The three near-infrared-emitting cationic iridium(III) complexes [Ir(pbq-g)2(N∧N)]+PF6– (pbq-g = phenylbenzo[g]quinoline; N∧N = bipyridine (1), 1,10-phenanthroline (2), 4,7-diphenyl-1,10-phenanthroline (3)) have been demonstrated as phosphorescent dyes in live cell imaging. These complexes with different ancillary ligands show similar near-infrared (NIR) emission with λmax,peak at 698 nm and λmax,shoulder at 760 nm in CH2Cl2 solutions, with a moderate quantum yield of around 3%. However, these complexes behave quite differently as NIR dyes for live cell imaging. Complexes 1 and 2 exhibit exclusive staining in the cytoplasm with good cell membrane permeability under excitation at 488 nm, while 3 gives almost no cell uptake, as further determined by flow cytometry. Although the lipophilicities of these complexes follow the order 1 < 2 < 3, their cytotoxicities are in the reverse order. The exceptionally low cytotoxicity of 3 could be attributed to its poor solubility in aqueous buffer and thus substantially low exposure dose. This comparative study suggested that the ancillary ligands could fine-tune the amphiphilicity and cytotoxicity of the cyclometalated iridium(III) complexes and thus might play a key role in the design of NIR-emitting iridium(III) complexes for practical applications in bioimaging.

Antibody memory is critical for protection against many human infectious diseases and is the basis for nearly all current human vaccines. Isotype switched immunoglobulin (Ig) G-expressing memory B cells are considered as one of the fundaments for the rapid, high affinity and high-titered memory antibody response. The detailed molecular mechanism of the enhanced activation of IgG-switched memory B cells upon BCR engagement with antigens has been an elusive question in immunology. In this review, we tried to discuss all the exciting new advances revealing the molecular mechanisms of the transmembrane signaling through mIgG cytoplasmic tail in IgG-switched memory B cells.

Adaptive lymphocytes express highly variable antigen receptors, allowing them to recognize a large variety of proteins, for example, derived from pathogens and tumor cells. Despite decades of investigations, the signaling mechanisms of these receptors are still incompletely understood. Super-resolution imaging studies revealed that antigen receptors, their coreceptors, and even some downstream signaling molecules tend to form dynamic nanometers-sized self-clusters in quiescent cells. Antigen stimulation induces the coalescence of these nanoclusters to form membrane proximal signalosomes that can mediate efficient signal transduction. In this review, we discuss the dynamic structures of T cell receptor and B cell receptor nanoclusters, the driving forces behind this spatial reorganization, as well as their potential relevance in the modulation of lymphocyte activation and function.