Defective negative regulation of antigen receptor signaling in Lyn-deficient B lymphocytes (original) (raw)
Related papers
Positive and negative roles of the tyrosine kinase Lyn in B cell function
Seminars in Immunology, 1998
The function of Lyn in B cell activation has been studied recently by examining the properties of B cells from mice in which the lyn gene has been inactivated by gene targeting. These mice show evidence of B cell hyperreactivity in vivo, as the number of B lymphoblastoid cells greatly increase with age, IgM levels increase by 10-fold or more, and autoantibodies to double-stranded DNA and other nuclear antigens become apparent. B cells from lyn yry mice also exhibit enhanced BCR-induced activation of MAP kinases, intracellular calcium elevation and proliferative responses in vitro. These phenomena may relate to participation of Lyn in events that serve to decrease B cell responses to antigen. Among the leading candidates for these suppressive events are the inhibition of B cell antigen receptor function by Fc␥ RIIb1 and by CD22. Although Lyn also participates positively in the initial events of B cell antigen receptor signal transduction, this function can also be supplied by other tyrosine kinases, presumably other Src-family kinases. In contrast, some aspects of inhibition by CD22 appear to be almost completely dependent upon Lyn and Fc␥ RIIb1 inhibition is also diminished in the absence of Lyn. Thus, the net effect of Lyn action is negative rather than positive for B cell activation. Key words: autoimmunity r CD22 r Fc␥ RIIb r Lyn r Src-family kinases ᮊ1998 Academic Press ACTIVATION OF B lymphocytes is initiated by contact Ž . of the B cell antigen receptor BCR with antigen and proceeds if the B cell receives additional stimulatory signals, which can include cytokines, membranebound molecules of helper T cells, such as CD40L, or polyclonal B cell activator molecules from bacterial cell walls. The extent and nature of required additio-From The George Williams Hooper Foundation,
European Journal of Immunology, 2005
B cell fate is determined by the strength of signals from the antigen receptor and from co-receptors that adjust the activation threshold and tune the B cell to its environment. These co-receptors have been broadly classified into inhibitory and enhancing groups, yet some, such as CD22, may have dual effects. CD22 recruits a variety of signal enhancers at the same time as Lyn-dependent phosphorylation leads to the binding of the inhibitory phosphatase SHP-1. To assess the relative importance of Lyn-and CD22dependent and -independent pathways, we generated Lyn and CD22 single-deficient mice and Lyn/CD22 double-deficient mice expressing the MD4 immunoglobulin transgene against hen egg lysozyme (Ig HEL ). This genetic approach has enabled us to compare the contributions of Lyn and CD22 to B cell development in vivo, independent of BCR specificity and in the presence and absence of self-antigen. Our results show that although the effects of Lyn are dominant in negative regulation of B cell hyperactivity, Lyn and CD22 have independent and additive effects on B cell survival. These findings emphasize the subtle nature of regulation at the BCR and the usefulness of genetic complementation to dissect common and parallel pathways.
1996
CD45 is a tyrosine phosphatase that is required for normal B cell receptor (BCR)-mediated signaling. It has been shown that Src-family tyrosine kinases such as Lyn could be a potential substrate for CD45. In vitro studies indicate that activities of Src family tyrosine kinases are regulated by tyrosine phosphorylation; C-terminal phosphorylation is inhibitory, and autophosphorylation is stimulatory. We report here that both autophosphorylation and C-terminal negative regulatory tyrosines of Lyn were hyperphosphorylated in CD45-deficient DT40 B cells. In this mutant cell, BCR-induced protein-tyrosine phosphorylation and calcium mobilization were severely compromised, as seen in Lyn-deficient cells. Consistent with this observation, Lyn activation upon receptor ligation was profoundly decreased in CD45deficient cells. Taken together, our results suggest that dephosphorylation of tyrosine residues at both autophosphorylation and negative regulatory sites is mediated by CD45 in vivo, and that dephosphorylation of C-terminal tyrosine is a prerequisite for participation of Lyn in BCR signaling.
Developmental Acquisition of the Lyn-CD22-SHP-1 Inhibitory Pathway Promotes B Cell Tolerance
The Journal of Immunology, 2009
To better understand whether autoimmunity in Lyn-deficient mice arises from compromised central or peripheral B cell tolerance, we examined BCR signaling properties of wild-type and Lyn-deficient B cells at different stages of development. Wild-type mature follicular B cells were less sensitive to BCR stimulation than were immature transitional stage 1 B cells with regard to BCRinduced calcium elevation and ERK MAPK activation. In the absence of Lyn, mature B cell signaling was greatly enhanced, whereas immature B cell signaling was minimally affected. Correspondingly, Lyn deficiency substantially enhanced the sensitivity of mature B cells to activation via the BCR, but minimally affected events associated with tolerance induction at the immature stage. The effects of CD22 deficiency on BCR signaling were very similar in B cells at different stages of maturation. These results indicate that the Lyn-CD22-Src homology region 2 domain-containing phosphatase-1 inhibitory pathway largely becomes operational as B cell mature, and sets a threshold for activation that appears to be critical for the maintenance of tolerance in the B cell compartment.
Sustained Activation of Lyn Tyrosine Kinase In Vivo Leads to Autoimmunity
Journal of Experimental Medicine, 2002
Genetic ablation of the Lyn tyrosine kinase has revealed unique inhibitory roles in B lymphocyte signaling. We now report the consequences of sustained activation of Lyn in vivo using a targeted gain-of-function mutation (Lyn up/up mice). Lyn up/up mice have reduced numbers of conventional B lymphocytes, down-regulated surface immunoglobulin M and costimulatory molecules, and elevated numbers of B1a B cells. Lyn up/up B cells are characterized by the constitutive phosphorylation of negative regulators of B cell antigen receptor (BCR) signaling including CD22, SHP-1, and SHIP-1, and display attributes of lymphocytes rendered tolerant by constitutive engagement of the antigen receptor. However, exaggerated positive signaling is also apparent as evidenced by the constitutive phosphorylation of Syk and phospholipase C ␥ 2 in resting Lyn up/up B cells. Similarly, Lyn up/up B cells show a heightened calcium flux in response to BCR stimulation. Surprisingly, Lyn up/up mice develop circulating autoreactive antibodies and lethal autoimmune glomerulonephritis, suggesting that enhanced positive signaling eventually overrides constitutive negative signaling. These studies highlight the difficulty in maintaining tolerance in the face of chronic stimulation and emphasize the pivotal role of Lyn in B cell signaling.
Journal of immunology (Baltimore, Md. : 1950), 1999
Using CD45-deficient clones from the immature B cell line, WEHI-231, we previously demonstrated that CD45 selectively dephosphorylates the Src-family protein tyrosine kinase Lyn and inhibits its kinase activity. To further define the mechanisms of CD45 action on Lyn, we metabolically labeled Lyn from CD45-positive and -negative WEHI-231 cells and analyzed cyanogen bromide fragments by SDS-PAGE analysis. Phosphoamino acid analysis confirmed that Lyn is tyrosine phosphorylated with little serine or threonine phosphorylation. In CD45-negative cells, two bands at 8.2 and 4.1 kDa were phosphorylated in the absence of B cell Ag receptor (BCR) ligation. The 8.2-kDa band corresponded to a fragment containing the positive regulatory site (Tyr397), as assessed by its size and its phosphorylation in an in vitro kinase assay. The 4.1-kDa band was phosphorylated by COOH-terminal Src kinase, suggesting that it contains the COOH-terminal negative regulatory site (Tyr508). CD45 was also shown to de...
Immunity, 2016
B1 and B2 B cells differ in their ability to respond to T-cell-independent (TI) antigens. Here we report that the Src-family kinase (SFK) regulator CD148 has a unique and critical role in the initiation of B1 but not B2 cell antigen receptor signaling. CD148 loss-of-function mice were found to have defective B1 B-cell-mediated antibody responses against the T-cell-independent antigens NP-ficoll and Pneumovax 23 and had impaired selection of the B1 B cell receptor (BCR) repertoire. These deficiencies were associated with a decreased ability of B1 B cells to induce BCR signaling downstream of the SFK Lyn. Notably, Lyn appeared to be selectively regulated by CD148 and loss of this SFK resulted in opposite signaling phenotypes in B1 and B2 B cells. These findings reveal that the function and regulation of Lyn during B1 cell BCR signaling is distinct from other B cell subsets.
International Immunology, 2002
The human and murine CD21 gene products have been functionally linked to B cell activation by the co-ligation of the BCR and the CD21/CD19/CD81 complexes. Binding of low levels of antigen complexed to the complement ligand(s) for CD21 enhances B cell activation compared to the stimulation caused by antigen alone. Mice lacking functional CD21 predispose to autoimmune responses suggesting that this receptor may also play a negative role: thus in the presence of excess complement-bearing immune complexes, B cell antigen-specific activation may be inhibited. This possibility was investigated using intracellular calcium elicitation analyses to follow BCR-mediated activation. Ligation of the BCR and limiting quantities of the CD21 receptor demonstrated the expected enhanced cellular response compared to BCR ligation alone: CD21 ligation alone demonstrated no alteration in calcium flux. However, co-ligation of the BCR with excess CD21 binding resulted in the elimination of the calcium response, suggesting that CD21 ligation was down-modulating the BCR response. Immunoprecipitation of kinases associated with the BCR and CD21/CD19/CD81 complexes demonstrated that Lyn is preferentially depleted from the BCR complex following excess binding of CD21. Localization of other kinases integral for B cell activation is not altered. These data suggest that excess CD21 ligand binding can negatively impact B cell activation by sequestering Lyn kinase away from the BCR complex.
A kinase-dead allele of Lyn attenuates autoimmune disease normally associated with Lyn deficiency
Journal of immunology (Baltimore, Md. : 1950), 2009
Lyn kinase, a member of the Src family of tyrosine kinases, functions as both a positive and negative regulator of B cell activation. In the absence of Lyn, BCR signaling is unregulated, leading to perturbed B cell development, hyperactive B cells, and lethal Ab-mediated autoimmune disease. We have generated a mutant mouse pedigree, termed Mld4, harboring a novel mutation in the gene encoding Lyn, which renders the protein devoid of kinase activity. Despite similarities between the phenotypes of Lyn(Mld4/Mld4) and Lyn(-/-) mice, the spectrum of defects in Lyn(Mld4/Mld4) mice is less severe. In particular, although defects in the B cell compartment are similar, splenomegaly, myeloid expansion, and autoantibody production, characteristic of Lyn(-/-) mice, are absent or mild in Lyn(Mld4/Mld4) mice. Critically, immune complex deposition and complement activation in Lyn(Mld4/Mld4) glomeruli do not result in fulminant glomerulonephritis. Our data suggest that BCR hypersensitivity is insuf...