Altered Functionality of Lipoprotein(a) Impacts on Angiogenesis in Diabetic Retinopathy.

Purpose: Diabetic retinopathy (DR) is a complication of type 2 diabetes mellitus (T2DM). Lipoprotein(a) (Lp(a)) contributes to the progression of DR, but how is unclear. In homeostasis of the retinal microvasculature, myeloid-derived pro-angiogenic cells (PACs) also play a pivotal role, and fail to function properly in diabetic conditions. Here, we explored the putative contribution of Lp(a) from patients with T2DM with/without DR and healthy controls on inflammation and angiogenesis of retinal endothelial cells (RECs), and on PAC differentiation. Subsequently, we compared the lipid composition of Lp(a) from patients to that from healthy controls. Methods: Lp(a)/LDL obtained from patients and healthy controls were added to TNF-alpha-activated RECs. Expression of VCAM-1/ICAM-1 was measured using flowcytometry. Angiogenesis was determined in REC-pericyte co-cultures stimulated by pro-angiogenic growth factors. PAC differentiation from peripheral blood mononuclear cells was determined by measuring expression of PAC markers. The lipoprotein lipid composition was quantified using detailed lipidomics analysis. Results: Lp(a) from patients with DR (DR-Lp(a)) failed to block TNF-alpha-induced expression of VCAM-1/ICAM-1 in REC whereas Lp(a) from healthy controls (healthy control [HC]-Lp(a)) did. DR-Lp(a) increased REC angiogenesis more than HC-Lp(a) did. Lp(a) from patients without DR showed intermediate profiles. HC-Lp(a) reduced the expression of CD16 and CD105 in PAC, but T2DM-Lp(a) did not. Phosphatidylethanolamine content was lower in T2DM-Lp(a) than in HC-Lp(a). Conclusions: DR-Lp(a) does not show the anti-inflammatory capacity seen with HC-Lp(a), but increases REC angiogenesis, and affects PAC differentiation less than HC-Lp(a). These functional differences in Lp(a) in T2DM-related retinopathy are associated with alterations in the lipid composition as compared to healthy conditions.

Aberration in myeloid-derived pro-angiogenic cells in type-2 diabetes mellitus; implication for diabetic retinopathy?

Purpose: Diabetic retinopathy (DR) is a major microvascular complication of type 2 diabetes mellitus (T2DM). Myelomonocytic proangiogenic cells (PAC) have been implicated in DR pathogenesis, but their functional and developmental abnormalities are unclear. In this study we assessed PAC characteristics from healthy controls, T2DM patients with DR (DR) and without (NoDR) in order to determine the consequence of the diabetic condition on PAC phenotype and function, and whether these differ between DR and NoDR patients. Methods: PAC were generated by culturing PBMC on fibronectin coating and then immunophenotyped using flow cytometry. Furthermore, cells were sorted based on CD14, CD105, and CD133 expression and added to an in vitro 3-D endothelial tubule formation assay, containing GFP-expressing human retinal endothelial cells (REC), pericytes, and pro-angiogenic growth factors. Tubule formation was quantified by fluorescence microscopy and image analysis. Moreover, sorted populations were analyzed for angiogenic mediator production using a multiplex assay. Results: The expression of CD16, CD105 and CD31, but not CD133, was lower in PAC from T2DM patients with or without DR. Myeloid and non-myeloid T2DM-derived sorted populations increased REC angiogenesis in vitro as compared to control cultures. They also showed increased S100A8 secretion, decreased VEGF-A secretion, and similar levels of IL-8, HGF, and IL-3 as compared to healthy control (HC)-derived cell populations. Conclusion: T2DM PAC are phenotypically and functionally altered compared to PAC from HC. Differences between DR and NoDR PAC are limited. We propose that impaired T2DM PAC provide inadequate vascular support and promote compensatory, albeit pathological, retinal neovascularization.

Basic Fibroblast Growth Factor Induces Adipogenesis in Orbital Fibroblasts: Implications for the Pathogenesis of Graves' Orbitopathy.

BACKGROUND: Basic fibroblast growth factor (bFGF) has been implicated in the pathogenesis of Graves' orbitopathy (GO). It stimulates several processes, including hyaluronan synthesis, involved in orbital tissue volume expansion and may act synergistically with platelet-derived growth factor (PDGF)-BB. PDGF-BB is known to stimulate adipogenesis in orbital fibroblasts, but the effect of bFGF on adipogenesis in orbital fibroblasts is so far unknown. This study was conducted to determine whether (i) bFGF induces adipogenesis in orbital fibroblasts, (ii) bFGF and PDGF-BB together exert an additive or synergistic effect on adipogenesis, and (iii) treatment directed at bFGF- and PDGF-BB signaling may potentially be of interest for the treatment of GO. METHODS: Orbital fibroblasts from GO patients and controls were cultured in adipocyte differentiation medium with or without bFGF and/or PDGF-BB at different concentrations. Adipogenesis was determined by Oil Red O staining and messenger RNA expression of the late adipocyte differentiation markers cell death-inducing DFFA-like effector C (CIDEC) and adiponectin (ADIPOQ). To demonstrate involvement of FGF-receptor and PDGF-receptor signaling, experiments were also conducted in the presence of dasatinib (inhibitor of PDGF-receptor) or nintedanib (inhibitor of PDGF-receptor and FGF-receptor). RESULTS: bFGF significantly stimulated adipogenesis by orbital fibroblasts, as shown by increased Oil Red O staining and CIDEC and ADIPOQ expression after 14 days of differentiation. Furthermore, an additive effect of bFGF/PDGF-BB co-stimulation on adipogenesis was observed at the lowest concentration (12.5 ng/mL) of the growth factors tested. Nintedanib completely inhibited bFGF-, PDGF-BB-, and bFGF/PDGF-BB-induced adipogenesis, while dasatinib only fully abrogated PDGF-BB-induced adipogenesis. CONCLUSION: bFGF induces adipogenesis in orbital fibroblasts and as such may contribute to GO. The additive effect of bFGF and PDGF-BB on adipogenesis, along with the observed inhibitory effects of dasatinib and nintedanib, point at independent receptor-mediated effects. This supports the hypothesis that multi-target directed therapy might be more efficient in the treatment of GO.

The JAK1/JAK2- inhibitor ruxolitinib inhibits mast cell degranulation and cytokine release.

BACKGROUND: Mastocytosis is characterized by the accumulation of aberrant mast cells (MC). Patients suffering from mastocytosis suffer from a wide range of symptoms due to increased levels of MC mediators. It would therefore be of great benefit to inhibit MC mediator release. However, to date there are few drugs available that are known to effectively lower MC mediator levels. The evidence for the involvement of the janus kinase 2 (JAK2)-signal transducer and activation of transcription 5 (STAT5) signalling pathway in MC activation is slowly accumulating. Interference with the JAK2-STAT5 pathway might inhibit MC mediator release. Ruxolitinib, a JAK1/JAK2 inhibitor, indeed decreases symptoms like pruritus and fatigue in patients with myeloproliferative neoplasms. Yet, detailed studies on how ruxolitinib affects human mast cell activity are lacking. OBJECTIVE: To investigate the effect of JAK1/2-inhibition with ruxolitinib in the human mast cell lines LAD2 and HMC1. METHODS: LAD2 and HMC1 were stimulated with substance P, codeine or the calcium ionophore A23817. The effect of ruxolitinib on mast cell degranulation (via measurement of ß-hexosaminidase, histamine release and CD63 membrane expression) and IL-6, IL-13, MCP-1 and TNF-α production was investigated. The involvement of STAT5 activation was explored using the selective STAT5 inhibitor pimozide. RESULTS: Ruxolitinib effectively inhibited codeine- and substance P-induced degranulation in a concentration-dependent manner. Ruxolitinib also significantly inhibited the production of IL-6, TNF-α and MCP-1 as induced by A23817 and substance P. Selective STAT5 inhibition with pimozide resulted in diminished degranulation and inhibition of cytokine production as induced by A23817 and substance P. CONCLUSIONS & CLINICAL RELEVANCE: This study demonstrates that the JAK1/JAK2 inhibitor ruxolitinib can inhibit MCactivity, possibly through prevention of STAT5 activation. This renders the JAK-STAT pathway as an interesting target for therapy to release symptom burden in mastocytosis and many other MC mediator-related diseases.

Dabigatran inhibits intravitreal thrombin activity.

PURPOSE: Proliferative vitreoretinopathy (PVR) is a vitreoretinal disorder in which retinal pigment epithelial (RPE) cell activation contributes to both formation of fibrotic retinal membranes and inflammation. Vitreous of patients with PVR contains increased thrombin activity which induces profibrotic and proinflammatory programs in RPE cells. Inhibition of intravitreal thrombin activity may thus represent a therapeutic option for PVR. In this study, we examined the capacity of the clinically available direct thrombin inhibitor dabigatran to inhibit thrombin activity in vitreous fluids. METHODS: ARPE-19 cells were cultured with the following: (i) thrombin, (ii) vitreous without thrombin activity and (iii) vitreous with elevated thrombin activity (PVR samples and thrombin spiked vitreous) either in the presence or absence of dabigatran (range: 10-5 to 10-7  M). Subsequently, CCL2, CXCL8, GMCSF, IL6 and PDGFB mRNA expression levels were determined by RQ-PCR and protein levels of 27 cytokines, chemokines and growth factors were detected in culture supernatants using a multiplex approach. In addition, the capacity of vitreous fluids obtained from patients after oral dabigatran intake was tested in an in vitro thrombin activity assay. RESULTS: Thrombin and vitreous fluids containing thrombin activity induced CCL2, CXCL8, GM-CSF, IL-6 and PDGF-BB expression by ARPE-19 cells, which was inhibited by dabigatran. In addition, dabigatran that reached the vitreous after repeated oral intake did inhibit thrombin activity in the in vitro activity assay. CONCLUSION: Proliferative vitreoretinopathy (PVR) is associated with increased intravitreal thrombin activity that activates profibrotic and proinflammatory pathways in RPE cells. Our findings provide evidence that this activation pathway can potentially be inhibited by dabigatran.

Histamine induces NF-κB controlled cytokine secretion by orbital fibroblasts via histamine receptor type-1.

Mast cells and their products are likely to be involved in regulating orbital fibroblast activity in Graves' Ophthalmopathy (GO). Histamine is abundantly present in granules of mast cells and is released upon mast cell activation. However, the effect of histamine on orbital fibroblasts has not been examined so far. Orbital tissues from GO patients and controls were analyzed for the presence of mast cells using toluidine blue staining and immunohistochemical detection of CD117 (stem cell factor receptor). Orbital fibroblasts were cultured from GO patients and healthy controls, stimulated with histamine and cytokines (IL-6, IL-8, CCL2, CCL5, CCL7, CXCL10 and CXCL11) were measured in culture supernatants. Also hyaluronan levels were measured in culture supernatants and hyaluronan synthase (HAS) and hyaluronidase (HYAL) gene expression levels were determined. In addition, histamine receptor subtype gene expression levels were examined as well as the effect of the histamine receptor-1 (HRH1) antagonist loratadine and NF-κB inhibitor SC-514 on histamine-induced cytokine production. Mast cell numbers were increased in GO orbital tissues. Histamine stimulated the production of IL-6, IL-8 and CCL2 by orbital fibroblasts, while it had no effect on the production of CCL5, CCL7, CXCL10, CXCL11 and hyaluronan. Orbital fibroblasts expressed HRH1 and loratadine and SC-514 both blocked histamine-induced IL-6, IL-8 and CCL2 production by orbital fibroblasts. In conclusion, this study demonstrates that histamine can induce the production of NF-κB controlled-cytokines by orbital fibroblasts, which supports a role for mast cells in GO.

Thrombin induces epithelial-mesenchymal transition and collagen production by retinal pigment epithelial cells via autocrine PDGF-receptor signaling.

PURPOSE: De-differentiation of RPE cells into mesenchymal cells (epithelial-mesenchymal transition; EMT) and associated collagen production contributes to development of proliferative vitreoretinopathy (PVR). In patients with PVR, intraocular coagulation cascade activation occurs and may play an important initiating role. Therefore, we examined the effect of the coagulation proteins factor Xa and thrombin on EMT and collagen production by RPE cells. METHODS: Retinal pigment epithelial cells were stimulated with factor Xa or thrombin and the effect on zonula occludens (ZO)-1, α-smooth muscle actin (α-SMA), collagen, and platelet-derived growth factor (PDGF)-B were determined by real-time quantitative-polymerase chain reaction (RQ-PCR), immunofluorescence microscopy, and HPLC and ELISA for collagen and PDGF-BB in culture supernatants, respectively. PDGF-receptor activation was determined by phosphorylation analysis and inhibition studies using the PDGF-receptor tyrosine kinase inhibitor AG1296. RESULTS: Thrombin reduced ZO-1 gene expression (P < 0.05) and enhanced expression of the genes encoding α-SMA and the pro-alpha1 chain of collagen type-1 (P < 0.05), indicating EMT. Also, ZO-1 protein expression declined on thrombin stimulation, whereas production of α-SMA and collagen increased. In contrast to thrombin, factor Xa hardly stimulated EMT by RPE. Thrombin clearly induced PDGF-BB production and PDGF-Rß chain phosphorylation in RPE. Moreover, AG1296 significantly blocked the effect of thrombin on EMT and collagen production. CONCLUSIONS: Our findings demonstrate that thrombin is a potent inducer of EMT by RPE via autocrine activation of PDGF-receptor signaling. Coagulation cascade-induced EMT of RPE may thus contribute to the formation of fibrotic retinal membranes in PVR and should be considered as treatment target in PVR.

Factor Xa and thrombin stimulate proinflammatory and profibrotic mediator production by retinal pigment epithelial cells: a role in vitreoretinal disorders?

BACKGROUND: Vitreoretinal disorders, including proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR) and exudative age-related macular degeneration (AMD), are a major cause of visual impairment worldwide and can lead to blindness when untreated. Loss of blood-retinal barrier (BRB) integrity associated with vitreoretinal fibrin deposition, inflammation, fibrosis and neovascularization contribute to the pathophysiological processes in these disorders. Retinal pigment epithelial (RPE) cells are well recognized to contribute to vitreoretinal inflammation/fibrosis and are likely to encounter contact with coagulation factor upon loss of BRB integrity. METHODS: An extensive study was performed in which we examined the effect of factor Xa and thrombin on the production of a broad panel of cytokines/chemokines and growth factors by RPE cells. For this purpose we used the ARPE-19 cell line as well as primary RPE cells, a glass slide based array that allows simultaneous detection of 120 cytokines/chemokines and growth factors, ELISA and real-time-quantitative PCR. The involved signaling cascade was examined using specific inhibitors for protease activated receptor (PAR)1, PAR2 and nuclear factor kappa-B (NF-κB). RESULTS: Factor Xa and thrombin regulated the production of cytokines and growth factors (including GM-CSF, IL-6, IL-8, MCP-3, PDGF-AA, PDGF-BB, TIMP-1 and TGF-α) that fit well in the pathobiology of vitreoretinal disease. Blocking studies revealed that the effects were mediated via PAR1 induced NF-κB activation. CONCLUSIONS: Our findings suggest that factor Xa and thrombin can drive vitreoretinal inflammation and fibrosis and should be considered as treatment targets in vitreoretinal disorders such as PVR, PDR and AMD.

Mild versus strong anti-inflammatory therapy during early sepsis in mice: a matter of life and death.

OBJECTIVE: A recent literature-based study suggested that low-dose corticosteroid treatment has a beneficial effect on mortality in septic patients, whereas high-dose corticosteroid treatment has not. This suggests that mild down-regulation of the inflammatory response during early sepsis may be beneficial while extensive reduction of the inflammatory response is not. To investigate this hypothesis, we examined the effect of dexamethasone in varying doses on cecal ligation and puncture-induced inflammation and mortality. DESIGN: Animal study. SETTING: University research laboratory. SUBJECTS: Male C57BL/6 mice. INTERVENTIONS: Mice were subjected to cecal ligation and puncture, and dexamethasone was administered intravenously at a dosage of 0.05 (L/DEX), 0.25 (M/DEX), or 2.5 (H/DEX) mg/kg body weight 20 mins postoperatively. Mice receiving phosphate-buffered saline served as controls. Survival was recorded up to 21 days and inflammatory markers were determined in plasma, lungs, liver, and kidney at 6 hrs following cecal ligation and puncture as well as bacterial load in blood and peritoneal fluid. MEASUREMENTS AND MAIN RESULTS: L/DEX treatment significantly improved survival compared with control mice, whereas treatment with higher concentrations of dexamethasone (M/DEX and H/DEX) did not. Treatment with either M/DEX or H/DEX was associated with significantly (p < .05) reduced cytokine plasma levels as compared with controls at 6 hrs after cecal ligation and puncture. In addition, M/DEX or H/DEX powerfully reduced cytokine messenger RNA expression in the lung, liver, and kidney. In contrast, treatment with L/DEX was associated with a mild, but nonsignificant, reduction of cytokine plasma levels. In addition, L/DEX moderately reduced cytokine messenger RNA expression in lung, liver, and kidney tissue and reduced the occurrence of bacteremia. CONCLUSIONS: A modest down-regulation of the early sepsis-associated inflammatory response improves survival in a murine cecal ligation and puncture model. We propose that the success of anti-inflammatory therapies in a septic setting fundamentally depends on finding a treatment balance that reduces the hyper-inflammation-induced pathology but still allows adequate defense against pathogens.

The ß-human chorionic gonadotropin-related peptide LQGV reduces mortality and inflammation in a murine polymicrobial sepsis model.

OBJECTIVE: Mortality in sepsis remains high and efforts to modulate the inflammatory response so far mostly failed to improve survival. The human chorionic gonadotropin-related tetrapeptide LQGV was recently shown to exert anti-inflammatory activity. The aim of this study was to assess the effect of LQGV on cecal ligation and puncture-induced mortality and inflammation. DESIGN: Animal study. SETTING: University research laboratory. SUBJECTS: Male C57BL/6 mice. INTERVENTIONS: To examine the effect of LQGV by itself on cecal ligation and puncture-induced mortality and inflammation, C57BL/6 mice were exposed to a moderate cecal ligation and puncture procedure (40% ligation and double puncture) with a mortality rate of approximately 80% within 5 days in control mice. In addition, to examine whether LQGV was of additive value to standard sepsis care (antibiotics and fluid resuscitation), a more severe cecal ligation and puncture procedure was used (80% ligation and double puncture), yielding approximately 100% mortality within 12 days in control mice. LQGV (5 mg/kg body weight), phosphate-buffered saline (as control), or dexamethasone (2.5 mg/kg body weight) was administered perioperatively. Survival was monitored for 21 days and inflammatory markers were determined in plasma, peritoneal cavity, and lungs. MEASUREMENTS AND MAIN RESULTS: LQGV significantly improved survival from 20% to 50% during the first 5 days after moderate cecal ligation and puncture. This was associated with reduced cytokine and E-selectin levels in peritoneal lavage fluid, lungs, and, to a lesser extent, in plasma. LQGV treatment also reduced pulmonary nuclear factor-κB activation and pulmonary damage. In the severe cecal ligation and puncture model, LQGV combined with fluid resuscitation and antibiotics resulted in significantly better survival (70%) than that observed with fluid resuscitation and antibiotics alone (30%). CONCLUSIONS: LQGV improves survival after cecal ligation and puncture. This is likely established by a modest reduction of the acute inflammatory response through a nuclear factor-κB-dependent mechanism. Furthermore, LQGV may be a valuable additive next to the standard care in polymicrobial sepsis.

Dietary restriction modifies certain aspects of the postoperative acute phase response.

BACKGROUND: Lifespan extension is achieved through long-term application of dietary restriction (DR), and benefits of short-term dietary restriction on acute stress and inflammation have been observed. So far, the effects of short-term DR in humans are relatively unknown. We hypothesized that short-term DR in humans reduces the acute phase response following a well defined surgical trauma. METHODS: Thirty live kidney donors were randomized between 30% preoperative dietary restriction followed by 1 d of fasting (n=17) or a 4 d ad libitum regimen (n=13) prior to surgery. Leukocyte subsets and numbers and serum cytokine levels were determined. Whole blood was stimulated with lipopolysaccharide (LPS) and cytokine production was determined. RESULTS: A clear trend towards lower numbers of postoperative circulating leukocytes was observed in the DR group. IL-8 serum levels were significantly higher in the DR group over the first 6 postoperative d (P=0.018). After LPS stimulation, significantly less TNF-α (P=0.001) was produced by blood obtained postoperatively compared with preoperative blood from the DR group. This was not observed in the control group. CONCLUSIONS: A relatively short preoperative dietary restriction regimen was able to modify certain aspects of the postoperative acute phase response. These data warrant further studies into the dietary conditions that improve stress resistance in humans. (Dutch Trial Registry number: NTR1875).

The beta-human chorionic gonadotropin-related peptide LQGV exerts anti-inflammatory effects through activation of the adrenal gland and glucocorticoid receptor in C57BL/6 mice.

The systemic inflammatory response syndrome is a complex host response to a variety of clinical insults, generally leading to severe pathology. The human chorionic gonadotropin ß-chain-related tetrapeptide leucine-glutamine-glycine-valine (LQGV) reduces hemorrhagic and LPS-induced systemic inflammatory response syndrome, but its mechanisms of action are not yet fully understood. Through the combination of in vivo, in vitro, and ex vivo approaches, we demonstrate that LQGV actively stimulates corticosterone production in mice and thereby suppresses in vivo TLR4-directed inflammation upon LPS administration. Blocking in vivo glucocorticosteroid receptor signaling reduced the prosurvival effect of LQGV. Also, upon multiple TLR activation by heat-killed Listeria monocytogenes, splenocytes from LQGV-treated mice produced significantly less TNF-α and IL-6, which was absent after in vitro blockage of the glucocorticosteroid receptor. Using adrenal gland and adrenal cell line cultures, we show that LQGV stimulates corticosterone production. Moreover, by using specific pharmacological inhibitors of the adrenocorticotropic hormone (ACTH) and luteinizing hormone receptors as well as of cAMP signaling, we demonstrate that LQGV stimulates the ACTH receptor. These data show that the ß-human chorionic gonadotropin-related tetrapeptide LQGV stimulates adrenal glucocorticosteroid production through activation of the ACTH receptor with consequent glucocorticoid receptor activation and immunosuppression in C57BL/6 mice.

Reduced experimental autoimmune encephalomyelitis after intranasal and oral administration of recombinant lactobacilli expressing myelin antigens.

Oral administration of autoantigens is a safe and convenient way to induce peripheral T-cell tolerance in autoimmune diseases like multiple sclerosis (MS). To increase the efficacy of oral tolerance induction and obviate the need for large-scale purification of human myelin proteins, we use genetically modified lactobacilli expressing myelin antigens. A panel of recombinant lactobacilli was constructed producing myelin proteins and peptides, including human and guinea pig myelin basic protein (MBP) and proteolipid protein peptide 139-151 (PLP(139-151)). In this study we examined whether these Lactobacillus recombinants are able to induce oral and intranasal tolerance in an animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Lewis rats received soluble cell extracts of Lactobacillus transformants intranasally three times prior to induction of EAE. For the induction of oral tolerance, rats were fed live transformed lactobacilli for 20 days. Ten days after the first oral administration EAE was induced. Intranasal administration of extracts containing guinea pig MBP (gpMBP) or MBP(72-85) significantly inhibited EAE in Lewis rats. Extracts of control transformants did not reduce EAE. Live lactobacilli expressing guinea pig MBP(72-85) fused to the marker enzyme beta-glucuronidase (beta-gluc) were also able to significantly reduce disease when administered orally. In conclusion, these experiments provide proof of principle that lactobacilli expressing myelin antigens reduce EAE after mucosal (intranasal and oral) administration. This novel method of mucosal tolerance induction by mucosal administration of recombinant lactobacilli expressing relevant autoantigens could find applications in autoimmune disease in general, such as multiple sclerosis, rheumatoid arthritis and uveitis.

Growth phase of orally administered Lactobacillus strains differentially affects IgG1/IgG2a ratio for soluble antigens: implications for vaccine development.

Lactobacillus strains with probiotic activity are major constituents of numerous common food products. Due to their 'generally regarded as safe'-status (GRAS-status), Lactobacillus strains can also be genetically engineered for use in oral immunotherapeutic applications, such as vaccination and T lymphocyte tolerance induction in autoimmune disease.In the current study, we demonstrate that the growth phase of orally administered individual Lactobacillus strains can differentially affect antigen-specific antibody subclasses IgG1 and IgG2a, which might reflect skewing of systemic activity of T helper cell type 2 (Th2) and T helper cell type 1 (Th1) pathways, respectively. Mice were orally fed different wild type Lactobacillus strains in log phase or stationary phase and immunized intraperitoneally with a T-cell dependent protein antigen. Sera were evaluated for the ratio of antigen-specific IgG1 and IgG2a antibodies. Stationary Lactobacillus murines and Lactobacillus casei cultures, but not two other Lactobacillus strains, evoked significantly higher IgG1/IgG2a ratios than log phase cultures, possibly relating to increased activity of the Th2-pathway. Despite normal variation in antibody responses against TNP-CGG among individual mice, a high correlation was found between the IgG1 and IgG2a responses of mice within experimental groups. This differential antibody response is likely due to growth phase-dependent differences in bacterial cell composition.Since Lactobacillus growth phase dependent skewing of antibody responses possibly reflecting T-cell pathways can inadvertently affect allergic and (auto)-immune responses, the current findings strongly caution against unidimensional views on the oral administration of individual Lactobacillus strains for probiotic or immunotherapeutic purposes, but also suggest additional possibilities for immune modulation.