Antigen Receptor–Induced Activation and Cytoskeletal Rearrangement Are Impaired in Wiskott-Aldrich Syndrome Protein–Deficient Lymphocytes

Abstract

The Wiskott-Aldrich syndrome protein (WASp) has been implicated in modulation of lymphocyte activation and cytoskeletal reorganization. To address the mechanisms whereby WASp subserves such functions, we have examined WASp roles in lymphocyte development and activation using mice carrying a WAS null allele (WAS − / −). Enumeration of hemopoietic cells in these animals revealed total numbers of thymocytes, peripheral B and T lymphocytes, and platelets to be significantly diminished relative to wild-type mice. In the thymus, this abnormality was associated with impaired progression from the CD44−CD25+ to the CD44−CD25− stage of differentiation. WASp-deficient thymocytes and T cells also exhibited impaired proliferation and interleukin (IL)-2 production in response to T cell antigen receptor (TCR) stimulation, but proliferated normally in response to phorbol ester/ionomycin. This defect in TCR signaling was associated with a reduction in TCR-evoked upregulation of the early activation marker CD69 and in TCR-triggered apoptosis. While induction of TCR-ζ, ZAP70, and total protein tyrosine phosphorylation as well as mitogen-activated protein kinase (MAPK) and stress-activated protein/c-Jun NH2-terminal kinase (SAPK/JNK) activation appeared normal in TCR-stimulated WAS − / − cells, TCR-evoked increases in intracellular calcium concentration were decreased in WASp-deficient relative to wild-type cells. WAS − / − lymphocytes also manifested a marked reduction in actin polymerization and both antigen receptor capping and endocytosis after TCR stimulation, whereas WAS − / − neutrophils exhibited reduced phagocytic activity. Together, these results provide evidence of roles for WASp in driving lymphocyte development, as well as in the translation of antigen receptor stimulation to proliferative or apoptotic responses, cytokine production, and cytoskeletal rearrangement. The data also reveal a role for WASp in modulating endocytosis and phagocytosis and, accordingly, suggest that the immune deficit conferred by WASp deficiency reflects the disruption of a broad range of cellular behaviors.

Vav1 transduces TCR signals required for LFA‐1 function and cell polarization at the immunological synapse

“…However, a number of recent reports have implicated these GTPases in the regulation of microtubules and cellular polarity: inhibition of Cdc42 inhibits polarization of the MTOC within a T cell hybridoma [32], Rac1 and Cdc42 transduce signals resulting in the phosphorylation and subsequent inhibition of the microtubule-destabilizing protein stathmin [33], and Cdc42 is required for integrin-induced MTOC polarization in astrocytes [34]. Such a Cdc42-dependent signal to the MTOC could be mediated by WASp, a Cdc42 effector, since WASp-deficient T cells also show defective polarization of the MTOC towards the T-cell/ APC contact site [35]. Further work is needed to establish which, if any, of these pathways may be operating during TCR signaling.…”

Chemokines: attractive mediators of the immune response

“…Recently, Haddad et al [104] demonstrated that CXCL12 induced T cell chemotaxis through Cdc42 activation and interaction with WASP. Mice with mutations in Vav or WASP exhibit deficiencies in T cell proliferation, cytoskeletal rearrangement and receptor capping [105,106]. These data indicate that cytoskeletal reorganization is important not only for T cell polarization but also for activation.…”

Impaired in vitro regulatory T cell function associated with Wiskott–Aldrich syndrome

“…Although WASp-deficient T cells respond poorly to TCR stimulation in vitro, their proliferative responses can be partially rescued by addition of IL-2, particularly in the presence of accessory cells (6,9). To investigate whether the defective suppressor function resulted from a failure of adequate cell activation, we prestimulated CD4 + CD25 + Treg cells in the presence of anti-CD3 plus IL-2 and accessory cells for three days.…”

“…The disorder is caused by mutations of WAS, the gene encoding the WAS protein, WASp, a key regulator of actin polymerization that is expressed in nonerythroid hematopoietic cells (2). T cells isolated from WASp-deficient mice and WAS patients show multiple defects including reduced TCR-induced proliferation and IL-2 production associated with impaired actin polymerization, defects which are likely to contribute to the immunodeficiency in WAS (6)(7)(8)(9).…”