Factors influencing fetal macrophage development: I. Reactions of the tumor necrosis factor-alpha cascade and their inhibitors

High levels of testosterone inhibit ovarian follicle development by repressing the FSH signaling pathway

The effect of high concentrations of testosterone on ovarian follicle development was investigated. Primary follicles and granulosa cells were cultured in vitro in media supplemented with a testosterone concentration gradient. The combined effects of testosterone and follicle-stimulating hormone (FSH) on follicular growth and granulosa cell gonadotropin receptor mRNA expression were also investigated. Follicle growth in the presence of high testosterone concentrations was promoted at early stages (days 1-7), but inhibited at later stage (days 7-14) of in vitro culture. Interestingly, testosterone-induced follicle development arrest was rescued by treatment with high concentrations of FSH (400 mIU/mL). In addition, in cultured granulosa cells, high testosterone concentrations induced cell proliferation, and increased the mRNA expression level of FSH receptor (FSHR), and luteinized hormone/choriogonadotropin receptor. It was concluded that high concentrations of testosterone inhibited follicle development, most likely through regulation of the FSH signaling pathway, although independently from FSHR downregulation. These findings are an important step in further understanding the pathogenesis of polycystic ovary syndrome.

Factors influencing fetal macrophage development: III. Immunocytochemical localization of cytokines and time-resolved expression of differentiation markers in organ-cultured rat lungs

BACKGROUND

Exogenous TNF alpha, IL-1 beta, M-CSF, and GM-CSF all stimulate growth of macrophages arising in explanted fetal rat lungs. The present study examines the intrinsic availability of these factors in intact and organ-cultured lungs and utilizes expression of cytokines and marker proteins to explore the differentiation pathway followed by phagocytes in vitro.

METHODS

Factors and markers were localized immunocytochemically in paraffin sections of 14- and 15-day fetal rat lungs and lungs organ-cultured up to 7 days on serum-containing medium solidified with agar. Western analyses for the cytokines were performed on lysates of whole 15-day lungs, and in situ hybridization of M-CSF receptor mRNA was carried out in sections of 14 + 2 day cultured lung.

RESULTS

IL-1 beta, M-CSF, and GM-CSF were demonstrated in the stroma of intact and cultured lungs by immunostaining, results confirmed by Western blotting. TNF alpha appeared to be absent. A few precursors (angular cells) expressed the macrophage lineage marker RM-1 as early as day 14, and immunostaining became stronger and more widespread as the population matured and expanded in cultures. The OX-6 antibody to Ia antigen first reacted with macrophages in 14 + 1 day explants, and within a week 50% of cells were positive. M-CSF and mRNA for its receptor were present at 14 + 2 days, as was PDGF, which had been demonstrated in the stroma and epithelium prior to explantation. Definite reactivity for IL-1 beta and GM-CSF followed at 14 + 4 and 14 + 5 days.

CONCLUSIONS

M-CSF, GM-CSF, and IL-1 beta, but not TNF alpha, are available to replicating angular cells before and during their conversion to phagocytes. Fetal lungs thus qualify as a hematopoietic tissue supportive of macrophages. The path of differentiation pursued in organ cultures involves early expression of structural elements (RM-1, Ia antigen) followed by synthesis of cytokines of the TNF alpha cascade. Immunostaining for both RM-1 and OX-6 suggests that fetal lung macrophages share a common heritage with antigen-presenting pulmonary dendritic cells.

Factors influencing fetal macrophage development: II. Effects of the PDGF subfamily of protein-tyrosine kinase receptor ligands as studied in organ-cultured rat lungs

BACKGROUND

Macrophage precursors in pseudoglandular rat lungs rapidly differentiate into phagocytes in organ culture, although this occurs only gradually in vivo. Macrophage colony-stimulating factor is vital for the process, but the possible importance of other ligands in the platelet-derived growth factor (PDGF) subfamily is scarcely appreciated.

METHODS

Macrophage development was compared in 15-day fetal rat lungs cultured on solid, serum-containing media with and without added stem cell factor (SCF) (100 ng/mL) or antibodies to PDGF-AA and -BB (10-15 micrograms/mL each). In addition, organ cultures and intact lungs were immunostained for PDGF-AA and -BB to confirm their presence in the tissues. Macrophage population growth was measured by coronal area assay.

RESULTS

SCF initially stimulated macrophage production. Thereafter, results varied depending on baseline production by control cultures: where this was vigorous, SCF-exposed explants performed similarly; where this was moderate, the SCF explants outperformed them 1.5-2.6 times over (P < 0.01-0.001). Inhibition of macrophage production by pyrrolidine dithiocarbamate (100 microM) was not significantly diminished in the presence of SCF (10 ng/mL). Immunoreactivity for PDGF-AA and -BB was prevalent in cells of the airway epithelium and stroma during the period macrophage precursors were converting, and both isoforms were detected in differentiating macrophages as early as 2 days in vitro. Nonetheless, exposure of cultures to anti-PDGFs had no significant effect on macrophage population growth.

CONCLUSIONS

Ligands of the PDGF subfamily differ greatly in their influence over development of fetal macrophages. Whereas the PDGFs are ineffective, SCF stimulates growth of macrophage precursors and early differentiating forms and enhances survival of older cells. It appears to act mainly in synergy with other growth factors present in fetal lungs. Furthermore, in the hierarchy of hematopoietic progenitors, the macrophage precursors may be ranked on a par with burst-forming units in the red cell lineage.