarily T cell receptor (TCR) specific, but TCR signals alone are not lethal to purified DP thymocytes. Here, we identify two distinct mechanisms by which TCR-specific death of DP thymocytes can be induced. One mechanism requires simultaneous TCR and costimulatory signals initiated by CD28. The other mechanism is initiated by TCR signals in the absence of simultaneous costimulatory signals and is mediated by subsequent interaction with antigen-presenting cells. We propose that these mechanisms represent two distinct clonal deletion strategies that are differentially implemented during development depending on whether immature thymocytes encounter antigen in the thymic cortex or thymic medulla.

Lineage commitment in the thymus: only the most differentiated (TCRhibcl-2hi) subset of CD4+CD8+ thymocytes has selectively terminated CD4 or CD8 synthesis.

Lineage commitment is a developmental process by which individual CD4+CD8+ (double positive, DP) thymocytes make a decision to differentiate into either CD4+ or CD8+ T cells. However, the molecular event(s) that defines lineage commitment is controversial. We have previously proposed that lineage commitment in DP thymocytes can be molecularly defined as the selective termination of CD4 or CD8 coreceptor synthesis. The present study supports such a molecular definition by showing that termination of either CD4 or CD8 synthesis is a highly regulated event that is only evident within the most differentiated DP subset (CD5hiCD69hiTCRhibcl-2hi). In fact, essentially all cells within this DP subset actively synthesize only one coreceptor molecule. In addition, the present results identify three distinct sub-populations of DP thymocytes that define the developmental progression of the lineage commitment process and demonstrate that lineage commitment is coincident with upregulation of TCR and bcl-2. Thus, this study supports a molecular definition of lineage commitment and uniquely identifies TCRhibcl-2hi DP thymocytes as cells that are already committed to either the CD4 or CD8 T cell lineage.

Negative selection of CD4+CD8+ thymocytes by T cell receptor-induced apoptosis requires a costimulatory signal that can be provided by CD28.

CD4+CD8+ thymocytes expressing self-reactive T cell antigen receptors (TCR) are deleted in the thymus as a consequence of TCR/self-antigen/major histocompatibility complex interactions. However, the signals that are necessary to initiate clonal deletion have not yet been clarified. Here we demonstrate that TCR engagement does not efficiently induce apoptosis of CD4+CD8+ thymocytes, although it generates signals that increase expression of CD5, a thymocyte differentiation marker. In fact, TCR signals fail to induce thymocyte apoptosis even when augmented by simultaneous engagement with CD4 or lymphocyte function 1-associated molecules. In marked contrast, signals generated by engagement of both TCR and the costimulatory molecule CD28 potently induce apoptosis of CD4+CD8+ thymocytes. Thus, the present results define a requirement for both TCR and costimulatory signals for thymocyte apoptosis and identify CD28 as one molecule that is capable of providing the necessary costimulus. These results provide a molecular basis for differences among cell types in their ability to mediate negative selection of developing thymocytes.

Early molecular events induced by T cell receptor (TCR) signaling in immature CD4+ CD8+ thymocytes: increased synthesis of TCR-alpha protein is an early response to TCR signaling that compensates for TCR-alpha instability, improves TCR assembly, and parallels other indicators of positive selection.

Differentiation of immature CD4+ CD8+ thymocytes into mature CD4+ or CD8+ T cells occurs within the thymus and is dependent upon expression of antigen receptor complexes (T cell receptor [TCR]) containing clonotypic alpha/beta proteins. We have recently found that CD4+ CD8+ thymocytes express low levels of surface TCR because of limitations placed on TCR assembly by the instability of nascent TCR-alpha proteins within the endoplasmic reticulum (ER) of immature thymocytes. Because TCR-alpha/beta expression increases during development, a molecular mechanism must exist for increasing the number of assembled TCR complexes present in immature CD4+ CD8+ thymocytes that have been signaled to differentiate into mature T cells, although no such mechanism has yet been described. In the current report we have examined the molecular consequences of intracellular signals generated by engagement of surface TCR complexes on immature CD4+ CD8+ thymocytes. Isolated TCR engagement generated signals that increased TCR-alpha RNA levels and increased synthesis of TCR-alpha proteins, which, in turn, significantly increased assembly of complete TCR-alpha/beta complexes in CD4+ CD8+ thymocytes. Increased TCR-alpha protein levels in TCR-signaled CD4+ CD8+ thymocytes was the result of increased synthesis and not increased stability of TCR-alpha proteins, indicating that TCR engagement compensates for, but does not correct, the inherent instability of TCR-alpha proteins in the ER of immature thymocytes. Consistent with the delivery by TCR engagement of a positive selection signal, TCR engagement also increased CD5 expression, decreased RAG-1 expression, and decreased CD4/CD8 coreceptor expression in immature CD4+ CD8+ thymocytes. These data identify amplified TCR-alpha expression as an initial response of immature CD4+ CD8+ thymocytes to TCR-mediated positive selection signals and provide a molecular basis for increased surface TCR density on developing thymocytes undergoing selection events within the thymus.

Identification of CD8 as a peanut agglutinin (PNA) receptor molecule on immature thymocytes.

Differentiation of most T lymphocytes occurs within the thymus and is characterized by variable expression of CD4/CD8 coreceptor molecules, increased surface density of T cell antigen receptor (TCR) alpha beta proteins, and decreased expression of glycan chains recognized by the galactose-specific lectin peanut agglutinin (PNA). Although appreciated for several decades that PNA agglutination is useful for the physical separation of immature and mature thymocyte sub-populations, the identity of specific PNA-binding glycoproteins expressed on immature thymocytes remains to be determined. In the current report, we studied the expression of PNA-specific glycans on immature and mature T cells and used lectin affinity chromatography and immunoprecipitation techniques to characterize PNA-binding glycoproteins on thymocytes. Our data demonstrate that PNA-specific glycans are localized on a relatively small subset of thymocyte surface proteins, several of which were specifically identified, including CD43, CD45, and suprisingly, CD8 molecules. CD8 alpha and CD8 alpha' proteins bound to PNA in the absence of CD8 beta expression showing that O-glycans on CD8 beta glycoproteins are not necessary for PNA binding and that glycosylation of CD8 alpha and CD8 alpha' proteins proceeds effectively in the absence of CD8 beta. Finally, we demonstrate that PNA binding of CD8 is developmentally regulated by sialic acid addition as CD8 proteins from mature T cells bound to PNA only after sialidase treatment. These studies identify CD8 as a PNA receptor molecule on immature thymocytes and show that PNA binding of CD8 on immature and mature T cells is developmentally regulated by sialic acid modification.

Receptor avidity and costimulation specify the intracellular Ca2+ signaling pattern in CD4(+)CD8(+) thymocytes.

Thymocyte maturation is governed by antigen-T cell receptor (TCR) affinity and the extent of TCR aggregation. Signals provided by coactivating molecules such as CD4 and CD28 also influence the fate of immature thymocytes. The mechanism by which differences in antigen-TCR avidity encode unique maturational responses of lymphocytes and the influence of coactivating molecules on these signaling processes is not fully understood. To better understand the role of a key second messenger, calcium, in governing thymocyte maturation, we measured the intracellular free calcium concentration ([Ca2+]i) response to changes in TCR avidity and costimulation. We found that TCR stimulation initiates either amplitude- or frequency-encoded [Ca2+]i changes depending on (a) the maturation state of stimulated thymocytes, (b) the avidity of TCR interactions, and (c) the participation of specific coactivating molecules. Calcium signaling within immature but not mature thymocytes could be modulated by the avidity of CD3/CD4 engagement. Low avidity interactions induced biphasic calcium responses, whereas high avidity engagement initiated oscillatory calcium changes. Notably, CD28 participation converted the calcium response to low avidity receptor engagement from a biphasic to oscillatory pattern. These data suggest that calcium plays a central role in encoding the nature of the TCR signal received by thymocytes and, consequently, a role in thymic selection.

Surface expression of a T cell receptor beta (TCR-beta) chain in the absence of TCR-alpha, -delta, and -gamma proteins.

The antigen receptor expressed by mature T cells has been described as a disulfide-linked alpha/beta or gamma/delta heterodimer noncovalently associated with CD3, a complex of transmembrane proteins that communicates signals from the T cell receptor (TCR) to the cell interior. Studies suggest that all component chains must assemble intracellularly before surface expression can be achieved. We described, however, a CD4+/CD8+ transformed murine thymocyte, KKF, that expresses surface TCR-beta chains in the absence of gamma, delta, and alpha proteins; these beta chains are only weakly associated with CD3-epsilon and CD3-zeta. Furthermore, KKF responds differently to stimulation through TCR-beta and CD3-epsilon, a functional dissociation that has been ascribed to a CD4+/CD8+ subpopulation of normal thymocytes. KKF's unique TCR structure may offer an explanation for the functional anomalies observed.

Separation of Notch1 promoted lineage commitment and expansion/transformation in developing T cells.

Notch1 signaling is required for T cell development. We have previously demonstrated that expression of a dominant active Notch1 (ICN1) transgene in hematopoietic stem cells (HSCs) leads to thymic-independent development of CD4(+)CD8(+) double-positive (DP) T cells in the bone marrow (BM). To understand the function of Notch1 in early stages of T cell development, we assessed the ability of ICN1 to induce extrathymic T lineage commitment in BM progenitors from mice that varied in their capacity to form a functional pre-T cell receptor (TCR). Whereas mice repopulated with ICN1 transduced HSCs from either recombinase deficient (Rag-2(-/)-) or Src homology 2 domain--containing leukocyte protein of 76 kD (SLP-76)(-/)- mice failed to develop DP BM cells, recipients of ICN1-transduced Rag-2(-/)- progenitors contained two novel BM cell populations indicative of pre-DP T cell development. These novel BM populations are characterized by their expression of CD3 epsilon and pre-T alpha mRNA and the surface proteins CD44 and CD25. In contrast, complementation of Rag-2(-/)- mice with a TCR beta transgene restored ICN1-induced DP development in the BM within 3 wk after BM transfer (BMT). At later time points, this population selectively and consistently gave rise to T cell leukemia. These findings demonstrate that Notch signaling directs T lineage commitment from multipotent progenitor cells; however, both expansion and leukemic transformation of this population are dependent on T cell-specific signals associated with development of DP thymocytes.

Primary non-Hodgkin's lymphoma of the CNS treated with BVAM or CHOD/BVAM chemotherapy before radiotherapy.

PURPOSE: To assess whether chemotherapy that includes drugs that cross the blood-brain barrier improves survival in primary CNS non-Hodgkin's lymphoma (PCNSL) when combined with radiotherapy. PATIENTS AND METHODS: Thirty-four patients, with no evidence of human immunodeficiency virus type 1 (HIV-1) infection, were treated with the related chemotherapy regimens of carmustine (BCNU), vincristine, cytarabine, and methotrexate (BVAM; 12 patients), cyclophosphamide, doxorubicin, vincristine, and dexamethasone (CHOD)/BVAM (17 patients) and intensified CHOD/BVAM (five patients) between 1986 and 1994. The median age was 60 years (range, 16 to 73) and 47% had a performance status of 3 or 4 (Eastern Cooperative Oncology Group [ECOG]/World Health Organization [WHO]). Ten patients were treated with BVAM chemotherapy between 1986 and 1989, and subsequently 17 patients were treated with CHOD/BVAM (cytarabine 3 g/m2). Twenty of these 27 patients received whole-brain radiotherapy (craniospinal in four). RESULTS: The complete response (CR) rate at the completion of chemotherapy was 63% for BVAM and 67% for CHOD/BVAM; more neutropenia occurred with CHOD/BVAM. The 5-year actuarial probability of survival of all 34 patients was 33% (95% confidence interval [CI], 14% to 52%), with so far only one recurrence after 2 years. Using multivariate analysis, age (P = .0005) and number of tumors at diagnosis (P = .0358) were prognostic factors. All five patients aged > or = 70 years died during or shortly after chemotherapy. Performance status was not an independent variable. CONCLUSION: The BVAM or CHOD/BVAM regimens can be delivered despite neutropenia without significant treatment delay or dose reduction in patients less than 70 years of age. Further intensification of this type of chemotherapy is probably not possible with patients of this age, many of whom have a poor performance status.

Clinical overlap between malaria and severe pneumonia in Africa children in hospital.

Data collected from 200 children admitted to a hospital on the Kenyan coast who met a broad definition of severe acute respiratory infection (ARI) indicated that simple clinical signs alone are unable absolutely to distinguish severe ARI and severe malaria. However, laboratory data showed that marked differences exist in the pathophysiology of unequivocal malaria and unequivocal ARI. Children in the former group had a higher mean oxygen saturation (97 vs. 94, P < 0.001), mean blood urea level (5.3 vs. 1.9 mmol/L, P < 0.001) and geometric mean lactate level (4.5 vs. 2.1 mmol/L, P < 0.001), and lower mean haemoglobin level (5.3 vs. 9.0 g/dL, P < 0.001) and base excess (-9.4 vs. -2.6, P < 0.001) than those in the latter group. Using these discriminatory variables it was estimated that up to 45% of children admitted with respiratory signs indicative of severe ARI probably had malaria as the primary diagnosis. Radiological examination supported this conclusion, indicating that pneumonia characterized by consolidation was uncommon in children with respiratory signs and a high malarial parasitaemia (> or = 10,000/microliters). There is no specific radiological sign of severe malaria. In practice, all children with respiratory signs warranting hospital admission in a malaria endemic area should be treated for both malaria and ARI unless blood film examination excludes malaria. In those with malaria and clinical evidence of acidosis, but no crackles, antibodies may be withheld while appropriate treatment for dehydration and anaemia is given. However, if clinical improvement is not rapid, antibiotics should be started.

Cerebral infarction after neuroendoscopic third ventriculostomy: case report.

OBJECTIVE AND IMPORTANCE: This case illustrates an unusual complication of neuroendoscopic third ventriculostomy. CLINICAL PRESENTATION: A 30-year-old man with established hydrocephalus was treated with neuroendoscopic third ventriculostomy during which bleeding occurred from a vessel deep in the floor of the third ventricle. He subsequently had a third nerve palsy and developed frontal lobe infarction. INTERVENTION: The complication was treated conservatively. The patient subsequently required shunting. CONCLUSION: The cause of the infarction is discussed. The general issue of complications of this procedure is explored with a call for more open reporting of such occurrences.

Subtemporal decompression: the treatment of noncompliant ventricle syndrome.

OBJECTIVE: To explore the effects of subtemporal decompression (STD) on the frequency of shunt revision and attendances with symptoms of raised intracranial pressure secondary to slit ventricle syndrome and slit ventricle-like syndrome. A renaming of these syndromes as noncompliant ventricle syndrome is suggested. METHOD: A retrospective review of the notes of all patients at our institution having STD from 1984 to 1997 was conducted. RESULTS: Twenty-eight patients underwent STD (age range, 4-31 yr). Thirty-two STD procedures were performed. The mean follow-up duration after STD was 5.3 years (range, 0-12 yr). The number of shunt revisions before STD was 128 (mean, 4.6 revisions; range, 0-30 revisions) and after STD was 28 (mean, 1.0 revision; range, 0-7 revisions). The number of attendances before STD was 213 (mean, 6.7 attendances; range, 1-31 attendances) and after STD was 57 (mean, 1.8 attendances; range, 0-10 attendances). Among 15 patients for whom there was sufficient clinical data, 7 revisions were required during the 3 years before STD and 22 during the 3 years after STD. There were 53 admissions during the 3 years before STD and 11 during the 3 years after STD. CONCLUSION: Although the overall incidence of shunt revision decreases, there is an early increase in the frequency of revision after STD. The number of admissions of patients with raised intracranial pressure symptoms reduces after STD, and we think that this is a more important factor in the consideration of this procedure than the number of recent revisions. We explore these arguments in this article.

Chronic extradural hematoma presenting 33 years after penetrating cranial trauma. Case report.

A case is reported of a 53-year-old normotensive man who presented, 33 years after a penetrating cranial war injury, with dysphasia of 10 month's duration, which proved to be due to a chronic extradural hematoma. The pathogenesis and symptomatology are discussed, and it is proposed that the lesion had been present since the original injury.

Some observations on aneurysms of the proximal internal carotid artery.

The author reports on 41 aneurysms of the proximal internal carotid artery (PICA) demonstrated in 36 patients with subarachnoid hemorrhage. The patients included a striking preponderance of women, and there was a high incidence of multiple aneurysms. In cases with multiple aneurysms the PICA aneurysm was usually found incidentally, a more distal aneurysm on the internal carotid artery being the source of hemorrhage. An infundibulum at the origin of a posterior communicating artery was unusually common in these patients. The origin of the ophthalmic artery is proposed as the angiographic landmark of the level at which the internal carotid artery penetrates the dura mater.

Multiple cerebral gummata. Case report.

The case of a patient with multiple small cerebral gummata presenting with severely raised intracranial pressure is reported. The diagnosis, which was quite unexpected, was based on positive serological tests for syphilis. Computerized tomography (CT) showed small enhancing lesions with intense cerebral edema. The patient was treated successfully with penicillin, and resolution of the lesions was observed on CT scanning over a 1-year period. The importance of "routine" serological testing is noted.

Listeria monocytogenes meningitis in a penicillin-allergic paediatric renal transplant patient.

Currently in many centres the extended spectrum cephalosporins (e.g. cefotaxime and ceftriaxone) are being used empirically for patients with suspected bacterial meningitis. We present a case of meningitis in a penicillin allergic paediatric renal transplant patient from whose cerebrospinal fluid (CSF) Listeria monocytogenes was cultured, despite four days of cefotaxime therapy. The patient was successfully treated with meropenem but required neuro-endoscopic intervention for hydrocephalus.

The intracranial complications of rhinosinusitis: can they be prevented?

OBJECTIVES/HYPOTHESIS: Reference textbooks on the intracranial complications of rhinosinusitis imply that many of the intracranial complications of rhinosinusitis can be prevented. We sought to examine whether or not this is true. STUDY DESIGN: A retrospective case series. METHODS: The study included 47 consecutive patients presenting with intracranial complications secondary to rhinosinusitis between 1992 to 1999 with a mean follow-up of 5 years and 1 month. RESULTS: The most common presenting symptoms of intracranial involvement were an altered mental state, headache, fever, seizure, vomiting, a unilateral weakness or hemiparesis, or a cranial nerve sign. These justify an urgent magnetic resonance imaging or computed tomography scan. The importance of imaging before a lumbar puncture cannot be overemphasized. Of particular note was the finding that 21 patients (45%) presented with a periorbital cellulitis or frontal swelling. Therefore, it does not follow that because a collection of pus presents anteriorly it precludes any intracranial involvement. More than half of our patients (55%) had visited their primary care physician with an upper respiratory tract infection and had been treated appropriately. Once any central symptoms or signs developed, there was little evidence of any significant delay in referral to our unit. Only six patients had a history of nasal disease, three having had recent sinus surgery and three having had nasal polyps. Nine patients had significant long-term morbidity, seven patients had epilepsy, one patient had dysphasia, and one patient had right arm weakness. The single death in our series was associated with a cavernous sinus thrombosis. CONCLUSIONS: The report emphasizes the need for surgeons to be alert to the diagnosis, particularly in patients with a periorbital abscess or frontal swelling. Sinus surgery has a role in obtaining pus for culture, as well as draining the sinus if it is in continuity with an intracranial collection. Intracranial infections secondary to rhinosinusitis occur sporadically and, although it appears that this cannot be prevented, early recognition and treatment are essential to reduce any subsequent morbidity or mortality.

Primary non-Hodgkin's lymphoma of the central nervous system: phase II study of chemotherapy (BVAM) prior to radiotherapy.

Ten patients were diagnosed as having primary non-Hodgkin's lymphoma of the central nervous system at University Hospital, Nottingham, between September 1986 and April 1989. None had clinical evidence of HIV-1 infection. All the patients started treatment with chemotherapy (BVAM), designed to cross the blood-brain barrier, followed by radiotherapy. Seven patients completed both chemotherapy and radiotherapy. Dose reduction during chemotherapy was necessary in three patients because of neutropenia. In two of the six patients with solitary tumours, complete resection was achieved surgically prior to treatment. Five of the remaining eight patients (63%) had radiological evidence of a complete response with chemotherapy. The other three patients had no response to chemotherapy but one had a complete response after radiotherapy. The two-year cause-specific survival of the 10 patients was 37%. Two of the three patients who had a postoperative performance status of 0 or 1 (ECOG/WHO) are alive and disease-free at 26 and 46 months from diagnosis. The median survival of the seven patients with a performance status of 2-4 was 10 months with two patients alive and disease-free at 19 and 26 months. The two-year cause-specific survival of these seven patients was 22%.