MHC class II antigen presentation pathway in murine tumours: tumour evasion from immunosurveillance?

Qualitative differences in the MHC class II antigen processing and presentation pathway may be instrumental in shaping the CD4+ T cell response directed against tumour cells. Efficient loading of many MHC class II alleles with peptides requires the assistance of H2-M, a heterodimeric MHC class II-like molecule. In contrast to the HLA-DM region in humans, the β-chain locus is duplicated in mouse, with the H2-Mb1 (Mb1β-chain distal to H2-Mb2 (Mb2) and the H2-Ma (Ma) α-chain gene). Here, we show that murine MHC class II and H2-M genes are coordinately regulated in murine tumour cell lines by T helper cell 1 (IFN-γ) and T helper cell 2 (IL-4 or IL-10) cytokines in the presence of the MHC class II-specific transactivator CIITA as determined by mRNA expression and Western blot analysis. Furthermore, Mαβ1 and Mαβ2 heterodimers are differentially expressed in murine tumour cell lines of different histology. Both H2-M isoforms promote equally processing and presentation of native protein antigens to H2-Ad- and H2-Ed-restricted CD4+ T cells. Murine tumour cell lines could be divided into three groups: constitutive MHC class II and CIITA expression; inducible MHC class II and CIITA expression upon IFN-γ-treatment; and lack of constitutive and IFN-γ-inducible MHC class II and CIITA expression. These differences may impact on CD4+ T cell recognition of cancer cells in murine tumour models. © 2000 Cancer Research Campaig

Strong amplitude-phase coupling in submonolayer quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 109, 201102 (2016) and may be found at https://doi.org/10.1063/1.4967833.Submonolayer quantum dots promise to combine the beneficial features of zero- and two-dimensional carrier confinement. To explore their potential with respect to all-optical signal processing, we investigate the amplitude-phase coupling (α-parameter) in semiconductor optical amplifiers based on InAs/GaAs submonolayer quantum dots in ultrafast pump-probe experiments. Lateral coupling provides an efficient carrier reservoir and gives rise to a large α-parameter. Combined with a high modal gain and an ultrafast gain recovery, this makes the submonolayer quantum dots an attractive gain medium for nonlinear optical signal processing

Feedback and injection locking instabilities in quantum-dot lasers: a microscopically based bifurcation analysis

We employ a nonequilibrium energy balance and carrier rate equation model based on microscopic semiconductor theory to describe the quantum-dot (QD) laser dynamics under optical injection and time-delayed feedback. The model goes beyond typical phenomenological approximations of rate equations, such as the α-factor, yet allows for a thorough numerical bifurcation analysis, which would not be possible with the computationally demanding microscopic equations. We find that with QD lasers, independent amplitude and phase dynamics may lead to less complicated scenarios under optical perturbations than predicted by conventional models using the α-factor to describe the carrier-induced refractive index change. For instance, in the short external cavity feedback regime, higher critical feedback strength is actually required to induce instabilities. Generally, the α-factor should only be used when the carrier distribution can follow the QD laser dynamics adiabatically.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Many-body and nonequilibrium effects on relaxation oscillations in a quantum-dot microcavity laser

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 97, 111102 (2010) and may be found at https://doi.org/10.1063/1.3488004.We investigate many-body and nonequilibrium effects on the dynamical behavior of a quantum-dot laser diode. Simulations, based on the Maxwell-semiconductor-Bloch equations, show strong dependence of the turn-on delay on initial cavity detuning, because of a dynamical shift in the quantum-dot distribution caused by band gap renormalization. Gain switch behavior is found to be insensitive to inhomogeneous broadening, because the balancing between many-body and free-carrier effects inhibits a cavity resonance walk-off. Both the relaxation oscillation damping and frequency are found to increase with decreasing inhomogeneous broadening widths. However, in contrast to bulk and quantum-well lasers, oscillation damping increases less than the frequency.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Influencing modulation properties of quantum-dot semiconductor lasers by carrier lifetime engineering

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 101, 131107 (2012) and may be found at https://doi.org/10.1063/1.4754588.The relaxation oscillation (RO) parameters and modulation properties of quantum-dot lasers are investigated depending on effective charge carrier scattering lifetimes of the confined quantum-dot states. We find three dynamical regimes of the laser, characterized by the level of synchronization between carrier dynamics in quantum-dots and quantum-well. For scattering rates similar to the RO frequency, a strong damping is found. On either side of this regime, simulations show low RO damping and improved dynamical response. Depending on the regime, the modulation response differs from conventional analytical predictions. Our results suggest the possibility of tailoring quantum-dot laser dynamical behavior via bandstructure engineering.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Broadband semiconductor light sources operating at 1060 nm based on InAs:Sb/GaAs submonolayer quantum dots

In this paper, we investigate the potential of submonolayer-grown InAs:Sb/GaAs quantum dots as active medium for opto-electronic devices emitting in the 1060 nm spectral range. Grown as multiple sheets of InAs in a GaAs matrix, submonolayer quantum dots yield light-emitting devices with large material gain and fast recovery dynamics. Alloying these structures with antimony enhances the carrier localization and red shifts the emission, whereas dramatically broadening the optical bandwidth. In a combined experimental and numerical study, we trace this effect to an Sb-induced bimodal distribution of localized and delocalized exciton states. While the former do not participate in the lasing process, they give rise to a bandwidth broadening at superluminescence operation and optical amplification. Above threshold laser properties like gain and slope efficiency are mainly determined by the delocalized fraction of carriers