Biomedical subjects

A Kettner

Publications and source records attributed to A Kettner.

17 recordsLinked to original sources

PubMed2002

In vivo kinetics of the immunoglobulin E response to allergen: bystander effect of coimmunization and relationship with anaphylaxis.

BACKGROUND: Murine models of hypersensitivity to allergens are useful tools for the evaluation of preclinical strategies to down-regulate the IgE response. OBJECTIVE: To monitor the long-term kinetics of T and B cell responses to allergen as a function of allergen dosage and to investigate the effect of parallel immunization with a second antigen; to correlate B cell response with anaphylaxis. METHODS: CBA/J mice were sensitized every other week by subcutaneous injections of phospholipase A2 (PLA2) and/or ovalbumin (OVA) adsorbed to alum. Specific antibody isotype responses, T cell proliferation, T cell cytokine production and anaphylaxis were assessed throughout the sensitization phase. RESULTS: Low-dose immunization with PLA2 (0.1 microg) favoured a long-term, specific T helper (Th)2 response with high IgE and IL-4 production in contrast to high-dose PLA2 (10 microg) immunization, which biased the immune response towards a Th1 response with high IgG2a and low IL-4 production. Parallel immunization with an unrelated antigen (ovalbumin) had a significant bystander effect on the immunization with PLA2, which was also dose-dependent. Finally, although anaphylaxis as measured by rectal temperature drop was allergen-specific, it could be induced in the high- and low-dose immunization groups, and was not solely dependent on IgE levels. CONCLUSION: Though low-dose allergen immunization appears to induce an efficient IgE response, the intensity and quality of this response may be modulated by bystander effects of parallel immunization and does not correlate strictly with anaphylaxis. This observation has relevance to the design of clinical immunotherapy protocols using murine model-based data.

Allergens↗

PubMed2001

Api m 6: a new bee venom allergen.

BACKGROUND: Characterization of the primary structure of allergens is a prerequisite for the design of new diagnostic and therapeutic tools for allergic diseases. OBJECTIVE: The purpose of this study was the identification and characterization of a low-molecular-weight, IgE-binding, bee venom (BV) allergen. METHODS: BV proteins were separated by using size exclusion chromatography and HPLC. IgE antibody binding to purified proteins was analyzed by means of immunoblotting, and T-cell response was analyzed by means of proliferation assay. Amino acid sequence was determined with 2 approaches, namely Edman degradation and carboxy terminal analysis with mass spectrometry. RESULTS: Api m 6, which migrated as an 8-kd band in SDS-PAGE, was frequently (42%) recognized by IgE from BV-hypersensitive patients. In addition, PBMCs from BV-hypersensitive patients, as well as from a normal control subject, proliferated in response to this allergen. Api m 6 exists as 4 isoforms of 7190, 7400, 7598, and 7808 d, respectively. Amino acid sequences obtained from HPLC-purified preparations revealed that the isoforms were constituted of a common central core of 67 residues, only differing in the amino- and carboxy-terminal ends. Api m 6 showed no significant sequence homology with known proteins. CONCLUSIONS: We have identified and sequenced a new BV allergen that elicits a strong IgE and T-cell response in a large number of BV-hypersensitive patients. Api m 6 should be considered in the diagnostic and therapeutic approach of BV immunotherapy on the basis of peptides or recombinant proteins.

Allergens↗

PubMed2000

Inducing tolerance by intranasal administration of long peptides in naive and primed CBA/J mice.

To assess the capacity of a peptide-based immunotherapy to induce systemic tolerance via the nasal route, we designed three long overlapping peptides of 44-60 aa covering the entire sequence of phospholipase A2 (PLA2), a major bee venom allergen. Both prophylactic and therapeutic intranasal administrations of long peptides to PLA2-hypersensitive CBA/J mice induced specific T cell tolerance to the native allergen. In prophylactic conditions, this tolerance was marked by a suppression of subsequent specific IgE response, whereas the therapeutic approach in presensitized mice induced a more than 60% decrease in PLA2-specific IgE. This decline was associated with a shift in the cytokine response toward a Th1 profile, as demonstrated by decreased PLA2-specific IgG1 and enhanced IgG2a levels, and by a decline in the specific IL-4/IFN-gamma ratios. T cell transfer from long peptide-tolerized mice to naive animals abrogated the expected anti-PLA2 IgE and IgG1 Ab response, as well as specific T cell proliferation, but enhanced specific IgG2a response upon sensitization with PLA2. These events were strongly suggestive of a clonal anergy affecting more profoundly Th2 than the Th1 subsets. In conclusion, these results demonstrate that allergen-derived long peptides delivered via the nasal mucosa may offer an alternative to immunotherapy with native allergens without the inherent risk of systemic anaphylactic reactions. Moreover, long peptides, in contrast to immunotherapy strategies based on short peptides, have the advantage of covering all potential T cell epitopes, and may represent novel and safe tools for the therapy of allergic diseases.

Administration, Intranasal↗

PubMed2000

Allergen-derived long peptide immunotherapy down-regulates specific IgE response and protects from anaphylaxis.

To evaluate a long peptide-based allergy vaccine in a murine model, CBA/J mice were sensitized with low dose alum-adsorbed phospholipase A2 (PLA2), a major bee venom allergen. Presensitized mice were treated by daily i.p. injections of a mixture of three long overlapping peptides (44- to 60-mer) spanning the entire PLA2 molecule (100 microg/peptide) for 6 consecutive days. This therapeutic approach induced a sharp drop in PLA2-specific IgE, an increase in specific IgG2a, and a marked T cell hyporesponsiveness. T cell cytokine secretion was characterized by a shift from a Th2 to a Th1 profile. Prophylactic treatment of naive mice with long peptides prior to sensitization with PLA2 induced a comparable modulation of B and T cell responses. Upon i.p. challenge with native PLA2, presensitized mice treated with the long peptide mixture were fully protected from anaphylaxis. This indicated that allergen-derived long overlapping peptides were safe and able to modulate an established Th2 response or to prevent its development. Furthermore, long peptide-based immunotherapy provided clinical protection against anaphylaxis, thus appearing as a promising approach of the therapy of allergic diseases.

Allergens↗

PubMed1999

IgE and T-cell responses to high-molecular weight allergens from bee venom.

BACKGROUND: Bee venom contains multiple allergens with a wide distribution of molecular weight. In contrast with conventional bee venom desensitization, peptide or recombinant allergen immunotherapy may have to take into account patients' individual patterns of humoral or cellular response. OBJECTIVE: To study immunoglobulin (Ig)E and T-cell responses to high-molecular weight bee venom allergens >/= 50 kDa. METHODS: Bee venom proteins were separated by size exclusion chromatography and fractions were characterized by one and two-dimensional gel electrophoresis. IgE antibody binding to bee venom fractions was analysed by immunoblotting and T-cell responses by proliferation assay. RESULTS: Among 38 bee venom-hypersensitive patients, IgE recognition pattern of bee venom allergens varied greatly. IgE bound mainly to phospholipase A2 and furthermore to several proteins >/= 50 kDa (50, 54, 69, 84 and 94 kDa). N-terminal sequences of these proteins showed no homology with known proteins. In addition, peripheral mononuclear cells from patients as well as from nonatopic donors strongly proliferated in response to those proteins. CONCLUSIONS: Although present in low amounts, high-molecular weight allergens from bee venom elicit strong IgE and T-cell responses, and may need to be considered as clinically relevant. Therefore, the development of peptide or recombinant protein-based immunotherapy for bee venom allergy may require careful characterization of such allergens.

Allergens↗

PubMed1997

Modulation of T-cell response to phospholipase A2 and phospholipase A2-derived peptides by conventional bee venom immunotherapy.

BACKGROUND: Immunologic mechanisms of desensitization are still incompletely understood. Safer methods of immunotherapy with reduced risks of anaphylaxis need to be developed. OBJECTIVE: To study the effects of conventional venom immunotherapy (VIT) on phospholipase A2(PLA2)-specific T cells and on T-cell reactivity to short and long synthetic peptides that map the PLA2 molecule. METHOD: Proliferation of a CD4+ cell-enriched peripheral blood mononuclear cell fraction and cytokine secretion by T cell lines from patients hypersensitive to bee venom and undergoing VIT in response to PLA2 and PLA2 synthetic peptides were measured. RESULTS: T-cell proliferation in response to three synthetic peptides, 40 to 60 amino acids long and mapping the entire PLA2 molecule with an overlap of 10 residues (1 to 59, 51 to 99, and 90 to 134) steadily increased during the first 14 weeks of VIT corresponding to the treatment period with incremental doses of antigen. These results are in contrast to the low proliferation indices obtained with short (15 amino acid-long) peptides, and the inability to characterize the immunodominant region of the molecule with short peptides. At the end of VIT (after 3 to 5 years), there was correspondingly, a marked decrease in T cell responsiveness to PLA2 and to its long synthetic peptides. This response was paralleled by a shift in the pattern of cytokine secretion by T cell lines from a T(H0)-type to a T(H1)-type pattern. CONCLUSION: After a transient increase in T-cell proliferation, late VIT was characterized by T-cell hyporesponsiveness to allergen and by modulation of cytokine secretion from a T(H0)-type to a T(H1)-type pattern. Because of their capacity to recruit multiple T-cell epitopes, long peptides mapping the entire PLA2 molecule appear to be efficient T cell stimulators and may represent potential candidates for peptide immunotherapy.

Adjuvants, Immunologic↗

PubMed1997

Delineation of PLA2 epitopes using short or long overlapping synthetic peptides: interest for specific immunotherapy.

BACKGROUND: Venom immunotherapy is definitely indicated in severe systemic anaphylactic reactions to bee stings, but is not devoided of risks of anaphylaxis. Safer methods of immunotherapy need to be developed. OBJECTIVE: To delineate phospholipase A2 T-cell epitopes using short 15mer vs long 40-60mer overlapping peptides, and to approach the potential interest of a venom immunotherapy based on the use of long peptides (1-60, 51-99, 90-134) mapping the whole phospholipase A2 molecule vs a restricted number of immunodominant epitopes. METHODS: Proliferation of a CD8+ T cell depleted peripheral blood mononuclear cell fraction and short-term T-cell lines from unselected bee venom hypersensitive patients in response to phospholipase A2 synthetic peptides. RESULTS: Whereas T-cell proliferation to 15mer overlapping peptides was weak, T-cell response to long overlapping peptides was in contrast vigorous in all patients, mostly directed to C-terminal peptide 90-134. Our results did not support the concept of rare dominant T-cell epitopes, and disclosed T-cell responses to multiple epitopes in several patients. No significant IgE-binding to long overlapping peptides was detected except in one patient against peptide 90-134. CONCLUSION: 15mer peptides might not be sensitive enough to fully delineate all potential T-cell epitopes scattered along the allergen. Since they do not bind IgE in vitro or only weakly, and taking into account a T-cell response frequently directed to multiple epitopes, long overlapping peptides may represent ideal tools for immunotherapy.

Bee Venoms↗

PubMed1997

Synthetic polypeptides corresponding to the non-repeat regions from the circumsporozoite protein of Plasmodium falciparum: recognition by human T-cells and immunogenicity in owl monkeys.

Synthetic polypeptides encompassing the non-repeated regions of the circumsporozoite protein (CSP) of Plasmodium falciparum are very immunogenic in mice and are recognized by sera from donors living in regions where malaria is endemic, both in Africa and South America. Long polypeptides, encompassing the N- or C-terminal regions, have now been used to demonstrate peptide-specific T cells in donors living in an endemic area of Colombia. Although the N-terminal peptide (22-125) was recognized almost exclusively by donors from the endemic area, the patterns of recognition of the C-terminal peptide (289-390) in donors from endemic and non-endemic areas were similar and like the pattern with smaller peptides. The availability of the long polypeptides made it possible to compare T-cell responses to the non-repeated regions of the CSP with the presence of peptide-specific antibodies. No correlation was found and no antibodies were detected in donors from non-endemic regions. The long polypeptides also elicited strong antibody and T-cell responses in owl monkeys (Aotus lemurinus). The antibodies generated against the synthetic peptides in such monkeys also recognized sporozoites, the natural infective form of the parasite. The results emphasise the potential of the peptides tested as malaria-vaccine candidates. Not only are they recognized by humans at both the B- and T-cell level but they also elicit strong responses in monkeys and encompass several distinct T-cell epitopes, thus overcoming the limitations of specific, major-histocompatibility-complex restriction.

Adolescent↗

PubMed1984

Cardiovascular and metabolic responses to submaximal exercise in hemodialysis patients.

Eight chronic hemodialysis (cHD) patients and six healthy sedentary controls (C) were exercised for 60 minutes at 52 +/- 8% (cHD patients) and 48 +/- 4% (C) of their maximal oxygen consumption levels. Plasma lactate levels at rest and during exercise were comparable in both groups. Respiratory exchange ratios were lower in cHD patients, but they increased during exercise to levels comparable to those of the C group. Despite comparable heart rates at rest, exercise of similar intensity led to lower heart rates at 30 and 60 minutes in cHD patients compared to C (P less than 0.05). The cHD patients had higher systolic and mean arterial pressures at rest than did C (P less than 0.05), but during exercise the increments in systolic and mean blood pressures were lower in cHD patients than they were in C (P less than 0.05). In spite of these blunted cardiovascular responses, plasma catecholamines increased during exercise in both groups. Plasma glucose levels were similar in both groups during exercise in spite of significantly higher plasma levels of insulin and glucagon in cHD patients throughout the exercise session (P less than 0.01). These data demonstrate that chronic cHD patients can exercise at a modest intensity for a prolonged period of time without untoward cardiovascular or metabolic responses. Their poor exercise response does not appear to be related to an inadequate activation of the sympathoadrenal system.

Adult↗

PubMed1984