Effect of lipopolysaccharide on mouse mast cell induction by a splenic cell culture system

Mechanisms of strain-dependent development of mast cells from mouse splenocytes

Mast cell development from spleen cells was not triggered by prostaglandin E1 (PGE1) or dibutyryl cAMP (db-cAMP) during a 12 day culture when the spleen cells were obtained from C57BL/6N and DBA/1 mice, but mast cells did develop when the spleen cells were obtained from C3H/HeN, BALB/c and ICR mice. A lack of endogenous IFN-gamma in the initial 2 days of the culture period was responsible for the failure. This was confirmed by adding neutralizing anti-IFN-gamma antibody and rIFN-gamma to the cultures and by determining IFN-gamma levels in the spleen cell cultures. Th1 cells in the spleens of C57Bl and DBA/1 mice were much more sensitive to PGE1 and db-cAMP than Th1 cells from other inbred mice strains, and consequently, IFN-gamma production was inhibited in spleen cell cultures of C57BL and DBA/1 mice on addition of PGE1 or db-cAMP. Furthermore, the different sensitivities of Th1 cells to PGE and db-cAMP were dependent on the different levels of IL-12 p40 monomers or homodimers in the spleen cell cultures. As the endogenous specific inhibitors of IL-12 p70 (heterodimers of p40 and p35), large amounts of IL-12 p40 monomers or homodimers in the spleen cell cultures of C57BL and DBA/1 mice enhanced the ability of PGE1 and db-cAMP to inhibit IFN-gamma production by antagonizing the activity of IL-12 heterodimers. These results indicate that the strain-dependent development of mast cells from mouse splenocytes is related to endogenous IFN-gamma levels, which are regulated by PGE, db-cAMP, IL-12 p70 and IL-12 p40.

Interleukin-4-triggered, STAT6-dependent production of a factor that induces mouse mast cell apoptosis

IL-4 can suppress mast cell development from mouse spleen, bone marrow and peritoneal cells by an indirect process that is dependent on the presence of macrophages. Mast cells undergo apoptosis when exposed to supernatants collected from cultures of IL-4-stimulated peritoneal cells due to the IL-4-induced production of an apoptosis-inducing factor in the cultures. This effect of IL-4 is shown to be dependent on STAT6 signaling, because IL-4 and IL-13 do not suppress mast cell development from the spleen and peritoneal cells of STAT6-/- mice. Moreover, supernatants from cultures of IL-4- and IL-13-stimulated peritoneal cells of STAT6-/- mice do not exhibit apoptosis-inducing activity. We confirm, by using deficient mice, neutralizing antibodies and recombinant cytokines, that IL-4-induced apoptosis is not related to the well-known apoptosis-inducing factors Fas, Fas ligand, TNF-alpha, TRAIL, TGF-beta or perforin. These results demonstrate a novel mechanism whereby IL-4 and IL-13 can suppress mast cell development by inducing the production of an apoptosis-inducing factor from macrophages.

Percutaneous application of peptidoglycan from Staphylococcus aureus induces mast cell development in mouse spleen

BACKGROUND

Previously, we found that percutaneous application of peptidoglycan (PEG) from Staphylococcus aureus increased the number of mast cells in the dermis, as seen in patients with atopic dermatitis. However, the origin of the mast cells infiltrating the dermis was not known. Our aim was to determine the origin of the skin mast cells induced by the percutaneous PEG application in mice.

METHODS

PEG was applied to barrier-disrupted abdominal skin of mice every 5 days. Twenty days after the first application, mast cells were detected in the spleen cells by alcian blue-safranin staining. Expression of mast cell proteases and cytokines in the skin or spleen was investigated by reverse transcription-polymerase chain reaction.

RESULTS

Percutaneous application of PEG increased the numbers of alcian blue-positive and safranin-negative mast cells in the spleen. Reverse transcription-polymerase chain reaction analysis of the spleen showed that these mast cells expressed mouse mast cell protease (MMCP)-1, MMCP-4, MMCP-5, and mast cell carboxypeptidase, suggesting that they were immature cells positioned developmentally between mucosal mast cells and connective tissue mast cells. In vitro long-term culture of spleen cells in the presence of PEG induced mast cell development. The features of these mast cells were coincident with those seen in the spleens of PEG-applied mice. Furthermore, when mice were intradermally injected, their skin showed increased levels of expression of mRNAs of MMCP-4, MMCP-5, and mast cell carboxypeptidase, but not MMCP-1. Similar mRNA expression was observed in the skin of PEG-applied mice.

CONCLUSIONS

Percutaneous application of PEG may lead to the development of mast cells in the spleens of mice and contribute to an increase in mast cell numbers in the dermis, as seen in the skin lesions of atopic dermatitis patients.

Endotoxin contamination in fetal bovine serum and its influence on tumor necrosis factor production by macrophage-like cells J774.1 cultured in the presence of the serum

Trace amounts of endotoxin (lipopolysaccharide: LPS) are assumed to contaminate commercially available fetal bovine serum (FBS) for tissue or cell culture during the manufacturing process. We examined how cultured cells were affected by the endotoxin and how much endotoxin was in the FBS. Macrophage-like J774.1 cells maintained in RPMI1640 medium supplemented with FBS containing low doses of LPS for 15 or 21 days showed less TNF production in response to LPS than the cells maintained under LPS-free conditions, and the affected responses of the cells were not recovered by an additional 21 day culture in medium with LPS-free FBS. Concentrations of LPS in 40 lots of FBS obtained from 13 international manufacturers were measured by a highly sensitive and LPS-specific chromogenic limulus assay. The median of endotoxin levels in these lots was 46 ng/ml and the maximum was 38.8 ng/ml. Relatively higher concentrations of LPS (> 1 ng/ml) or lower levels (< 10 pg/ml) were found in 9 and 6 lots, respectively. The majority of the FBS lots contained various levels of (1-->3)-beta-D-glucan, and all lots contained high-density lipoprotein (HDL). However, no correlation was found between LPS and (1-->3)-beta-D-glucan or HDL level in the lots. Each FBS was added to macrophage-like J774.1 cells which had been maintained in LPS-free medium. Five lots of FBS induced significant TNF production by the cells without addition of any stimulant. These active 5 FBS contained relatively higher levels of LPS and pretreatment of the FBS with polymyxin B eliminated their ability to induce TNF production. No correlation was found between (1-->3)-beta-D-glucan levels in FBS and the TNF-inducing capability of FBS. These results show that considerable lots of FBS contain significant levels of LPS, which must affect cell culture.

Tumor Necrosis Factor-α– and Interleukin-6–Triggered Mast Cell Development From Mouse Spleen Cells

We previously showed that interleukin-3 (IL-3) alone is not sufficient, although it is essential for murine mucosal-type mast cell development and that prostaglandin E (PGE) and interferon-γ (IFN-γ) are critical for survival or differentiation of mast cell precursors. We also confirmed that IL-4 is a key inhibitor for mast cell precursors despite being a growth factor of mast cells. In the present work, mouse spleen cells were cultured with recombinant (r) IL-1β, rIL-5, rIL-6, rIL-9, granulocyte-macrophage colony-stimulating factor (GM-CSF ), stem cell factor (SCF ), tumor transforming growth factor-β (TGF-β), or tumor necrosis factor-α (TNF-α) in the presence of endogenous IL-3. After 12 days of culture, mast cell development was induced by rIL-6 and rTNF-α. rIL-1β, rIL-5, rGM-CSF, rTGF-β and even the mast cell growth factors, rIL-9 and rSCF, failed to induce mast cell development. However, unlike IL-9 and SCF, IL-6 and TNF-α did not promote the growth of mast cells already developed. Macrophage may be one of the responsive cells of IL-6 and TNF-α in the cultures, because removal of macrophages greatly reduced the mast cell development induced by the cytokines. The actions of TNF-α and IL-6 were inhibited by indomethacin, an inhibitor for prostaglandin synthesis, and by neutralizing anti–IFN-γ and anti–IL-3 antibodies. rIL-4, when added at the start of the culture, also inhibited mast cell development induced by rIL-6 and rTNF-α. Nevertheless, neutralizing anti–IL-6 and anti–TNF-α antibodies did not suppress mast cell development induced by PGE and IFN-γ. TNF-α and IL-6 enhanced IFN-γ production, but suppressed IL-4 production in the cultures. Mast cell numbers induced were inversely and directly proportional to IL-4 and IFN-γ levels, respectively. These results indicate that inflammatory mediators as triggers are important for mast cell development, although they are not the mast cell growth factors.