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Sustained activation of Lyn tyrosine kinase in vivo leads to autoimmunity.

Hibbs ML, Harder KW, Armes J, Kountouri N, Quilici C, Casagranda F, Dunn AR, Tarlinton DM - J. Exp. Med. (2002)

Bottom Line: However, exaggerated positive signaling is also apparent as evidenced by the constitutive phosphorylation of Syk and phospholipase Cgamma2 in resting Lyn(up/up) B cells.Similarly, Lyn(up/up) B cells show a heightened calcium flux in response to BCR stimulation.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.

View Article: PubMed Central - PubMed

Affiliation: Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch. Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria 3050, Australia.

ABSTRACT
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 Cgamma2 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.

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Histology, immunohistochemistry, survival, autoantibodies, and immunofluorescence analysis of Lyn+/+ and Lyn mutant mice. (a) Spleen from a Lyn+/+ mouse showing lymphoid follicles with germinal centers. (b) Spleen from a Lynup/up mouse showing lymphoid follicles with numerous multinucleate giant cells (arrows). (c) Higher power view of Lyn+/+ spleen. (d) Higher power view of Lynup/up spleen depicting multinucleate giant cells within a lymphoid follicle (arrows). Spleen sections from (e) Lyn+/+, (f) Lyn+/up, and (g) Lynup/up mice stained with B220 and CD3 to detect B (brown) and T cells (blue). Spleen sections from (h) Lyn+/+, (i) Lyn+/up, and (j) Lynup/up mice stained with IgM (brown) and IgD (blue) to detect marginal zones (IgMhi). (k) Kaplan-Meier survival curve showing the percent survival of a cohort of 20 male and 20 female Lyn+/+, Lyn+/up, Lynup/up, and Lyn−/− mice. (l) Male Lynup/up mouse of 10 mo of age showing extensive edema. (m) Low power view of a renal cortex from a Lyn+/+ mouse showing several normal glomeruli. (n) Low power view of Lynup/up renal cortex showing two very enlarged sclerotic glomeruli. (o) High power view of Lyn+/+ renal cortex showing a normal glomerulus. (p) High power view of Lynup/up renal cortex showing a severely damaged glomerulus with lobularity and sclerosis. View of the renal cortex from (q) Lyn+/+ and (r) Lynup/up mice stained with anti-Ig. Glomeruli are indicated with arrows. View of the renal cortex from (s) Lyn+/+ and (t) Lynup/up mice stained with anti-IgG. Glomeruli are indicated with arrows. Immunofluorescence analysis of HEp-2 cells stained with antisera from (u) female Lyn+/+, (v) male Lyn+/up, (w) female Lynup/up, and (x) male Lynup/up mice.
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fig7: Histology, immunohistochemistry, survival, autoantibodies, and immunofluorescence analysis of Lyn+/+ and Lyn mutant mice. (a) Spleen from a Lyn+/+ mouse showing lymphoid follicles with germinal centers. (b) Spleen from a Lynup/up mouse showing lymphoid follicles with numerous multinucleate giant cells (arrows). (c) Higher power view of Lyn+/+ spleen. (d) Higher power view of Lynup/up spleen depicting multinucleate giant cells within a lymphoid follicle (arrows). Spleen sections from (e) Lyn+/+, (f) Lyn+/up, and (g) Lynup/up mice stained with B220 and CD3 to detect B (brown) and T cells (blue). Spleen sections from (h) Lyn+/+, (i) Lyn+/up, and (j) Lynup/up mice stained with IgM (brown) and IgD (blue) to detect marginal zones (IgMhi). (k) Kaplan-Meier survival curve showing the percent survival of a cohort of 20 male and 20 female Lyn+/+, Lyn+/up, Lynup/up, and Lyn−/− mice. (l) Male Lynup/up mouse of 10 mo of age showing extensive edema. (m) Low power view of a renal cortex from a Lyn+/+ mouse showing several normal glomeruli. (n) Low power view of Lynup/up renal cortex showing two very enlarged sclerotic glomeruli. (o) High power view of Lyn+/+ renal cortex showing a normal glomerulus. (p) High power view of Lynup/up renal cortex showing a severely damaged glomerulus with lobularity and sclerosis. View of the renal cortex from (q) Lyn+/+ and (r) Lynup/up mice stained with anti-Ig. Glomeruli are indicated with arrows. View of the renal cortex from (s) Lyn+/+ and (t) Lynup/up mice stained with anti-IgG. Glomeruli are indicated with arrows. Immunofluorescence analysis of HEp-2 cells stained with antisera from (u) female Lyn+/+, (v) male Lyn+/up, (w) female Lynup/up, and (x) male Lynup/up mice.

Mentions: To determine if spleen or lymph node architecture was disrupted in Lynup/up mice, histological sections were examined. Like Lyn+/+ spleen, Lynup/up spleen contained lymphoid follicles, although germinal centers were not apparent and there was a loss of red/white pulp definition (Fig. 7 , a–d). Surprisingly, large numbers of multinucleate giant cells were present within lymphoid follicles and in follicle marginal zones (Fig. 7, b and d). Multinucleate giant cells were also found in lymph nodes, liver, and within the thymus where they were concentrated around the medulla/cortex interface (not depicted). SIRPα, a protein that is tyrosine phosphorylated in a Lyn-dependent manner (27), is reported to be involved in macrophage fusion (40), suggesting that this phenotype may arise through its disregulated activity in Lynup/up macrophages.


Sustained activation of Lyn tyrosine kinase in vivo leads to autoimmunity.

Hibbs ML, Harder KW, Armes J, Kountouri N, Quilici C, Casagranda F, Dunn AR, Tarlinton DM - J. Exp. Med. (2002)

Histology, immunohistochemistry, survival, autoantibodies, and immunofluorescence analysis of Lyn+/+ and Lyn mutant mice. (a) Spleen from a Lyn+/+ mouse showing lymphoid follicles with germinal centers. (b) Spleen from a Lynup/up mouse showing lymphoid follicles with numerous multinucleate giant cells (arrows). (c) Higher power view of Lyn+/+ spleen. (d) Higher power view of Lynup/up spleen depicting multinucleate giant cells within a lymphoid follicle (arrows). Spleen sections from (e) Lyn+/+, (f) Lyn+/up, and (g) Lynup/up mice stained with B220 and CD3 to detect B (brown) and T cells (blue). Spleen sections from (h) Lyn+/+, (i) Lyn+/up, and (j) Lynup/up mice stained with IgM (brown) and IgD (blue) to detect marginal zones (IgMhi). (k) Kaplan-Meier survival curve showing the percent survival of a cohort of 20 male and 20 female Lyn+/+, Lyn+/up, Lynup/up, and Lyn−/− mice. (l) Male Lynup/up mouse of 10 mo of age showing extensive edema. (m) Low power view of a renal cortex from a Lyn+/+ mouse showing several normal glomeruli. (n) Low power view of Lynup/up renal cortex showing two very enlarged sclerotic glomeruli. (o) High power view of Lyn+/+ renal cortex showing a normal glomerulus. (p) High power view of Lynup/up renal cortex showing a severely damaged glomerulus with lobularity and sclerosis. View of the renal cortex from (q) Lyn+/+ and (r) Lynup/up mice stained with anti-Ig. Glomeruli are indicated with arrows. View of the renal cortex from (s) Lyn+/+ and (t) Lynup/up mice stained with anti-IgG. Glomeruli are indicated with arrows. Immunofluorescence analysis of HEp-2 cells stained with antisera from (u) female Lyn+/+, (v) male Lyn+/up, (w) female Lynup/up, and (x) male Lynup/up mice.
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fig7: Histology, immunohistochemistry, survival, autoantibodies, and immunofluorescence analysis of Lyn+/+ and Lyn mutant mice. (a) Spleen from a Lyn+/+ mouse showing lymphoid follicles with germinal centers. (b) Spleen from a Lynup/up mouse showing lymphoid follicles with numerous multinucleate giant cells (arrows). (c) Higher power view of Lyn+/+ spleen. (d) Higher power view of Lynup/up spleen depicting multinucleate giant cells within a lymphoid follicle (arrows). Spleen sections from (e) Lyn+/+, (f) Lyn+/up, and (g) Lynup/up mice stained with B220 and CD3 to detect B (brown) and T cells (blue). Spleen sections from (h) Lyn+/+, (i) Lyn+/up, and (j) Lynup/up mice stained with IgM (brown) and IgD (blue) to detect marginal zones (IgMhi). (k) Kaplan-Meier survival curve showing the percent survival of a cohort of 20 male and 20 female Lyn+/+, Lyn+/up, Lynup/up, and Lyn−/− mice. (l) Male Lynup/up mouse of 10 mo of age showing extensive edema. (m) Low power view of a renal cortex from a Lyn+/+ mouse showing several normal glomeruli. (n) Low power view of Lynup/up renal cortex showing two very enlarged sclerotic glomeruli. (o) High power view of Lyn+/+ renal cortex showing a normal glomerulus. (p) High power view of Lynup/up renal cortex showing a severely damaged glomerulus with lobularity and sclerosis. View of the renal cortex from (q) Lyn+/+ and (r) Lynup/up mice stained with anti-Ig. Glomeruli are indicated with arrows. View of the renal cortex from (s) Lyn+/+ and (t) Lynup/up mice stained with anti-IgG. Glomeruli are indicated with arrows. Immunofluorescence analysis of HEp-2 cells stained with antisera from (u) female Lyn+/+, (v) male Lyn+/up, (w) female Lynup/up, and (x) male Lynup/up mice.
Mentions: To determine if spleen or lymph node architecture was disrupted in Lynup/up mice, histological sections were examined. Like Lyn+/+ spleen, Lynup/up spleen contained lymphoid follicles, although germinal centers were not apparent and there was a loss of red/white pulp definition (Fig. 7 , a–d). Surprisingly, large numbers of multinucleate giant cells were present within lymphoid follicles and in follicle marginal zones (Fig. 7, b and d). Multinucleate giant cells were also found in lymph nodes, liver, and within the thymus where they were concentrated around the medulla/cortex interface (not depicted). SIRPα, a protein that is tyrosine phosphorylated in a Lyn-dependent manner (27), is reported to be involved in macrophage fusion (40), suggesting that this phenotype may arise through its disregulated activity in Lynup/up macrophages.

Bottom Line: However, exaggerated positive signaling is also apparent as evidenced by the constitutive phosphorylation of Syk and phospholipase Cgamma2 in resting Lyn(up/up) B cells.Similarly, Lyn(up/up) B cells show a heightened calcium flux in response to BCR stimulation.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.

View Article: PubMed Central - PubMed

Affiliation: Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch. Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria 3050, Australia.

ABSTRACT
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 Cgamma2 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.

Show MeSH
Related in: MedlinePlus