Human pre-B cell receptor signal transduction: evidence for distinct roles of PI3kinase and MAP-kinase signalling pathways

Pre-BCR acts as a critical checkpoint in B cell development. However, its signalling cascade still remains indistinctly characterised in human. We investigated pre-BCR signalling pathway to examine its regulation in normal primary pre-B lymphocytes and pre-B cell lines. In cell lines, early signalling events occurring after pre-BCR stimulation include phosphorylation of Lyn, Blk and Syk together with ZAP70, Btk, Vav, PLC-γ2 and various adaptor proteins, such as BLNK, LAB, LAT and SLP-76. Further downstream, these molecules induced activation of the PI3K/AKT and MAP-kinase resulting in an augmentation of canonical NF-κB pathways and cFos/AP1 activation. PI3K and MAPK exerted opposing effects on the pre-BCR-induced activation of the canonical NF-κB and c-Fos/AP1 pathways. Immediate nuclear export of FoxO3A and delayed import of IRF4 were additional events observed after pre-BCR crosslinking in primary cells. Pre-BCR-induced down-regulation of Rag1, Rag2, E2A and Pax5 transcripts occurred in a PI3K-dependent manner. Finally we bring evidence that pre-BCR stimulation or co stimulation with CD19 enhances cell cycle signal.

Interleukin-7 induces apoptosis of 697 pre-B cells expressing dominant-negative forms of STAT5: evidence for caspase-dependent and -independent mechanisms

The transcription factors STAT5A and STAT5B (STAT: signal transducer and activator of transcription) play a major role in the signaling events elicited by a number of growth factor and cytokine receptors. In this work, we aimed to investigate the role of STAT5 in human precursor B cell survival by introducing dominant-negative (DN) forms of STAT5A or STAT5B in the 697 pre-B cell line. All clones expressing DN forms of either transcription factor exhibited a higher spontaneous apoptotic rate that was massively enhanced upon interleukin-7 (IL-7) stimulation. This was associated with caspase 8 cleavage, mitochondrial transmembrane potential disruption and caspase 3 activation. However, the DN forms of STAT5 did not alter the expression of Bcl-2, Bax, Bcl-x, Bim, A1 and Mcl1 proteins in IL-7-stimulated cells. The pancaspase inhibitor Z-Val-Ala-Asp-fluoromylmethyl ketone partially suppressed IL-7-mediated mitochondrial transmembrane potential disruption and cell death, suggesting that IL-7 induced the death of DN STAT5 expressing 697 cells through caspase-dependent and -independent mechanisms that both require mitochondrial activation.

TGF-beta1 modulates Fas (APO-1/CD95)-mediated apoptosis of human pre-B cell lines

We have previously shown that Fas-induced apoptosis is markedly enhanced by IL-7 in human pre-B but not pro-B cell lines. In addition, pre-B cell receptor (pre-BCR) ligation significantly potentiates the IL-7 effects on Fas-triggered pre-B cell death. We show herein that transforming growth factor (TGF)-beta 1 sharply reduces Fas-induced death rate of pre-B but not pro-B cells. TGF-beta 1 causes inhibition of Fas-mediated disruption of mitochondrial transmembrane potential and cleavage of caspase 8, Bid and caspase 3. Bcl2 expression is markedly increased in TGF-beta 1-treated pre-B cells, whereas cellular FLICE-like inhibitory protein long (c-FLIPL), Bcl-XL, Bax, and Bad expression remains unchanged. TGF-beta 1 causes a selective growth arrest of pre-B cells in G0/G1 phase of the cell cycle and induces a partial down-modulation of both Fas and pre-BCR expression. All TGF-beta 1-mediated effects, but Bcl2 up-regulation, can be reproduced by the LY294002 phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor but not by inhibitors of the MAPK/ERK (MEK) and Janus kinase (Jak)/STAT pathways, which promote cell death. Akt phosphorylation is strongly inhibited by TGF-beta1 in pre-B but not pro-B cells and is not modified by Fas engagement. Altogether, our findings suggest that TGF-beta1 prevents Fas-induced apoptosis of pre-B lines by inhibiting PI3K pathway and by enhancing expression of Bcl2. They also suggest that the PI3K/Akt pathway is involved in the control of Fas and pre-BCR expression, a checkpoint in B cell development.

[Use of an experimental Chlamydia trachomatis salpingitis model for evaluating the effectiveness of antibiotics and anti-inflammatory agents on fertility]

OBJECTIVES

An experimental model of Chlamydia trachomatis salpingitis was developed in mice to study the effect of combination antibiotic and antiinflammatory therapy on restoring fertility after tubal infection.

METHODS

The mice were infected by injection via the ovarian bursa with a suspension containing a human strain of Chlamydia trachomatis sevar F. After treatment with antibiotics alone or in combination with antiinflammatory agents, fertility was studied at 4 months.

RESULTS

With doxycycline and ofloxacine, there was not a significant difference in fertility between animals treated with antibiotics alone and those treated with antibiotics and antiinflammatory agents. However, a piroxicam and azythromycin combination improved fertility with a longer delay than with azythromycin alone. The most important factor appeared to be the antibiotic treatment.

CONCLUSION

Associating an antiinflammatory agent was not shown to have a beneficial effect in reducing infertility after Chlamydia trachomatis salpingitis.

Use of an experimental model of chlamydial salpingitis in mice for the evaluation of activity of antibiotics and anti-inflammatory drugs on fertility

An experimental animal model has been used to study the separate and combined use of antibiotics and anti-inflammatories in the treatment of salpingitis. The addition of an anti-inflammatory did not seem to help preserve fertility.

Establishment of hybridomas secreting monoclonal antibodies to Chlamydia psittaci

Eleven stable anti-Chlamydia hybrid clones by fusions between X63-Ag8653 myelomas and immune splenocytes from Chlamydia psittaci immunized F1 (C57BL6 X BALB/c) mice have been established which react with the 12 reference Chlamydia strains (seven C. trachomatis and five C. psittaci. Ten of these monoclonal antibodies are directed against the genera-specific epitope (40,000 MW component) for which prolonged immunization seems to be responsible.

[Effect of various antiseptics on Chlamydia trachomatis]

We compared the activity of different antiseptics (chlorhexidine, picloxidine dichlorhydrate, povidone-iodine, and noxythiolin) on Chlamydia trachomatis using two techniques. In the first, an antigenic preparation obtained from a Chlamydia trachomatis-infected cell culture was used. Different times of contact and different concentrations were studied. The antigen-antiseptic mixture was inoculated on healthy cell cultures and infected cells were counted 48 hours later. In the second technique, previously infected cells were incubated with antiseptics at different concentrations for 48 hours. Results are given as a percentage of infected cells. Chlorhexidine and picloxidine dichlorhydrate have a rapid action on Chlamydia trachomatis. Noxythiolin requires a longer period (2 hours) to be active. Povidone-iodine exhibits no activity on Chlamydia trachomatis.

[Kinetic study of the antibodies in OF 1 and C57Bl mice infected with Chlamydia trachomatis and Chlamydia psittaci. Its application to the interpretation of the serological results in human chlamydioses]

The kinetics of antibodies to C. trachomatis and C. psittaci was studied in OF 1 and inbred C 57 Bl mice, inoculated intravenously (IV) or intraperitoneally. Antibodies were detected by a micro-immunofluorescence (MIF) test. Antibody kinetics depends on many factors (genetic particularities of the mice, route of inoculation, chlamydial strain). The response is more specific when mice are inoculated with C. trachomatis than with C. psittaci; heterospecific antibodies appear later in C 57 Bl mice than in OF 1 mice inoculated IV with C. trachomatis. These results are used to explain the serological findings in 6 cases of human chlamydial infections. The type, species and genus specificities of antibody responses to chlamydial infections are discussed.

[Susceptibility of the macrophages of inbred strain mice to Chlamydia psittaci]

Chlamydia psittaci was injected in the peritoneal cavity of different strains of inbred mice. Not all of them develop a clinical disease; some, such as C 3 H, are very susceptible and died within 6 days. C 57 BL, however, are resistant even to a very high dose. We still do not know the exact mechanism of the natural resistance. This is the reason why we are trying to analyse the role of the macrophage. This cell is particularly important in C. psittaci infection, because it harbours the obligate intracellular organisms which multiply inside the cytoplasm. Peritoneal macrophages of three different strains of mice (C 3 H, AKR and C 57 BL) were cultured following Fauve's technique [4]. 48 h after, the macrophages were inoculated with a suspension of C. psittaci. Hela 229 were used as control. 48, 78 and 92 h after inoculation, amount of inclusion in each category of macrophages and Hela cells was determined. C 57 BL macrophages cultured from mice resistant to Chlamydia psittaci allowed the in vitro multiplication of the same bacteria: 72 h after inoculation, 100% of the macrophages were infected and a large inclusion could be seen. C 3 H macrophages cultured from mice very susceptible to Chlamydia psittaci seemed less susceptible in vitro than the C 57 BL macrophages; 72 h after inoculation, 50% only of the infected macrophages showed intracytoplasmic inclusion: AKR macrophages were also susceptible, although AKR mice recover from C. psittaci infection. In conclusion, the difference of susceptibility, as displayed by several strains of inbred mice infected by C. psittaci, cannot be explained by the difference of susceptibility of their macrophages.