Collective fluorescence and decoherence of a few nearly identical quantum dots

We study the collective interaction of excitons in closely spaced artificial molecules and arrays of nearly identical quantum dots with the electromagnetic modes. We discuss how collective fluorescence builds up in the presence of a small mismatch of the transition energy. We show that a superradiant state of a single exciton in a molecule of two dots with realistic energy mismatch undergoes a two-rate decay. We analyze also the stability of subdecoherent states for non-identical systems.Comment: 7 pages, 5 figure

Cas9-Primed Adaptive Immunity During the CRISPR-Cas Response

Prokaryotes have developed numerous defense strategies to combat the constant threat of viruses (bacteriophages) that endanger them. Clustered, regularly interspaced short palindromic repeats (CRISPR) loci provide archaea and bacteria with adaptive immune systems that allow them to counteract these rapidly evolving genetic parasites. These diverse systems all generally contain two components: a set of CRISPR-associated (cas) genes and a series of repetitive DNA elements intercalated with variable sequences known as spacers. Following viral infection, these sequences are acquired from the viral genome and integrated in the CRISPR array as new spacers. Spacers are then transcribed into CRISPR RNAs (crRNAs) that direct the Cas nucleases to destroy the invader following sequence-specific recognition of either DNA or RNA. Thus, spacers function as a form of immunologic memory that can be called upon again and again to defend the cell from reinfection. In type II CRISPR-Cas systems, spacer sequences direct the Cas9 nuclease to target infecting bacteriophages and cleave their double-stranded (ds)DNA genomes. Whether and how pre-exiting anti-viral spacers in type II systems affect memory generation and the acquisition of new spacers is unknown. Here, in my thesis work, I demonstrate that previously acquired spacers promote additional spacer capture from the vicinity of the Cas9 cut site at an enhanced rate. I go on to show that Cas9-mediated dsDNA break (DSB) formation is required for spacer-mediated spacer acquisition and that the rate of spacer acquisition is correlated with the efficiency of Cas9 cleavage. As a result of this mechanism, cells with preexisting viral immunity can utilize their spacerderived crRNAs to direct the acquisition of additional spacers in a new phase of immune response known as primed spacer acquisition or priming. A consequence of priming is that immune cells can acquire additional spacers as Cas9 destroys the infecting virus. I go on to show that spacers acquired during Cas9- mediated priming endow potent benefits to bacterial communities faced with virulent bacteriophages. In particular, priming suppresses the emergence of CRISPR escaper and related viruses that emerge during Cas9 targeting. I show that this anti-viral immunity is achieved in three ways. Firstly, priming expands the hosts immune repertoire, thereby improving the existing anti-phage immunity. In addition, I show that primed spacer acquisition allows the host to contain the propagation escapers that have mutations in their target sequence that abrogate Cas9 targeting. Finally, by preemptively immunizing the host with additional spacers during the initial Cas9 targeting response, priming allows the host to anticipate secondary infections by escaper and related viruses. This “prophylactic” immunity is a unique feature in CRISPR systems that allows type II systems to overcome future threats from viruses that would have overcome the defense provided by the initial anti-viral spacer. CRISPR-Cas immune systems allow their host to rapidly adapt to the viruses that challenge them. Collectively, my thesis work has revealed a new phases of the type II-A CRISPR-Cas9 immune response that is fundamental to how these systems defend their hosts against bacteriophages

Contribution of dendritic cells to stimulation of the murine syngeneic mixed leukocyte reaction

We have studied the proliferative response of unprimed T cells to syngeneic dendritic cells (DC) (syngeneic mixed leukocyte rection [SMLR]) in cultures of mouse spleen and lymph node. T cells purified by passage over nylon wool contain few DC and exhibit little proliferative activity during several days of culture. Addition of small numbers of purified syngeneic DC induces substantial, dose-dependent, T cell-proliferative responses that peak at day 4-5. B cells purified on anti-Ig-coated plates do not respond to DC at all doses tested. DC cultures medium does not induce proliferation, and coculture of DC and T cells is required. Purified mouse B and T lymphocytes stimulate SMLR weakly if at all. Likewise, peritoneal and spleen macrophages are weak or inactive. Therefore, DC are potent and possibly unique primary cells for stimulating the SMLR in mice. sIg- spleen lymph node cells show extensive background proliferative responses in vitro, and fail to respond to small numbers of purified DC. If the sIg- cells are treated with anti-Ia and complement, or passed over nylon wool, DC are removed and proliferative activity falls. Proliferative activity is restored by adding back DC at levels similar to those present in sIg- cells (1-2%). Thus, DC-dependent, T cell proliferation probably occurs in all spleen and lymph node cultures. As expected from previous work (6), DC are also potent inducers of allogeneic MLR. On a per DC basis, the syngeneic response is 10 times weaker than the allogeneic MLR, and it is not accompanied by the development of cytotoxic lymphocytes. The magnitude of the SMLR was not altered by antigen priming, and DC maintained in isologous rather than fetal calf serum were active stimulators. Therefore, syngeneic stimulation appears to be an intrinsic property of DC, and modification by exogenous agents does not seem to be required. Coculture of DC and T cells results in the development of cell clusters that can be isolated and characterized directly. The clusters account for 10-20% of the viable cells in the culture, but contain \u3e80% of the responding T cells and stimulating DC by morphologic and surface-marker criteria. The efficient physical association of DC and responding T cells implies specific cell-cell recognition. We conclude that the SMLR reflects the ability of T cells, or some subpopulation of T cells, to interact with and proliferate in response to small numbers of DC

Yellow fever 17D as a vaccine vector for microbial CTL epitopes: protection in a rodent malaria model

The yellow fever vaccine 17D (17D) is safe, and after a single immunizing dose, elicits long-lasting, perhaps lifelong protective immunity. One of the major challenges facing delivery of human vaccines in underdeveloped countries is the need for multiple injections to achieve full efficacy. To examine 17D as a vector for microbial T cell epitopes, we inserted the H-2Kd–restricted CTL epitope of the circumsporozoite protein (CS) of Plasmodium yoelii between 17D nonstructural proteins NS2B and NS3. The recombinant virus, 17D-Py, was replication competent and stable in vitro and in vivo. A single subcutaneous injection of 105 PFU diminished the parasite burden in the liver by ∼70%. The high level of protection lasted between 4 and 8 wk after immunization, but a significant effect was documented even 24 wk afterwards. Thus, the immunogenicity of a foreign T cell epitope inserted into 17D mimics some of the remarkable properties of the human vaccine. Priming with 17D-Py followed by boosting with irradiated sporozoites conferred sterile immunity to 90% of the mice. This finding indicates that the immune response of vaccine-primed individuals living in endemic areas could be sustained and magnified by the bite of infected mosquitoes

Tolerogenic dendritic cells

Dendritic cells (DCs) have several functions in innate and adaptive immunity. In addition, there is increasing evidence that DCs in situ induce antigen-specific unresponsiveness or tolerance in central lymphoid organs and in the periphery. In the thymus DCs generate tolerance by deleting self-reactive T cells. In peripheral lymphoid organs DCs also induce tolerance to antigens captured by receptors that mediate efficient uptake of proteins and dying cells. Uptake by these receptors leads to the constitutive presentation of antigens on major histocompatibility complex (MHC) class I and II products. In the steady state the targeting of DC antigen capture receptors with low doses of antigens leads to deletion of the corresponding T cells and unresponsiveness to antigenic rechallenge with strong adjuvants. In contrast, if a stimulus for DC maturation is coadministered with the antigen, the mice develop immunity, including interferon-γ-secreting effector T cells and memory T cells. There is also new evidence that DCs can contribute to the expansion and differentiation of T cells that regulate or suppress other immune T cells. One possibility is that distinct developmental stages and subsets of DCs and T cells can account for the different pathways to peripheral tolerance, such as deletion or suppression. We suggest that several clinical situations, including autoimmunity and certain infectious diseases, can be influenced by the antigen-specific tolerogenic role of DCs

Dendritic cells of the mouse: Identification and characterization

We have identified and characterized a distinctive population of dendritic cells (DCs) in mouse spleen, lymph nodes, thymus, and liver. Dendritic cells can adhere to tissue culture surfaces but otherwise differ considerably from macrophages, the other major class of adherent cell. Morphological differences are evident by phase contrast and electron microscopy, and by cytochemistry. Dendritic cells exhibit little or no binding and phagocytosis of opsonized particles. During culture, they retain their unusual morphological features and surface markers, but lose the capacity to adhere. All DCs express and synthesize Ia antigens for several days in vitro, whereas only a subpopulation of mouse macrophages expresses Ia in all organs we have studied. Thus, DCs can be distinguished from macrophages in several independent and stable traits. Highly enriched preparations of the 2 cell types have been obtained. Spleen DCs are derived from bone marrow and are present in nude mice. Dendritic cells do not proliferate, but exhibit a rapid turnover. Other features in their life history are not known. We are studying the contribution of DCs to several immune responses. In all organs we have studied, they are powerful stimulators of the primary mixed leukocyte reaction. B cells, T cells, and macrophages from these organs are weak or inactive. Dendritic cells are potent accessory cells in T cell proliferative responses to mitogens and tuberculin antigens. These dendritic cells and Langerhans cells may belong to a similar lineage, but to date, Birbeck granules, surface ATPase, and binding of opsonized erythrocytes have not been demonstrated in spleen dendritic cells. However, in functional assays, both DCs and Langerhans cells synthesize Ia antigens and contribute to transplantation reactions, accessory cell function, and the development of contact sensitivity

Studies of the cell surface of mouse dendritic cells and other leukocytes

Nussenzweig, M.C., Steinman, R.M., Unkeless, J.C., Witmer, M.D., Gutchinov, B., and Cohn, Z.A. Studies of the cell surface of mouse dendritic cells and other leukocytes. J. Exp. Med. 154: 168-187, 1981https://digitalcommons.rockefeller.edu/historical-scientific-reports/1006/thumbnail.jp

Studies of the cell surface of mouse dendritic cells and other leukocytes

[No abstract available

A monoclonal antibody specific for mouse dendritic cells

Dendritic cells (DC) are a small subpopulation of lymphoid cells with distinctive cytologic features, surface properties, and functions. This report describes the DC-specific antibody (Ab) secreted by clone 33D1. Rat spleen cells immune to mouse DC were fused to the P3U myeloma. Hybrid culture supernatants were screened simultaneously against DC, a macrophage (MΦ) cell line, and mitogen-stimulated lymphoblasts. 33D1 Ab specifically killed 80-90% of DC from spleen and lymph node, but no other leukocytes, including Ia+ and Ia- MΦ (Ia, I-region-associated antigen). Quantitative binding studies with 3H-labeled 33D1 Ab showed that DC had an average of 14,000 binding sites per cell. Binding to DC was inhibited with Fab fragment of 33D1 Ab but not with a panel of other monoclonal antibodies, including anti-Ia Ab. Adherence and flotation procedures that enriched for DC enriched for 3H-labeled 33D1 Ab binding in parallel. 33D1 antigen was not detectable on: MΦ from spleen, peritoneal cavity, and blood; three MΦ cell lines; lymphocytes; granulocytes; platelets; and erythroid cells. DC continued to express the 33D1 antigen after 4 days in culture, whereas MΦ and lymphocytes did not acquire it. Quantitative and autoradiographic studies confirmed that spleen and lymph node suspensions contain less than 1% DC. We conclude that 33D1 Ab detects a stable and specific DC antigen and can be used to monitor DC content in complex lymphoid mixtures