CD45R, CD44 and MHC class II are signaling molecules for the cytoskeleton-dependent induction of dendrites and motility in activated B cells

Class I myosins in B-cell physiology: functions in spreading, immune synapses, motility, and vesicular traffic

Myosins comprise a family of motor proteins whose role in muscle contraction and motility in a large range of eukaryotic cells has been widely studied. Although these proteins have been characterized extensively and much is known about their function in different cellular compartments, little is known about these molecules in hematopoietic cells. Myosins expressed by cells from the immune response are involved in maintaining plasma membrane tension, moving and secreting vesicles, endo- and exocytotic processes, and promoting the adhesion and motility of cells. Herein, we summarize our current understanding of class I myosins in B cells, with an emphasis on the emerging roles of these molecular motors in immune functions.

Injection of colchicine intra-hippocampal cortical area 1 enhances novelty seeking behavior

Objective:

Colchicine, a potent neurotoxin derived of plant has been recently identified as a degenerative toxin of small pyramidal cells in the hippocampal cortical area 1 (CA1). In this study, the effect of the alkaloid intra hippocampal CA1 on the novelty seeking behavior in the conditioning task was measured.

Materials and Methods:

Injections of colchicine (1-75 μg/rat, intra-CA1) were performed in cannulated male Wistar rats while being settled in the stereotaxic apparatus. Control group was solely injected saline (1 μl/rat, intra-CA1). One week later, after recovery, all the animals passed the novelty seeking paradigm using an unbiased conditioning task. They were habituated with the conditioned place preference (CPP) apparatus on day 1. Then they were confined in one part of the CPP box for 3 more days. Finally, the animals were tested in the last day. To evaluate, the possible cell injury effect of the toxin on the pyramidal cells of the CA1 both the motivational staying signal in the parts of the box and the non-motivational locomotive signs of the rats were measured.

Results:

Based on the present study, the alkaloid caused significant novelty seeking behavior at higher doses. It also affected the compartment entering behavior in the colchicine received group. However, the alkaloid did not show the significant effect on sniffing, rearing or grooming in the rats.

Conclusion:

Injection of colchicine intra-CA1 may impair the neuronal transmission of motivational information by the pyramidal cells in the dorsal hippocampus.

Differential localization of unconventional myosin I and nonmuscle myosin II during B cell spreading

Cross-linking of CD44 in vitro promotes chemokinesis and actin-based dendrite formation in T and B cells. However, the mechanisms by which the adhesion molecule CD44 induces cytoskeleton activation in lymphocytes are still poorly understood. In this study, we have investigated whether myosin isoforms are involved in CD44-dependent dendrite formation in activated B cells. Pharmacological inhibition of myosin with 2,3-butanedione monoxime strongly affected spreading and dendrite formation, suggesting that these cellular motors may participate in these phenomena. Furthermore, immunofluorescence analysis showed differences in subcellular localization of class I and class II myosin during B cell spreading. In response to CD44 cross-linking, myosin-1c was polarized to lamellipodia, where F-actin was high. In contrast, the distribution of cytosplasmic nonmuscle class II myosin was not altered. Expressions of myosin-1c and II were also demonstrated in B cells by Western blot. Although the inhibition of PLCgamma, PI3K and MEK-1 activation affected the spreading and dendrite formation in activated B cells, only PLCgamma and MEK-1 inhibition correlated with absence of myosin-1c polarization. Additionally, myosin-1c polarization was observed upon cross-linking of other surface molecules, suggesting a common mechanism for B cell spreading. This work shows that class I and class II myosin are expressed in B cells, are differentially distributed, and may participate in the morphological changes of these cells.

Role of CD44 and hyaluronic acid (HA) in activation of alloreactive and antigen-specific T cells by bone marrow-derived dendritic cells

In the current study, the role played by hyaluronic acid (HA) and its receptor CD44 on the activation and functions of dendritic cells (DCs) was investigated. Activation of DCs with HA enhanced their ability to stimulate allogeneic and antigen (Ag)-specific T cells markedly. HA treatment upregulated the expression of costimulatory molecules such as CD40, CD80, and CD86 on DCs. Cell mixing experiments using DC or T cells from CD44 wild-type or CD44 knockout mice as well as blocking studies with anti-CD44 monoclonal antibodies revealed that CD44 expression on T cells but not DC played a critical role in Ag-specific T-cell responsiveness. Also, the HA-induced activation of DC was independent of CD44. When conjugate formation between Ag-pulsed DCs and Ag-specific T cells was studied, the deficiency of CD44 on T cells rather than on DCs was found to play a key role in T-cell-DC interaction. Together, these data demonstrated that HA can activate DC independently of CD44; however, CD44 expressed on Ag-specific T cells plays a critical role in its interaction with DC and resultant expansion of T cells.

MHC class II signaling in antigen-presenting cells

The MHC class II molecules have been recognized as signaling receptors for more than a decade, and recent work has revealed the importance of their signaling for the immune response. Today, we know that the function of MHC class II molecules on antigen-presenting cells (APCs) is not limited to their role as antigen-presenting structures; they are flexible receptors that, by triggering a variety of signaling pathways, can regulate APC activities from proliferation and maturation to apoptosis. Recent advances have provided insights into how these molecules might accommodate such regulation.

The spreading of B lymphocytes induced by CD44 cross-linking requires actin, tubulin, and vimentin rearrangements

CD44 is a polymorphic family of adhesion molecules widely distributed on cells and tissues. CD44 is up-regulated on activated lymphocytes, and it can function as a receptor, mediating rolling and migration. Although it has been demonstrated that anti-CD44 antibodies bound to tissue-culture plates induce multidirectional emission of retractile dendrites ("spreading") in activated murine B lymphocytes, the involvement of cytoskeleton elements in this phenomenon is largely unknown. In this work, it is shown that the generation of dendrites induced by CD44 cross-linking in activated B cells depends on actin, microtubules, and vimentin reorganization. Immunofluorescence analysis showed that dendrite formation began with actin polymerization, and its extension was favored by microtubules and intermediate filaments of vimentin oriented to the polymerized actin. Pretreatment of activated B lymphocytes with cytochalasin E inhibited the dendrites formation; moreover, when cells were treated with this drug at different time points during the dendrite formation process, the stability of the dendrites was affected. In contrast, although the treatment with colchicine and nocodazole (tubulin polymerization inhibitors) inhibited the dendrites formation, it did not inhibit the initial phase of actin polymerization. According to these results, B cell spreading and dendrite formation induced by anti-CD44 antibodies require coordinated rearrangements of actin, microtubules, and vimentin, being the actin cytoskeleton, the most important element that confers stability and drives the morphological changes during B cell spreading, conceivably preparing B lymphocytes for locomotion.

Enforced and prolonged CD40 ligand expression triggers autoantibody production in vivo

CD40, a glycoprotein expressed on B lymphocytes plays an important role in B cell development, growth and differentiation. The ligand for the CD40 is a 39-kDa glycoprotein (CD154) expressed on the surface of activated T lymphocytes and is essential for thymus-dependent humoral immunity. The expression of CD154 is tightly regulated and its transient expression reduces the chances of potentially deleterious bystander activation of B cells. Stimulation through CD40 has been studied in vitro by using antibodies against CD40, by membranes of activated T cells or lately, by CD154 transfected cells. In this work we have evaluated the outcome of CD40-CD40 ligand interaction in vitro and in vivo by using CD154-transfected L929 cells. In vitro assays showed that CD154-L929 cells can induce on B cells: IL-4-dependent proliferation, up-regulation of CD23, CD54 and class II molecules and can also rescue WEHI-231 B cell lymphoma from anti-IgM-induced apoptosis. Interestingly, in vivo assays revealed that when CD154-L929 cells were inoculated into the spleen, mice developed a strong but transient production of anti-erythrocyte autoantibodies. Through B lymphocyte activation with CD154-transfected L929 cells both in vitro and in vivo, our data reveal that enforced and prolonged expression of CD40 ligand overcomes the tightly regulated mechanisms of B cell activation, triggering the production of autoantibodies. This system might be used to evaluate the early steps of an autoimmune response and the role of CD40-CD154 in the induction of primary responses in vivo.

Differential endocytotic characteristics of a novel human B/DC cell line HBM-Noda: effective macropinocytic and phagocytic function rather than scavenging function

In order to characterize a novel human B cell-lineage dendritic cell line (B/DC line) as an antigen-presenting cell (APC), we compared three types of endocytosis (micropinocytosis via a clathrin-coated pit, macropinocytosis via membrane ruffling, and phagocytosis) among myeloid-related, macrophage (Mphi) cell lines and a B/DC line. In the present examination, we used a unique human dendritic cell (DC) line, HBM-Noda (Noda). Flow cytometric and immunocytochemical analyses revealed that Noda not only expresses some DC markers, but also it expresses some B-cell associated markers. Noda shows strong capacities to stimulate allogenic T cells, to produce immunoglobulin G (IgG), and to perform immunoglobulin gene rearrangement. These data strongly suggest that Noda is a B-cell lineage DC line. The endocytic differences among these cell lines were as follows. (1) The level of micropinocytosis of Noda was significantly less than that of conventional human Mphi cell lines, and the formation of a clathrin-coated pit was not observed in Noda. (2) The level of macropinocytosis of Noda was also smaller than that of conventional Mphi cells indicating that the active membrane ruffling of Noda induces rapid recycling. (3) Phagocytosis of opsonized sheep red blood cells (SRBC) was performed more efficiently in Noda than in other Mphi cell lines. Collectively, these data suggest that in human bone marrow cells, we can identify a unique DC subtype, B/DC line, which develops through a lymphoid DC-differentiation pathway, and DC in this lineage plays an important role in the host immune response because of its effective uptake of a variety of size of antigens by using the skillful membrane ruffling and surface receptors