An Inflamed and Infected Reconstructed Human Epidermis to Study Atopic Dermatitis and Skin Care Ingredients

Atopic dermatitis (AD), the most common inflammatory skin disorder, is a multifactorial disease characterized by a genetic predisposition, epidermal barrier disruption, a strong T helper (Th) type 2 immune reaction to environmental antigens and an altered cutaneous microbiome. Microbial dysbiosis characterized by the prevalence of Staphylococcus aureus (S. aureus) has been shown to exacerbate AD. In recent years, in vitro models of AD have been developed, but none of them reproduce all of the pathophysiological features. To better mimic AD, we developed reconstructed human epidermis (RHE) exposed to a Th2 pro-inflammatory cytokine cocktail and S. aureus. This model well reproduced some of the vicious loops involved in AD, with alterations at the physical, microbial and immune levels. Our results strongly suggest that S. aureus acquired a higher virulence potential when the epidermis was challenged with inflammatory cytokines, thus later contributing to the chronic inflammatory status. Furthermore, a topical application of a Castanea sativa extract was shown to prevent the apparition of the AD-like phenotype. It increased filaggrin, claudin-1 and loricrin expressions and controlled S. aureus by impairing its biofilm formation, enzymatic activities and inflammatory potential.

Revisiting the Roles of Filaggrin in Atopic Dermatitis

The discovery in 2006 that loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and can predispose to atopic dermatitis (AD) galvanized the dermatology research community and shed new light on a skin protein that was first identified in 1981. However, although outstanding work has uncovered several key functions of filaggrin in epidermal homeostasis, a comprehensive understanding of how filaggrin deficiency contributes to AD is still incomplete, including details of the upstream factors that lead to the reduced amounts of filaggrin, regardless of genotype. In this review, we re-evaluate data focusing on the roles of filaggrin in the epidermis, as well as in AD. Filaggrin is important for alignment of keratin intermediate filaments, control of keratinocyte shape, and maintenance of epidermal texture via production of water-retaining molecules. Moreover, filaggrin deficiency leads to cellular abnormalities in keratinocytes and induces subtle epidermal barrier impairment that is sufficient enough to facilitate the ingress of certain exogenous molecules into the epidermis. However, although FLG null mutations regulate skin moisture in non-lesional AD skin, filaggrin deficiency per se does not lead to the neutralization of skin surface pH or to excessive transepidermal water loss in atopic skin. Separating facts from chaff regarding the functions of filaggrin in the epidermis is necessary for the design efficacious therapies to treat dry and atopic skin.

The Actin-Based Motor Myosin Vb Is Crucial to Maintain Epidermal Barrier Integrity

Myosin Vb (Myo5b) is an unconventional myosin involved in the actin-dependent transport and tethering of intracellular organelles. In the epidermis, granular keratinocytes accumulate cytoplasmic lamellar bodies (LBs), secretory vesicles released at the junction with the stratum corneum that participate actively in the maintenance of the epidermal barrier. We have previously demonstrated that LB biogenesis is controlled by the Rab11a guanosine triphosphate hydrolase, known for its ability to recruit the Myo5b motor. In order to better characterize the molecular pathway that controls LB trafficking, we analyzed the role of F-actin and Myo5b in the epidermis. We demonstrated that LB distribution in granular keratinocytes was dependent on a dynamic F-actin cytoskeleton. Myo5b was shown to be highly expressed in granular keratinocytes and associated with corneodesmosin-loaded LB. In reconstructed human epidermis, Myo5b silencing led to epidermal barrier defects associated with structural alterations of the stratum corneum and a reduced pool of LB showing signs of disordered maturation. Myo5b depletion also disturbed the expression and distribution of both LB cargoes and junctional components, such as claudin-1, which demonstrates its action on both LB trafficking and junctional complex composition. Together, our data reveal the essential role of Myo5b in maintaining the epidermal barrier integrity.

Defects of corneocyte structural proteins and epidermal barrier in atopic dermatitis

The main function of the epidermis is to establish a vital multifunctional barrier between the body and its external environment. A defective epidermal barrier is one of the key features of atopic dermatitis (AD), a chronic and relapsing inflammatory skin disorder that affects up to 20% of children and 2-3% of adults and often precedes the development of allergic rhinitis and asthma. This review summarizes recent discoveries on the origin of the skin barrier alterations in AD at the structural protein level, including hereditary and acquired components. The consequences of the epidermal barrier alteration on our current understanding of the pathogenesis of AD, and its possible implications on the treatment of patients, are discussed here.

Distribution and antimicrobial susceptibility of bacteria from adults with community-acquired pneumonia or complicated skin and soft tissue infections in France: the nationwide French PREMIUM study

The empirical therapy of community-acquired pneumonia (CAP) and complicated skin and soft tissue infections (cSSTIs) must be based on updated bacterial distribution and susceptibility data. A nationwide study consecutively collected 1288 isolates from CAP (n=467) and cSSTIs (n=821) from 18 French hospitals between 2012 and 2013. The MIC values of commonly used antimicrobial agents, including ceftaroline, were determined. Bacterial distribution featured Pneumococcus, Haemophilus influenzae, and Staphylococcus aureus for CAPs and S. aureus, β-hemolytic streptococci and Enterobacteriaceae for cSSTIs. Antimicrobial susceptibility testing indicated i) the sustained third-generation cephalosporins and levofloxacin activity against pneumococci and H. influenzae, ii) no methicillin-resistant Staphylococcus aureus emergence among respiratory pathogens, iii) the high in vitro activity of ceftaroline against staphylococci from cSSTIs (98.7% susceptibility), and iv) the worrisome decreasing fluoroquinolone and third-generation cephalosporin susceptibilities among Enterobacteriaceae. This laboratory-based survey depicts a contrasting situation and supports the scoring of patients for the resistant pathogen risk before empirical therapy.

Gem GTPase acts upstream Gmip/RhoA to regulate cortical actin remodeling and spindle positioning during early mitosis

Gem is a small guanosine triphosphate (GTP)-binding protein within the Ras superfamily, involved in the regulation of voltage-gated calcium channel activity and cytoskeleton reorganization. Gem overexpression leads to stress fiber disruption, actin and cell shape remodeling and neurite elongation in interphase cells. In this study, we show that Gem plays a crucial role in the regulation of cortical actin cytoskeleton that undergoes active remodeling during mitosis. Ectopic expression of Gem leads to cortical actin disruption and spindle mispositioning during metaphase. The regulation of spindle positioning by Gem involves its downstream effector Gmip. Knockdown of Gmip rescued Gem-induced spindle phenotype, although both Gem and Gmip accumulated at the cell cortex. In addition, we implicated RhoA GTPase as an important effector of Gem/Gmip signaling. Inactivation of RhoA by overexpressing dominant-negative mutant prevented normal spindle positioning. Introduction of active RhoA rescued the actin and spindle positioning defects caused by Gem or Gmip overexpression. These findings demonstrate a new role of Gem/Gmip/RhoA signaling in cortical actin regulation during early mitotic stages.

[Impact of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence increasing on barrier precautions implementation in a university hospital]

AIM OF THE STUDY

The French national surveillance program of multidrug-resistant bacteria (MDR) shows an increase of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence. The objectives of this study were to assess: the incidence of EBLSE in a large French university hospital between 2005 and 2010, and the difference of barrier precautions implementation between ESBL and other MDR.

METHODS

The ESBLE incidence measure used data from the laboratory of bacteriology. The application of isolation and barrier precautions was analyzed from the MRB national surveillance data over a 3-year period from 2006 to 2008. Data were entered and analyzed using Epi Info software. The Chi(2) test was used for the comparison of proportions.

RESULTS

The overall incidence of ESBLE was significantly higher in 2010 than in 2005 (0.20/1000 patients-days vs 0.03/1000 patients-days, respectively) (P<0.001). The same was observed for Escherichia coli incidence with rates ranging from 0.02/1000 patients-days in 2005 to 0.15/1000 patients-days in 2010. Isolation precautions for patients with EBLSE were applied in relation for most patients with MRB (ESBLE vs others), without significant difference.

CONCLUSION

The surveillance programme of MRB showed a significant increase of ESBLE, especially for E. coli. Isolation and barrier precautions were used for most patients with MRB, including ESBLE.

The GTPase Gem and its partner Kif9 are required for chromosome alignment, spindle length control, and mitotic progression

Within the Ras superfamily, Gem is a small GTP-binding protein that plays a role in regulating Ca(2+) channels and cytoskeletal remodeling in interphase cells. Here, we report for the first time that Gem is a spindle-associated protein and is required for proper mitotic progression. Functionally, loss of Gem leads to misaligned chromosomes and prometaphase delay. On the basis of different experimental approaches, we demonstrate that loss of Gem by RNA interference induces spindle elongation, while its enforced expression results in spindle shortening. The spindle length phenotype is generated through deregulation of spindle dynamics on Gem depletion and requires the expression of its downstream effector, the kinesin Kif9. Loss of Kif9 induces spindle abnormalities similar to those observed when Gem expression is repressed by siRNA. We further identify Kif9 as a new regulator of spindle dynamics. Kif9 depletion increases the steady-state levels of spindle α-tubulin by increasing the rate of microtubule polymerization. Overall, this study demonstrates a novel mechanism by which Gem contributes to the mitotic progression by maintaining correct spindle length through the kinesin Kif9.

The membrane-tubulating potential of amphiphysin 2/BIN1 is dependent on the microtubule-binding cytoplasmic linker protein 170 (CLIP-170)

Amphiphysins are BIN-amphiphysin-RVS (BAR) domain-containing proteins that influence membrane curvature in sites such as T-tubules in muscular cells, endocytic pits in neuronal as well as non-neuronal cells, and possibly cytoplasmic endosomes. This effect on lipid membranes is fulfilled by diverse amphiphysin 2/BIN1 isoforms, generated by alternative splicing and showing distinct structural and functional properties. In this study, our goal was to characterize the functional role of a ubiquitously expressed amphiphysin 2/BIN1 by the characterization of new molecular partners. We performed a two-hybrid screen with an isoform of amphiphysin 2/BIN1 expressed in HeLa cells. We identified CLIP-170 as an amphiphysin 2/BIN1-interacting molecule. CLIP-170 is a plus-end tracking protein involved in microtubule (MT) stability and recruitment of dynactin. The binding between amphiphysin 2/BIN1 and CLIP-170 is dependent on the N-terminal part of amphiphysin 2 (mostly the BAR domain) and an internal coiled-coil region of CLIP-170. This partnership was confirmed by GST pull-down assay and by co-immunoprecipitation in HeLa cells that express endogenous amphiphysin 2 (mostly isoforms 6, 9 and 10). When overexpressed in HeLa cells, amphiphysin 2/BIN1 leads to the formation of intracellular tubules which can closely align with MTs. After MT depolymerization by nocodazole, amphiphysin 2-stained tubules disappear, and reappear after nocodazole washout. Furthermore, depletion of CLIP-170 by RNAi induced a decrease in the proportion of cells with amphiphysin 2-stained tubules and an increase in the proportion of cells with no tubules. This result suggests the existence of a mechanistic link between the two types of tubules, which is likely to involve the +TIP protein, CLIP-170. Amphiphysin 2/BIN1 may be an anchoring point on membranes for CLIP-170, and consequently for MT. Then, the pushing force of polymerizing MT could help amphiphysin 2/BIN1 in its tubulation potential. We propose that amphiphysin 2/BIN1 participates in the tubulation of traffic intermediates and intracellular organelles first via its intrinsic tubulating potential and second via its ability to bind CLIP-170 and MT.

Caspase-8 sumoylation is associated with nuclear localization

The cysteine protease caspase-8 plays a pivotal role in the initiation of different apoptotic pathways and controls the maturation and differentiation of various cell types including neurons, fibroblasts and lymphocytes. Specific substrates of caspase-8 are present in both the cytoplasm and the nucleus, which may determine the ultimate biological effect of caspase-8. However, the mechanisms regulating the cellular localization of caspase-8 are still unknown. We show here that, in contrast to other caspases such as caspase-9 and -3, caspase-8 can be sumoylated at lysine 156. This sumoylation (i) is associated with the nuclear localization of caspase-8 and (ii) did not impair caspase-8 activation.

B Cell Receptor-Mediated Apoptosis of Human Lymphocytes Is Associated with a New Regulatory Pathway of Bim Isoform Expression

Studies in Bim-deficient mice have shown that the proapoptotic molecule Bim plays a key role in the control of B cell homeostasis and activation. However, the role of Bim in human B lymphocyte apoptosis is unknown. We show in this study that, depending on the degree of cross-linking, B cell receptors can mediate both Bim-dependent and apparent Bim-independent apoptotic pathways. Cross-linked anti-mu Ab-mediated activation induces an original pathway governing the expression of the various Bim isoforms. This new pathway involves the following three sequential steps: 1) extracellular signal-regulated kinase-dependent phosphorylation of the BimEL isoform, which is produced in large amounts in healthy B cells; 2) proteasome-mediated degradation of phosphorylated BimEL; and 3) increased expression of the shorter apoptotic isoforms BimL and BimS.

Sorting nexin 4 and amphiphysin 2, a new partnership between endocytosis and intracellular trafficking

Endocytosis is a regulated physiological process by which membrane receptors and their extracellular ligands are internalized. After internalization, they enter the endosomal trafficking pathway for sorting and processing. Amphiphysins consist of a family of proteins conserved throughout evolution that are crucial elements of the endocytosis machinery in mammalian cells. They act as adaptors for a series of proteins important for the endocytic process, such as dynamin. In order to improve our knowledge of amphiphysin function, we performed a two-hybrid screen with the N-terminal part of murine amphiphysin 2 (residues 1-304). One of the interacting clones corresponded to sorting nexin 4 (SNX4), a member of the SNX family of proteins which are suspected to regulate vesicular trafficking. This interaction was confirmed in vivo by co-immunoprecipitation. Immunofluorescence analysis revealed that amphiphysin 2 might bind reticulo-vesicular structures present throughout the cell body and be associated with SNX4 on these structures. In an endocytosis assay, overexpressed C-terminal or full-length SNX4 was able to inhibit transferrin receptor endocytosis as efficiently as the SH3 domain of amphiphysin 2. At lower levels of expression, SNX4 colocalized with transferrin-containing vesicles, some of which were also positive for amphiphysin 2. These results indicate that SNX4 may be part of the endocytic machinery or, alternatively, that SNX4 may associate with key elements of endocytosis such as amphiphysin 2 and sequester them when overexpressed. The presence of amphiphysin 2 on intracellular vesicles and its interplay with SNX4, which is likely to take part in intracellular trafficking, suggest that amphiphysin 2 is not only a regulator of the early steps of endocytosis. It could also play a role at the surface of the endocytic vesicle that has just been formed and of the future endosomes, in order to regulate intracellular trafficking.

Ataxin-7 interacts with a Cbl-associated protein that it recruits into neuronal intranuclear inclusions

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by expansion of a CAG repeat in the coding region of the SCA7 gene. The disease primarily affects the cerebellum and the retina, but also many other central nervous system (CNS) structures as the disease progresses. Ataxin-7, encoded by the SCA7 gene, is a protein of unknown function expressed in many tissues including the CNS. In normal brain, ataxin-7 is found in the cytoplasm and/or nucleus of neurons, but in SCA7 brain ataxin-7 accumulates in intranuclear inclusions. Ataxin-7 is expressed ubiquitously, but mutation leads to neuronal death in only certain areas of the brain. This selective pattern of degeneration might be explained by interaction with a partner that is specifically expressed in vulnerable cells. We used a two-hybrid approach to screen a human retina cDNA library for ataxin-7-binding proteins, and isolated R85, a splice variant of Cbl-associated protein (CAP). R85 and CAP are generated by alternative splicing of the gene SH3P12 which we localized on chromosome 10q23-q24. The interaction between ataxin-7 and the SH3P12 gene products (SH3P12GPs) was confirmed by pull-down and co-immunoprecipitation. SH3P12GPs are expressed in Purkinje cells in the cerebellum. Ataxin-7 colocalizes with full-length R85 (R85FL) in co-transfected Cos-7 cells and with one of the SH3P12GPs in neuronal intranuclear inclusions in brain from a SCA7 patient. We propose that this interaction is part of a physiological pathway related to the function or turnover of ataxin-7. Its role in the pathophysiological process of SCA7 disease is discussed.

RLIP76, an effector of the GTPase Ral, interacts with the AP2 complex: involvement of the Ral pathway in receptor endocytosis

RLIP76 is a modular protein that was identified as a putative effector of Ral, a GTPase activated during Ras signaling. To explore further the contribution of the Ral-RLIP76 pathway to Ras signaling, we have looked for partners of RLIP76. Mu2, the medium chain of the AP2 complex is shown to interact with RLIP76. We show also that in vivo endogenous AP2 and RLIP76 form a complex and that this in vivo interaction is independent of cells being stimulated by a growth factor. Furthermore, RLIP76 differentiates AP2 from AP1 in vivo as RLIP76 differentiates mu2 from mu1 in vitro and in two hybrid assays. We show that activated Ral interferes with both tranferrin receptor endocytosis and epidermal growth factor (EGF) receptor endocytosis in HeLa cells. We propose a model where the Ral-RLIP76 pathway connects signal transduction and endocytosis through interaction on one hand between the Ras-Ral pathway and RLIP, on the other hand between RLIP and proteins belonging to the endocytotic machinery.

Nitric oxide and l-arginine cause an accumulation of utrophin at the sarcolemma: a possible compensation for dystrophin loss in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), a severe X-linked recessive disorder which results in progressive muscle degeneration, is due to a lack of dystrophin, a membrane cytoskeletal protein. An approach to treatment is to compensate for dystrophin loss with utrophin, another cytoskeletal protein with over 80% homology with dystrophin. Utrophin is expressed, at the neuromuscular junction, in normal and DMD muscles and there is evidence that it may perform the same cellular functions as dystrophin. So, the identification of molecules or drugs that could up-regulate utrophin is a very important goal for therapy. We show that in adult normal and mdx mice (an animal model of Duchenne myopathy) treated with l-arginine, the substrate of nitric oxide synthase (NOS), a pool of utrophin localized at the membrane appeared and increased, respectively. In normal and mdx myotubes in culture, l-arginine, nitric oxide (NO), or hydroxyurea increased utrophin levels and enhanced its membrane localization. This effect did not occur with d-arginine, showing the involvement of NOS in this process. The NO-induced increase in utrophin was prevented by oxadiazolo-quinoxalin-1-one, an inhibitor of a soluble guanylate cyclase implicated in NO effects. These results open the way to a potential treatment for Duchenne and Becker dystrophies.

Nitric oxide transforms serotonin into an inactive form and this affects neuromodulation

Nitric oxide is a highly reactive molecule, diffusible and therefore ubiquitous in the central nervous system. Consequently, nitric oxide or nitric oxide-derived nitrogen oxides must enter into contact with neuromodulators and they can modify these molecules, especially monoamines, and thus change their regulatory action on synaptic transmission. We tested this possibility on a well-known, identified cholinergic synapse of Aplysia buccal ganglion, in which we have found that evoked acetylcholine release was decreased by extracellularly applied serotonin. We show that this modulatory effect of serotonin was largely reduced not only in the presence of 3-morpholinosydnonimine, a nitric oxide donor, but also when endogenous nitric oxide synthase was activated. We have shown that this decrease in the serotonin effect is due to the formation of chemical derivatives of serotonin, mainly a symmetric serotonin dimer, 4-nitroso-serotonin and 4-nitro-serotonin, which are ineffective in reproducing the modulatory effect of serotonin. Serotonin is involved in the regulation of several central functions, such as sleep-wake activity or mood. The consequences of chemical modifications of serotonin by nitric oxide must be taken into account in physiological as well as pathological situations. In addition, our results highlight the importance of the physiological implications of interactions between free radicals and neuromediators in the nervous system.

A Sos-derived peptidimer blocks the Ras signaling pathway by binding both Grb2 SH3 domains and displays antiproliferative activity

With the aim of interrupting the growth factor-stimulated Ras signaling pathway at the level of the Grb2-Sos interaction, a peptidimer, made of two identical proline-rich sequences from Sos linked by a lysine spacer, was designed using structural data from Grb2 and a proline-rich peptide complexed with its SH3 domains. The peptidimer affinity for Grb2 is 40 nM whereas that of the monomer is 16 microM, supporting the dual recognition of both Grb2 SH3 domains by the dimer. At 50 nM, the peptidimer blocks selectively Grb2-Sos complexation in ER 22 (CCL 39 fibroblasts overexpressing epidermal growth factor receptor) cellular extracts. The peptidimer specifically recognizes Grb2 and does not interact with PI3K or Nck, two SH3 domain-containing adaptors. The peptidimer was modified to enter cells by coupling to a fragment of Antennapedia homeodomain. At 10 microM, the conjugate inhibits the Grb2-Sos interaction (100%) and MAP kinase (ERK1 and ERK2) phosphorylation (60%) without modifying cellular growth of ER 22 cells. At the same concentration, the conjugate also inhibits both MAP kinase activation induced by nerve growth factor or epidermal growth factor in PC12 cells, and differentiation triggered by nerve growth factor. Finally, when tested for its antiproliferative activity, the conjugate was an efficient inhibitor of the colony formation of transformed NIH3T3/HER2 cells grown in soft agar, with an IC50 of around 1 microM. Thus, the designed peptidimers appear to be interesting leads to investigate signaling and intracellular processes and for designing selective inhibitors of tumorigenic Ras-dependent processes.

A new member of the amphiphysin family connecting endocytosis and signal transduction pathways

Src homology 3 (SH3) domains are conserved modules which participate in protein interaction by recognizing proline-rich motifs on target molecules. To identify new SH3-containing proteins, we performed a two-hybrid screen with a proline-rich region of human SOS-1. One of the specific SOS-1 interacting clones that were isolated from a mouse brain cDNA library defines a new protein that was named amphiphysin 2 because of its homology to the previously reported amphiphysin. Amphiphysin 2 is expressed in a number of mouse tissues through multiple RNA transcripts. Here, we report the amino acid sequence of a brain form of amphiphysin 2 (BRAMP2) encoded by a 2. 5-kilobase mRNA. BRAMP2 associates in vitro with elements of the endocytosis machinery such as alpha-adaptin and dynamin. On a biosensor surface, the BRAMP2/dynamin interaction appeared to be direct and partly dependent on a proline-rich sequence of dynamin. Association with dynamin was also observed in PC12 cells after cell stimulation with nerve growth factor, suggesting that amphiphysin 2 may be connected to receptor-dependent signaling pathways. This hypothesis is strengthened by the ability of BRAMP2 to interact with the p21(ras) exchange factor SOS, in vitro, as a possible point of interconnection between the endocytic and signaling pathways.

B cell antigen receptor-mediated apoptosis. Importance of accessory molecules CD19 and CD22, and of surface IgM cross-linking

Engagement of the B cell Ag receptor can induce a suicide pathway in various B cell types. Earlier studies showed that anti-IgM mAb treatment triggers apoptotic death in the Burkitt lymphoma-derived cell line, Ramos. We show that two B cell surface molecules, CD19 and CD22, which have been reported to interact either functionally or structurally with the B cell Ag receptor, also stimulate cell suicide when sufficiently aggregated, both in the Ramos and EBV-infected Ramos AW cell lines. In conditions of lower cross-linking, both molecules enhance the apoptotic response induced by a suboptimal dose of anti-IgM mAb in Ramos cells, reinforcing the notion that CD19 and CD22 may be involved in the death pathway and modulate Ag-induced B cell apoptosis. Similar outcomes were obtained with human tonsillar B cells, which enter the death program upon treatment with cross-linked anti-IgM, -CD19, or -CD22 mAbs. These results indicate that Ag-induced B cell suicide may affect mature B cells in the periphery and may be regulated via the interaction of CD19 and/or CD22 with their respective ligand(s). Early tyrosine phosphorylations were analyzed by Western blotting. The biologic outcome of these various treatments--cell survival or death--could not be related to any detectable new tyrosine-phosphorylated substrate, further questioning the biochemical basis of apoptosis signaling.

B cell antigen receptor-mediated apoptosis. Importance of accessory molecules CD19 and CD22, and of surface IgM cross-linking

Engagement of the B cell Ag receptor can induce a suicide pathway in various B cell types. Earlier studies showed that anti-IgM mAb treatment triggers apoptotic death in the Burkitt lymphoma-derived cell line, Ramos. We show that two B cell surface molecules, CD19 and CD22, which have been reported to interact either functionally or structurally with the B cell Ag receptor, also stimulate cell suicide when sufficiently aggregated, both in the Ramos and EBV-infected Ramos AW cell lines. In conditions of lower cross-linking, both molecules enhance the apoptotic response induced by a suboptimal dose of anti-IgM mAb in Ramos cells, reinforcing the notion that CD19 and CD22 may be involved in the death pathway and modulate Ag-induced B cell apoptosis. Similar outcomes were obtained with human tonsillar B cells, which enter the death program upon treatment with cross-linked anti-IgM, -CD19, or -CD22 mAbs. These results indicate that Ag-induced B cell suicide may affect mature B cells in the periphery and may be regulated via the interaction of CD19 and/or CD22 with their respective ligand(s). Early tyrosine phosphorylations were analyzed by Western blotting. The biologic outcome of these various treatments--cell survival or death--could not be related to any detectable new tyrosine-phosphorylated substrate, further questioning the biochemical basis of apoptosis signaling.

CD22 associates with the human surface IgM-B-cell antigen receptor complex

The B-cell surface molecule CD22, when cross-linked, modulates signaling through the surface IgM (sIgM)-B-cell receptor (BCR) complex. Here we analyzed the basis of this interaction between CD22 and the human sIgM complex. After lysis of B cells or B-cell lines in digitonin, CD22 coimmunoprecipitated a kinase activity that in vitro-phosphorylated two polypeptides of 150 and 130 kDa on tyrosine residues. By immunoblot analysis with a rabbit anti-serum specific for a synthetic peptide of CD22, we found these proteins to be CD22 itself. Furthermore, the phosphorylated 150-kDa CD22 was found in the sIgM-BCR complex maintained by digitonin, along with Ig alpha/mb-1, Ig beta/B29, and a 75-kDa polypeptide precipitated by an antiserum specific to protein-tyrosine kinase PTK72. CD22 is likely to be an important signaling partner in the sIgM-BCR complex since it is very rapidly and strikingly phosphorylated after sIgM is cross-linked and since it contains the antigen recognition homology I (ARHI) motif, present in other antigen receptor molecules.

Characterization of molecular components associated with surface immunoglobulin M in human B lymphocytes: presence of tyrosine and serine/threonine protein kinases

To characterize the signal transduction through the antigen receptor (AgR) on human B lymphocytes, we analyzed its association with other molecular components. The surface IgM (sIgM) complex isolated in digitonin contains two surface expressed polypeptides--the previously described Ig alpha and Ig beta proteins--covalently linked to each other in a 48/39-kDa heterodimer. We show herein that the human sIgM complex isolated from the Burkitt's lymphoma cell line, Ramos, or from dense tonsillar B cells contains additional molecules--160 kDa and 75 kDa in size--and enzymatic activities able to phosphorylate on tyrosine as well as serine/threonine residues the 39-, 48-, 75- and 160-kDa polypeptides. By specific immunoprecipitation with antibodies to src-family kinases, we consistently detected p56lyn in the sIgM complex. In the Ramos cell line, both p56lck and p59fyn activity were also observed, although to a much lesser extent than p56lyn. These kinases are associated with sIgM before cell stimulation. As shown by two-dimensional electrophoresis, they interact in a tight complex with multimeric forms of the Ig alpha and Ig beta components. The kinases are active in vitro but must be highly regulated in vivo: Western blotting with anti-phosphotyrosine antibodies revealed that stimulation of the AgR on viable B cells increased detectable phosphotyrosine residues on the components present in the sIgM complex. Based on these phosphorylation changes, the 39-, 48-, 75- and 160-kDa molecules are likely to be functionally active elements in an IgM complex crucial for the transduction of the antigenic signal.

Immunoregulatory functions of paf-acether. VI. Dual effect on human B cell proliferation

The role of paf-acether (paf), a phospholipid cytokine, in the modulation of human B cell function was investigated. Paf, from 1 x 10(-5) M to 10(-6) M, decreased B cell proliferation induced by both phorbol myristate acetate (PMA) and anti-IgM antibodies (anti-IgM Ab). By contrast, 1 x 10(-7) M to 1 x 10(-9) M paf enhanced PMA triggered, but not anti-IgM triggered B cell proliferation. B cell proliferation was modulated between 24 and 72 hr of culture indicating that the effect of paf did not merely reflect a shift in proliferation kinetics. Interestingly, paf also enhanced the spontaneous proliferation of a Burkitt lymphoma-derived B cell line, Raji, which suggests that paf can directly act on B cells. The modulatory effect of paf on peripheral blood B cells was independent of PMA concentration, yet the effect on Raji cells was dependent upon cell density. The data suggest that paf is a potent modulator of B cell function, and may be involved in the control of humoral immune response.

Thymic B cells from myasthenia gravis patients are activated B cells. Phenotypic and functional analysis

Thymic cell populations from 12 patients displaying myasthenia gravis were submitted to a phenotypic and functional study. Immunofluorescence analysis of thymic sections revealed the presence in germinal centers of B lymphocytes expressing the B cell markers--CD19, CD21, IgD, or IgM. After T cell and macrophage depletion of thymic single cell suspensions, B cell-enriched populations were isolated. Enriched B cells expressed at variable levels activation markers such as CD71, 4F2, CD23, and B8.7, indicating that a marked proportion of them are activated. Moreover, addition of B cell growth factor 12kDa and to a lesser extent of rIL-2 induced a spontaneous proliferation of these B cell populations. These functional and phenotypic signs of activation may reveal the first steps of an autoimmune response against acetylcholine receptor as enriched B cell populations have the capacity to spontaneously secrete anti-acetylcholine receptor antibody.

Thymic B cells from myasthenia gravis patients are activated B cells. Phenotypic and functional analysis

Thymic cell populations from 12 patients displaying myasthenia gravis were submitted to a phenotypic and functional study. Immunofluorescence analysis of thymic sections revealed the presence in germinal centers of B lymphocytes expressing the B cell markers--CD19, CD21, IgD, or IgM. After T cell and macrophage depletion of thymic single cell suspensions, B cell-enriched populations were isolated. Enriched B cells expressed at variable levels activation markers such as CD71, 4F2, CD23, and B8.7, indicating that a marked proportion of them are activated. Moreover, addition of B cell growth factor 12kDa and to a lesser extent of rIL-2 induced a spontaneous proliferation of these B cell populations. These functional and phenotypic signs of activation may reveal the first steps of an autoimmune response against acetylcholine receptor as enriched B cell populations have the capacity to spontaneously secrete anti-acetylcholine receptor antibody.

B8.7 antigen is present on B-cell precursor acute lymphocytic leukemia. Correlation with the low molecular weight B-cell growth factor responsiveness of these cells

The purpose of this study was to analyze the expression of B8.7 antigen and its implication in the low molecular weight B-Cell growth factor (LMW BCGF) proliferative pathway at the early stages of the human B-cell differentiation. After an overnight incubation in culture medium of B-cell precursor acute lymphoblastic leukemias (ALL), we demonstrated the presence of B8.7 antigen in 18 of 25 cases (72%). Such an incubation also induced a significant increase in the LMW BCGF responsiveness of ALL cells (P less than 0.03). In addition, we showed a significant correlation between B8.7 expression and the ability of pre-B ALL cells to respond to LMW BCGF. As previously described for normal B cells, the anti-B8.7 monoclonal antibody inhibited the LMW BCGF-dependent proliferation of pre-B ALL cells in a dose-dependent manner. These data indicate that B8.7 antigen is expressed and may be functionally related to the LMW BCGF pathway at the pre-B cell stages of differentiation. These results also suggest that human B-cell precursor ALL are not only phenotypically similar to their normal B lymphocyte counterparts, but are also sensitive to the same immunoregulatory cytokines that control normal cell growth.

B8.7 antigen expression on B-CLL cells and its relationship to the LMW-BCGF responsiveness

In this work, we studied the expression of B8.7 antigen on B lymphocytes from patients suffering from B type chronic lymphocytic leukemia (B-CLL) as well as on non Hodgkin lymphoma cells (NHL). B8.7 is an activation marker, which has been reported to be associated with the capacity of activated B cells to respond to LMW-BCGF. B lymphocytes of 11 out of 22 patients tested were B8.7 positive. With the exception of one case, LMW-BCGF is able to induce DNA synthesis by these cells in the absence of costimulation by anti-mu antibodies (anti-mu Ab). The LMW-BCGF dependent proliferation of these malignant cells is inhibited by the anti-B8.7 monoclonal antibody (anti-B8.7 MoAb), in the same line as that of normal B cells. These results obtained with monoclonal B cells confirm that the B8.7 molecule is involved in the signalling pathway of the LMW-BCGF.

Effects of some poorly digestible carbohydrates on bile acid bacterial transformations in the rat

The effects of ingestion of poorly digestible carbohydrates on bacterial transformations of cholic acid and beta-muricholic acid were studied in rats fed on increasing levels of lactose, lactulose, amylomaize or potato starches. Each level was given for 3 weeks and, at the end of each dietary treatment, bile acid faecal composition was analysed and a group of six rats was killed every 4 h during 24 h to determine the amounts of fermented carbohydrate and fermentation characteristics (caecal pH, volatile fatty acids (VFA) and lactic acid concentrations). Fermentation of carbohydrates decreased caecal pH and enhanced caecal VFA and lactic acid concentrations. Irrespective of the poorly digestible carbohydrate, the variation of bacterial transformation always occurred in the same way: the bacterial transformation of beta-muricholic acid into hyodeoxycholic acid was the first to disappear, while omega-muricholic acid formation increased; second, cholic acid transformation decreased and finally all bile acid transformations were strongly affected. There was a significant correlation between bile acid transfer and the minimal caecal pH in vivo. This effect of pH was similar in vitro. To determine whether the levels of bacteria which transformed bile acids were modified, rats fed on the highest amounts of poorly digestible carbohydrates were introduced into isolators and carbohydrate feeding was stopped. Caecal pH recovered its initial value but bile acid transformations remained changed, suggesting that the intestinal microflora were modified by ingestion of fermentable carbohydrates.

Expression of the B8.7 antigen on hairy cells and relation with the LMW-BCGF response

Hairy cells are classified as B cell tumors at a preplasma cell stage of differentiation and are believed to represent cells undergoing a switch process. These cells are stimulated in vitro to DNA synthesis and multiplication in the presence of the lymphokine LMW-BCGF. We have tested the level of expression on these cells of the newly described B8.7 activation marker which has been reported to be associated with the capacity of various B cells to respond to LMW-BCGF. The presence of this marker has been readily detected on the hairy cells of 10 of the 12 patients tested in this study; interestingly, for one of the negative cases, the tumor cells were unable to proliferate in response to LMW-BCGF. As on normal B cells, a marked inhibition of the LMW-BCGF dependent response could be achieved in the presence of a monoclonal anti-B8.7 antibody, sustaining the proposal that the B8.7 molecule is involved in the signaling pathway of this growth factor. IFN-alpha is highly efficient in the therapy of hairy cell leukemia (HCL), and we confirm in the present study that IFN-alpha also inhibits the LMW-BCGF dependent proliferation of hairy cells in vitro. In addition, we show that this inhibition is independent of a significant modulation of the B8.7 antigen, a molecule putatively associated with the LMW-BCGF receptor.

A B cell-restricted activation antigen (B8.7) functionally related to the low molecular weight B cell growth factor receptor

A novel monoclonal antibody (anti-B8.7) is reported which recognizes an epitope expressed either on in vitro activated B cells or on a fraction of fresh large B cells (putatively in vivo preactivated). B8.7 antigen is also present on two out of eight B cell lines tested and is characterized as a membrane component displaying an approximate molecular weight of 55,000 to 60,000. By contrast, B8.7 is absent from resting B cells, monocytes, resting or activated T cells, and from the eight non-B cell lines tested. After in vitro activation, B8.7 antigen appears later than the transferrin receptor and its expression increases until day 3. The anti-B8.7 monoclonal antibody induces a dose-related inhibition of the low molecular weight B cell growth factor-dependent proliferation of activated B cells, whereas it does not affect their response to interleukin 2. This strongly suggests that the B8.7 epitope is present on a molecule selectively involved in the interaction between B cells and a B cell growth factor.

A B cell-restricted activation antigen (B8.7) functionally related to the low molecular weight B cell growth factor receptor

A novel monoclonal antibody (anti-B8.7) is reported which recognizes an epitope expressed either on in vitro activated B cells or on a fraction of fresh large B cells (putatively in vivo preactivated). B8.7 antigen is also present on two out of eight B cell lines tested and is characterized as a membrane component displaying an approximate molecular weight of 55,000 to 60,000. By contrast, B8.7 is absent from resting B cells, monocytes, resting or activated T cells, and from the eight non-B cell lines tested. After in vitro activation, B8.7 antigen appears later than the transferrin receptor and its expression increases until day 3. The anti-B8.7 monoclonal antibody induces a dose-related inhibition of the low molecular weight B cell growth factor-dependent proliferation of activated B cells, whereas it does not affect their response to interleukin 2. This strongly suggests that the B8.7 epitope is present on a molecule selectively involved in the interaction between B cells and a B cell growth factor.

Reactivity of Leu-1+ tonsillar B cells to a high molecular weight B cell growth factor

This work was focused on the responsiveness of B cells from blood and tonsils to typical B cell growth factors (BCGF) in the absence of anti-mu antibody. This direct responsiveness was not observed with small dense B cells from either organ. Large tonsillar B cells but not large blood B cells did respond directly to a high m.w. BCGF (m.w. 50,000 BCGF), whereas large B cells from both organs responded directly to the low m.w. BCGF (m.w. 20,000 BCGF). The tonsillar B cells directly responsive to the m.w. 50,000 BCGF express the 4F2 marker and thus belong to a population of in vivo-preactivated B cells. Moreover, this direct responsiveness to the m.w. 50,000 BCGF is localized in Leu-1+ tonsillar B cells. The Leu-1+ and Leu-1- tonsillar B cell subsets do not differ in their responsiveness to the m.w. 50,000 BCGF upon costimulation with anti-mu antibody and to the m.w. 20,000 BCGF regardless of the presence of anti-mu antibody. Thus, the Leu-1+ subset present in tonsils shows a particular reactivity to a high m.w. BCGF.

Reactivity of Leu-1+ tonsillar B cells to a high molecular weight B cell growth factor

This work was focused on the responsiveness of B cells from blood and tonsils to typical B cell growth factors (BCGF) in the absence of anti-mu antibody. This direct responsiveness was not observed with small dense B cells from either organ. Large tonsillar B cells but not large blood B cells did respond directly to a high m.w. BCGF (m.w. 50,000 BCGF), whereas large B cells from both organs responded directly to the low m.w. BCGF (m.w. 20,000 BCGF). The tonsillar B cells directly responsive to the m.w. 50,000 BCGF express the 4F2 marker and thus belong to a population of in vivo-preactivated B cells. Moreover, this direct responsiveness to the m.w. 50,000 BCGF is localized in Leu-1+ tonsillar B cells. The Leu-1+ and Leu-1- tonsillar B cell subsets do not differ in their responsiveness to the m.w. 50,000 BCGF upon costimulation with anti-mu antibody and to the m.w. 20,000 BCGF regardless of the presence of anti-mu antibody. Thus, the Leu-1+ subset present in tonsils shows a particular reactivity to a high m.w. BCGF.

Functional heterogeneity of nonresting B cells in human blood

Among human peripheral blood B cells we localized the precursors of two interleukin-dependent B cell activation processes: the specific response to a particulate antigen, trinitrophenylated polyacrylamide beads (TNP-PAA) and the polyclonally induced response to pokeweed mitogen. In both cases the precursors belong to the OKB7+, sIgD-, mouse red blood cell- subpopulation. However, they differ when cell density, reflecting the stage of activation reached by B cells in peripheral blood, is considered. Only B cells of intermediate density respond to TNP-PAA, whereas the optimal response to pokeweed mitogen is obtained with the cells displaying the lower density. The lack of response of the more dense (resting) B cells to TNP-PAA suggests that the T dependency of this antigen is not based on linked recognition, and fits with our demonstration that this particulate antigen can trigger B cells in the presence of T cell factor. More importantly, our results show that nonresting B cells are functionally heterogeneous according to their degree of preactivation: the responsiveness to specific signals provided by a nonmitogenic hapten-carrier conjugate would be acquired before that to polyclonal activators.

Dietary fiber and cholesterol and bile acid metabolism in axenic (germfree) and holoxenic (conventional) rats. III. Effect of non-sterilized pectin

Axenic (germfree) and holoxenic (conventional) rats were given a pectin-containing diet (5%) or a pectin-free diet. The diet was not sterilized and the axenic state was maintained by the addition of antibiotics. Pectin modified little or not at all the quantity of bile acids in the small intestine, fecal bile acid excretion and fecal elimination of the sum of cholesterol and bile acids. It similarly decreased the concentration of liver cholesterol and the amount of bile acids in the cecum and large intestine of both germfree and conventional rats. Pectin decreased the absorption coefficient of dietary cholesterol and its plasma concentration and increased fecal cholesterol elimination in conventional rats but not in germfree animals. The data imply that some of the actions of pectin depend on the presence of the intestinal flora but the exact nature of this relationship is unclear.

Effect of wheat bran upon gastro-intestinal transit in germ-free and conventional rats

Germ-free and conventional rats were fed a semi-synthetic diet including 10% wheat bran for 1 month. They were compared to similar rats fed the same diet without bran. Transit of polyethylene glycol (PEG) 4000 was studied in giving the marker either in saline or in the diet. The presence of a bacterial flora was found to accelerate small intestine transit and total transit. The ingestion of solid food slowed gastric emptying but had little effect on small intestine transit. Wheat bran slowed gastric emptying of PEG in most of the experimental groups. It had no significant effect on small intestine transit except in germ-free rats having received the marker in solid food. It accelerated total transit in germ-free and conventional rats. The results suggest that bran mainly exerts its action in the hindgut. The role of microflora in this action of bran is discussed.

Effect of amylomaize starch on cholesterol and bile acid metabolisms in germfree (axenic) and conventional (holoxenic) rats

Germfree and conventional rats were given a semi-synthetic diet containing either normal cornstarch or an amylomaize starch. The experimental groups thus formed were compared to assess the effects of these two types of starch and to determine if digestive tract microflora was involved in these effects. The presence of amylomaize starch decreased body growth in germfree and conventional rats, increasing food intake in the former and decreasing it in the latter. In conventionals, amylomaize starch decreased the apparent digestibility of the ration only slightly, while in germfrees it diminished apparent digestibility considerably. The cecal weight of germfree animals was not modified by amylomaize starch but that of conventional rats was increased fourfold. In both types of rat, amylomaize starch largely decreased the plasma concentration of cholesterol, largely increased the total amount of bile acids in the small intestine but slightly modified the fecal elimination of cholesterol and bile acids. It augmented the cholesterol concentration in the liver of germfrees and decreased it in conventionals while, on the contrary, it diminished the total amount of bile acids in the hind gut in the former and augmented it in the latter. This starch did not change bile acid deconjugation in conventional rats but considerably decreased other bacterial transformations of cholesterol and bile acids. Digestive tract microflora was undoubtedly involved in the action of amylomaize starch on cecal weight, ration digestibility, food intake, hepatic cholesterol concentration, the amount of bile acid in the hind gut and obviously in the transformation of cholesterol and bile acids. It did not play a role in the other effects of this starch: the strong decrease in the concentration of plasma cholesterol was the direct effect of amylomaize starch on rat metabolism.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. I. -- Effect of wheat bran

Axenic (GF) and holoxenic (CV) rats were given a semi-synthetic diet containing no fiber (0) or 10 p. 100 bran (B). The GFO, GFB, CVO and CVB groups were compared to assess the action of the flora and the bran. The bran diet did not change body growth, food intake or cecal water content. It caused only a slight decrease in the digestive utilization of the diet in the holoxenic rats and a decline in cecal weight in the axenic rats. The bran diet modified unabsorbed cholesterol transit in both types of rats, and slightly altered dietary cholesterol absorption which was a little lower in axenics than in holoxenics. In the former (GF), the bran-containing diet dit not change either the plasma or the hepatic cholesterol concentration. In the latter (CV), it increased plasma cholesterol which was lower in CVO rats than in the other three groups and decreased hepatic cholesterol which was thus lower in the CVB lot than in the others. The bran diet reduced fecal cholesterol elimination in axenic and holoxenic rats. This decrease was a little higher in the latter. The digestive tract microbial flora was thus implicated in the effect of bran on those characteristics of cholesterol metabolism. The bran did not change fecal bile acid composition in the axenics. In the holoxenics, it contributed to make this composition uniform because without bran, individual compositions varied. The microbial flora thus changed many aspects of bran action on cholesterol and bile acid metabolisms. But total cholesterol and bile acid elimination was only slightly affected by those two factors.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. II. Effect of pectin

Axenic and holoxenic rats were fed with a semi-synthetic diet containing 5 p. 100 pectin as the only fiber. Although the microbial flora of the digestive tract converted most of the bile acids in holoxenic rats, it hardly changed the other characteristics of cholesterol and bile acid metabolisms, except intestinal bile salt pools which were much larger in the axenic rats. When the pectin-containing and pectin-free diets were compared, it appeared that the former diet increased cecal weight, especially in axenic rats, but slightly modified cholesterol and bile acid metabolisms. However, the values of some characteristics of those metabolisms varied individually in the holoxenic rat fed with the pectin-containing diet, while they were very homogeneous in the other groups. This heterogeneity might result from pectin-digestive tract microbial flora interactions which would vary among individuals.

Variations of bile salt pool size and secretion rate in rats according to the modes of sterilization and preparation of a semi-synthetic diet

A semi-synthetic diet was sterilized by irradiation and given to rats as pellets, powder or paste obtained by admixing an equal amount of water. The bile salt pool increased from the first to the third treatment. That effect disappeared when the starch was replaced by sucrose or when the diet was autoclaved instead of irradiated. The bile duct secretion of bile salts varied according to the bile salt pool. Hypotheses are proposed to explain the relationship between the form of the diet and bile salt pool size and secretion.

Bacterial formation of omega-muricholic acid in rats

In the feces of conventional rats, the amount of omega-muricholic and hyodeoxycholic acids vary according to the diet. To understand this phenomenon, we investigated the bacterial formation of these bile acids. The present paper reports the first isolation, from conventional rat feces, of a strain of Clostridium group III which transforms beta-muricholic acid, the main bile acid in germfree rats, into omega-muricholic acid.

Measurement of fecal bile acid excretion in gnotobiotic rats: comparison of gas-liquid chromatography and [4(-14C)] cholesterol isotopic equilibrium

Gas-liquid chromatography (G.L.C.) and the method of [4(-14C)] cholesterol isotopic equilibrium (C.I.E.) were used to determine the fecal bile acid excretion in gnotobiotic rats. The same samples were submitted to both methods. In these conditions, it was observed that the fecal bile acid excretions determined by G.L.C. were 38% of lower than when determined by C.I.E. In thin-layer chromatographic analyses (T.L.C.) of the bile acid extracts obtained from rats in which a [4(-14C)] cholesterol isotopic equilibrium was established, 33 to 35% of the radioactivity of this fraction was not observed in the rat primary bile acids. No bile acids could be observed in G.L.C. made with eluates obtained from the T.L.C. areas containing this radioactivity. It therefore appears that the difference observed in the results obtained by G.L.C. and C.I.E. is due to the fact that chemical species which are not measured by the former method can be determined by the latter one. T.L.C. analyses of bile acid extracts from axenic rats in which either a [26(-14C)] cholesterol or a [2,4(-3H)] cholic acid and [24(-14C)] chenodeoxycholic acid equilibrium were established, lead to the conclusion that the chemical composition of these undetermined substances is complex: part of these substances comes from the transformation of bile acids; another part is made of molecules which maintain the 26(-14C) of cholesterol.

[Action of the microbial flora of the digestive tract on the biosynthesis of cholic acid in the rat (author's transl)]

Axenic and holoxenic (conventional) rats were fed a diet containing trace amounts of [2,4-3H]cholic and [24-14C]chemodeoxycholic acids. In the feces of both groups of rats, the percentage of labelled bile acids which were 3H-labelled was slightly different. In the experimental conditions used, the intestinal microflora only slightly modified the synthesis of 12alpha-hydroxylated bile acids.

[Formation of omega-muricholic acid and fecal excretion of biliary acids in rats]

Two groups of Rats which were fed the same diet, excreted fecal bile acids of different patterns: in one group, the feces contained a large amount of omega-muricholic acid and very little hydrodeoxycholic acid; in the other group the reversed composition was observed. The first group excreted more total bile acids than the second. This observation suggests that the formation of a large amount of omega-muricholic acid results in an increase in total bile acid fecal excretion.

[The effect of dietary lactose on the ileal absorption of sodium taurocholate in rats]

When Rats were fed a lactose containing diet, both the absorption rate of sodium taurocholate at the level of ileum and the contents of bile acids of the small intestine were increased. On the contrary, feeding of lactose did not modify the daily fecal excretion of bile acids. It therefore appears that dietary lactose increases the intestinal pool of bile acids by increasing their ileal absorption rate and that this effect of lactose is not subordinated to a modification of bile acid synthesis.