RAGs and Regulation of Autoantibodies

Autoreactive antibodies are etiologic agents in a number of autoimmune diseases. Like all other antibodies these antibodies are produced in developing B cells by V(D)J recombination in the bone marrow. Three mechanisms regulate autoreactive B cells: deletion, receptor editing, and anergy. Here we review the prevalence of autoantibodies in the initial antibody repertoire, their regulation by receptor editing, and the role of the recombinase proteins (RAG l and RAG2) in this process

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

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

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

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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

Igβ tyrosine residues contribute to the control of B cell receptor signaling by regulating receptor internalization

Immunoglobulin (Ig)α and Igβ initiate B cell receptor (BCR) signaling through immune receptor tyrosine activation motifs (ITAMs) that are targets of SH2 domain–containing kinases. To examine the function of Igβ ITAM tyrosine resides in mature B cells in vivo, we exchanged these residues for alanine by gene targeting (IgβAA). Mutant mice showed normal development of all B cell subtypes with the exception of B1 cells that were reduced by fivefold. However, primary B cells purified from IgβAA mice showed significantly decreased steady-state and ligand-mediated BCR internalization and higher levels of cell surface IgM and IgD. BCR cross-linking resulted in decreased Src and Syk activation but paradoxically enhanced and prolonged BCR signaling, as measured by cellular tyrosine phosphorylation, Ca++ flux, AKT, and ERK activation. In addition, B cells with the ITAM mutant receptor showed an enhanced response to a T-independent antigen. Thus, Igβ ITAM tyrosines help set BCR signaling threshold by regulating receptor internalization

Human Autoantibody Silencing by Immunoglobulin Light Chains

Several newly arising human antibodies are polyreactive, but in normal individuals the majority of these potentially autodestructive antibodies are removed from the repertoire by receptor editing or B cell deletion in the bone marrow. To determine what proportion of naturally arising autoantibodies can be silenced by immunoglobulin (Ig) light chain receptor editing, we replaced the light chains in 12 such antibodies with a panel of representative Igκ and Igλ chains. We found that most naturally arising autoantibodies are readily silenced by light chain exchange. Thus, receptor editing may account for most autoreactive antibody silencing in humans. Light chain complementarity determining region (CDR) isoelectric points did not correlate with silencing activity, but Igλ genes were more effective than Igκ genes as silencers. The greater efficacy of Igλ chains as silencer of autoreactivity provides a possible explanation for the expansion and altered configuration of the Igλ locus in evolution

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