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C Burkhart

Publications and source records attributed to C Burkhart.

9 recordsLinked to original sources
PubMed1995

Role of T helper cell precursor frequency on vesicular stomatitis virus neutralizing antibody responses in a T cell receptor beta chain transgenic mouse.

During most immune responses, T cells help antigen-specific B cells to make antibodies against the antigen. One of the contributions of T cells to antibody production is the induction of isotype switching from IgM to IgG, which is the most abundant isotype in blood serum during recall responses. Other features of memory responses are faster kinetics and higher titers of antibody in the serum. What causes a primary immune response to be different from a secondary is not yet very clear and, particularly, the influence of precursor frequencies of T and B cells on memory responses still remains to be answered. To address this issue, a transgenic (tg) mouse line (ADA) was developed; it expresses the beta chain (V beta 2) of a major histocompatibility complex class II-restricted T cell receptor (TcR) specific for the glycoprotein (G) of vesicular stomatitis virus (VSV) serotype Indiana (VSV-IND). These mice exhibit an increased precursor frequency of VSV-specific CD4+ T cells that leads to enhanced neutralizing IgG production against VSV in vivo in unprimed mice. The data indicate that increased frequency of naive specific helper T cells alone may account for features of a memory phenotype such as high titer of antibodies and isotype switching.

Amino Acid Sequence↗
PubMed1994

Virus or a hapten-carrier complex can activate autoreactive B cells by providing linked T help.

We investigated the mechanism leading to an IgG autoantibody response in two transgenic mouse lines expressing the glycoprotein of vesicular stomatitis virus (VSV-G). Previous experiments have shown that these animals do not mount a transgene-specific IgG response upon stimulation with purified VSV-G or infection with recombinant vaccinia virus expressing VSV-G. However, infection of VSV-G transgenic animals with wild-type vesicular stomatitis virus, serotype Indiana, readily induced VSV-G-specific, neutralizing IgG autoantibodies. We have tested whether this labile state of tolerance reflected differential availability of VSV-G-specific T help. For this, we immunized transgenic mice with the self-antigen VSV-G covalently coupled to sperm-whale myoglobulin (VSV-G-SWM), to provide new T helper epitopes that are linked to the B cell epitope; co-injected uncoupled VSV-G and SWM served as control. High titers of VSV-G specific IgG autoantibodies were detected in serum of mice immunized with VSV-G-SWM but not after co-injection of uncoupled VSV-G and SWM. Transgenic animals depleted of CD4+ T cells prior to injection of VSV-G-SWM failed to mount an IgG response. Priming of transgenic mice with the foreign carrier did not accelerate the IgG autoantibody response to VSV-G-SWM, suggesting that B cells were limiting the rate of the response. Thus, self-reactive B cells could be triggered to produce IgG, if they received linked T help specific for a foreign carrier determinant provided either by a classical carrier determinant or a virus.

Animals↗
PubMed1994

Localization of T helper cell epitopes in the vesicular stomatitis virus: the nucleoprotein is responsible for serotype cross-reactive T help.

The glycoprotein (G) of vesicular stomatitis virus (VSV) is known to contain the biologically relevant sites for virus-neutralizing antibodies as well as T helper (Th) cell epitopes. The capacity of other VSV proteins to elicit potent Th cell responses has not yet been investigated. Additionally, a short-lived cross-reactivity between the two serologically distinct VSV serotypes Indiana (IND) and New Jersey (NJ) on the T helper cell level has been reported. Here we address the question of whether the VSV nucleoprotein (N) or matrix protein (M) can elicit T help to VSV-G-specific B cells and which of the VSV proteins contains the elements responsible for the IND/NJ cross-reactivity. The N, G, and M of the VSV Indiana serotype produced in a recombinant baculovirus system were assayed for the ability to activate VSV-specific Th cells to induce immunoglobulin class switch of neutralizing antibody responses in vivo in C57BL/6 (H-2b) mice. All three VSV-IND proteins helped in the production of neutralizing IgG antibodies to the homologous VSV-Indiana serotype but only VSV-IND N was able to trigger an IgG response to the heterologous VSV-New Jersey serotype. This data suggest that Th epitope(s) in the VSV-IND N are responsible for the observed cross-reactivity of T helper cells.

Animals↗
PubMed1994

Characterization of T-helper epitopes of the glycoprotein of vesicular stomatitis virus.

The T-helper (Th) cell epitopes in the glycoprotein (GP) of vesicular stomatitis virus serotype Indiana (VSV-IND) were analyzed with a complete panel of overlapping synthetic peptides. Three Th-cell epitopes in C57BL/6 (H-2b) mice and two epitopes in BALB/c (H-2d) mice were defined by their ability to stimulate in vitro proliferation of virus-primed, CD8+ T-cell-depleted spleen cells in a class II-restricted manner. A series of CD4+, I-Ab-restricted T-cell hybridomas from VSV-primed C57BL/6 mice were characterized by their production of interleukin-2 and interleukin-3 upon stimulation with VSV-IND or purified VSV GP in vitro. Of nine hybridomas derived from three independent fusions, five were specific for amino acids (aa) 415 to 433 (p8) of VSV-IND GP, three recognized aa 52 to 71 (p41), and one reacted against aa 316 to 335 (p17). Fluorocytometric analysis of Th hybridomas or VSV-stimulated T-cell lines with monoclonal antibodies specific for the T-cell receptor V beta chain did not reveal obvious correlations between the T-cell receptor V beta gene segment used and the epitope recognized. All three peptides recognized by H-2b mice and both epitopes recognized by H-2d mice which were characterized in primed T-cell populations were capable of activating specific Th cells in vivo as measured by the induction of antibody class switch from immunoglobulin M (IgM) to IgG. Thus, the epitopes are relevant for VSV GP-specific Th response in vivo and are able to provide functional help for the production of anti-VSV-specific neutralizing IgG antibodies.

Amino Acid Sequence↗
PubMed1994

Vesicular stomatitis virus Indiana glycoprotein as a T-cell-dependent and -independent antigen.

The neutralizing immunoglobulin M (IgM) response to vesicular stomatitis virus (VSV) has been shown to be largely T-cell independent in several T-cell-deficient models of mice. By using different antigen froms of VSV, VSV antigen doses could be graded in vivo (infectious > > UV inactivated > formalin inactivated). The present study reveals a T-cell-dependent component of the neutralizing IgM response in nude mice given intravenous injections of low doses of noninfectious UV-inactivated VSV serotype Indiana (VSV-IND) only if the mice are transfused with VSV-IND-specific helper T cells. Instead, nude mice immunized with infectious VSV, which leads to greater antigen doses in vivo, were able to mount an IgM response in the absence of T cells. These results indicate that the IgM response to low doses of VSV-IND glycoprotein (G) is T-cell dependent. Nude mice immunized with infectious VSV also made a variable but low VSV-IND-neutralizing IgG response. A VSV-IND matrix (M)-specific helper T-cell line rendered this response more consistent, much higher, and longer lasting. Thus (i) VSV-G induces a mostly T-cell-independent but partially T-cell-dependent IgM (the latter can be visualized best at low doses of antigen) and (ii) the antibody response to VSV in nude mice proceeds through steps, i.e., IgM and IgG, that are dose dependent. The results suggest that the predominant role of helper T cells may be to expand and maintain the individual steps of differentiating B cells.

Animals↗
PubMed1992

Guidelines for rapid assessment of abdominal pain indicative of acute surgical abdomen.

Abdominal pain is one of the most frequently described reasons for ambulatory visits. The complaint of abdominal pain requires an orderly and thorough approach because even mild or non-specific pain can denote a potentially life-threatening intra-abdominal pathology. The majority of patients with acute abdomen can be diagnosed by a direct and concise history, and a thorough physical examination supplemented by simple laboratory and radiologic testing. This article includes key history, physical and clinical indicators that should suggest to the clinician the need for immediate surgical intervention. When an acute abdomen is suspected, the goal of patient management is to rapidly and accurately diagnose the patient preoperatively, and to provide a timely referral to the appropriate surgeon or gynecologist.

Abdomen, Acute↗
PubMed1992

[The effect of Belzer and Bretschneider cardioplegia solutions on myocardial energy metabolism. A study with 31phosphorus magnetic resonance spectroscopy in an animal model].

The aim of our study was to test the effectiveness of two cardioplegic solutions and to compare the level of high energy phosphates in the myocardium. We investigated 18 hearts of pigs (obtained from a slaughter-house) with 31phosphorusmagnetic resonance spectroscopy (31P-MRS) In this experiment coronary arteries were cannulated and reperfused with arterial blood to revitalize the heart. When the heart showed regular pulsations coronary arteries were perfused for cardioplegia either with the UW-(Belzer-) or with the HTK-(Bretschneider-)solution. For 31P-MRS, a magnet with a magnetic flux density of 4.7 Tesla (T) was available. Relative concentrations from phosphocreatine (PCr/beta-ATP; high-energy phosphate) and inorganic phosphate (Pi/MDP; MDP = methylendiphosphonat = reference solution; low-energy phosphate) were calculated from the spectra. As a result of this study, the HTK-solution showed a significantly higher PCr/beta-ATP-ratio in the myocardium than the UW-solution during the examination time of 3 h. After plegia of the myocardial area from the right coronary artery PCr/beta-ATP-ratios were lower in comparison with the left coronary artery distribution area. The calculation of Pi/MDP-ratios proved that Pi was higher in the myocardium after application of the UW-solution compared to HTK-solution. The kinetics of the metabolites showed an approximately linear and parallel decrease of PCr/beta-ATP-ratios after cardioplegia with both solutions during the examination time.

Animals↗