Regulation and chance in the ontogeny of B and T cell antigen receptor repertoires

The adaptive immune system has to economically generate a large array of T and B cell antigen receptors (T cell receptors [TCRs], B cell receptors [BCRs]) that eliminate both longstanding and novel antigens from the host while preventing the production of deleterious (e.g., autoreactive) antigen receptors. Our studies focus on the mechanisms that shape the development of these antigen receptor repertoies during human ontogeny. The key to BCR and TCR diversity is the third complementarity determining region (CDR3) of the variable domain, which in the immunoglobulin heavy chain and TCR β chain, is created by the junction between the variable, diversity, and joining gene segments. The CDR3 diversity is constrained by overrepresentation of gene segments and lack of N regions during the first trimester of gestation and then increases exponentially during ontogeny until it reaches adult levels months after birth. This process parallels, and may contribute to, the stepwise acquisition of the ability to respond to specific antigens. Recent studies indicate that maturation of the CDR 3 repertoire is not accelerated by premature exposition to extrauterine antigen and thus appears to follow a strictly developmentally regulated program whose pacemaker(s) is still unknown.     

Brain Parenchymal and Microvascular Amyloid in Alzheimer's Disease

Brains of patients with Alzheimer disease/senile dementia of Alzheimer type (AD/SDAT) develop a progressive accumulation of amyloid, which deposits primarily in the form of characteristic parenchyma!'plaques' (senile or neuritic plaques/SP's) and as mural deposits in the walls of capillaries and arterioles (cerebral amyloid angiopa-thy/CAA). A major component of this amyloid is a small and unique peptide composed of 39–43 amino acids, beta/A4, which is cleaved from a much larger precursor protein (APP) that has several isoforms. Brain amyloid can be detected in autopsy or biopsy brain tissue by classical, immunohistochemical and ultrastructural (including immuno-electron microscopic) methods of varying sensitivity and specificity. Beta/A4 amyloid deposition is remarkably variable (e.g. predominantly parenchyma! or vascular, or a mixture of parenchymal and vascular) among patients with AD/SDAT. Despite its abundance in the brains of AD/SDAT patients, the precise role of beta/A4 in the pathogenesis of the neurological deficit, neocortical atrophy and progressive synapse loss associated with AD/SDAT has yet to be determined. However, mutations in the gene that encodes APP are clearly associated with familial AD syndromes in which there is significant brain amyloid deposition. CAA, in addition to its association with AD/SDAT, can result in hemorrhagic and (possibly) ischemic forms of stroke. Work with recently developed transgenic mice which express large amounts of beta/A4 in the central nervous system is likely to elucidate mechanisms by which the protein is selectively deposited in the brain in a parenchymal or microvascular form, and how it contributes to the pathogenesis of neurodegeneration.     

Latency of multiple skin conductance responses in differential classical conditioning

Latencies of multiple skin conductance responses were observed in 30 female undergraduate students who participated in a classical differential conditioning experiment employing a 10 sec interstimulus interval (ISI). Responses occuring in both the early and late portions of the ISI were examined. Pairing delayed the onset of early responses and hastened the onset of responses occuring later in the ISI. Additionally, the latency changes observed did not appear to be an artifact of the higher response frequencies typically associated with conditioning.     

A novel regulation mechanism of DNA repair by damage-induced and RAD23-dependent stabilization of xeroderma pigmentosum group C protein

Primary DNA damage sensing in mammalian global genome nucleotide excision repair (GG-NER) is performed by the xeroderma pigmentosum group C (XPC)/HR23B protein complex. HR23B and HR23A are human homologs of the yeast ubiquitin-domain repair factor RAD23, the function of which is unknown. Knockout mice revealed that mHR23A and mHR23B have a fully redundant role in NER, and a partially redundant function in embryonic development. Inactivation of both genes causes embryonic lethality, but appeared still compatible with cellular viability. Analysis of mHR23A/B double-mutant cells showed that HR23 proteins function in NER by governing XPC stability via partial protection against proteasomal degradation. Interestingly, NER-type DNA damage further stabilizes XPC and thereby enhances repair. These findings resolve the primary function of RAD23 in repair and reveal a novel DNA-damage-dependent regulation mechanism of DNA repair in eukaryotes, which may be part of a more global damage-response circuitry.     

Comparison of complement fixation and hemagglutination inhibition assays for detecting antibody responses following influenza virus vaccination

Complement fixation (CF) was compared to hemagglutination inhibition (HI) as a method for identifying antibody responses to influenza virus vaccination. CF assays were performed at two different laboratories using paired (pre- and postvaccination) sera from 38 vaccinated laboratory employees; HI assays were performed at a third laboratory. As expected, most vaccinees (31/38 = 82%) responded to at least one of three influenza virus antigens as measured by HI. In contrast, only 21% (8/38) of vaccinees showed a response by CF at laboratory 1, and only 29% (11/38) showed a response by CF at laboratory 2. These findings indicate that due to low sensitivity, CF assays should not be used to assess the antibody response to influenza virus vaccination.     

Evaluation of a western blot method for the detection of Yersinia antibodies: evidence of serological cross-reactivity between Yersinia outer membrane proteins and Borrelia burgdorferi

Yersinia enterocolitica and Yersinia pseudotuberculosis have been identified as causative organisms of reactive arthritis in humans. We evaluated a Western blot assay which uses Yersinia outer membrane proteins as antigens for the detection of Yersinia antibodies as a replacement for the complement fixation (CF) assay. Clinical agreement, sensitivity, and specificity were determined by testing 19 positive and 21 negative serum samples by the CF assay, Western blot assay, and enzyme-linked immunosorbent assay (ELISA). The CF assay and ELISA were compared to the Western blot assay, which was the reference method used in this study. Sera with antibodies that could potentially cross-react with Yersinia were also tested by the Western blot assay. The agreement, sensitivity, and specificity of the CF method were 61%, 26%, and 95%, respectively; and those for the ELISA were 89%, 95%, and 82%, respectively. The prevalences of Yersinia antibodies in 50 healthy donors were 6% for immunoglobulin G (IgG), 2% for IgA, and 2% for IgM. Sera positive for Bartonella henselae, Brucella, Chlamydia pneumoniae, and Rickettsia rickettsii antibodies showed cross-reactivity by the Western blot assay. The highest cross-reactivity was observed with Borrelia burgdorferi; 5 of 11 (45%) specimens were cross-reactive by the IgM-specific assay. Overall, the Western blot assay performs acceptably and is more sensitive than the CF assay, warranting replacement of the CF assay in the laboratory. Due to the evidence of cross-reactivity, particularly with B. burgdorferi, which can cause an oligoarthritis similar to reactive arthritis, the diagnosis of reactive arthritis should be based on clinical findings and complete serologic analysis of the potential causative infectious pathogens.     

Site-specific homologous recombination mutagenesis in group B streptococci

We describe the use of suicide vectors to generate site-specific mutations in group B streptococcus. This is accomplished by cloning gene-specific sequences into a temperature sensitive plasmid and selecting for clones which have undergone homologous recombination. The recombinan clones can be easily isolated by selecting for clones which have retained the antibiotic resistance markers that are present on the vector or cloned into the gene-specific sequences. To confirm the fidelity of the recombination events, PCR analysis is performed on chromosomal DNA isolated from the recombinant clones. Using this strategy, we have generated site- specific insertions in several capsule genes and have found that these insertions occurred as expected and that the mutations result in loss of capsule expression. In this report, we specifically detail the construction of cpsB mutants by single and double cross-over recombination and demonstrate that the resulting strains are acapsular.     

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases.This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.     

Report of a child with aortic aneurysm,orofacial clefting,hemangioma, upper sternal defect,and Marfanoid features: Possible PHACE syndrome

We report a female patient who had a scalp hemangioma, a cleft uvula, an upper sternal defect, pectus excavatum, arachnodactyly, pes planus, and joint hypermobility. She had rupture of an aortic aneurysm after minor trauma at 11 years of age. At 17 years of age, elective repair of a dilated, ectatic aorta was complicated by cerebral ischemia. Other vascular abnormalities in the proband included an aneurysm of the left subclavian artery, atresia of the right carotid artery, and calcified cerebral aneurysms. We believe that the proband's physical anomalies are best described by the PHACE (posterior fossa brain malformations, hemangiomas, arterial anomalies, coarctation of the aorta and cardiac defects, and eye abnormalities) phenotypic spectrum. This spectrum of physical anomalies also includes sternal clefting and hemagiomas as part of the sternal malformation/vascular dysplasia (SM/VD) association, as found in our patient, and the acronym PHACES has also been used. We consider that the PHACE phenotypic spectrum is likely to be broader than previously recognized and includes orofacial clefting and aortic dilatation and rupture. Our patient also had skeletal anomalies that lead to consideration of Marfan syndrome as a diagnosis. It should be recognized that there is clinical overlap between PHACE syndrome and Marfan syndrome when aortic dilatation is present. We would also like to emphasize the minor nature of the cutaneous findings in our patient despite her severe vascular complications. This is in contrast to previous reports of large or multiple hemangiomas in PHACE syndrome. Published 2002 Wiley‐Liss, Inc.