Surface-enhanced infrared absorption with Si-doped InAsSb/GaSb nano-antennas.

We demonstrate surface enhanced infrared absorption spectroscopy using 1-dimensional highly doped semiconductors based on Si-doped InAsSb plasmonic nano-antennas. Engineering the plasmonic array to support the localized surface plasmon resonance aligned with the molecular vibrational absorption mode of interest involves finely setting the doping level and nano-antenna width. Heavily doped nano-antennas require a wider size compared to lightly doped resonators. Increasing the doping level, and consequently the width of the nano-antenna, enhances the vibrational absorption of a ~15 nm thick organic layer up to 2 orders of magnitude compared to the unstructured sample and therefore improves sensing. These results pave the way towards molecule fingerprint sensor manufacturing by tailoring the plasmonic resonators to get a maximum surface enhanced infrared absorption at the target vibrational mode.

Elongated unique DNA strand deposition on microstructured substrate by receding meniscus assembly and capillary force.

Ordered deposition of elongated DNA molecules was achieved by the forced dewetting of a DNA solution droplet over a microstructured substrate. This technique allows trapping, uncoiling, and deposition of DNA fragments without the need of a physicochemical anchoring of the molecule and results in the combing of double stranded DNA from the edge of microwells on a polydimethylsiloxane (PDMS) substrate. The technique involves scanning a droplet of DNA solution caught between a movable blade and a PDMS substrate containing an array of microwells. The deposition and elongation appears when the receding meniscus dewets microwells, the latter acting here as a perturbation in the dewetting line forcing the water film to break locally. Thus, DNA molecules can be deposited in an ordered manner and elongated conformation based solely on a physical phenomenon, allowing uncoiled DNA molecules to be observed in all their length. However, the exact mechanism that governs the deposition of DNA strands is not well understood. This paper is an analysis of the physical phenomenon occurring in the deposition process and is based on observations made with the use of high frame/second rate video microscopy.

Control by Ig genes of the responsiveness to a neutralization viral B cell epitope.

In the present study, we analyzed the capacity of seven strains of mice to produce Abs against the neutralization poliovirus C3 B cell epitope, chemically or genetically linked to two different carrier proteins (MalE and keyhole limpet hemocyanin) or to recombinant hepatitis B surface Ag particles. Following immunization with these different immunogens, all strains of mice developed high Ab titers against the carrier proteins. However, only four strains of mice developed a significant Ab response against the poliovirus C3 B cell epitope. Indeed, in contrast to BALB/c, DBA/1, DBA/2, and 129 sv mice, C57BL/6, C3H, and CBA/J mice failed to produce anti-C3 Abs after immunization with the various C3 immunogens. Using various H-2 congenic strains on BALB/c or C57BL/10 background, this study clearly showed that the response to the C3 B cell epitope is not controlled by MHC genes. In contrast, analysis of anti-C3 Ab responses in IgH congenic mouse lines on BALB/c or C57BL/6 background demonstrated that the capacity to respond to this B cell epitope is controlled by genes closely linked to V(H) genes. This study therefore represents the first demonstration that the V(H) polymorphism can limit the Ab response to a viral neutralization epitope, and therefore has important implications for vaccine development.

Stimulation of a memory B cell response does not require primed helper T cells.

The use of universally immunogenic T cell epitopes, such as those identified in tetanus toxin or malaria circumsporozoite protein, could represent a major improvement in the development of synthetic vaccines. However, one limitation of this approach is the lack of T cell cross-reactivity between the vaccine and the pathogen. To determine whether the memory B cell response elicited by immunization with a synthetic peptide containing a B cell epitope linked to a T cell epitope can be restimulated by the same B cell epitope linked to different T cell epitope(s), we used a synthetic peptide which contains non-overlapping B and T cell determinants from hepatitis B surface antigen (HBsAg) of hepatitis B virus (HBV). The results of this study clearly show that primed T cells can increase the antibody response against a B cell epitope linked to the priming T cell determinant. However, the antibody response obtained was weaker than that obtained after two injections of the peptide containing both B and T cell epitopes, showing the important role played by memory B cells in secondary antibody responses. Moreover, a strong antibody response against the B cell epitope was elicited by boosting mice with the B cell epitope linked to a heterologous carrier, thus demonstrating that a strong B cell memory response can be revealed in the absence of primed T cells. These results therefore provide new important information for the design of synthetic or recombinant vaccines.

B cells do not present antigen covalently linked to microspheres.

B cells have been shown to present antigen to T cells very efficiently through their capacity to capture antigens by their membrane immunoglobulin. This direct cognate interaction of T and B cells results in the proliferation and differentiation of B cells. This concept has been established using soluble proteins. However, most of the antigens to which the immune system is exposed are included in complex particulate structures such as bacteria or parasites. The capacity of B cells to present these large and complex antigens is still unclear. To address this question we have studied the presentation by trinitrophenyl (TNP)-specific B cells of the same antigen TNP-KLH (keyhole limpet haemocyanin), either in a soluble form or covalently linked to poly(acrolein) microspheres, from 0.25 to 1.5 microns in diameter. In the presence of irradiated splenocytes or purified macrophages as a source of antigen-presenting cells (APC), KLH-specific T cells proliferated in response to soluble TNP-KLH or to TNP-KLH coupled to beads. In contrast, TNP-specific memory B cells were totally ineffective in presenting the TNP-KLH beads to KLH-specific T cells whereas they presented very efficiently soluble TNP-KLH. Similar results were obtained with the A20 B lymphoma or with lipopolysaccharide (LPS)-activated TNP-specific B cells. These results therefore indicate that B cells are unable to present large size particulate antigens such as bacteria or parasites.

Clonal anergy of memory B cells in epitope-specific regulation.

Immunization of carrier (keyhole limpet hemocyanin (KLH)) primed mice with the hapten-carrier TNP-KLH induces specific suppression for the IgG anti-TNP-response without interfering with the response to epitopes on the carrier molecule. To examine the status of hapten-specific memory B cells from suppressed mice, highly enriched populations of TNP-specific memory B cells were purified from the spleen of TNP-KLH (control) or KLH/TNP-KLH (suppressed) immunized mice and tested in vitro for their ability to respond to TD or TI (TNP-KLH, TNP-LPS) antigenic challenge in presence of a KLH-specific Th cell line. Similar numbers of TNP-specific B cells with the characteristics of memory B cells were obtained from control and suppressed mice. TNP-specific B cells from suppressed mice could be triggered to IgG production by TNP-LPS but had an impaired ability to differentiate into IgG-secreting cells in response to TNP-KLH. This impaired IgG response to TNP-KLH was not due to an active suppression by a subset of TNP-specific B cells, or to an impedence of memory cells to a class switching but to an intrinsic memory B cell defect. TNP-specific B cells from suppressed mice were as efficient as memory B cells from control mice to present TNP-KLH to KLH-specific Th cells and to proliferate in response to T cell help. Our data support the view that the effector mechanism of epitope specific regulation does not interfere with the development of hapten-specific memory B cells but that these cells have an intrinsic defect that prevents their differentiation into active IgG antibody secreting cells in response to a T-dependent antigenic challenge.

Induction of murine hemopoietic growth factors by toxic shock syndrome toxin-1.

Toxic shock syndrome toxin-1 (TSST-1), an extra-cellular 22 kDa single chain protein produced by most Staphylococcus aureus strains isolated from patients with toxic shock syndrome (TSS), induces modifications of blood cell values similar to those observed during TSS. We therefore analyzed the effects of TSST-1 on the proliferation and differentiation of murine granulocyte-macrophage progenitor cells (CFU-culture) and the eventual role of endotoxin in this response. TSST-1 had no direct effect on the proliferation of CFU-culture and was unable to influence the CSF-induced proliferation and differentiation of these progenitors. In contrast, TSST-1 was a potent inducer in spleen cell cultures of a factor with an ability to induce both colony formation by bone marrow cells and proliferation of an IL-3-dependent cell line. Nanogram amounts of TSST-1 were able to induce the release of CSF activity in spleen cell cultures from both normal and LPS-hyporesponsive mice. Cells from C3H/HeJ mice were as responsive as cells from C3H/He Pas mice. Furthermore, in spleen cell cultures from normal mice, TSST-1 and LPS did not act synergistically to induce CSF activity. Nanogram amounts of TSST-1 were also able to induce CSF activity in vivo but failed to induce IL-3 activity in the serum and organ-conditioned media from TSST-1-treated mice.

Induction of colony-stimulating activity in mice by injection of liposomes containing lipophilic muramyl peptide derivatives.

Colony-stimulating factor (CSF) activity induction by lipophilic derivatives of three muramyl peptides, glyceryl dipalmitate-MDP derivatives, was studied in vivo and in vitro and compared to the activity of the same compounds incorporated within freeze-dried liposomes. Two lipophilic derivatives (MDP-GDP and MDPGBe-GDP) were able to induce CSF activity in vivo and in vitro. The incorporation of these compounds within appropriately designed liposomes composed of distearoylphosphatidylcholine and phosphatidylserine (DSPC/PS) increased their ability to induce CSF activity in vivo but completely abrogated their ability to induce CSF activity in vitro. Furthermore, the phospholipid composition of liposomes influenced the efficacy of glycopeptide liposomal incorporation. Thus, the serum CSF-inducing effect of MDP-GDP was considerably enhanced by incorporation of this compound within liposomes composed of DSPC/PS at a molar ratio 7:0.3 but was not modified if the DSPC/PS molar ratio was 7:3. The lipophilic derivative of MDP (D-D), MDP (D-D)-GDP, was unable to induce CSF activity in vivo or in vitro but surprisingly became active in vivo after entrapment within DSPC/PS liposomes (molar ratio 7:0.3). Our results show that appropriate liposomes may be suitable carriers to deliver CSF activity-inducing agents to macrophages in vivo.