Light-induced electron transfer in porphyrin-calixarene conjugates.

The fluorescence from a set of porphyrin-calixarene complexes is quenched upon addition of benzo-1,4-quinone (BQ) in fluid solution. In N,N-dimethylformamide solution, fluorescence quenching involves both static and dynamic interactions but there are no obvious differences between porphyrins with or without the appended calixarene. Under such conditions, the static quenching behaviour is attributed to pi-complexation between the reactants and it is concluded that the calixarene cavity does not bind BQ. An additional static component is apparent in dichloromethane solution. This latter effect involves partial fluorescence quenching, for which the intramolecular rate constant can be obtained by time-resolved fluorescence spectroscopy. The derived rate constants depend on molecular structure in a manner consistent with fluorescence quenching being due to electron transfer. In all cases, however, the dominant quenching step involves diffusional contact between the porphyrin nucleus and a non-bound molecule of BQ.     

Regulation of IgA differentiation in CH12LX B cells by lymphokines. IL-4 induces membrane IgM-positive CH12LX cells to express membrane IgA and IL-5 induces membrane IgA-positive CH12LX cells to secrete IgA

In these studies we utilized the Ag (SRBC)-reactive B cell line CH12LX to study isotype switching. CH12LX cells are a stable population of B cells mainly bearing membrane IgM (mIgM) (98 to 99%) with a small population of B cells bearing membrane IgA (mIgA) (1 to 2%). LPS induced a 5- to 10-fold increase in the secretion of both Ig, whereas a lymphokine-rich supernatant of D10 T cells induced a greater increase in the secretion of IgA than IgM. Analysis of the latter effect with recombinant lymphokines disclosed that rIL-4 induced an increase in the number of mIgA+ cells (6 to 15%) with minimal effect on IgA secretion, whereas IL-5 induced increased IgA secretion but had no effect on mIgA expression. The addition of both lymphokines induced increased mIgA expression and IgA secretion. No effect on mIgA expression or IgA secretion was seen with other lymphokines, including IL-1, IL-2, IL-3, IL-6, GM-CSF, and IFN-gamma. The rIL-4 effect on CH12LX cells represents true differentiation rather than selective proliferation for the following reasons: first, subclones of CH12LX cells respond to IL-4-containing T cell supernatant in the same fashion as the original cell line; second, culture of CH12LX cells with IL-4 causes the appearance of large numbers of dual-bearing mIgM/mIgA cells as well as mIgA+ cells and a dual-bearing mIgM/mIgA line was obtained by cloning CH12LX after stimulation with an IL-4-containing supernatant; third, sorted mIgA+ and mIgA- CH12LX cells had similar rates of proliferation in the presence or absence of IL-4. In further studies, it was found that IL-5 causes IgA secretion by mIgA+ but not mIgA- CH12LX cells indicating that it is acting as a post-isotype switch differentiation factor. These studies are consistent with the view that IL-4 and IL-5 act in a sequential fashion to induce IgA expression and secretion in CH12LX cells, IL-4 inducing differentiation of mIgM+ cells to mIgA+ cells and IL-5 enhancing the IgA secretion by the resulting mIgA-bearing cells.     

Photophysical investigation of the triplet manifold of mono- and bis-phenylethynyl-(2,2′:6′,2″-terpyridine) ruthenium(II) complexes

A complete photophysical study has been carried out on an octahedral ruthenium(II) complex, incorporating two 4′-phenylethynyl-2,2′:6′,2″-terpyridine ligands. Weak emission is observed from the complex in fluid solution at room temperature, but both emission yield and lifetime increase as the temperature is lowered. Luminescence is confirmed to occur exclusively from the lowest energy triplet metal-to-ligand, charge-transfer (MLCT) state, though higher-lying MLCT and metal-centered states are required to adequately model the non-radiative decay kinetics. A comparison of parameters associated with deactivation of the complex and its counterpart, where only one terpy ligand incorporates the phenylethynyl unit, indicates that only the electron-vibrational coupling element is affected. It is also revealed that the extent of electron delocalisation at the triplet level does not critically depend on the number of 4-phenylethynyl-2,2′:6′,2″-terpyridine ligands in the complex.     

T lymphocytes that express CD4 and the alpha beta-T cell receptor but lack Thy-1. Preferential localization in Peyer's patches

Thy-1- T cells expressing CD4 and the alpha beta-TCR have been identified in murine lymphoid tissues. These cells are particularly prevalent in Peyer's patches (PP), representing 17 +/- 3% of PP CD4 T cells, whereas they are much less prevalent in spleen, lymph nodes, lamina propria, or peritoneum. Phenotypic studies of fresh-isolated PP T cells demonstrate that all PP CD4 T cells (both Thy-1- and Thy-1+) express CD3, alpha beta-TCR, and CD5 (Lyt-1), whereas none coexpress CD8 (Lyt-2). Thy-1- and Thy-1+ CD4 T cell lines generated from PP also coexpress CD3 and alpha beta-TCR, but are heterogeneous in expression of CD5 and again do not coexpress CD8. Further studies revealed that Thy-1- CD4+ T cells were not present in nude mice. Short term stimulation of Thy-1+ CD4+ PP T cells with anti-CD3 resulted in loss of Thy-1 in a substantial fraction of these cells. Functional studies of Thy-1- and Thy-1+ CD4+ PP T cells indicate that fresh-isolated Thy-1- CD4+ cells do not proliferate in response to insoluble anti-CD3 but do proliferate when stimulated with soluble anti-CD3 in the presence of feeder cells. In contrast, Thy-1+ CD4+ cells proliferate well to both stimuli. However, Thy-1- CD4+ PP T cells adapted to in vitro culture exhibit vigorous proliferative responses when stimulated with either form of anti-CD3. Evaluation of lymphokine secretion by fresh-isolated Thy-1- and Thy-1+ CD4+ PP T cells revealed that both make substantial amounts of IL-2; however, Thy-1- T cells made less IL-4 than their Thy-1+ counterparts. Neither population made IL-5 or IFN-gamma. Similarly, Thy-1- and Thy-1+ CD4 T cell lines made similar amounts of IL-2; again Thy-1- T cells made less IL-4; and in this case Thy-1- T cells made IL-5 albeit significantly less than the Thy-1+ cells. Finally, immunohistochemical studies suggested that many of the CD4+ T cells in PP germinal centers were Thy-1-, indicating that Thy-1- and Thy-1+ CD4 T cells differ in their distribution within the PP. These studies thus define a phenotypically and functionally distinct T cell population which is most prevalent in murine Peyer's patches.