Humoral immune responses are typically characterized by primary IgM antibody responses followed by secondary antibody responses associated with immune memory and composed of IgG, IgA, and IgE. Here, we measured acute humoral responses to SARS-CoV-2, including the frequency of antibody-secreting cells and the presence of SARS-CoV-2–specific neutralizing antibodies in the serum, saliva, and bronchoalveolar fluid of 159 patients with COVID-19. Early SARS-CoV-2–specific humoral responses were dominated by IgA antibodies. Peripheral expansion of IgA plasmablasts with mucosal homing potential was detected shortly after the onset of symptoms and peaked during the third week of the disease. The virus-specific antibody responses included IgG, IgM, and IgA, but IgA contributed to virus neutralization to a greater extent compared with IgG. Specific IgA serum concentrations decreased notably 1 month after the onset of symptoms, but neutralizing IgA remained detectable in saliva for a longer time (days 49 to 73 post-symptoms). These results represent a critical observation given the emerging information as to the types of antibodies associated with optimal protection against reinfection and whether vaccine regimens should consider targeting a potent but potentially short-lived IgA response.

A major dogma in immunology has it that the IgM antibody response precedes secondary memory responses built on the production of IgG, IgA and, occasionaly, IgE. Here, we measured acute humoral responses to SARS-CoV-2, including the frequency of antibody-secreting cells and the presence of specific, neutralizing, antibodies in serum and broncho-alveolar fluid of 145 patients with COVID-19. Surprisingly, early SARS-CoV-2-specific humoral responses were found to be typically dominated by antibodies of the IgA isotype. Peripheral expansion of IgA-plasmablasts with mucosal-homing potential was detected shortly after the onset of symptoms and peaked during the third week of the disease. While the specific antibody response included IgG, IgM and IgA, the latter contributed to a much larger extent to virus neutralization, as compared to IgG. However, specific IgA serum levels notably decrease after one month of evolution. These results represent a challenging observation given the present uncertainty as to which kind of humoral response would optimally protect against re-infection, and whether vaccine regimens should consider boosting a potent, although, at least in blood, fading IgA response.

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We have demonstrated electrical tuning in ring resonators fabricated from silicon-on-insulator wafers by incorporating nematic liquid crystals ͑NLCs͒ as the waveguide top and side cladding material. Photolithographically defined electrodes aligned around the ring resonator were used to control the orientation of the NLCs to modulate the cladding refractive index and, hence, the resonant wavelengths of the ring resonator. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1630370͔Microring resonators, fabricated with conventional semiconductor processing methods in silicon, offer significant advantages over the existing telecommunication filter technology and may be the foundation of future dense-wavelengthdivision-multiplexing ͑DWDM͒ filters. 1-5The high refractive index ͑RI͒ contrast available in silicon-oninsulator ͑SOI͒ ring resonators enables low loss and high-Q filters fabricated with radii down to a few microns.6,7 Such resonators can be designed as notch filters for adding or dropping individual channels in the telecommunication bands and can be densely integrated in photonic networks. For reconfigurable DWDM systems, and to compensate for temperature changes, it is desirable to tune the precise channel frequency dropped by such resonator add/drop multiplexers.Two primary methods exist to control the optical path length of a ring resonator and thus tune its resonant frequency. To statically tune a ring resonator one can either adjust the physical dimensions ͑in particular its circumference͒ or the refractive indices of the constituent materials of the resonator. Dynamically tunable resonators provide another level of functionality over statically tuned resonators and are most practically obtained by controlling the refractive indices of the constituent materials. Dynamic tuning is commonly achieved by thermally changing the RI, traditionally by introducing a heater close to the resonator. 8 However, power dissipation may provide a serious problem in such tunable ring resonator designs, especially when many resonators have to be integrated in a DWDM multiplexing system. In this letter we demonstrate the dynamic tuning of a ring resonator by changing the RI of its cladding via the orientation of the nematic liquid crystals ͑NLC͒.The resonator system under study, as shown in Fig. 1, was fabricated from a SOI wafer with silicon thickness of 205 nm and oxide thickness of 1 m, ring radius of 5 m, and ring and waveguide widths of 500 nm. The resonator was coupled to one waveguide, which served as both the input and output port and was separated from the resonator by a 100 nm gap. Modulation electrodes were then photolithographically defined and deposited using standard lift-off processing. The left and right electrodes were approximately 4.0 m wide and were spaced about 400 and 300 nm from the resonator, respectively ͑Fig. 1͒. The modulation electrodes were designed to preferentially orient the directors of the NLC molecules parallel ͑azimuthally oriented͒ to the resonator. To minimize their electrostatic ene...

We discuss our approach to monolithic intergration of Ge photodectors with CMOS electronics for high-speed optical transceivers. Receivers based on Ge waveguide photodetectors achieve a sensitivity of −14.2 dBm (10−12 bit error rate (BER)) at 10 Gbps and 1550 nm.